El Niño Event and Climate Anomalies in 2015/2016
1 Analysis of the process and mechanisms of genesis and development for 2014-2016 mega El Niño event
2016, 39(6):722-734.
DOI: 10.13878/j.cnki.dqkxxb.20161028003
Abstract:
The present paper has mainly analysed the process and mechanisms of genesis and development of the 2014-2016 mega El Niño event.It is shown that the entire lifecycle of the event is about 2 years(from April 2014 to May 2016),with four stages identified for its evolutive process:(1)Early and continuous westerly wind bursts(December 2013 to April 2014).The continuous three westerly wind burstsnot only changed the state of the easterly trade wind prevailing tropical central and easterly in the Pacific for long period of time,but also changed the cold water state in this region for the most recent 12 years,thus leading to SST rise and warming.Until early spring 2014,the SSTA exceeded 0.5℃,marking the possible occurrence of a new El Niño event.(2)Alternative weakening period(June 2014 to August 2015).Six westerly wind bursts continued to occur,thus maintaining and enhancing the warming of the equatorial central and eastern Pacific,while at the same time overcoming two periods of SST warming decrease or barrier,so that the initial development of El Niño was not aborted,and even changed into the stage of strong El Niño.Correspondingly,in the sub layer of the equatorial central and eastern Pacific,six warm Kelvin waves were observed to propagate eastward.The heat contents of these oceanic waves not only maintained the continuous warming in the equatorial central and eastern Pacific,but also caused El Niño to change from CP to EP type.(3)Peak period of development (September 2015 to February 2016).Two stronger westerly wind bursts were observed,which corresponded to very vigorous convective activity on the equatorial central and eastern Pacific.Rapid warming occurred in the Niño3.4 region,with 3℃observed in November 2015,classified as the mega-El Niño event.(4)Accelerating weakening stage(March to May 2016).The intensity of the El Niño rapidly weakened from 2 to 0.5℃ in the Niño3.4 region,then accelerated the transition to the cold water phase.In July to August 2016,the SSTA in the Niño3.4 region already approached -0.5℃.This rapid phase shift is a manifestation of the theory of delayed oscillation.From the above results,it is concluded that the development and shift of warm and cold phases is observationally consistent with the mechanism derived from the paradigm of the current theory of recharge oscillation and/or delayed oscillation theory.This clearly demonstrates that the results of the El Niño theory effectively underpin the development of related operational prediction.
The present paper has mainly analysed the process and mechanisms of genesis and development of the 2014-2016 mega El Niño event.It is shown that the entire lifecycle of the event is about 2 years(from April 2014 to May 2016),with four stages identified for its evolutive process:(1)Early and continuous westerly wind bursts(December 2013 to April 2014).The continuous three westerly wind burstsnot only changed the state of the easterly trade wind prevailing tropical central and easterly in the Pacific for long period of time,but also changed the cold water state in this region for the most recent 12 years,thus leading to SST rise and warming.Until early spring 2014,the SSTA exceeded 0.5℃,marking the possible occurrence of a new El Niño event.(2)Alternative weakening period(June 2014 to August 2015).Six westerly wind bursts continued to occur,thus maintaining and enhancing the warming of the equatorial central and eastern Pacific,while at the same time overcoming two periods of SST warming decrease or barrier,so that the initial development of El Niño was not aborted,and even changed into the stage of strong El Niño.Correspondingly,in the sub layer of the equatorial central and eastern Pacific,six warm Kelvin waves were observed to propagate eastward.The heat contents of these oceanic waves not only maintained the continuous warming in the equatorial central and eastern Pacific,but also caused El Niño to change from CP to EP type.(3)Peak period of development (September 2015 to February 2016).Two stronger westerly wind bursts were observed,which corresponded to very vigorous convective activity on the equatorial central and eastern Pacific.Rapid warming occurred in the Niño3.4 region,with 3℃observed in November 2015,classified as the mega-El Niño event.(4)Accelerating weakening stage(March to May 2016).The intensity of the El Niño rapidly weakened from 2 to 0.5℃ in the Niño3.4 region,then accelerated the transition to the cold water phase.In July to August 2016,the SSTA in the Niño3.4 region already approached -0.5℃.This rapid phase shift is a manifestation of the theory of delayed oscillation.From the above results,it is concluded that the development and shift of warm and cold phases is observationally consistent with the mechanism derived from the paradigm of the current theory of recharge oscillation and/or delayed oscillation theory.This clearly demonstrates that the results of the El Niño theory effectively underpin the development of related operational prediction.
2 Impact of Arctic warming and the super El Niño in winter 2015/2016 on the East Asian climate anomaly
2016, 39(6):735-743.
DOI: 10.13878/j.cnki.dqkxxb.20161008002
Abstract:
The influence of El Niño on the East Asian climate has been studied extensively.Generally,East Asia is warmer than normal in winter when El Niño occurs.During winter 2015/2016,an extreme El Niño event took place-one that was almost the strongest since records began.However,the winter of 2015/2016 was not much warmer than usual.By contrast,East Asia was even colder than normal in January 2016.At the same time,the Arctic experienced extreme warming in winter 2015/2016,which might have had an influence on the winter climate of East Asia.Therefore,in this study,the influences of Arctic warming and the super El Niño during winter 2015/2016 on the East Asian winter climate was investigated using the ENSO index of the Climate Prediction Center of NOAA,along with NCEP/NCAR reanalysis data,for the period 1980-2016.In winter 2015/2016,a super El Niño emerged in the central tropical Pacific.In January 2016,there was a dominant anomalous anticyclone over the western North Pacific and an anomalous cyclone over the Northeast Pacific.Meanwhile,a southerly anomaly was observed over East Asia,which was confined to the area south of 30°N.This meant that there was a particularly evident response of atmospheric circulation in January 2016 to the forcing of ENSO.However,significantly warmer conditions were not observed over East Asia as expected.On the contrary,it was much colder than normal in January.It is interesting to find that the northerly wind in the domain(30-50°N,110-125°E) was stronger in January 2016,which could explain the colder conditions over East Asia.The Rossby wave activity in January 2016 indicates a wave source over the Barents-Kara seas,suggesting that the colder conditions over East Asia might have been related to the Arctic warming that occurred in January 2016.To address this issue,an Arctic temperature index was defined as the area-weighted mean in the Barents-Kara seas(70-80°N,30-70°E).The statistical results from the reanalysis data during 1980-2016 revealed that the warming in the Barents-Kara seas was concurrent with a significant negative temperature anomaly over East Asia.The teleconnection between the Arctic and East Asian temperature was well supported by an obvious southeastward propagation of Rossby waves.Further analysis suggested that the warming in the Barents-Kara seas could induce anomalous ascending motion in situ.The anomalous ascending motion extended eastwards (around 70-90°E) and turned southwards due to the Coriolis force,and finally descended in Siberia(50-70°N,60-100°E).As the air mass accumulated over Siberia,the Siberian high was intensified,leading to anomalous northerly flow in its east,which favored the cold conditions over East Asia.To verify the combined effect of the Arctic warming and El Niño,a statistical prediction model was established via the multivariate linear regression of surface air temperature(SAT) onto the Arctic temperature index and Niño3.4 index.It was found that the hindcasted SAT anomaly over East Asia in January 2016 resembled the observed counterpart well,with a spatial correlation coefficient of 0.71.This implied that the Arctic warming and super El Niño during winter 2015/2016 can to some extent explain the colder than expected conditions in East Asia.
