Abstract:The eyewall replacement cycle plays an important role in changes regarding typhoon intensity and inner-core structure.In this study,in order to investigate the influences of large-eddy simulation(LES) on eyewall replacement,two ideal numerical experiments were conducted,of which one was coupled with LES.The study results indicate that the typhoon intensity of the LES experiment was stronger with larger inflow in the boundary layers.It took the two typhoon approximately 20-22 hours to complete the entire eyewall replacement,but the typhoon in the LES experiment had a faster enclosing of the outer eyewall.At the same time,the intensity and updraft in the outer eyewall were also greater.After the eyewall replacement,the typhoon in the LES experiment continued to intensify,and its intensity became greater than it was before the eyewall replacement.Of more importance is that the LES can more effectively simulate the downdraft within the moat region which is at the outside of the inner eyewall.In addition,the downward motion can more effectively induce the formation and development of convections near the outer eyewall regions,and is in line with the observational features found by previous studies.

Abstract:In the strong atmospheric baroclinic zone of the North Pacific at mid-latitude,the spread activities of synoptic-scale eddy are frequent,which maintain atmospheric circulation through the moisture,momentum and energy transport.In order to further study the relationship between the occurrence and development of synoptic-scale eddy and large-scale circulation,this paper selected 114 strong and 87 weak days of the western developing pattern synoptic-scale eddy (WSE) by using the reanalysis data from 1981 to 2013,and gave the variations of dynamic and thermal forcing caused by the WSE anomalies.Meanwhile,it analyzed the interaction between the WSE and mean flow from the perspective of energy transformation and the relationship between the WSE and the Western Pacific (WP) teleconnection pattern.Results show that the WSE affects mean flow through dynamic and thermal forcing.The dynamic forcing mainly makes the westerly currents over the mid-latitudes of North Pacific accelerate and move northward,while the thermal forcing weakens atmospheric baroclinicity over mid-latitudes.Meanwhile,the strong WSE is beneficial to increase the conversion of baroclinic available potential energy to eddy kinetic energy and eddy kinetic energy to mean flow in the lower troposphere over Northwest Pacific,and to increase the conversion of mean flow to eddy kinetic energy in the upper troposphere over mid-latitudes.In addition,the WSE has a certain effect on maintaining the negative phase of the WP teleconnection pattern through its interaction with the mean flow.

Abstract:In this study,the interannual variability of wind power input(WPI) is investigated by MITgcm.The response of WPI to climate change is also analyzed.The result of the simulation indicates that the responses of the WPI to the world ocean to the climate change signifycantly.The areas of high value of time-mean WPI to the ocean are located in the middle and high latitude regions,such as the South China Sea,Kuroshio Current and Gulf Stream,due to the fact that the synoptic scale disturbance of atmosphere is significant in these areas.Moreover,the areas of high decadal variability of the WPI to the ocean are located in the South China Sea and Storm Tracks.The value of max WPI increases and the area of max WPI shifts northward in the North Atlantic,resulting from the strengthening and northward-shifting Storm Tracks in the positive phase of North Atlantic Oscillation(NAO).However,there is a greater amount of WPI that travels into the Gulf Stream when the phase of NAO is negative.The WPI to the South China Sea has been increasing with the increasing intensity of Westerlies in the recent decades,and the area of max WPI has shifted southward as the Westerlies shift southward in the Southern Hemisphere.Similarly,the WPI to the Antarctic coastal current increases significantly during this period.The Empirical Orthogonal Function(EOF) analysis shows that the variability of the WPI to the North Atlantic Ocean is dominated by the NAO,while the second and third modes indicate the distributions of the WPI to the oceans during positive phase or negative phase of the NAO.The Southern Annual Mode (SAM) leads to the first EOF mode in the South China Sea,while the second and third modes are related to the El Niño-Southern Oscillation (ENSO).The decadal variability of the WPI to the South China Sea has been increasing significantly in recent decades,while it has decreased in middle and high latitudes in the northern hemisphere.

Abstract:Based on the data from the TIGGE datasets of European Centre for Medium-Range Weather Forecasts(ECMWF),Japan Meteorological Agency(JMA),National Centers for Environmental Prediction(NCEP),China Meteorological Administration(CMA) and United Kingdom Met Office(UKMO),the Kalman filter method was applied to conduct multimodel ensemble forecasts of the surface air temperature and precipitation.The results show that the multimodel ensemble forecasts by using Kalman filter are superior to those of the bias-removed ensemble mean(BREM) and other individual models.However,the forecast results of Kalman filter method vary for different meteorological elements and different forecast lead times.For the surface air temperature forecast in China,Kalman filter method shows the best forecast capability while for the precipitation forecast,it has a higher TS score than the BREM.However,with longer forecast lead time,the TS scores for heavy rains are approximately equivalent to those of the best individual model UKMO.So the Kalman filter method does not improve the forecast capability of heavy rains significantly.To sum up,the root mean square error(RMSE) of surface air temperature and precipitation forecasts based on Kalman filter is the smallest among those of the multimodel ensemble forecasts and each individual model forecasts.

