Abstract:Known as the third pole of the Earth,the Roof of the World and the Water Tower of Asia,the Tibetan Plateau accounts for 1/4 of China's territory.The Tibetan Plateau and its heat source play important roles in the weather and climate of East Asia and the world as a whole.In this study,clarifying the atmospheric heat source over the Tibetan Plateau and its influence will help to deepen our relevant knowledge,improve the forecasting ability of weather system occurrence and development in the plateau region,and advance the forecast level of precipitation in the plateau region.In this paper,relevant researches regarding the atmospheric heat source over the Tibetan Plateau are systematically summarized,including the acquisition and characteristics of the atmospheric heat source over the Tibetan Plateau,which includes the calculation of the atmospheric heat source over the Tibetan Plateau and its spatial and temporal distribution and evolution characteristics;the influence of atmospheric heat source over the Tibetan Plateau on monsoon and precipitation;and the influence of the atmospheric heat source over the Tibetan Plateau on the weather systems,which includes the influence on the South Asian High,Western Pacific Subtropical High,plateau vortex and plateau shear line.The future research on the atmospheric heat source over the Tibetan Plateau is prospected and some aspects worthy of further research are proposed based on the basis of summarizing the existing research progress and achievements.

Abstract:In this study,based on the 1-5 d forecasts of Global Forecasting System(GFS),as well as the observations from meteorological stations throughout China,the effect of the model topographic altitude bias (TAB) on the surface air temperature forecast is investigated.The results show that if the TAB is excessively large,it may severely affect the forecast skill,and lead to excessively large forecast error.As the forecast lead time becomes longer,the root-mean-square error (RMSE) of the 2 m air temperature forecast increases slightly as well.By comparing the effect of the TAB and the increasing forecast lead time on the model forecast performance,the effect of the TAB on the model forecast skill becomes greater.Both two types of calibration schemes,namely the linear regression with and without vertical correction can reduce the model forecast errors,while the former has better calibration performance.

Abstract:In this study,based on the daily temperature dataset from ERA-Interim analysis during 1979-2014,and according to the temperature lapse rate interpolation method,the tropopause pressure over the Tibetan Plateau and other regions in the same latitudes are calculated.First,the seasonal variation and long-term trends of the tropical tropopause pressure over the Tibetan Plateau,in comparison to those over other regions in the same latitudes,are discussed.Next,the relationships between the tropical tropopause pressure and upper air temperature are preliminary addressed.The results of the study are as follows:1)In terms of seasonal change,with the exceptions of December and January,the tropical tropopause pressure over the Tibetan Plateau is lower than that over other regions in the same latitudes in each month.In addition,compared with other regions in the same latitudes,the single structure of the tropical tropopause pressure,mean temperature in the upper troposphere,and mean temperature in the lower stratosphere over the Tibetan Plateau are shown to be more distinct.2)The tropical tropopause pressure the Tibetan Plateau and other regions in the same latitudes display a close relation with the upper air temperature,i.e.when the mean temperature in the upper troposphere (in the lower stratosphere) increases (decreases),the tropical tropopause pressure decreases.Furthermore,the tropical tropopause pressure the Tibetan Plateau is more closely linked with the mean temperature in the upper troposphere than that over other regions in the same latitudes.3)From 1979 to 2014,both the tropical tropopause pressure of the Tibetan Plateau and non-plateau regions decreased with time during each month,especially in spring and winter.Meanwhile,compared with the other regions in the same latitudes,the upward (downward) trends of the mean temperature in the upper (lower) troposphere of the Tibetan Plateau were faster all year round,which led to a more rapid tropical tropopause pressure decline on the Tibetan Plateau.

Abstract:Due to the lack of quantitative data regarding Arctic risk assessment,the difficulties in quantifying qualitative knowledge,and the subjectivity in determining weight factors,the traditional risk assessment methods cannot be effectively solved.Therefore,in this paper the quantitative analysis of qualitative knowledge is realized by introducing the "cloud model".First,the objectivity of the weights is improved by the fuzzy analytic hierarchy process (AHP).Next,in response to the change of the Arctic regional response and its geopolitics and the game of interests under the background of climate change,the above methods and techniques are improved.This paper then presents an evaluation model and experimental simulation of interest games and security risks in the Arctic,and proposes some research opinions and information pertaining to decision-making consultation.

