Abstract:The "dry gets drier,wet gets wetter" paradigm has become a template slogan for assessing current and future climate changes.However,the assessment and prediction of this paradigm is mainly the global average result affected by ocean changes,and there is great uncertainty about water resources changes over land,especially in complex terrain areas.This study summarizes the changes of global terrestrial water resources,especially in high altitude areas.Differences between global and regional climate models are compared.The response mechanism of terrestrial water resources to warming is revealed.The main surface and human activity factors that affect the terrestrial water resources change are further analyzed.This paperproposes that the accurate description of land surface processes and the high resolution fine characterization and simulation of surface hydrothermal conditions and their heterogeneity can provide more accurate lower boundary conditions for the climate system.The dynamic downscaling simulation based on the fine description of the boundary conditions under the land surface is an effective way to improve the simulation performance of spatial distribution of precipitation in complex terrain areas,which will lay a foundation for the study of water resources and their changes in land,especially in high altitude mountain areas.

Abstract:The southwest vortex is a meso-α-scale vortex formed on the southeast side of the Qinghai-Tibet Plateau in China.It is one of the main weather systems that cause heavy rainfall in summer half year in China.This paper briefly reviews the latest research results of the southwest vortex since 2000,mainly including the artificial intelligence recognition of the southwest vortex,the long-term variation and climatological characteristics of the frequency of the southwest vortex,the ensemble forecast of the southwest vortex,and the first discovery of the binary southwest vortex.On this basis,some issues that need to be further discussed in this research field are summarized,including the external forcing factors related to the frequency variation of the southwest vortex,the relationship between the topographic Rossby wave,gravity wave and the southwest vortex caused by the special topography of the Qinghai-Tibet Plateau,the formation mechanism of the binary southwest vortex,and the difference of formation mechanism between of the binary southwest vortex and the classic southwest vortex.

Abstract:The cloud imaging probe (CIP) and precipitation imaging probe (PIP) are two important measurement instruments in cloud microphysics and weather modification research.Limited by the instrument’s measuring principles,the quality of data from CIP and PIP is degraded by the influence of the artificial particles.Therefore,a data processing software to improve the data quality is urgently needed.In this study,based on the data structure knowledge and analysis of the factors affecting the accuracy of the airborne measurement,a method to improve the data quality is proposed.Utilizing the LabVIEW graphical programming language,we developed a software program to process the CIP and PIP’s data,which realizes the function of data quality control.The software can read the imaging data from CIP and PIP,identify the artificial particles,and calculate the cloud microphysical parameters,thereby satisfying the requirements of the CIP and PIP’s data quality control.The software that we developed was then applied to process the image data measured from a precipitation stratus cloud above Shanxi on April 20,2010.The acquired results reflect the vertical structure and particle spectrum evolution of the cloud,and this suggests that the software is quite helpful toward cloud and precipitation microphysics research.

Abstract:In this study,based on the NECP/NCAR reanalysis data and statistical data from 38 stations located in Sichuan Province,and combined with the Long-term Drought and Flood alternative index (LDFAI),the relationship between the time evolution characteristics of long-term drought and flood alternative in summer and atmospheric circulation of typical years in Sichuan Province was analyzed.The results show the following:1) The interannual variation of summer drought and flood alternative index in Sichuan Province differs greatly,the occurrence of the drought to flood being greater than that of flood to drought;however,the drought to flood alternative is declining,while the intensity for flood to drought is quite high.2) Comparing the drought season of drought to flood with flood season of flood to drought,the western Pacific subtropical high is located westward,and is quite strong.The water vapor transport in the South China Sea and western Pacific cannot easily reach Sichuan,and the precipitation level is lower,with more frequent drought.Comparing the flood season of drought to flood with drought season of flood to drought,the circulation warp direction movement is stronger,while the mid-high latitudes ridges are clearly fluctuating,which is conducive to the formation of precipitation when the cold air in the middle and high latitudes traveling south meets the warm and humid air in the low latitude going north,thereby resulting in greater precipitation and increased floods.