The influence of El Niño on the East Asian climate has been studied extensively.Generally,East Asia is warmer than normal in winter when El Niño occurs.During winter 2015/2016,an extreme El Niño event took place-one that was almost the strongest since records began.However,the winter of 2015/2016 was not much warmer than usual.By contrast,East Asia was even colder than normal in January 2016.At the same time,the Arctic experienced extreme warming in winter 2015/2016,which might have had an influence on the winter climate of East Asia.Therefore,in this study,the influences of Arctic warming and the super El Niño during winter 2015/2016 on the East Asian winter climate was investigated using the ENSO index of the Climate Prediction Center of NOAA,along with NCEP/NCAR reanalysis data,for the period 1980-2016.In winter 2015/2016,a super El Niño emerged in the central tropical Pacific.In January 2016,there was a dominant anomalous anticyclone over the western North Pacific and an anomalous cyclone over the Northeast Pacific.Meanwhile,a southerly anomaly was observed over East Asia,which was confined to the area south of 30°N.This meant that there was a particularly evident response of atmospheric circulation in January 2016 to the forcing of ENSO.However,significantly warmer conditions were not observed over East Asia as expected.On the contrary,it was much colder than normal in January.It is interesting to find that the northerly wind in the domain(30-50°N,110-125°E) was stronger in January 2016,which could explain the colder conditions over East Asia.The Rossby wave activity in January 2016 indicates a wave source over the Barents-Kara seas,suggesting that the colder conditions over East Asia might have been related to the Arctic warming that occurred in January 2016.To address this issue,an Arctic temperature index was defined as the area-weighted mean in the Barents-Kara seas(70-80°N,30-70°E).The statistical results from the reanalysis data during 1980-2016 revealed that the warming in the Barents-Kara seas was concurrent with a significant negative temperature anomaly over East Asia.The teleconnection between the Arctic and East Asian temperature was well supported by an obvious southeastward propagation of Rossby waves.Further analysis suggested that the warming in the Barents-Kara seas could induce anomalous ascending motion in situ.The anomalous ascending motion extended eastwards (around 70-90°E) and turned southwards due to the Coriolis force,and finally descended in Siberia(50-70°N,60-100°E).As the air mass accumulated over Siberia,the Siberian high was intensified,leading to anomalous northerly flow in its east,which favored the cold conditions over East Asia.To verify the combined effect of the Arctic warming and El Niño,a statistical prediction model was established via the multivariate linear regression of surface air temperature(SAT) onto the Arctic temperature index and Niño3.4 index.It was found that the hindcasted SAT anomaly over East Asia in January 2016 resembled the observed counterpart well,with a spatial correlation coefficient of 0.71.This implied that the Arctic warming and super El Niño during winter 2015/2016 can to some extent explain the colder than expected conditions in East Asia.
2016, 39(6):744-755.
DOI: 10.13878/j.cnki.dqkxxb.20160814003
Abstract:
Real-time seasonal climate prediction was performed in China during the extremely strong El Niño event of 2015/2016,through a combination of dynamical and statistical climate prediction.Generally,real-time summer(winter) climate prediction in China starts in February(October) in every year.The results showed that,although the NCEP-CFSv2 coupled model predicted the evolution of the extremely strong El Niño event in 2015/2016 well,its performance in predicting the summer rainfall anomaly of 2015 and the winter temperature of 2016 at 160 stations in China was limited.Compared to observation,CFSv2 predicted a stronger East Asian summer monsoon and weaker East Asian winter monsoon.One of the reasons for this is that CFSv2 is poor at predicting the extratropical climate system.Thus,based on the climate prediction direct outputs of the NCEP-CFSv2 model,we created a hybrid dynamical and statistical prediction model for forecasting the precipitation anomaly and temperature anomaly at 160 stations in China in 2015/2016.The skill of the hybrid of statistical and dynamical prediction model was higher than that of the direct prediction results of the NCEP-CFSv2 model.The spatial anomaly correlation coefficient(ACC) of summer rainfall at 160 stations in China in 2015 increased from 0.21 to 0.31(exceeding the 99% significance level),along with the percentage of the same sign of the rainfall anomaly improving to 60% from 50%.The model reproducedthe observed flood pattern in southern China,as well as the drought pattern in summer 2015.Meanwhile,the prediction ACC of winter temperature in China in 2016 increased to 0.32 from 0.19,and the percentage of the same sign of the temperature anomaly increased to 75% from 62%.Moreover,the year-to-year increment prediction method proposed by Fan et al.(2007) was applied successfully to predict summer rainfall over the Yangtze River valley in 2015,and winter temperature over North China in 2016.The year-to-year increment method predicts the year-to-year increment of the climate variable instead of the climate anomaly,in which the year-to-year increment of the climate is defined as the climate variable of the current year minus that of the previous year.The year-to-year increment of the climate variable was firstly predicted by the statistical or dynamical model,and then the predicted climate anomaly or climate variable of the current year could be obtained by adding the predicted year-to-year increment to the observed one of the previous year.The advantage of the year-to-year increment is that it can amplify the prediction signal,especially the extra tropical climate signal.Furthermore,as the observed climate in the previous year is an accurate value containing the interannual and interdecadal signals,it further promotes the level of accuracy in predicting the interannual and interdecadal climate variable.The results showed that the summer rainfall anomaly over the middle and lower reaches of the Yangtze River valley in 2015 could be predicted successfully by the year-to-year increment;the predicted(observed) value in 2015 was 38.6%(31%).Meanwhile,the upward trend of the summer rainfall anomaly over the middle and lower reaches of the Yangtze River valley since the 1980s,and the downward trend since 2000,were also reproduced.The model reproduced the warming trend since the 1970s,and the slowly cooling trend since 1998,with the predicted(observed) winter temperature anomaly over North China being 1.20℃(0.51℃).However,there is still a long way to go in terms of improving the prediction skill level in China to a sufficiently high level.The extratropical climate prediction skill should be improved by improvement to thedynamical model.It is necessary to explore how to combine the dynamical climate model with the statistical climate model more effectively.Importantly,climate theory,methods and techniques,models,as well as climate dynamics suited for climate variability in China,should be further developed.
Real-time seasonal climate prediction was performed in China during the extremely strong El Niño event of 2015/2016,through a combination of dynamical and statistical climate prediction.Generally,real-time summer(winter) climate prediction in China starts in February(October) in every year.The results showed that,although the NCEP-CFSv2 coupled model predicted the evolution of the extremely strong El Niño event in 2015/2016 well,its performance in predicting the summer rainfall anomaly of 2015 and the winter temperature of 2016 at 160 stations in China was limited.Compared to observation,CFSv2 predicted a stronger East Asian summer monsoon and weaker East Asian winter monsoon.One of the reasons for this is that CFSv2 is poor at predicting the extratropical climate system.Thus,based on the climate prediction direct outputs of the NCEP-CFSv2 model,we created a hybrid dynamical and statistical prediction model for forecasting the precipitation anomaly and temperature anomaly at 160 stations in China in 2015/2016.The skill of the hybrid of statistical and dynamical prediction model was higher than that of the direct prediction results of the NCEP-CFSv2 model.The spatial anomaly correlation coefficient(ACC) of summer rainfall at 160 stations in China in 2015 increased from 0.21 to 0.31(exceeding the 99% significance level),along with the percentage of the same sign of the rainfall anomaly improving to 60% from 50%.The model reproducedthe observed flood pattern in southern China,as well as the drought pattern in summer 2015.Meanwhile,the prediction ACC of winter temperature in China in 2016 increased to 0.32 from 0.19,and the percentage of the same sign of the temperature anomaly increased to 75% from 62%.Moreover,the year-to-year increment prediction method proposed by Fan et al.(2007) was applied successfully to predict summer rainfall over the Yangtze River valley in 2015,and winter temperature over North China in 2016.The year-to-year increment method predicts the year-to-year increment of the climate variable instead of the climate anomaly,in which the year-to-year increment of the climate is defined as the climate variable of the current year minus that of the previous year.The year-to-year increment of the climate variable was firstly predicted by the statistical or dynamical model,and then the predicted climate anomaly or climate variable of the current year could be obtained by adding the predicted year-to-year increment to the observed one of the previous year.The advantage of the year-to-year increment is that it can amplify the prediction signal,especially the extra tropical climate signal.Furthermore,as the observed climate in the previous year is an accurate value containing the interannual and interdecadal signals,it further promotes the level of accuracy in predicting the interannual and interdecadal climate variable.The results showed that the summer rainfall anomaly over the middle and lower reaches of the Yangtze River valley in 2015 could be predicted successfully by the year-to-year increment;the predicted(observed) value in 2015 was 38.6%(31%).Meanwhile,the upward trend of the summer rainfall anomaly over the middle and lower reaches of the Yangtze River valley since the 1980s,and the downward trend since 2000,were also reproduced.The model reproduced the warming trend since the 1970s,and the slowly cooling trend since 1998,with the predicted(observed) winter temperature anomaly over North China being 1.20℃(0.51℃).However,there is still a long way to go in terms of improving the prediction skill level in China to a sufficiently high level.The extratropical climate prediction skill should be improved by improvement to thedynamical model.It is necessary to explore how to combine the dynamical climate model with the statistical climate model more effectively.Importantly,climate theory,methods and techniques,models,as well as climate dynamics suited for climate variability in China,should be further developed.
4 Analysis of different monthly prediction skills over China during the 2015/2016 super El Niño event
2016, 39(6):756-765.