Abstract:The most advanced mesoscale WRF model in the world is used to simulate the genesis process of tropical cyclones.When the grid resolution is increased from 9 km to 3 km,the cumulus parameterization scheme in 3 km grid does not work,so the microphysical scheme is used to simulate the characteristics of convective-scale system in the 3 km domain.As a result,the formation process of tropical cyclone in the model becomes slow.If the 3 km domain is added after the low pressure disturbance has developed to a certain extent,the formation process tends to accelerate.This study is focused on the analysis of the phenomenon.Results show that the low-level (950-700 hPa) vertical shear of horizontal wind speed decreases by using only the microphysical scheme,which is not conducive to the development of convection.The decrease of low-level vertical shear is mainly due to the difference of vertical momentum advection between the two experiments.During the 6 h after adding the inner nest,the convective-scale (removing the area average component) vertical momentum advection at low-level is double on average and 5 times in maximum compared to control experiment.The increase of momentum mixing in the low-level is due to the increase of vertical velocity simulated by microphysical scheme.In addition,the CAPE (convective available potential energy) is rapidly consumed by using only the microphysical scheme.The decreases of low-level vertical shear and CAPE are not conducive to the development of convection near the disturbance center,resulting in the delay of genesis and development of tropical cyclone.This study demonstrates that there are still some problems in simulating the real development process of convection during the formation of tropical cyclone with the present microphysical schemes in WRF model.

Abstract:70 tropical cyclones(TCs) were formed in the belt within the range of 0°-5°N in the western North Pacific basin during the period of 1979 to 2012,accounting for 8% of the total TCs.In addition,64% of these were intensified to typhoons.However,studies regarding such near-equatorial TCs are rare.In this study,the best track from Joint Typhoon Warning Center,the reanalysis from European Centre for Medium-Range Weather Forecasts interim,and the National oceanic and atmospheric administration optimum interpolation sea surface temperature are used to diagnose the interannual,interdecadal and seasonal characteristics of the near-equatorial TCs.The large-scale circulation and cyclonegesis are mainly investigated.The results show that the near-equatorial TCs have obvious interannual and interdecadal variations and opposite seasonal variations contrast with the total TCs over the western North Pacific.The large-scale environmental fields of near-equatorial TC genesis are characterized by a cyclonic circulation within the northeasterly and northwesterly wind.The dynamic term of absolute vorticity in the lower troposphere and thermal term of relative humidity in the middle troposphere are the main contributors to the formation of the near-equatorial TCs.The higher positive vorticity in the lower troposphere and relative humidity in the middle troposphere are required compared with the TCs formed in the belt within the range of 5°-10°N.

Abstract:By using the GSI (Gridpoint Statistical Interpolation) assimilation system developed by NCEP (National Centers for Environmental Prediction) and the global spectrum prediction model of GSM (Global Spectral Model) as the cyclic assimilation system,the thirteenth typhoon in 2017 was selected for a case study.The two assimilation schemes of all sky and clear sky were used to make assimilation comparison test on AMSU-A (The Advanced Microwave Sounding Unit-A) radiance observation,and the authors implemented 5-day forecast on typhoon "HATO" to study the impact of AMSU-A full-sky radiance assimilation on the development of typhoon HATO.The results showed that errors in typhoon path,typhoon center pressure and typhoon's maximum wind speed predicted by the all-sky assimilation scheme were smaller than those by the clear-sky assimilation scheme.The full-sky assimilation scheme was more accurate in the simulation of typhoon HATO's life cycle,and it was closer to the lowest pressure of the best path of the typhoon released by China Meteorological Administration.The result forecasted by the clear sky assimilation scheme was weaker and the typhoon intensity at its mature stage could not be predicted.The full-sky assimilation scheme could increase the thick cloud coverage area of the low-level passage.The amount of radiance data assimilation increased by 10% of the total amount of AMSUA assimilation observations,and thereby improved the thermal field structure of the weather system in the marine area.