Abstract:In this study,the spatial-temporal features of eight extreme precipitation indices selected in the Yangtze-Huaihe River Basin during 1979-2011 are analyzed to assess the reanalysis datasets of ERA-Interim and NCEP/DOE,using the observational data from meteorological stations as a reference.The results are as follows:1)The consecutive wet day(CDD),day of heavy rainfall (R10mm,R20mm) and the extreme indices based on percentiles(R95p,R99p) are distributed with low values in the north and high values in the south,while the consecutive dry day is distributed with a positive phase.In addition,the intensity indices(Rx1day,Rx5day) show high values along the coast of Zhejiang.2)The R10mm and R20mm show decreasing trends in most regions,with the exception of the marginal areas of the basin,where weak increasing trends are observed.3)The intensity indices averaged over the basin tend to increase with time.The annual cycles of these indices demonstrate bell-shaped patterns,with peaks in July.In late summer and winter,there is a more obvious trend of increasing with age,while in autumn it decreases with age.4)The two reanalysis datasets show both advantages and weaknesses when presenting the extreme indices.The ERA-Interim performs better in producing the spatial patterns of R10mm,CDD and percentile indices,as well as the linear trend of CDD.It also produces better inter-annual variations of intensity and percentile indices.However,its ability to reproduce the trend distribution of CWD is weak.On the other hand,NCEP/DOE is better at presenting the spatial pattern of R20mm,as well as the linear trends of intensity and percentile indices.However,its ability to express the trend of the duration index is weak.5)The two reanalysis datasets can reasonably reproduce the interannual variation characteristics of R10mm,R20mm,CDD and seasonal variation characteristics of intensity indices.

Abstract:In this study,the severe convective rain process occurring in Hongan,Hubei Province is simulated using the Weather Research and Forecasting Model(WRF).The results show that the severe convective weather developed under the condition of abundant water vapor,divergence in high-level,convergence in low-level,and unstable stratification.Simulated rainfall and radar reflectivity are in high agreement with the situation,and evaporation of raindrops is significant under the cloud.After the sensitivity experiments of reducing the evaporation of rainwater to half,quarter and zero,the radar reflectivity is weakened,and is shown to have great influences on the evolution of the convective process.The characteristics of the rain zone are similar to those of the original scheme,and the regional average precipitation is weakened.Reducing evaporation causes the precipitation intensity in precipitation initial occurrence stage and dissipation stage to be enhanced and weakened in the development of the precipitation process.At the same time,the weakening of the vertical airflow and reduction of graupel content are caused by the weakening of raindrop evaporation.In summary,the evaporation has an influence on the dynamics,thermal structures,cloud microphysical structures and processes of convective clouds.

Abstract:In this study,the empirical orthogonal function(EOF) was performed at the anomaly field of the 600-station winter mean temperature in China during the period of 1979-2012.Then,using the observed antecedent Arctic sea ice concentration(SIC) and Eurasian snow cover(SNC) data,the key areas where SIC and SNC anomalies in autumn have significant effects on the principal variation of following temperature in China are calculated,and based on those areas,the SIC and SNC indices are built.Next,the standard linear regression models which can be used to predict the mean winter temperature at individual stations are established,using one or two cryospheric predictor indices.Through the statistical cross-validation,the mean of the anomaly correlation coefficient(ACC) and root mean square error skill score(RMSESS) between the observed and predicted temperatures are used to quantitatively evaluate the predictive skill of cryospheric factors for the winter mean temperature in China.The results show that the skill of hindcasts is greatly different among regions between the single September SIC predictor and November SNC predictor.The SIC index has more noticeable skill on central north China,while the November SNC index has more noticeable skill on northeastern China.While hindcasts using both September SIC and November SNC predictors are better than the single on area and score,almost all stations except the Tibetan Plateau area show significant skill.The grid points with superior skill are centered on north-central,northeastern and northern China,where the regional average ACC is 0.58,and the method outperforms a climatological hindcast is 18.7%.The results obtained in this study suggest that it is very important to incorporate cryosphere variability in seasonal prediction systems.