DOI: 10.13878/j.cnki.dqkxxb.20161007001
Abstract:
The ENSO cycle is a strong signal in atmosphere-ocean interaction,and plays a significant role in the global climate,including the East Asia monsoon region.Typically,in the developing phase of El Niño,the convection is strong in the east-central tropical Pacific,and weak in the west tropical Pacific and Maritime continent.In the following summer,the northwest subtropical high is weaker than normal,and is located southward from its normal position.As a result,the southwest jet stream from the Bay of Bengal is weaker than normal,and carries less moisture to mainland China.In the decaying phase of El Niño,the Philippines anti-cyclone can persist until summer,and the northwest subtropical high is strong and located westward from its normal position.The southwest jet stream from the Bay of Bengal is much stronger than normal and carries more moisture to mainland China.In addition,the Yangtze River typically experiences flood events.Aside from the ENSO cycle,the vertical averaged eddy temperature difference between the Asian and Pacific may have less influence on the East Asia summer monsoon.The Asian-Pacific Oscillation(APO) and its associated indexes can be used to identify this difference.With higher APO index years,in the upper troposphere the summer South Asian high and North Pacific trough are stronger,while the westerly jet stream over Asia and easterly jet stream over South Asia are strengthened.Further more,in the lower troposphere the Asian low and North Pacific subtropical high are stronger.The anomalous westerly prevails over South Asia,and the Meiyu front is located northward from its normal position.Such a circulation pattern may lead to greater rainfall in northern China,southern China and South Asia.Further analysis shows that the combined impact of the ENSO phase and APO index has different predictability for the East Asia climate.This paper will study the 2015/2016 monthly prediction skill differences under the background of super strong El Niño events and different APO index conditions.The data used in the paper include station precipitation data,BCC_DERF2.0 hindcast and forecast data,NCEP/NCAR reanalysis data,and the scores of NCC issued monthly precipitation forecast.Some of the results are obtained through verification methods and diagnostic techniques,as follows:(1) During the super El Niño event occurring from 2015 to 2016,the skills of the issued monthly precipitation prediction are high/stable in 2015(El Niño developing phase),and low/unstable in 2016(El Niño decaying phase).The skills of the key circulation predicted by BCC_DERF2.0 show results similar to the precipitation.Further analysis indicates that Asia-Pacific Oscillation(APO) may play another important role in the predictability of monthly scale prediction in 2015 and 2016.(2) The APO index is low in summer 2015 and high in summer 2016.The effect of low APO on East Asia circulation is consistent with that of the El Niño developing phase in 2015,while that of the high APO on East Asia circulation is not consistent with that of the El Niño decaying phase in 2016.That is to say,the eddy temperature difference between the Asian and Pacific in 2016 is favorable for strong Asia summer monsoons,while the El Niño decaying phase leads to weak summer monsoons.(3) The circulations in 2016 show some typical features of higher APO index conditions,and BCC_DERF2.0 can predict most of the features of the high APO index conditions in 2016.The summer rainfall anomaly in 2016 shows that both the Yangtze River and northern China experienced flood disasters.These facts imply that the climate features in 2016 are multi-factor results.(4) The combined effect of the APO index and El Niño phase may have different predictabilities on the monthly East Asian circulation.The skill of BCC_DERF2.0 depends on these two factors,as does the monthly precipitation in 2015 and 2016.
The ENSO cycle is a strong signal in atmosphere-ocean interaction,and plays a significant role in the global climate,including the East Asia monsoon region.Typically,in the developing phase of El Niño,the convection is strong in the east-central tropical Pacific,and weak in the west tropical Pacific and Maritime continent.In the following summer,the northwest subtropical high is weaker than normal,and is located southward from its normal position.As a result,the southwest jet stream from the Bay of Bengal is weaker than normal,and carries less moisture to mainland China.In the decaying phase of El Niño,the Philippines anti-cyclone can persist until summer,and the northwest subtropical high is strong and located westward from its normal position.The southwest jet stream from the Bay of Bengal is much stronger than normal and carries more moisture to mainland China.In addition,the Yangtze River typically experiences flood events.Aside from the ENSO cycle,the vertical averaged eddy temperature difference between the Asian and Pacific may have less influence on the East Asia summer monsoon.The Asian-Pacific Oscillation(APO) and its associated indexes can be used to identify this difference.With higher APO index years,in the upper troposphere the summer South Asian high and North Pacific trough are stronger,while the westerly jet stream over Asia and easterly jet stream over South Asia are strengthened.Further more,in the lower troposphere the Asian low and North Pacific subtropical high are stronger.The anomalous westerly prevails over South Asia,and the Meiyu front is located northward from its normal position.Such a circulation pattern may lead to greater rainfall in northern China,southern China and South Asia.Further analysis shows that the combined impact of the ENSO phase and APO index has different predictability for the East Asia climate.This paper will study the 2015/2016 monthly prediction skill differences under the background of super strong El Niño events and different APO index conditions.The data used in the paper include station precipitation data,BCC_DERF2.0 hindcast and forecast data,NCEP/NCAR reanalysis data,and the scores of NCC issued monthly precipitation forecast.Some of the results are obtained through verification methods and diagnostic techniques,as follows:(1) During the super El Niño event occurring from 2015 to 2016,the skills of the issued monthly precipitation prediction are high/stable in 2015(El Niño developing phase),and low/unstable in 2016(El Niño decaying phase).The skills of the key circulation predicted by BCC_DERF2.0 show results similar to the precipitation.Further analysis indicates that Asia-Pacific Oscillation(APO) may play another important role in the predictability of monthly scale prediction in 2015 and 2016.(2) The APO index is low in summer 2015 and high in summer 2016.The effect of low APO on East Asia circulation is consistent with that of the El Niño developing phase in 2015,while that of the high APO on East Asia circulation is not consistent with that of the El Niño decaying phase in 2016.That is to say,the eddy temperature difference between the Asian and Pacific in 2016 is favorable for strong Asia summer monsoons,while the El Niño decaying phase leads to weak summer monsoons.(3) The circulations in 2016 show some typical features of higher APO index conditions,and BCC_DERF2.0 can predict most of the features of the high APO index conditions in 2016.The summer rainfall anomaly in 2016 shows that both the Yangtze River and northern China experienced flood disasters.These facts imply that the climate features in 2016 are multi-factor results.(4) The combined effect of the APO index and El Niño phase may have different predictabilities on the monthly East Asian circulation.The skill of BCC_DERF2.0 depends on these two factors,as does the monthly precipitation in 2015 and 2016.
2016, 39(6):766-777.
DOI: 10.13878/j.cnki.dqkxxb.20160824001
Abstract:
Based on the seasonal mean sea surface temperature(SST) in HadISST,precipitation in CMAP and wind field in the NCEP/NCAR reanalysis dataset,the decaying phase of the 2015/2016 super El Niño event and its associated western North Pacific atmospheric circulation anomaly are investigated in this study.The 2015/2016 El Niño event not only exhibits strong intensity in the mature winter,but also declines rapidly in the subsequent spring and terminates in the summer.During the 2015/2016 winter,the SST anomaly over the central and eastern tropical Pacific is greater than two standard deviations,and is 60% more than the intensity in the composite observations of other El Niño events.This case is recognized as a super El Niño event,but it rapidly declines in the subsequent spring and transforms into a La Niña event in the summer.Additionally,an anticyclonic circulation anomaly persists over the western North Pacific(WNPAC),accompanied by the rapid decline of El Niño.On the one hand,the strong El Niño intensity and its accompanying warming over the Indian Ocean contribute to the steady persistence of the WNPAC associated with the 2015/2016 super El Niño event.On the other hand,the anomalous easterlies over the central and western equatorial Pacific,induced by the strong WNPAC,favor the rapid decline of the El Niño decaying phase.Furthermore,a thorough comparison of the 2015/2016 El Niño event to the cases of 1982/1983 and 1997/1998 suggests that their decaying phases are quite different,despite all being super El Niños with similar wintertime intensity.The 1982/1983 El Niño declines slowly and persists into the following autumn,whereas the 1997/1998 case declines rapidly and has already terminated in the following summer.The length of the El Niño decaying phase is associated with the strength of the springtime WNPAC.The 1982/1983(1997/1998) El Niño is related to a weak(strong) WNPAC in the decaying phase.On the one hand,the decaying rate of the 2015/2016 El Niño is faster than the 1982/1983 case,due to the stronger WNPAC in the 2015/2016 El Niño than that in the 1982/1983 event.On the other hand,the warmest center in the 2015/2016 case is close to the central equatorial Pacific,where the negative SST anomaly first emerges.Thus,although the WNPAC is stronger in 1997/1998 case,the decaying length is similar to the 2015/2016 event.The results imply a complicated interaction between the WNPAC and the El Niño decaying phase,which needs to be further studied.