Abstract:The weekly cycle of air quality in a given location reflects the impact of human activity there.In the present study,the characteristic of weekly cycle of air pollution in Anhui Province,China,is assessed based on hourly time series of six air pollutants:PM_2.5,PM₁₀,CO,NO₂,SO₂ and O₃.In order to better understand the weekly cycle,a new definition of the weekly cycle departure percentage (WCDP) series is proposed,based on the sliding average series of the original hourly data.Specifically,the WCDP of a given time is the percentage deviation of the average value of the corresponding 24-hour window from the averaged value of the corresponding 168-hour window.The advantage of the WCDP series is that the daily cycle component and low-frequency component are filtered out,while the weekly cycle component is retained.Based on the composite analysis and Bayes statistics analysis performed on the WCDP,it is found that that PM_2.5,PM₁₀,CO and NO₂ have much stronger weekly cycles,while O₃ shows the weakest weekly cycle.Among the four seasons,the weekly cycle in summer is weaker than the other seasons,which results from the superior diffusion capacity in summer.Based on the first principal component,it can be found that all variables except O₃ have almost the same cycle pattern,i.e.an accumulative process began on Wednesday,and a decreasing process after Saturday.However,the weekly cycle of O₃ has a lag of over 12 hours more than the other five variables,indicating a lag relationship between O₃ and its photochemical precursors at the weekly cycle scale.The results of the present paper indicate that it is preferable to explore the weekly cycle process,but not only the weekend/weekday ratio;in addition,the WCDP defined in this study is a useful tool for exploring the weekly cycle of air pollution or other meteorological variables.

Abstract:Based on the daily minimum temperature data of 376 national stations in Northwest China and NCEP FNL reanalysis data from 2000 to 2013,the temperature drop amplitude of the stations and the 500 hPa low-frequency height field in Eurasia were analyzed.An extended-range forecast model of cold wave at stations in Northwest China was established by the partial least squares regression method,and the cold wave day and the non-cold wave day in January 2017 were predicted as an example.The cold wave forecast experiment was carried out using the data in Northwest China in winter half year from 2014 to 2017 (728 d in total).Results show that the model can well predict cold wave days and non-cold wave days 10—30 d in advance.The average number of stations with temperature drop≥8 ℃ predicted 10—30 d in advance for cold wave days is 32.9,with the highest hit rate of 67％,while the average number for non-cold wave days is 2.7.The forecast results of cold wave days in Northwest China during the extended-range of winter half year from 2014 to 2017 show that,the average station hit rate predicted by the model 10—30 d in advance is 11.5％,and the empty rate is 70.3％.It is a cold wave day,When the number of stations with temperature drop≥8 ℃ exceeds 15.The average CS score is 0.1,and the predicted cold wave day corresponds to the actual cold wave day best.Therefore,the model can be used to predict the cold wave during the extended-range in Northwest China,and has a certain reference value.

Abstract:With the increasing impact of human activities on climate change,the extreme weather events such as extreme precipitation occur more frequently and people pay more attention on probabilistic precipitation forecast.Since there is still a large error in precipitation ensemble forecast,it is of great significance to calibrate the forecast.Based on the daily 24 h accumulated precipitation forecasts obtained from the global ensemble forecast system of ECMWF (the European Centre for Medium-Range Weather Forecasts) with 24—168 h forecast lead times in East and South China from 8 February 2015 to 31 December 2016,NN (neutral network) model and NN-GI (neutral network-geographic information) model using feedforward neural network were established to improve probabilistic precipitation forecast and evaluate the results before and after calibration.Results show that after the correction of NN model and NN-GI model,the precipitation probabilistic forecasts are improved obviously.Compared with ECMWF raw ensemble forecasts,CRPSs of precipitation probabilistic forecasts from NN model and NN-GI model with 168 h forecast lead time decrease by around 16.00％ and 21.27％,respectively.Meanwhile,compared with NN model,NN-GI model takes into account the geographic information difference of each grid point,and the overall improvement of forecasting skills in the region is better.However,NN-GI model has better performance,indicating that the machine leaning approach can improve the probabilistic forecast of the precipitation more significantly by taking into account the geographic information of each grid point in the model.

