Current Issue

• Assessment of Freeze-thaw Process Simulation in Qinghai-Tibetan Plateau by Different Parameterization Schemes based on Noah-MP Land Surface Model
• Huolin LIU;Zeyong HU;Geng HAN;Changchun PEI
• 2020 Vol. 39 (1): 1-14.  DOI:10.7522/j.issn.1000-0534.2019.00009
• Abstract ( ) HTML ( ) PDF (3488KB) ( )
• Considering the large simulation bias of the freezing-thawing process from land surface models, an comparative analysis of the freeze-thaw process parameterization schemes based on Noah-MP land surface model are carried out and the simulations of different freeze-thaw process parameterization schemes are verified by observation data. Results show that the Noah-MP land surface model can capture the characteristics of freezing-thawing process. The freeze-thaw process simulation is quite sensitive to the freeze-thaw parameterization scheme. From the freezing phase to the melting phase, the simulated values of the four experimental groups are significantly different. Before the freezing phase and after the melting phase, the simulated values of the four experimental groups are quite consistent.Compared with the super cooled liquid water parameterization scheme, the frozen soil permeability parameterization scheme is more sensitive to the simulation of soil temperature during freezing-thawing period. Different super cooled liquid water parameterization schemes can cause large differences in simulated soil moisture.The simulation of surface energy flux is quite sensitive to the freeze-thaw parameterization scheme.There are significant differences in the simulation values of the surface energy flux by four tests during freezing phase, freezing stability phase and melting phase.

• Evaluation on Simulated Snow Depth over Qinghai-Tibetan Plateau with BCC-CSM(m) Model during Recent 30 Years and Its Impact on Precipitation in Summer
• Minhong SONG;Tongwen WU;Yu ZHANG;Shaobo ZHANG;Yinping LONG;Yang LI
• 2020 Vol. 39 (1): 15-23.  DOI:10.7522/j.issn.1000-0534.2019.00076
• Abstract ( ) HTML ( ) PDF (3693KB) ( )
• In order to obtain the effective, long?term sequence and regional scale data suitable for the snow study of the Qinghai?Tibetan Plateau (QTP), utilizing the snow depth data over the QTP from BCC?CSM(m) model and satellite remote, the sensible heat flux data from ECMWF and precipitation data from National Meteorological Information Center, the simulation performance of the snow depth over the QTP from BCC?CSM(m) model was evaluated and the influences of snow depth over the QTP on summer precipitation in China were analyzed to provide the reference for predicting summer precipitation in China.The main conclusions are as follows: (1) The spatial and temporal characteristics of winter snow over the QTP can been better reproduced by the snow depth data from BCC?CSM(m) model.It can be regarded as an alternative snow data with high resolution over the QTP lacking of the measured snow data.(2) It is shown that there occurs an inverse change over the QTP between snow in winter and surface sensible heat in spring.That is, the surface sensible heat is low in spring in the areas with more snow in winter over the QTP, due to the blocking effect of snow cover.While in the areas with less snow cover, the opposite is true.(3) The influences of four winter snow modes over the QTP on summer precipitation in China are different.There are the significantly positive correlation area in the middle and lower reaches of the Yangtze River, Sichuan, North Xinjiang, the eastern Northeast China and the southern QTP, and the negatively correlation ones in South China and the northern Northeast China.(4) By using the EOF analyses, the four spatial distribution modes of snow depth over the QTP in winter are given, i.e.the snowy type in the whole region, the snowless type in the whole region, the more southeast and less northwest type and the less southeast and more northwest type.