Abstract:Based on the monthly sea surface temperature(SST) data from American National Oceanic and Atmospheric Administration,NCEP/NCAR monthly reanalysis data of wind field,potential height field and humidity as well as daily rainfall data from 753 stations provided by the Chinese National Meteorological Information Center,the characteristics of abnormal SST distribution,summer precipitation in eastern China in the following year and atmospheric circulation anomalies of two strong El Niño events in 1997/1998 and 2015/2016 were compared and analyzed.The results showed that:1)The 2015/2016 El Niño event had been the longest and strongest one since 1950 and the magnitude of SST near the date-line was larger than that in 1997/1998;2)During the following summer of 1997/1998 El Niño,more precipitation occurred in the west of the southern China,the north of Jiangnan area to the Yangtze river basin,the northern part of Huang-Huai area to the southern part of North China and Northeast China;precipitation intensity was weaker and the distribution of anomalous rainfall was smaller in the following summer of 2015/2016,in which the heavy rain belt mainly distributed in the Yangtze river basin,Huang-Huai area and the northern area of the Great Bend of the Yellow River;3)It was found that the Western North Pacific subtropical high(WNPSH) was strong and its location was to the west of its usual position while the ridge line was to the south of its usual position in the following summer of 1997/1998;the abnormally strong mass transportation vertically and upwards,the horizontal wind field of the upper and lower levels and the anomalous convergence of water vapor flux were all favorable for precipitation in the Yangtze river basin and Northeast China in the following year of 1997/1998 El Niño event;in 2016,the WNPSH was weaker and the ridge line was to the north and east of its usual position;the weaker horizontal and vertical circulation anomalies as well as weaker water vapor conditions made the coverage and intensity of summer precipitation weaker.Considering the SST distribution pattern and the impact on rainfall in the eastern China in the following summer,the strong El Niño event of 2015/2016 was still different from the traditional eastern type events.

Abstract:Taking a typical MTC (multiple tropical cyclogenesis) event in midsummer of 2018 as an example,this paper investigates the effects of multi-scale circulations (including large-scale circulation,intra-seasonal oscillation (ISO) and tropical waves) on MTC,and discusses the deviation of vertical disturbance field of the whole atmosphere in MTC active and inactive phases.The results are as follows.(1)The western North Pacific (WNP) undergoes a 16 d MTC active phase with eight tropical cyclones (TCs) generated in sequence and a 19 d MTC inactive phase with only one TC generated in midsummer of 2018.(2)During the MTC active phase,the cross-equatorial airflow strengthens,and the monsoon trough strengthens and extends eastward.The atmospheric circulation configuration of low-level convergence and upper-level divergence over South China Sea (SCS) and WNP is conducive to TC formation.(3)The northward propagation of ISO (intraseasonal oscillation) in East Asia and WNP in summer has a significant modulation effect on the sub-seasonal variation of MTC.The SCS and WNP are just in a northward wet (dry) phase of a strong ISO during the MTC active (inactive) phase.(4)The formation of eight TCs in the MTC active phase is all related to tropical waves,of which five are affected by two kinds of tropical waves simultaneously.Tropical waves provide triggering conditions for TC formation by changing the local thermal and dynamic conditions.(5)The combined effects of multi-scale circulation eventually leads to significant differences in the vertical structure characteristics of temperature-pressure disturbance field configuration,vertical motion disturbance and specific humidity disturbance in the MTC active and inactive phases.The application of the disturbance analysis method provides a new idea for MTC extended range forecast.

Abstract:Based on the CCSM3 (Community Climate System Model version 3) model of the US National Center for Atmospheric Research,this paper studies the interdecadal response characteristics of climate in China under different mean intensities of Atlantic Meridional Overturning Circulation (AMOC) in the freshwater disturbance tests.Results show that the changes of surface temperature and precipitation intensity in China are closely related to the changes of AMOC intensity on interdecadal scale,but the response characteristics of China climate on interdecadal scale are different under different mean intensities.Under the high mean intensity,the surface temperature in China increases,the precipitation in northern China increases,and the precipitation in southern China decreases,whereas under the low mean intensity,the opposite is true.Under different mean intensities,the spatial distributions of the first EOF eigenvectors of annual mean surface temperature and precipitation in China are significantly different:Under the high mean intensity,the surface temperature presents a uniform distribution pattern in the whole region of China,and the precipitation presents a "-+-" type rain belt distribution from north to south;under the low mean intensity,the surface temperature shows a dipole distribution pattern of north-south inversion in China,and the precipitation shows a "-+" type rain belt distribution from north to south.Compared with the low mean intensity,the interdecadal variation scales of the time coefficients of the first EOF modes are longer under the high mean intensity.