Based on the seasonal mean sea surface temperature(SST) in HadISST,precipitation in CMAP and wind field in the NCEP/NCAR reanalysis dataset,the decaying phase of the 2015/2016 super El Niño event and its associated western North Pacific atmospheric circulation anomaly are investigated in this study.The 2015/2016 El Niño event not only exhibits strong intensity in the mature winter,but also declines rapidly in the subsequent spring and terminates in the summer.During the 2015/2016 winter,the SST anomaly over the central and eastern tropical Pacific is greater than two standard deviations,and is 60% more than the intensity in the composite observations of other El Niño events.This case is recognized as a super El Niño event,but it rapidly declines in the subsequent spring and transforms into a La Niña event in the summer.Additionally,an anticyclonic circulation anomaly persists over the western North Pacific(WNPAC),accompanied by the rapid decline of El Niño.On the one hand,the strong El Niño intensity and its accompanying warming over the Indian Ocean contribute to the steady persistence of the WNPAC associated with the 2015/2016 super El Niño event.On the other hand,the anomalous easterlies over the central and western equatorial Pacific,induced by the strong WNPAC,favor the rapid decline of the El Niño decaying phase.Furthermore,a thorough comparison of the 2015/2016 El Niño event to the cases of 1982/1983 and 1997/1998 suggests that their decaying phases are quite different,despite all being super El Niños with similar wintertime intensity.The 1982/1983 El Niño declines slowly and persists into the following autumn,whereas the 1997/1998 case declines rapidly and has already terminated in the following summer.The length of the El Niño decaying phase is associated with the strength of the springtime WNPAC.The 1982/1983(1997/1998) El Niño is related to a weak(strong) WNPAC in the decaying phase.On the one hand,the decaying rate of the 2015/2016 El Niño is faster than the 1982/1983 case,due to the stronger WNPAC in the 2015/2016 El Niño than that in the 1982/1983 event.On the other hand,the warmest center in the 2015/2016 case is close to the central equatorial Pacific,where the negative SST anomaly first emerges.Thus,although the WNPAC is stronger in 1997/1998 case,the decaying length is similar to the 2015/2016 event.The results imply a complicated interaction between the WNPAC and the El Niño decaying phase,which needs to be further studied.
6 Characteristics and particularity of local air-sea processes for the 2015/2016 super El Niño event
2016, 39(6):778-787.
DOI: 10.13878/j.cnki.dqkxxb.20160825001
Abstract:
Based on the latest monthly global reanalyzed NOAA(National Oceanic and Atmospheric Administration) sea surface temperature(SST) and NCEP(National Centers for Environmental Prediction)/NCAR(National Center for Atmospheric Research) atmospheric circulation data,we analyzed the characteristics of the local air-sea processes for the 2015/2016 super El Niño event,and the differences with previous(1982/1983 and 1997/1998) super El Niño events are also discussed.The 2015/2016 super El Niño event can be regarded as the strongest on record,since the corresponding indices of El Niño duration,peak intensity and accumulated SST anomaly remain the strongest among the existing three super El Niño events.The location of the tropical SST anomaly was displaced further west compared with the 1982/1983 and 1997/1998 events.As a result,the SST of the 2015/2016 El Niño event was colder in the tropical eastern Pacific and warmer in the central Pacific than that of the previous two super El Niño events.Due to nonlinear responses of the convectional precipitation to the SST anomaly,precipitation anomalies were weaker in the tropical eastern Pacific and much stronger in the central Pacific during the 2015/2016 El Niño event than those during the previous two super El Niño events,which was particularly evident from the El Niño December to the following April.Moreover,the 1982/1983 and 1997/1998 super El Niño events exhibited obvious southward shifts of the atmospheric responses from the equator to 5°S in the tropical central Pacific during the mature-to-decay phase.However,the precipitation and the westerly wind anomalies during the same phase of the 2015/2016 event were mainly located near the equator and the meridional movements were not as robust as those during the 1982/1983 and 1997/1998 events.The intensities of the ENSO combination mode,which results from the interaction between ENSO and the annual cycle,were also weaker during the 2015/2016 event than those during the previous two super El Niño events,and so was the anomalous western North Pacific anticyclone.Further analyses reveal that these particular phenomena in the 2015/2016 super El Niño were the consequence of the westward shift of the SST anomaly in the tropical central Pacific from winter 2015 to spring 2016.The relatively cold climatological SST north of the equator increased and exceeded the convection threshold,which favored the convection activities both south and north of the equator and led to the weakened meridional movement of the atmospheric responses.
Based on the latest monthly global reanalyzed NOAA(National Oceanic and Atmospheric Administration) sea surface temperature(SST) and NCEP(National Centers for Environmental Prediction)/NCAR(National Center for Atmospheric Research) atmospheric circulation data,we analyzed the characteristics of the local air-sea processes for the 2015/2016 super El Niño event,and the differences with previous(1982/1983 and 1997/1998) super El Niño events are also discussed.The 2015/2016 super El Niño event can be regarded as the strongest on record,since the corresponding indices of El Niño duration,peak intensity and accumulated SST anomaly remain the strongest among the existing three super El Niño events.The location of the tropical SST anomaly was displaced further west compared with the 1982/1983 and 1997/1998 events.As a result,the SST of the 2015/2016 El Niño event was colder in the tropical eastern Pacific and warmer in the central Pacific than that of the previous two super El Niño events.Due to nonlinear responses of the convectional precipitation to the SST anomaly,precipitation anomalies were weaker in the tropical eastern Pacific and much stronger in the central Pacific during the 2015/2016 El Niño event than those during the previous two super El Niño events,which was particularly evident from the El Niño December to the following April.Moreover,the 1982/1983 and 1997/1998 super El Niño events exhibited obvious southward shifts of the atmospheric responses from the equator to 5°S in the tropical central Pacific during the mature-to-decay phase.However,the precipitation and the westerly wind anomalies during the same phase of the 2015/2016 event were mainly located near the equator and the meridional movements were not as robust as those during the 1982/1983 and 1997/1998 events.The intensities of the ENSO combination mode,which results from the interaction between ENSO and the annual cycle,were also weaker during the 2015/2016 event than those during the previous two super El Niño events,and so was the anomalous western North Pacific anticyclone.Further analyses reveal that these particular phenomena in the 2015/2016 super El Niño were the consequence of the westward shift of the SST anomaly in the tropical central Pacific from winter 2015 to spring 2016.The relatively cold climatological SST north of the equator increased and exceeded the convection threshold,which favored the convection activities both south and north of the equator and led to the weakened meridional movement of the atmospheric responses.
2016, 39(6):788-800.
DOI: 10.13878/j.cnki.dqkxxb.20161012010
Abstract:
El Niño is one of the most important climate variations at interannual scales.It can influence the global climate by changing the character of the sea-air system every 3-7 years,including the activity of tropical storms(TSs) and typhoons over the western North Pacific(WNP).Composite results of El Niño events show that there are more TS systems with longer lifetime and greater strength occurring more to the southeast over the WNP in the summer of El Niño developing years because of the changed mean position of Walker circulation.However,this is not the case for the 2015/2016 super El Niño year.The typhoon season over the WNP is generally from June to October.Climatologically(1979-2015),there are only 2.8 TSs generated during January to May before the onset of the typhoon season.Among them,about 1.4 TS systems may develop into a typhoon system.However,seven(five) TS(typhoon) systems occurred over the WNP in January to May in 2015,based on the JTWC best-track dataset.This is 2.5(3.6) times larger than the climate mean,suggesting that the typhoon season in 2015 started earlier than usual.To investigate what mechanisms induced the earlier onset of the typhoon season in 2015,we diagnosed the large-scale environments from ERA-Interim and NOAA ERSST data.The results show that the unusual growth of TS activity in early 2015 was related to the anomalous air-sea conditions of the 2015/2016 super El Niño event.The anomalous warming over the central equatorial Pacific associated with the abortion of the 2014/2015 El Niño was accompanied by a cyclonic anomaly,low-level convergence and increased atmospheric moisture content over the WNP,where tropical cyclones were generated.We further analyzed the genesis potential index(GPI) to understand the relative roles of different dynamic and thermodynamic effects in the increased number of typhoons during January to May 2015,as compared to the climatological state.The results of the GPI diagnosis indicated that the dynamic(low-level vorticity and vertical velocity) and thermodynamic(potential intensity related to sea surface and air temperature and atmospheric relative humidity in the lower to middle levels) factors both contributed positively to the increases in typhoon genesis during January to May in 2015.The low-level vorticity anomaly showed the largest contribution,while the enhanced relative humidity was the secondary contributor.The former may have been related to the Rossby wave response to the warm sea surface temperature in the central equatorial Pacific.The low-level westerly wind associated with the cyclonic anomaly may have weakened the trade winds and vertical wind shear.The processes related to increased moisture content were examined in detail through moisture budget diagnosis.The leading term was related to the advection of low-level seasonal mean moisture in the warm pool via the anomalous ascending motion of the Walker circulation.The strengthened vertical moisture advection rapidly increased from November 2014 to January 2015 and reached its maximum value in February 2015,resulting in mid-level moistening and atmospheric diabatic heating.Apart from the influence of large-scale air-sea conditions,3-10-day synoptic-scale disturbances and 10-90-day intraseasonal oscillation were also enhanced during January to May 2015,favoring the genesis and development of tropical depressions/typhoon systems.