Abstract:Based on the NCEP/NCAR and ERA-Interim reanalysis data,the multiple linear regression analysis is used to study impacts of different configurations of Western Pacific teleconnection (WP) and North Atlantic Oscillation (NAO) on winter surface temperature in southeastern China.Results show that in the positive phase year of WP,the middle and low latitudes Pacific Ocean is controlled by abnormal warm high,whose local effects make a warmer winter in southeastern China.In the positive phase year of NAO,the north and south teleconnection wave trains regulate the north and south branch troughs systems respectively,which synergistically make a colder winter around 30°N in southeastern China.Considering the interaction of the two teleconnection patterns,when WP and NAO are in the same phase,their opposite effects are partially offset,and the temperature change in southeastern China in winter is not significant.In positive WP phase and negative NAO phase,the synchronous heating effects make a warmer winter in southeastern China.In negative WP phase and positive NAO phase,the synchronous cooling effects make a colder winter in southeastern China.

Abstract:This study utilized the monthly NOAA sea surface temperature(SST) data for the past 38 years,as well as the Western Pacific Subtropical High(WPSH) characteristic indexes of the National Climate Center(NCC),and the NINO3.4 indexes of the United States Climate Prediction Center(CPC).The main modes of the SST anomalies(SSTA) on the tropical Indo-Pacific Ocean were examined using the Empirical Orthogonal Function(EOF) and linear regression analysis methods.In addition,the possible relationships between those modes and the intensities and locations of the anomalies of the WPSH were examined.Finally,based on the observed relationships,prediction models of the area were established,which included the intensities and west ridge point indexes of the WPSH.The results showed that the three leading modes explained 61.58％ of the variances of the SSTA in the Indo-Pacific Ocean,which accurately reflected the main characteristics of the SSTA.Among these,it was determined that the most important SSTA mode(EOF1) in the Indo-Pacific Ocean was a zonal tripolar mode,which explained 39.73％ of the variances of the SSTA,and displayed periods of approximately 5 years and 11 years.In terms of seasonal variations,it was observed to be the most obvious during the winter months.The second mode(EOF2) showed a dipole distribution of positive anomalies ranging from the tropical Indian Ocean to the Western Pacific Ocean,and negative anomalies in the central Pacific Ocean.It was also found to have a 3-year interannual period and an obvious long-term linear trend.The spatial field of the third mode(EOF3) displayed a dipole type over the southern Indian Ocean and another dipole type over the equatorial Pacific Ocean.It also had the appearance of "seesaw" anomalies between the southeastern Indian Ocean and the tropical central Pacific Ocean,on both sides of the marine continents(MC).The time coefficients of both the EOF2 and EOF3 displayed two peaks per year.The former was mainly obvious during the months of June and October,and the latter was most obvious during the months of April and August.This study found that these three modes were closely related to the occurrences of anomalous signals,such as El Niño in the Pacific Ocean,and basin modes and Ningaloo Niño in the Indian Ocean.Among the three modes,it was determined that the EOF1 may lead to the El Niño/La Niña events in the Pacific Ocean and IOBM in the Indian Ocean.Therefore,it was considered that the EOF1 could be used to explain why the El Niño/La Niña and IOBM often occurred together.Moreover,it was believed that the IOD events probably occurred due to the anomalous eastward moving of one pole near the MC in the tripolar mode to the Indian Ocean.However,the second mode(EOF2) reflected the features when the SSTA was weak over the Pacific Ocean.However,the IOBM over the Indian Ocean was obvious during some of the examined years.In addition,the first two modes had stable and significant correlations with the anomalous areas,intensity,and west ridge point indexes of the WPSH during the summer months.However,it was found that the significant correlations between the anomalous WPSH ridge and the first mode during the early spring months,as well as the third mode during the summer months,had suddenly become weaker after 2006.In the current study,according to the aforementioned stable correlations over the past 30 years,the indexes of the WPSH area,intensity,and west ridge point can potentially be accurately forecasted for the next eight years.