• Spatial-temporal Characteristics of Snow and Influence Factors in the Qinghai-Tibetan Plateau from 1961 to 2014
• Qi JIANG;Siqiong LUO;Xiaohang WEN;Shihua Lü
• 2020 Vol. 39 (1): 24-36.  DOI:10.7522/j.issn.1000-0534.2019.00022
• Abstract ( ) HTML ( ) PDF (9121KB) ( )
• Using observed daily data, which include the snow depth, the number of snow?cover days, temperature and precipitation data, from 110 meteorological stations over the Qinghai?Tibetan Plateau from 1961 to 2014, the spatial?temporal characteristics of the snow depth and the number of snow?cover days in Qinghai?Tibetan Plateau were analyzed and the relationship between them and climatic and geographical factors were explored.The results showed the annual average of the snow depth and the number of snow?cover days were 0.26 cm and 23.78 d, respectively.And the distribution was uneven on the spatial and seasonal scales.The great value of the snow depth and the number of snow?cover days did not completely coincide.As for trend analysis, both the depth and the number of days with snow cover showed a slow decline trend, which was -0.0080±0.0086 cm·(10a)^-1 (p=0.36) and -0.64±0.47 d·(10a)^-1 (p=0.17), respectively.But the trend was not significant in mathematical statistics.The trend varied significantly from stations to stations.The snow depth and the number of snow?cover days in spring, winter and annual were characterized by the interdecadal variation of “decrease?increase?decrease”, while it showed “increasing?decreasing” in autumn.Temperature highly corresponded to the snow depth and the number of snow?cover days while precipitation was highly correlated with the snow depth and the number of snow?cover days in winter.The depth and days of snow cover decreased with the increase of sea level altitude.Latitude showed a high correlation with the number of snow?cover days while the correlation with the snow depth was not obvious.

• Evaluation of Land Surface Temperature and 2 m Air Temperature fromFive Reanalyses Datasets across North China in Winter
• Shuai SHAN;Runping SHEN;Chunxiang SHI;Lei BAI;Shuai SUN
• 2020 Vol. 39 (1): 37-47.  DOI:10.7522/j.issn.1000-0534.2019.00003
• Abstract ( ) HTML ( ) PDF (9632KB) ( )
• Using daily land surface temperature and 2 m air temperature in situ observations across northern China during 2011 -2016 in winter, The reanalysis detests of ERA5, MERRA2, JRA55, CRA-interim and CFSR are evaluated, the bias of land surface temperature with and without snow condition are discussed based on MOD10C1.The results are shown that: (1) The applicability of five reanalyses air temperature is good, especially in northeastern China.The overall Bias of air temperature in 5 reanalyse datasets are under 1 ℃.The land surface temperature perform obvious cold bias, except that ERA5 perfomed an overall bias of -0.34 ℃; (2) There are correlations of land surface temperature bias and land cover, reanalyses do bad in forest area in simulating land surface temperature, while good in grass area.And the cold bias of land surface temperature with snow cover is greater than that without snow cover in cultivated area and forest area.(3) Compared with the bias numerical value of land surface temperature itself, snow affect the land surface temperature simulating slightly, we should focus on improving the simulation in forest area.

• Numerical Simulation of Cloud Precipitation and Cloud Microphysical Process in Nagqu Area on August 7, 2014
• Shucheng YIN;Maoshan LI;Xiaoran LIU;Xingyu SONG;Zhao Lü;Lei SHU;Lingzhi WANG;Wei FU
• 2020 Vol. 39 (1): 48-57.  DOI:10.7522/j.issn.1000-0534.2019.00062
• Abstract ( ) HTML ( ) PDF (7310KB) ( )
• This paper used the mesoscale model WRF to simulate a convective cloud precipitation process in the Nagqu area of the Qinghai-Tibetan Plateau from August 7 to August 8, 2014.The WRF model can better simulate the precipitation, rainfall center and rainfall level of the convective cloud precipitation process in the Nagqu area.The simulation results show that the phase particles are distributed in different height layers, and the distribution position has no obvious change with time.The change of mass density with time can basically reflect the characteristics of ground precipitation changes.The simulated source of rain, snow and graupel indicates that cloud water contributes the most to precipitation.The process of condensation and collision is the main process of snow and graupel growth.The combination of smelting and cloud water accelerates the movement of cloud water to rainwater.Transform to make precipitation on the ground.It can be seen from the evolution characteristics of cloud microphysical processes over time that the ice phase particle process plays an important role in the process of plateau precipitation.In the whole process, graupel plays an important role in the formation of precipitation cloud water and rain water also play an important role in the formation of graupel.