El Niño is one of the most important climate variations at interannual scales.It can influence the global climate by changing the character of the sea-air system every 3-7 years,including the activity of tropical storms(TSs) and typhoons over the western North Pacific(WNP).Composite results of El Niño events show that there are more TS systems with longer lifetime and greater strength occurring more to the southeast over the WNP in the summer of El Niño developing years because of the changed mean position of Walker circulation.However,this is not the case for the 2015/2016 super El Niño year.The typhoon season over the WNP is generally from June to October.Climatologically(1979-2015),there are only 2.8 TSs generated during January to May before the onset of the typhoon season.Among them,about 1.4 TS systems may develop into a typhoon system.However,seven(five) TS(typhoon) systems occurred over the WNP in January to May in 2015,based on the JTWC best-track dataset.This is 2.5(3.6) times larger than the climate mean,suggesting that the typhoon season in 2015 started earlier than usual.To investigate what mechanisms induced the earlier onset of the typhoon season in 2015,we diagnosed the large-scale environments from ERA-Interim and NOAA ERSST data.The results show that the unusual growth of TS activity in early 2015 was related to the anomalous air-sea conditions of the 2015/2016 super El Niño event.The anomalous warming over the central equatorial Pacific associated with the abortion of the 2014/2015 El Niño was accompanied by a cyclonic anomaly,low-level convergence and increased atmospheric moisture content over the WNP,where tropical cyclones were generated.We further analyzed the genesis potential index(GPI) to understand the relative roles of different dynamic and thermodynamic effects in the increased number of typhoons during January to May 2015,as compared to the climatological state.The results of the GPI diagnosis indicated that the dynamic(low-level vorticity and vertical velocity) and thermodynamic(potential intensity related to sea surface and air temperature and atmospheric relative humidity in the lower to middle levels) factors both contributed positively to the increases in typhoon genesis during January to May in 2015.The low-level vorticity anomaly showed the largest contribution,while the enhanced relative humidity was the secondary contributor.The former may have been related to the Rossby wave response to the warm sea surface temperature in the central equatorial Pacific.The low-level westerly wind associated with the cyclonic anomaly may have weakened the trade winds and vertical wind shear.The processes related to increased moisture content were examined in detail through moisture budget diagnosis.The leading term was related to the advection of low-level seasonal mean moisture in the warm pool via the anomalous ascending motion of the Walker circulation.The strengthened vertical moisture advection rapidly increased from November 2014 to January 2015 and reached its maximum value in February 2015,resulting in mid-level moistening and atmospheric diabatic heating.Apart from the influence of large-scale air-sea conditions,3-10-day synoptic-scale disturbances and 10-90-day intraseasonal oscillation were also enhanced during January to May 2015,favoring the genesis and development of tropical depressions/typhoon systems.
2016, 39(6):801-812.
DOI: 10.13878/j.cnki.dqkxxb.20160908001
Abstract:
A super El Niño event occurred in 2015/2016.The sea surface temperature (SST) anomaly in the Niño3 area in the winter of 2015/2016 was over 2.5℃.This strong El Niño was an Eastern Pacific type event and had strong impacts on global climate conditions.In the present paper,by employing NCEP/NCAR reanalysis,Hadley SST and CMAP precipitation data,we examine the impacts of this El Niño event on the Australian summer monsoon circulation and precipitation anomalies from the peak phase to the decaying phase of the 2015/2016 strong El Niño event.We also examine the mechanism behind these impacts.Affected by this El Niño event,the precipitation in most areas of Australia significantly decreased,and in some areas even reduced by 60% to 80%.Two mechanisms can explain the influence of this El Niño event on Australian rainfall.The first is horizontal circulation anomaly-related.A Gill-type response of the atmosphere to the SST anomalies in the tropical region occurred,inducing horizontal circulation anomalies and hence weakening the Australian summer monsoon.Specifically,negative SST anomalies in the equatorial western Pacific during both the peak and decaying phases of the 2015/2016 strong El Niño event led to negative heat source anomalies locally,resulting in two anomalous anticyclonic circulations that were respectively situated on the northern and southern sides of the equator.The anomalous anticyclonic circulation in the region south of the Maritime Continent(MC) region weakened the Australian summer monsoon,suppressing the upward movement locally and hence reducing the rainfall over Australia.The second mechanism is vertical circulation-related.During the super El Niño event of 2015/2016,anomalous vertical circulation existed,with its upward motion branch in the equatorial eastern and central Pacific and downward branch in Australia.This anomalous vertical circulation directly bridged the gap between the central equatorial Pacific and Australia,facilitating the reduction in precipitation over Australia.During the peak phase of this El Niño event,anomalous Walker circulation was observed,with upward motion in the central equatorial Pacific due to the positive anomalies of SST,but downward motion in the MC regions.Meanwhile,another vertical circulation system was well defined in a slanted vertical plane from Australia northeastwards to the central equatorial Pacific.This was,of course,related to the weakened Australian summer monsoon.As a result,this northeast-southwest cell of vertical circulation played an important role in maintaining negative anomalies of rainfall over Australia.Moreover,the anomalous upward motion was observed in the southern part of China,which associated in a compensative manner with the downward motion in the MC regions and Australia.These anomalous vertical motions formed an anomalous vertical circulation system that meridionally connected Australia and southern China.This vertical circulation suggests a possible indirect effect of a weakened East Asian winter monsoon anomaly,as induced by this super El Niño event,on the Australian summer monsoon.All the results presented in this study will be beneficial for a better understanding of the underlying mechanisms of Australian monsoon variations in association with super ENSO events,as well as for uncovering clues to predicting Australian summer rainfall.
A super El Niño event occurred in 2015/2016.The sea surface temperature (SST) anomaly in the Niño3 area in the winter of 2015/2016 was over 2.5℃.This strong El Niño was an Eastern Pacific type event and had strong impacts on global climate conditions.In the present paper,by employing NCEP/NCAR reanalysis,Hadley SST and CMAP precipitation data,we examine the impacts of this El Niño event on the Australian summer monsoon circulation and precipitation anomalies from the peak phase to the decaying phase of the 2015/2016 strong El Niño event.We also examine the mechanism behind these impacts.Affected by this El Niño event,the precipitation in most areas of Australia significantly decreased,and in some areas even reduced by 60% to 80%.Two mechanisms can explain the influence of this El Niño event on Australian rainfall.The first is horizontal circulation anomaly-related.A Gill-type response of the atmosphere to the SST anomalies in the tropical region occurred,inducing horizontal circulation anomalies and hence weakening the Australian summer monsoon.Specifically,negative SST anomalies in the equatorial western Pacific during both the peak and decaying phases of the 2015/2016 strong El Niño event led to negative heat source anomalies locally,resulting in two anomalous anticyclonic circulations that were respectively situated on the northern and southern sides of the equator.The anomalous anticyclonic circulation in the region south of the Maritime Continent(MC) region weakened the Australian summer monsoon,suppressing the upward movement locally and hence reducing the rainfall over Australia.The second mechanism is vertical circulation-related.During the super El Niño event of 2015/2016,anomalous vertical circulation existed,with its upward motion branch in the equatorial eastern and central Pacific and downward branch in Australia.This anomalous vertical circulation directly bridged the gap between the central equatorial Pacific and Australia,facilitating the reduction in precipitation over Australia.During the peak phase of this El Niño event,anomalous Walker circulation was observed,with upward motion in the central equatorial Pacific due to the positive anomalies of SST,but downward motion in the MC regions.Meanwhile,another vertical circulation system was well defined in a slanted vertical plane from Australia northeastwards to the central equatorial Pacific.This was,of course,related to the weakened Australian summer monsoon.As a result,this northeast-southwest cell of vertical circulation played an important role in maintaining negative anomalies of rainfall over Australia.Moreover,the anomalous upward motion was observed in the southern part of China,which associated in a compensative manner with the downward motion in the MC regions and Australia.These anomalous vertical motions formed an anomalous vertical circulation system that meridionally connected Australia and southern China.This vertical circulation suggests a possible indirect effect of a weakened East Asian winter monsoon anomaly,as induced by this super El Niño event,on the Australian summer monsoon.All the results presented in this study will be beneficial for a better understanding of the underlying mechanisms of Australian monsoon variations in association with super ENSO events,as well as for uncovering clues to predicting Australian summer rainfall.