Abstract:The typhoon Megi (1617) was a large-scale and strong tropical cyclone. After typhoon Megi landed on 28 September 2016,different types of heavy rainfall were induced by body circulation and peripheral circulation of the typhoon,which was the difficulty of heavy rainfall forecasting for typhoon landing in autumn. Based on the convectional meteorological observation data and NCEP 1°×1° reanalysis data etc.,this paper diagnosed and compared the causes of different types of heavy rainfall in Zhejiang and Jiangxi provinces. Results show that there are obvious differences in atmospheric stratification structure between convective precipitation in southeastern Zhejiang and stable precipitation in southern Jiangxi. The trough in middle and high latitudes is far away from typhoon Megi. Cold air intrusion mainly occurs in the northwest side of typhoon from the lower level,destroying the low-level warm core structure of the typhoon. The dry and cold air at middle level around the typhoon is transported by southeast wind to southeastern Zhejiang. The dry and cold air is overlaid on the lower warm and wet airflow,forming an unstable stratification of upper cold and lower warm. Meanwhile,dry and cold air from the upper troposphere sinks into the middle and lower levels of typhoon circulation (dry intrusion),which results in local extreme heavy rainfall near Wencheng in Zhejiang. In southern Jiangxi,because the lower level is occupied by wet and cold air,the stratification is relatively stable and the precipitation develops slowly compared to that in Zhejiang. The low-level southeast jet stream provides abundant moisture for the heavy rainfall in the peripheral circulation of typhoon. The mountain topography in southeastern Zhejiang has played an increasing role in precipitation. The trigger effects of unstable stratification and transport of middle-level cold air on convectional heavy rainfall can be used as references for forecasting of precipitation characteristics and intensity of landing typhoon.

Abstract:In the present paper,using the latest aerosol optical thickness(AOD) data(Collection 6) derived from the Moderate Resolution Imaging Spectroradiometer(MODIS) on board the Terra spacecraft,the National Centers for Environmental Prediction Final(NCEP FNL) Operational Global Analysis data,Climate Prediction Center(CPC) Merged Analysis of Precipitation(CMAP) data,CERES syn1deg Ed4 monthly average data,NCEP/National Center for Atmospheric Research(NCAR) reanalysis data from March 2000 to February 2017,the possible relation of AOD variations with winter monsoon is investigated.According to the AOD values,five different pollution levels are defined.The results show that the abnormally high AOD value in eastern China is related to the anomaly of wind speed.The negative correlation is most obvious in northern China.In winter,the averaged AOD over eastern China has a high negative correlation with the climatic variables.When the AOD is abnormally high(low),the short-wave solar radiation reaching the ground reduces(increases);the surface temperature declines(rises);the atmosphere is cooling(heating);the surface precipitation displays characteristics of "lower inland,and higher in the southeast" ("higher inland,lower in the southeast");and the influence of wind speed anomalies on the regional distribution of AOD anomalies is significantly different.When the AOD anomaly is high (low),the surface wind speed in northern China is small(large) and large(small) in the Jianghuai region.The case analysis shows that the anomalously high AOD in 2013 is due to the weak zonal wind and the weak Aleutian low pressure.These results have scientific significance for deepening our understanding of the relationship between the changes in winter monsoon and aerosol pollution.

Abstract:In this study,based on the fog-haze dataset from the National Meteorological Information Center,and NCEP/NCAR reanalysis data and sea ice concentration(SIC) dataset from the British Atmospheric Data Centre,for the timespan of January 1981 to February 2017,the effects of Barents-Kara Seas' ice in both autumn and winter on the East Asian winter monsoon and changes of winter fog and haze events in eastern China have been discussed.The results suggest the following:The changes of the Barents-Kara Seas' ice since autumn have greatly affected the strength of the zonal circulation and the East Asian trough Asian over mid-high latitudes and the intensity of the East Asian winter monsoon.The Barents-Kara Seas' ice is one of the important factors affecting the winter haze events in eastern China,but it has less significantly affected the winter fog weather.Less sea ice in the Barents-Kara Seas strengthens zonal circulation over mid-high latitudes of Asia,while the East Asian trough and influence of the East Asian winter monsoon are weakened,which provides favorable conditions for the atmospheric pollutants gathering in the horizontal direction.Meanwhile,positive temperature anomalies exist in the middle and lower tropospheres,and the difference between the temperature of the higher layer and surface decreases,which is not conducive to the development of convection,thereby causing the the atmospheric conditions to be more stable,and providing favorable conditions to the atmospheric pollutants' gathering in the vertical direction.The influence of the both horizontal and vertical directions leads to haze weather in eastern China.