Abstract:The data from the FY-4A satellite have a higher temporal and spatial resolution when compared with the data obtained from the FY-2 satellites.This indicates the recent development of China's geostationary meteorological satellites.In order to promote the practical applications of the FY-4A satellite data in a model and investigate the impacts of observational errors on the assimilation and forecasting accuracy of the atmospheric motion vector (AMV) of the FY-4A satellite,this study carried out in-depth research experiments.The observational errors of the AMVs derived from the high-level water vapor channels and infrared channels of the FY-4A were first calculated and analyzed.The vertical profiles revealed that when compared with the default observational errors of the assimilation system,the new observational errors of the high-level water vapor channel had decreased with height between 700 hPa and 200 hPa.In addition,the new observational errors of the infrared channels were smaller below 800 hPa than above 700 hPa,where the vertical structural features were more pronounced.A series of assimilation and forecasting experiments were carried out using the default observational errors and the new observational errors.It was determined that according to the average RMSE profiles,the results using the new errors were significantly improved in the wind field when compared with results using the default errors.At the same time,the heights at which the RMSE of the wind field had displayed maximum improvement corresponded to the heights at which the number of observations were the largest.Also,the new observational errors of the infrared channels were observed to more widely influence the wind field than that of the high-level water vapor channels since the data from the infrared channels were distributed on almost every layer.Furthermore,the track and intensity forecasting results of the "Hato" and "Pakhar" typhoon systems were discussed in this study in order to further examine the impacts of observational errors on the accuracy of the forecasting results.The results of the typhoon forecasting results indicated that the new observational errors could significantly improve the track forecasting,as well as increase the accuracy of the intensity predictions to some extent.

Abstract:The physical mechanisms which caused the distinctive evolution features of the 1988 to 1989 La Niña Event were investigated suing an oceanic mixed-layer heat budget analysis method which incorporated two sets of ocean reanalysis data.The results showed that in a typical La Niña event,after the peak has been reached,slow decay will occur during the first half of year+1.Then,the La Niña will re-develop into another La Niña during the following winter.In contrast,the special 1988 to 1989 La Niña event was observed to undergo a fast decay after its peak,and it then recovered to a climatological mean state by the end of the second year.The heat budget analysis results indicated that an anomalous zonal advection term related to wind force had contributed to the distinctive differences in the decaying rates between the typical and special 1988 to 1989 La Niña.During the decaying period,there was an anomalous anticyclone over the western North Pacific Ocean in the typical La Niña.In contrast,an anomalous cyclone event had occurred during the special 1988 to 1989 La Niña.The anomalous easterly winds south of an anticyclone can trigger upwelling Kelvin waves which propagate eastward,which maintain the cold SSTA in the equatorial eastern Pacific Ocean during a typical La Niña event.However,the anomalous westerly winds south of a cyclone can induce downwelling Kelvin waves propagating eastward,which caused the special 1988 to 1989 La Niña event to decay faster and then recover to a mean state by the end of the following year.

Abstract:Based on the objective analysis data of NCEP FNL and theprecipitation data from China’s automatic station and CMORPH,this paper carried out a synoptic background analysis of a heavy precipitation process in Shanghai from August 23 to 24,2015.A quantitative analysis of the specific impact of the 1515 typhoon known as "Typhoon Swan" on this precipitation process was conducted by means of the potential vorticity inversion method,so as to explore the mechanism of the rainstorm process,and the following main conclusions were drawn:1) The method of vorticity inversion is able to accurately reflect the characteristics of the westerly trough,typhoon and sub-tropical high pressure and other important weather systems,and can effectively reproduce the evolution of these systems;2) The main cause of this precipitation process was the intersection of north cold air and northeast air flow over the long-distance typhoon;3) By comparing the original field with the analysis field after removing the typhoon,it can be observed that the water vapor flux corresponding to the disturbance of Typhoon Swan accounts for 53.3％,which is the water vapor input of the precipitation;4) Typhoon Swan provided certain thermal conditions for the precipitation area.After the typhoon had been deducted,the large value area and warm wet tongue of the original analysis field disappeared,while the corresponding frontal area also disappeared.