2016, 39(6):813-826.
DOI: 10.13878/j.cnki.dqkxxb.20161108001
Abstract:
The different influences of moderate El Niño and 2015/2016 extreme El Niño on winter and spring precipitation over southeast China,Yangtze-Huaihe Rivers Basins and southwest China are invested,based on monthly precipitation of 160 stations in China,OISST and NCEP/NCAR circulation datasets.The results are as follows:in the winter of moderate El Niño,anomalous warmer sea surface temperature(SST) over equatorial central-eastern Pacific triggers a pair of anomalous anticyclone over northwest Pacific and around Japan.The anomalous southwesterly enhances water vapor from South China Sea-northwest Pacific(SCS-WNP) to eastern China and causes positive anomalies of precipitation over southeast China and Yangtze-Huaihe Rivers Basins.On contrast,the equatorial central-eastern Pacific SST gets much warmer in the winter of 2015/2016 extreme El Niño.Meanwhile,anomalous cooler surface and lower troposphere temperature over eastern China intensify continental cold high,which results in northerly anomalies over north of Yangtze River.It is responsible for the increase of precipitation over southeast China and the decrease of precipitation over Yangtze-Huaihe Rivers Basins.Compare to the decaying phase of moderate El Niño in the spring,the increase of precipitations over southeast China and southwest China is attributed to anomalous warmer SST over northwest Indian Ocean and southeast Indian Ocean.The numerical experiments of CAM5 model demonstrate that the anomalous warmer SST over northwest Indian Ocean leads to southwesterly anomaly and triggers anomalous anticyclonic circulations over the Bay of Bengal and northwest Pacific,which is responsible for an increase in water vapor from the Indian Ocean and SCS-WNP to southwest China and southeast China.The anomalous warmer SST over southeast Indian Ocean arouses local ascending motion,and then it strengthens anomalies of descent over SCS-WNP and ascent over southeast China,resulting in positive anomalies of southeast China rainfall.
The different influences of moderate El Niño and 2015/2016 extreme El Niño on winter and spring precipitation over southeast China,Yangtze-Huaihe Rivers Basins and southwest China are invested,based on monthly precipitation of 160 stations in China,OISST and NCEP/NCAR circulation datasets.The results are as follows:in the winter of moderate El Niño,anomalous warmer sea surface temperature(SST) over equatorial central-eastern Pacific triggers a pair of anomalous anticyclone over northwest Pacific and around Japan.The anomalous southwesterly enhances water vapor from South China Sea-northwest Pacific(SCS-WNP) to eastern China and causes positive anomalies of precipitation over southeast China and Yangtze-Huaihe Rivers Basins.On contrast,the equatorial central-eastern Pacific SST gets much warmer in the winter of 2015/2016 extreme El Niño.Meanwhile,anomalous cooler surface and lower troposphere temperature over eastern China intensify continental cold high,which results in northerly anomalies over north of Yangtze River.It is responsible for the increase of precipitation over southeast China and the decrease of precipitation over Yangtze-Huaihe Rivers Basins.Compare to the decaying phase of moderate El Niño in the spring,the increase of precipitations over southeast China and southwest China is attributed to anomalous warmer SST over northwest Indian Ocean and southeast Indian Ocean.The numerical experiments of CAM5 model demonstrate that the anomalous warmer SST over northwest Indian Ocean leads to southwesterly anomaly and triggers anomalous anticyclonic circulations over the Bay of Bengal and northwest Pacific,which is responsible for an increase in water vapor from the Indian Ocean and SCS-WNP to southwest China and southeast China.The anomalous warmer SST over southeast Indian Ocean arouses local ascending motion,and then it strengthens anomalies of descent over SCS-WNP and ascent over southeast China,resulting in positive anomalies of southeast China rainfall.
2016, 39(6):827-834.
DOI: 10.13878/j.cnki.dqkxxb.20160801022
Abstract:
A super cold wave occurred in South China in January 2016 against the background of the extremely strong El Niño of 2016/2016.Cities in the Yangtze River Delta experienced their coldest temperatures since 1991;for example,the minimum temperature in Nanjing was -10℃.Also,new records for minimum temperature were set in South China;for example,the minimum temperature in Fuzhou was -1.9℃.To analyze the dynamic mechanism involved,Plumb's wave activity flux(WAF) and local Eliassen-Palm flux were computed using ERA-Interim reanalysis data.Harmonic analysis along the parallel circles was performed firstly,to extract the 1-4 wave signal,revealing evident modulation by transient waves of the atmospheric longwave anomalies.The previous positive anomaly of the sea surface heat flux in the North Atlantic in December 2015 benefitted the maintenance of the later Atlantic blocking.The energy of the atmospheric long waves was propagated from the Atlantic blocking to the midlatitudes in East Asia along the great circle.The Urals blocking and transverse trough in East Asia developed well.The meridional distribution of the atmospheric disturbance centers led to more cold air in the transverse trough.Before the outbreak of the cold wave,two transient wave trains were located in Eurasia.The northern one lay along western Europe to East Asia and modulated the rotation of the transverse trough.At the same time,the southern one lay along western Europe to the Bay of Bengal and weakened the India-Burma trough.They came together to favor cold advection moving southwards to South China.The cold wave then occurred in South China.
A super cold wave occurred in South China in January 2016 against the background of the extremely strong El Niño of 2016/2016.Cities in the Yangtze River Delta experienced their coldest temperatures since 1991;for example,the minimum temperature in Nanjing was -10℃.Also,new records for minimum temperature were set in South China;for example,the minimum temperature in Fuzhou was -1.9℃.To analyze the dynamic mechanism involved,Plumb's wave activity flux(WAF) and local Eliassen-Palm flux were computed using ERA-Interim reanalysis data.Harmonic analysis along the parallel circles was performed firstly,to extract the 1-4 wave signal,revealing evident modulation by transient waves of the atmospheric longwave anomalies.The previous positive anomaly of the sea surface heat flux in the North Atlantic in December 2015 benefitted the maintenance of the later Atlantic blocking.The energy of the atmospheric long waves was propagated from the Atlantic blocking to the midlatitudes in East Asia along the great circle.The Urals blocking and transverse trough in East Asia developed well.The meridional distribution of the atmospheric disturbance centers led to more cold air in the transverse trough.Before the outbreak of the cold wave,two transient wave trains were located in Eurasia.The northern one lay along western Europe to East Asia and modulated the rotation of the transverse trough.At the same time,the southern one lay along western Europe to the Bay of Bengal and weakened the India-Burma trough.They came together to favor cold advection moving southwards to South China.The cold wave then occurred in South China.
2016, 39(6):835-844.