Abstract:Using WRF model coupled with multilayer urban canopy scheme BEP(Building Environment Parameterization) and BEM(Building Energy Model) scheme,a simulation was conducted to explore characteristics and causes of Chongqing urban heat island and impact of local circulation on it. There were two simulation cases conducted,one was URBAN case that utilized real Chongqing land use data,another was NOURBAN case that replaced urban category with crop in order to understand impact of urban on Chongqing heat island. Results show that:(1)WRF model produces good results compared to observed 2 m air temperature. Errors mainly occur at noon temperature peak and morning temperature valley,which are caused by the characteristics of urban land use and unreal building parameters. (2)BEP+BEM scheme can simulate well spatial and temporal features of urban heat island in Chongqing. Spatial distribution of temperature in Chongqing is influenced by topography and urban underlying surface. When closer to the city,greater temperature is affected by the urbanization,and higher temperature locates at low elevation. (3)Urban 3D surface leads to trap effect in urban surface albedo(Total reflectivity of urban surface is low),and the urban upward shortwave radiation is less than about 20 in suburbs. Sensible heat is a major factor in urban energy balance however latent heat in suburbs. The larger urban surface heat storage and the waste heat of air-conditioner released to the atmosphere at night are important reasons for urban heat island conformation. (4)The background wind field is mainly southeast wind in the simulated area. The wind speed is higher in mountain area and lower in urban area,which reflects the aerodynamic effects of dense urban buildings on the low-level atmospheric flow field,as well as the characteristics of valley wind circulation over complex valley terrain. There are high mountains in the western and southeastern sides of the city,which block the outflow from the city,let the background wind to climb or circle around the mountains,and contribute to the enhancement of urban heat island.

Abstract:This paper analyzes the connection and possible mechanism between sea surface temperature anomaly (SSTA) in the northern tropical Atlantic (NTA) and the South China Sea summer monsoon (SCSSM) using HadiSST data,CMAP precipitation data and NCEP/NCAR reanalysis data.The observation analysis shows that there is a significant negative correlation between NTA SSTA and SCSSM in summer.Positive NTA SSTA can cause cyclonic circulation anomalies in the subtropical East Pacific to Atlantic region of the Northern Hemisphere,which is conducive to abnormal ascending (descending) motion in the tropical Atlantic (tropical central Pacific) region.The motions can cause the anomalous anticyclone circulation in the northwestern Pacific region,and the south wind anomalies on the west side of the anticyclone circulation anomaly enhance the SCSSM.The SCSSM seasonal prediction model is constructed by using spring NTA index,SST anomaly index in southeastern Indian Ocean,SST anomaly index in North Pacific,South Pacific Ocean Meridional Dipole (SPOMD),and Niño3.4 index.Correlation coefficient between the observed SCSSM index and the hindcast of the model is 0.81,showing that the model can predict SCSSM well.

Abstract:Strong convection is an important weather phenomenon impacting flight safety,and frequently causes sudden changes in meteorological elements.AMDAR data have high spatial and temporal resolution,which can provide vital information for the nowcasting of severe weather in airport terminal areas.This paper extracts the three-dimensional wind vector and temperature profiles,and produces the wind shear warning analysis diagram in the horizontal and vertical directions,using AMDAR data from the Baiyun Airport Terminal Area.The case study involves the strong convection on April 17,2011 in Guangdong Province,and the AMDAR data,together with multi-source information such as Doppler weather radar,satellite and sounding,are analyzed.The study results show that the three-dimensional early warning indication on the wind vector-time height profile of the AMDAR data has a guiding significance for nowcasting strong convection at the airport.When strong wind shear occurs below 1 km,the threat to aircraft take-off and landing is serious,and the vertical distribution of the horizontal wind direction from the AMDAR data is very serious.In addition,the echo characteristics in the strong divergence region of the Doppler weather radar are confirmed.The high spatial and temporal resolution ADMAR wind speed and temperature disturbance can reveal the wind shear and turbulence in the atmosphere.The real-time and intensive vertical observation information provided by the AMDAR data is helpful to develop the products of nowcasting and early warning,and to compensate for the shortage of sounding data.

Abstract:Artificial intelligence nowcasting based on generative adversarial networks (GAN) has been conducted by using abundant radar echo images from 12 S-band Doppler radars in Guangdong province during the period from 2015 to 2017.Radar echo images were convoluted for 5 times in order to build the initial forecasting model.Afterwards,several confrontation trainings took place between the model images and real radar echo images,resulting in the loss function.The model was optimized constantly.Given that the model images were similar to the real radar echo images,the outputs of optimum model would be used for nowcasting.The experiments of four precipitation events in Guangdong province during 2018 suggested that the 60 min forecasted position,shape and intensity of radar echo in convective systems by GAN mostly coincide with the observations.However,the forecasted area of strong radar echo is larger than that of the observed radar echo.Furthermore,the GAN method could not forecast the precipitation caused by stratus clouds well.The GAN method could forecast moderate radar echoes quite well,while its forecast capability for strong radar echoes needs to be improved.