Abstract:Based on the standardized precipitation evapotranspiration index (SPEI),this study applied statistical observational analysis and numerical simulations (CAM 5.3),so as to analyze the characteristics of spring drought in North China (NC) from 1955 to 2018,as well as the impacts of the North Atlantic (NA).The results showed that the main spatial distribution pattern of spring drought in NC was uniform throughout the entire region,and,in the past 60 years,there were 22 drought years and 14 flood years.The main atmospheric circulations of the NC spring drought years were the enhanced continental high,weakened upper westerly jet,and downward movement in NC.Aside from these,both observational analysis and numerical simulation results showed that the warm sea surface temperature (SST) in the NA could cause spring drought in NC.The mechanism is as follows:warm SST in NA can lead to a "+-+" wave train such as the "Silk Road Pattern" with its center above the NA,Europe-western Asia and NC;this wave train would then enhance the continental high over NC,which could cause the downward movements;these downward movements are not conducive to precipitation,and will lead to the air undergoing adiabatic heating;in addition,NC lies to the south of the upper anticyclone circulation,which leads to NC being controlled by the northeast airflow,thus signifying that the warm and humid airflow from the Southwest is weakened.In summary,the wave train causes the high temperature and reduced rain in NC,which is conducive to drought.When the SST in the NA grows cold,the center of the wave train would be reversed,which in turn would cause the continental high over NC to weaken.

Abstract:In this paper,the minute rainfall data with high time resolution is used,and combined with the data of the LS8000 lightning locator,to analyze the processes of lightning and precipitation in Shenzhen caused by the weather patterns of typhoon,low pressure,southwest monsoon and shear line types,from 2014 to 2017.Based on the statistics features of duration,precipitation frequency and peak value,the temporal and spatial distribution characteristics of precipitation and lightning,and the radar echo height caused by weather flow patterns are discussed.The study results show that the short-term heavy precipitation accompanied by lightning activity caused by the four types of weather flow patterns mainly occurs from early morning to 08:00 BST,and in the afternoon.The lightning activity corresponding to the short-term heavy precipitation produced by the typhoon type mainly occurs at the precipitation intensity from 20 to 30 mm·h^-1,and the main type of lightning is negative cloud to ground lightning flashes.More than 80％ of the lightning activities in the low pressure,southwest monsoon and shear line types mainly occur when the precipitation intensity is greater than 50 mm·h^-1.For convective activities with precipitation of less than 40 mm·h^-1,the shear line type is the main weather system that produces precipitation with lightning activity of this magnitude,and the average frequency of cloud to ground lightning is more frequent than the other types.In particular,the radar echo height of convective activity is mainly 2—4 km,due to the weather system,and about 72％ of convective processes have a 0℃ level height of less than 5 km.

Abstract:Based on the observed sea surface temperature (SST) data from 1880 to 2009 and the simulated SST datasets under four scenarios (piControl,historical,RCP2.6 and RCP4.5) in the CMIP5 (Coupled Model Intercomparison Project phase 5) models,this paper evaluated the simulation performance of CMIP5 models for two most important interdecadal scale modes (Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO)),and further investigated their future projection under different warming scenarios.Results show that the multi-model ensemble can reproduce the interdecadal variation centers of sea surface temperature in North Pacific,East Pacific and North Atlantic under historical and piControl scenarios,but the simulatedamplitudes of AMO mode and PDO mode are weak,especially PDO mode in East Pacific.By evaluating the spatial and temporal characteristics of AMO mode and PDO mode under historical scenario,this paper ranks the ability of models that simulate AMO mode and PDO mode,and suggeststhat CESM1-CAM5,FGOALS-g2,GISS-E2-H-CC,MIROC5 and NorESM1-ME are five better models and the multi-model ensemble is best.Under different warming scenarios,the spatial characteristics of AMO mode and PDO mode are basically consistent and the amplitude differencesamong different warming scenarios are not obvious.However,with the increase of global warming,AMO modeand PDOmode are characterized by the decrease of variance contribution,especially AMO mode.