DOI: 10.13878/j.cnki.dqkxxb.20160828010
Abstract:
The El Niño Southern Oscillation is the most significant interannual scale signal of global tropical air sea systems.It can affect the East Asian monsoon system through the teleconnection form of air-sea interaction,following which it has an impact on climate in China.Therefore,El Niño is one of the most important predictors of short-term climate in China.El Niño events typically begin in the spring and summer,mature in the autumn and winter,and subside in the spring and summer of the following year.Considering the hysteretic response of the atmosphere to the ocean,El Niño can have an influence on the atmospheric circulation over East Asia,and even the precipitation in China in decaying years of El Niño.Therefore,the anomalies of summer rainfall in China and atmospheric circulation over East Asia in the decaying years of two super El Nino events(2015/2016 and 1997/1998) were compared,in order to improve the understanding of the relationship between El Niño events and climate anomalies in China,as well as to provide a reference for short-term climate prediction.Specifically speaking,the percentage of precipitation anomaly in China,water vapor flux anomaly,anomaly of water vapor flux divergence,geopotential height anomaly,western end of the ridge and position of the ridge of the subtropical high and sea surface temperature anomaly in the decaying years of two super El Nino events were analyzed,by means of the monthly mean precipitation data of 160 meteorological observation stations in China,along with the circulation index,Indian Ocean Basin-wide Warming index from the National Climate Center of China Meteorological Administration,monthly mean geopotential height,wind,specific humidity and surface pressure from the American National Centers for Environmental Prediction,and the Optimum Interpolation Sea Surface Temperature version 2 data from the American National Oceanic and Atmospheric Administration.The results are as follows.Summer rainfall frequently occurs on a large scaleand flood disaster is serious in 2016 and 2008.However,summer rainfall anomalies in the two years also have different characteristics.The area of summer precipitation positive anomaly in 2016 is more concentrated than that in 1998,but the intensity of precipitation in 2016 is lower than that in 1998.In June and July 2016,the positive anomalous precipitation is maintained in the area to the north of the Yangtze River.By August,the positive anomalous precipitation area is significantly reduced.There is only a small range of rainfall in southern China,which is mainly caused by typhoons.Therefore,the seasonal moving features of the rain band are not significant,while the area of the rainfall positive anomaly gradually moves from south to north during the summer of 1998,which is consistent with the traditional process of the precipitation of the monsoon.The difference of summer rainfall in 2016 and 2008 in China is closely related to the difference of the anomaly of water vapor flux divergence caused by the anomaly of atmospheric circulation.The Pacific Subtropical High in summer 1998 is more robust and located more to the west than that of summer 2016,and the ridge of the Pacific Subtropical High in summer 1998 is more to the south than that of 2016.Moreover,the Pacific Subtropical Highin June and July is located more to the southwest in 1998 than 2016,while the Pacific Subtropical High in August is more to the west in 2016 than 1998,and more to the north than usual.These differences of the Pacific Subtropical High can partially explain the differences between the 2016 and 2008 summer rainfall in China.Further more,one possible reason for the difference of the Pacific Sub tropical High in June and July in 1998 and 2016 is that the Western Equatorial Pacific sea surface temperature in 1997/1998 is colder than that in 2015/2016.The difference of the North western Equatorial Pacific sea surface temperature may also attribute to the difference of the Subtropical High in August of 1998 and 2016.
The El Niño Southern Oscillation is the most significant interannual scale signal of global tropical air sea systems.It can affect the East Asian monsoon system through the teleconnection form of air-sea interaction,following which it has an impact on climate in China.Therefore,El Niño is one of the most important predictors of short-term climate in China.El Niño events typically begin in the spring and summer,mature in the autumn and winter,and subside in the spring and summer of the following year.Considering the hysteretic response of the atmosphere to the ocean,El Niño can have an influence on the atmospheric circulation over East Asia,and even the precipitation in China in decaying years of El Niño.Therefore,the anomalies of summer rainfall in China and atmospheric circulation over East Asia in the decaying years of two super El Nino events(2015/2016 and 1997/1998) were compared,in order to improve the understanding of the relationship between El Niño events and climate anomalies in China,as well as to provide a reference for short-term climate prediction.Specifically speaking,the percentage of precipitation anomaly in China,water vapor flux anomaly,anomaly of water vapor flux divergence,geopotential height anomaly,western end of the ridge and position of the ridge of the subtropical high and sea surface temperature anomaly in the decaying years of two super El Nino events were analyzed,by means of the monthly mean precipitation data of 160 meteorological observation stations in China,along with the circulation index,Indian Ocean Basin-wide Warming index from the National Climate Center of China Meteorological Administration,monthly mean geopotential height,wind,specific humidity and surface pressure from the American National Centers for Environmental Prediction,and the Optimum Interpolation Sea Surface Temperature version 2 data from the American National Oceanic and Atmospheric Administration.The results are as follows.Summer rainfall frequently occurs on a large scaleand flood disaster is serious in 2016 and 2008.However,summer rainfall anomalies in the two years also have different characteristics.The area of summer precipitation positive anomaly in 2016 is more concentrated than that in 1998,but the intensity of precipitation in 2016 is lower than that in 1998.In June and July 2016,the positive anomalous precipitation is maintained in the area to the north of the Yangtze River.By August,the positive anomalous precipitation area is significantly reduced.There is only a small range of rainfall in southern China,which is mainly caused by typhoons.Therefore,the seasonal moving features of the rain band are not significant,while the area of the rainfall positive anomaly gradually moves from south to north during the summer of 1998,which is consistent with the traditional process of the precipitation of the monsoon.The difference of summer rainfall in 2016 and 2008 in China is closely related to the difference of the anomaly of water vapor flux divergence caused by the anomaly of atmospheric circulation.The Pacific Subtropical High in summer 1998 is more robust and located more to the west than that of summer 2016,and the ridge of the Pacific Subtropical High in summer 1998 is more to the south than that of 2016.Moreover,the Pacific Subtropical Highin June and July is located more to the southwest in 1998 than 2016,while the Pacific Subtropical High in August is more to the west in 2016 than 1998,and more to the north than usual.These differences of the Pacific Subtropical High can partially explain the differences between the 2016 and 2008 summer rainfall in China.Further more,one possible reason for the difference of the Pacific Sub tropical High in June and July in 1998 and 2016 is that the Western Equatorial Pacific sea surface temperature in 1997/1998 is colder than that in 2015/2016.The difference of the North western Equatorial Pacific sea surface temperature may also attribute to the difference of the Subtropical High in August of 1998 and 2016.
12 Study on the characteristics of air temperature in summer following El Niño events over East China
2016, 39(6):845-854.
DOI: 10.13878/j.cnki.dqkxxb.20130427001
Abstract:
Using the HadISST and NCEP/NCAR reanalysis data,a diagnosis and analysis was carried out for the abnormal temperature over eastern China(EC) during El Niño events in the following summer beginning from 1949.The results show that,in the summer after EP+CP El Niño,the negative temperature anomaly appeared in the Shandong-Huaihe Basin and along the coast of southern China,while the other areas showed positive anomaly.The EP El Niño,EC showed negative anomaly throughout,and the range in the north was greater than that to the south of the Yangtze River.For the CP El Niño,the temperature throughout the north was down more than that in the south of the Yangtze River.The corresponding atmospheric circulation analyses indicated that,in the summer after the three types of El Niño events,the anomalous zonal vertical circulation of the equatorial region(5°S-5°N) was shown to appear as three circles,but their anomolies not only had differences in strength,the latitude ranges were also different.In the summer after EP+CP El Niño events or EP El Niño events,there were two abnormal Walker circulations in the equatorial Pacific,while in the summer following CP El Niño events there were two Walker circulation anomalies in the equatorial India Ocean.The intensity and range of the subtropical high in the Western Pacific Ocean at 500 hPa was one of the main reasons for the difference of temperature distribution in EC during the summer after the three types of El Niño events.In the summer following EP+CP El Niño events,the 500 hPa geopotential height anomaly showed "sandwich" type distribution over eastern China.The eastern part of northeast China,the Shandong Peninsula and southern China area were positive anomalies,while the other regions were reduced to some extent,and the negative anomaly amplitude decreased from north to south.In the summer after EP El Niño events,the 500 hPa geopotential height had different degrees of reduction over EC,the meridional circulation was strengthened,which was conducive to the cold air travelling southward,thus the temperature was significantly lower than normal,the intensity of the subtropical high in the Western Pacific was weakened,its coverage decreased,and there was a certain degree of negative temperature anomaly in southern China.In the summer after CP El Niño events,the meridional circulation was relatively strong at the 500 hPa geopotential height over EC,which was conducive to the cold air travelling southward to the north of the Yangtze River region,the temperature was low in the north,the West Pacific subtropical high travelled southward,with a rather flat shape,the effect range of the subtropical high increased and its strength increased slightly,and the effect of the subtropical high on southern China strengthened,so that the temperature in southern China increased.However,the effect of the subtropical high to the north of the Yangtze River weakened and caused the temperature there to drop;the transportation of the southwest warm and humid air at 850 hPa also had a significant effect on this.