Abstract:The spatial distribution of summer precipitation in eastern China in 2015 shows a reverse phase relationship between north (Hetao area,HT) and south (the middle and lower reaches of Yangtze River Valley,YRV).The precipitation anomalies in HT and central India (CI) are below-normal,while those are above-normal in YRV.The absolute maximum of summer precipitation anomaly percentage in the above three areas in 2015 is more than 55%.The formation mechanism of precipitation anomalies in East and South Asia during boreal summer of 2015 is mainly due to the development phase of El Niño event at the same time.An anticyclone circulation anomaly in the Philippine Islands and its adjacent regions,a cyclone circulation anomaly in the Yangtze-Huaihe region to the Japanese archipelago,and the geopotential height anomaly field in the lower troposphere and the water vapor transport anomaly field in the whole troposphere also have the same spatial distribution,which also reveals the spatial distribution of negative EAP (East Asian-Pacific)/PJ (Pacific-Japan) teleconnection.It is beneficial to less precipitation in HT and more precipitation in YRV.The tropical Pacific SSTA weakens the Walker circulation in the tropical region,which contributes to the descending motion over the western tropical Pacific.The abnormal tropospheric easterly prevails in the tropical Indian Ocean,which weakens the Indian summer monsoon and results in below-normal precipitation in CI during boreal summer.Meanwhile,the lower troposphere over India is controlled by an anomalous anticyclone.The westerly anomaly on the northern side of the anomalous anticyclone moves eastward along the southern edge of the Tibetan Plateau,which enhances the anomalous water vapor transport associated with EAP/PJ teleconnection.Therefore,it is conducive to maintaining and strengthening the below-normal precipitation in HT and the above-normal precipitation in YRV.

Abstract:In order to understand the physical features of the output results of localized mesoscale WRF (Weather Research Forecast) model before the occurrence of short-time severe rainfall in Yunnan Province and to reveal the effect of physical quantities on the prediction of short-time severe rainfall,WRF numerical prediction model was used to simulate five short-time severe rainfall events in the main flood season (June-August) of Yunnan in 2016.Using the high spatial and temporal resolution data output from the model,some physical quantities of water vapor,dynamic and unstable condition classes were calculated for 85 samples in five processes 6 hours before the occurrence of short-time severe rainfall.The distribution characteristics of physical quantities and their relationships with short-time severe rainfall are analyzed by box-line graph,and the thresholds of physical quantities are determined by empirical cumulative distribution function graph.Research shows that water vapor quantity sample values distribute intensively,and the values increase gradually with the approaching of short-time severe rainfall.The median and average values of 6 km vertical wind shear of dynamic class change little with time,and the threshold values of 6 km vertical wind shear of all times are lower than 12 m/s,which indicates that the vertical wind shear is weak before short-time severe rainfall.In the unstable condition class,the convective available potential energy (CAPE) sample data have greater dispersion,so CAPE has no instruction significance for short-time severe rainfall.The data of LI index,K index and 700 hPa pseudo equivalent potential temperature samples have less dispersion,and the upper and lower limits of the median value,average value and threshold of K index increase significantly one hour before the occurrence of short-time severe rainfall.The concentration of K index data is the highest one hour before short-time severe rainfall,and the larger K index value corresponds well with the short-time severe rainfall.The method of estimating the location of short-time severe rainfall by the physical quantity threshold value can improve the prediction performance of Yunnan localized WRF model to short-time severe rainfall.