Using the HadISST and NCEP/NCAR reanalysis data,a diagnosis and analysis was carried out for the abnormal temperature over eastern China(EC) during El Niño events in the following summer beginning from 1949.The results show that,in the summer after EP+CP El Niño,the negative temperature anomaly appeared in the Shandong-Huaihe Basin and along the coast of southern China,while the other areas showed positive anomaly.The EP El Niño,EC showed negative anomaly throughout,and the range in the north was greater than that to the south of the Yangtze River.For the CP El Niño,the temperature throughout the north was down more than that in the south of the Yangtze River.The corresponding atmospheric circulation analyses indicated that,in the summer after the three types of El Niño events,the anomalous zonal vertical circulation of the equatorial region(5°S-5°N) was shown to appear as three circles,but their anomolies not only had differences in strength,the latitude ranges were also different.In the summer after EP+CP El Niño events or EP El Niño events,there were two abnormal Walker circulations in the equatorial Pacific,while in the summer following CP El Niño events there were two Walker circulation anomalies in the equatorial India Ocean.The intensity and range of the subtropical high in the Western Pacific Ocean at 500 hPa was one of the main reasons for the difference of temperature distribution in EC during the summer after the three types of El Niño events.In the summer following EP+CP El Niño events,the 500 hPa geopotential height anomaly showed "sandwich" type distribution over eastern China.The eastern part of northeast China,the Shandong Peninsula and southern China area were positive anomalies,while the other regions were reduced to some extent,and the negative anomaly amplitude decreased from north to south.In the summer after EP El Niño events,the 500 hPa geopotential height had different degrees of reduction over EC,the meridional circulation was strengthened,which was conducive to the cold air travelling southward,thus the temperature was significantly lower than normal,the intensity of the subtropical high in the Western Pacific was weakened,its coverage decreased,and there was a certain degree of negative temperature anomaly in southern China.In the summer after CP El Niño events,the meridional circulation was relatively strong at the 500 hPa geopotential height over EC,which was conducive to the cold air travelling southward to the north of the Yangtze River region,the temperature was low in the north,the West Pacific subtropical high travelled southward,with a rather flat shape,the effect range of the subtropical high increased and its strength increased slightly,and the effect of the subtropical high on southern China strengthened,so that the temperature in southern China increased.However,the effect of the subtropical high to the north of the Yangtze River weakened and caused the temperature there to drop;the transportation of the southwest warm and humid air at 850 hPa also had a significant effect on this.
2016, 39(6):855-864.
DOI: 10.13878/j.cnki.dqkxxb.20130427001
Abstract:
The new El Niño phenomenons named central Pacific(CP) El Niño are discussed all over the world in the most nearly three decades.Specially,two types of CP El Niño which have different sea surface temperature anomalies(SSTA) structures are investigated in recent years.In order to recognize the different sea-air interaction processes of two types of CP El Niño comprehensively,in this research,we base on monthly Hadley Center sea surface temperature(HadISST),European Centre for Medium-Range Weather Forecasts(ECMWF) ocean subsurface temperature and NCEP/NCAR reanalysis datasets for 1979-2012,the characteristics of two types of central Pacific(CP) El Niño and coupled atmospheric processes are studied.The results show that there are two types of CP El Niño,the difference lies in sea surface temperature anomalies distribution in the tropical pacific.A type of CP El Niño(CP-Ⅰ El Niño) events have symmetrical structure about the equator in the winter,the warming center locate at Niño4 regions and stretch eastward into eastern pacific.Another type of CP El Niño(CP-Ⅱ El Niño),the sea surface temperature anomalies change in phase between Niño4 regions and tropical northeast pacifc areas (NEP,15-25°N,130-110°W),a banded and asymmetric structure of SSTA forms in the winter and shows horseshoe-shaped cold SSTA distribution in the western pacific.Further research indicates that the subsurface temperature anomalies(SOTA) of two types of El Niño are different.In the CP-Ⅰ El Niño winter,a zonal dipole mode forms between western and central-eastern pacific,the subsurface temperature of central-eastern pacific raise significantly,the meridional structure are also symmetric,a major positive SOTA center locates at the equator.However,in the CP-Ⅱ El Niño winter,a zonal dipole mode confines in the western and central pacific,the warming develop at the upper subsurface in the central pacific,the SOTA in the eastern pacific are tiny.Meridional SOTA also confine in the north hemisphere,two major positive anomalies center locate at the the equator and near 10°N.Characteristics of atmospheric circulation have distinct difference among CP-Ⅰ El Niño and CP-Ⅱ El Niño.In the CP-Ⅰ El Niño winter,the abnormal upwelling branch of walker circulation are over equator near the longitude of 180°,the abnormal downwelling branch locate at equatorial western and eastern pacific which responded to symmetric SSTA.In the low level atmosphere,there are significant westerly wind anomalies and convergent meridional wind anomalies in the equatorial area.The Hadley circulation intensify in the low latitude regions.However the mass transport between 20°N and 30°N are reduced which lead to southward move of downwelling branch of the Hadley circulation.In the CP-Ⅱ El Niño winter,the cross-equatorial southwest flow strengthen in the low level atmosphere,the upwelling center of Walker circulation move to north hemisphere which responded to asymmetric SSTA,the Hadley circulation weak in the low latitude regions to the contrary.In addition,the sea surface heat flux are investigated preliminary.In the August to December,the positive sea surface heat flux anomalies are observed in the CP-Ⅱ El Niño,which contribute to the warming in the central pacific and tropical northeast pacific.It shows that the wind-evaporation-SST processes exist in the tropical ocean.contrarily,in the CP-Ⅱ El Niño,negative sea surface heat flux anomalies damp the developments of SSTA.
The new El Niño phenomenons named central Pacific(CP) El Niño are discussed all over the world in the most nearly three decades.Specially,two types of CP El Niño which have different sea surface temperature anomalies(SSTA) structures are investigated in recent years.In order to recognize the different sea-air interaction processes of two types of CP El Niño comprehensively,in this research,we base on monthly Hadley Center sea surface temperature(HadISST),European Centre for Medium-Range Weather Forecasts(ECMWF) ocean subsurface temperature and NCEP/NCAR reanalysis datasets for 1979-2012,the characteristics of two types of central Pacific(CP) El Niño and coupled atmospheric processes are studied.The results show that there are two types of CP El Niño,the difference lies in sea surface temperature anomalies distribution in the tropical pacific.A type of CP El Niño(CP-Ⅰ El Niño) events have symmetrical structure about the equator in the winter,the warming center locate at Niño4 regions and stretch eastward into eastern pacific.Another type of CP El Niño(CP-Ⅱ El Niño),the sea surface temperature anomalies change in phase between Niño4 regions and tropical northeast pacifc areas (NEP,15-25°N,130-110°W),a banded and asymmetric structure of SSTA forms in the winter and shows horseshoe-shaped cold SSTA distribution in the western pacific.Further research indicates that the subsurface temperature anomalies(SOTA) of two types of El Niño are different.In the CP-Ⅰ El Niño winter,a zonal dipole mode forms between western and central-eastern pacific,the subsurface temperature of central-eastern pacific raise significantly,the meridional structure are also symmetric,a major positive SOTA center locates at the equator.However,in the CP-Ⅱ El Niño winter,a zonal dipole mode confines in the western and central pacific,the warming develop at the upper subsurface in the central pacific,the SOTA in the eastern pacific are tiny.Meridional SOTA also confine in the north hemisphere,two major positive anomalies center locate at the the equator and near 10°N.Characteristics of atmospheric circulation have distinct difference among CP-Ⅰ El Niño and CP-Ⅱ El Niño.In the CP-Ⅰ El Niño winter,the abnormal upwelling branch of walker circulation are over equator near the longitude of 180°,the abnormal downwelling branch locate at equatorial western and eastern pacific which responded to symmetric SSTA.In the low level atmosphere,there are significant westerly wind anomalies and convergent meridional wind anomalies in the equatorial area.The Hadley circulation intensify in the low latitude regions.However the mass transport between 20°N and 30°N are reduced which lead to southward move of downwelling branch of the Hadley circulation.In the CP-Ⅱ El Niño winter,the cross-equatorial southwest flow strengthen in the low level atmosphere,the upwelling center of Walker circulation move to north hemisphere which responded to asymmetric SSTA,the Hadley circulation weak in the low latitude regions to the contrary.In addition,the sea surface heat flux are investigated preliminary.In the August to December,the positive sea surface heat flux anomalies are observed in the CP-Ⅱ El Niño,which contribute to the warming in the central pacific and tropical northeast pacific.It shows that the wind-evaporation-SST processes exist in the tropical ocean.contrarily,in the CP-Ⅱ El Niño,negative sea surface heat flux anomalies damp the developments of SSTA.
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