Abstract:Clouds typically cover about 60% of the Earth's atmosphere,and this has an important influence on the radiation balance of the Earth's atmosphere system.At the same time,clouds are also one of the most important factors affecting climate change.The net radiation obtained by the ground system and the different heating distributions caused by radiation are strongly affected by cloud.It is important to understand the cloud macro and micro-physical properties in order to study the cloud radiation effects and improve the numerical model parameterization scheme.This paper aims to study the microphysical parameter retrieval of stratus cloud and its radiation effects.The microphysical parameters of the layered cloud mainly include the effective radius,number concentration,liquid water content and optical thickness.Synergetic measurements from mm-wavelength cloud radar and microwave radiometer were used to retrieve the cloud microphysical parameters of stratus case at Shou Country,Anhui Province,China on November 11,2015.The retrievals were coupled into a radiative transfer model,known as SBDART,for cloud radiative effect simulation.SBDART is a software tool that computes plane-parallel radiative transfer under clear and cloudy conditions,both within the Earth's atmosphere and at the surface.All important processes affecting the ultraviolet,visible,and infrared radiation fields are included.The code is a combination of a sophisticated discrete ordinate radiative transfer module,low-resolution atmospheric transmission models,and Mie scattering results for light scattering by water droplets and ice crystals.Shortwave radiation flux and longwave radiation flux comparisons were carried out between the simulations and observations one at the ground surface.The results show the following:1)The retrievals of stratus cloud from the synergetic measurements were reliable.2)The ground-surface shortwave and longwave radiative fluxes can be simulated in real-time with the SBDART radiative transfer model.3)In the cloud parameters of the inversion,the influence of the optical thickness on the radiation fluxes on the ground is the largest.The greater the optical thickness of the cloud is,the smaller the solar shortwave radiation reaching the ground will be,and the smaller the ground reflection shortwave radiation will be.In addition,the higher the cloud temperature is,the greater the infrared long-wave radiation emitted by the cloud will be.The long-wave radiation from the ground is the Planck's function of the ground temperature,which varies with the ground temperature.4)The cloud shortwave radiative forcing is negative with cooling effect on the surface,while the longwave radiative forcing is positive with warming effect on the surface.5) The cloud net radiative forcing at the ground surface changes significantly with time,depending on the solar zenith angle and cloud parameters.

Abstract:This paper simulated a heavy rainfall case caused by a Jiang-Huai cyclone which occurred in southern Anhui Province from 1200 UTC July 4 to 0600 UTC July 5,2014.The simulated results on the warm front are consistent with the observations,and are used to investigate multiple convective rain belts' structure and the causes for their appearance near the warm front.The results indicate that the single convections in both the simulated and observed situations are all under 300 hPa,and continued for around 2-3 hours,with maximum lengths of 100 km and widths of 10 km.Between bands,their spacings are about 50-100 km,and all of them are tilting east-southern with height.All of the single convective bands have several common circulation characteristics:on the east of the convective region there is a corresponding warm rising air distributed from its low-level to high-level;the upper western convective zones are controlled by cold areas;and close to the ground,there is a similar cold pool,while the updraft south of the convective belts is favored by the convections' back building and forming belted structures.On the single convective rain belts,there is an area of 0 < Ri < 1 at 800 hPa and an area of I_EPV<0.In stable stratification,the wind field is distributed in a roller shape,with the structure characteristics of the existence of gravitational waves.There is convective instability at 600-700 hPa and an area of I_EPV>0.It can be concluded that warm rising air under conditional symmetric unstable conditions around 800 hPa triggered conditional symmetric instability and gravity waves,along with convective instability above 700 hPa.This implies that the main cause of the single convective rain belts' formation is symmetric-convective instability.

Abstract:In the present study,based on the maximum and minimum surface air temperatures of 587 stations in China,ERA-interim reanalysis soil moisture(SM) data and the extended reconstructed sea surface temperature(ERSST) data,the possible linear connection between the previous(spring and winter) sea surface temperature(SST),soil moisture and summer extreme temperature in China during the period of 1979-2009 is investigated.Statistical summer extreme temperature prediction models were developed using Barnett-Presisendorfer Canonical Correlation Analysis(BP-CCA),the Ensemble Canonical Correlation(ECC) method,and newly defined summer extreme temperature indices.In addition,the scores for the prediction models with predictive skill in the independent sample tests were calculated.The results showed that the summer extreme temperature in China has a close relationship with the previous SST and SM anomaly,while the spatial distribution of the previous SST anomaly was similar to the PDO pattern,and the previous SM anomaly in southern China,the Tibetan Plateau,northeastern China and the western part of northwestern China.The cross-validation tests showed that the BP-CCA models based on the previous winter predictors had higher predictive skill than those based on the previous spring predictors.Meanwhile,the BP-CCA models based on SM had higher predictive skill than those based on SST.Additionally,the independent sample tests showed that the ECC models based on the previous SM and SST had high predictive skill for summer extreme temperature in China.The study results revealed that the previous soil moisture and sea surface temperature contain valuable signals for summer extreme temperature in eastern China,and can be considered for inclusion in summer extreme temperature prediction operations.