• The Characteristics of Summer Precipitation in China since 1981and its Relationship with SST and Pre-circulation
• Qifen LI;Zhehong WU;Xingju WANG;Donghai ZHANG;Mei XIAO
• 2020 Vol. 39 (1): 58-67.  DOI:10.7522/j.issn.1000-0534.2018.00148
• Abstract ( ) HTML ( ) PDF (2951KB) ( )
• The characteristics of summer precipitation in China from 1981 to 2017 and its relationship with SST and pre?circulation in global were discussed using the NCEP reanalysis data and the monthly mean precipitation data of 160 stations in China based on EOF， Mann?Kendall， wavelet analysis and SVD analysis.The results show that， the first EOF mode of summer precipitation in China had the characteristics of uniform regional and interdecadal changes， the second EOF mode had the characteristics that the northeast in China and the other regions was opposite and had interannual changes.Summer precipitation especially in the Inner Mongolia area from 1981 to 1997 was relatively less than that from 1998 to 2017， while during 2014 -2017 compared with 1998 to 2013， summer rainfall in south of China was more than in north.Summer precipitation in the northern regions and the Yangtze River basin changed suddenly in 1997， while the south’s changed suddenly in 2013 .The north had 26 ~ 30 years， 9 ~11 years and 5 ~ 6 years， the south had 20 ~ 22 years， 12 ~ 13 years， and the Yangtze River Basin had 16 years， 6 ~ 10 years of periodic changes.In the context of interdecadal variation， summer precipitation in China was also interannual variation.SST of the East Pacific in winter was negatively correlated with the Western Pacific Ocean， the India Ocean and the Atlantic and this had interdecadal variation， and that led to a consistent and interdecadal change of the next year’s summer precipitation in China.While SST of the Eastern Pacific， the Indian Ocean， the western Atlantic in winter was inversely correlated with the Western Pacific and the Northeastern Atlantic and this had inter?annual changes， that led to the north?south inversion of the next year’s summer precipitation.SST affected the next year’s summer rainfall by influencing atmospheric circulation such as sea level pressure， 500 hPa height field.Through the continuous observation of the atmospheric circulation in the key area in winter and in spring， it can be used as one of the bases for predicting summer precipitation in the next year.

• Study on Precipitation and Extreme Precipitation in the Wet Season in Sichuan Basin based on CMIP5 Models
• Hao YU;Yunjun ZHOU;Qian LI;Qi JIANG;Weiteng QIU;Di WU;Xuefeng CUI
• 2020 Vol. 39 (1): 68-79.  DOI:10.7522/j.issn.1000-0534.2019.00007
• Abstract ( ) HTML ( ) PDF (7475KB) ( )
• Sichuan Basin is an important agricultural and economic center in China.Precipitation in wet season, especially extreme precipitation, is particularly important.This paper evaluates possible future changes in wet season precipitation and extreme precipitation based on multiple model results of the Coupled Model Inter-comparison Project Phase 5(CMIP5).First, the CRU data was used to test the models' ability to simulate the May-September precipitation in Sichuan Basin from 1971 to 2000.The results show that 17 of the 31 models had better simulation capabilities, and pass the 99% of the spatial correlation reliability test.The results successfully reproduce the spatial pattern of “east more and west less”.The ratio of the standard deviation of 21 patterns to observations is less than 2.5.The average precipitation bias of all models is less than 50%.On this basis, we select three best-performing models, and after the correction we will perform the MME to display the spatial distribution characteristics of average precipitation and wet season extreme precipitation thresholds in the Sichuan Basin in early 21st century (2010 -2039)、 middle period (2040 -2069) and late period (2070 -2099), in the case of RCP2.6, RCP4.5, and RCP8.5.The results show that in the case of RCP2.6, compared to the climatology of 1971 -2000, precipitation in wet season of Sichuan Basin shows a "decreasing-increasing-decreasing" trend from east to west, and there is no obvious change over time.In the case of RCP4.5 and RCP8.5, the characteristics are different from those of RCP2.6, showing a "increasing-decreasing-increasing" situation from east to west.The average precipitation in wet season in the east of basin generally increases, and the variability in some regions even reached 20%.For the spatial distribution of extreme precipitation thresholds, the characteristics are similar to the average precipitation.In the three cases, the large-value areas are in a north-south trending strip-like zone in the east of the basin.This area includes major cities in Sichuan, such as Chengdu, Ya'an, Meishan, Leshan, and it has an increasing trend over time.The precipitation simulated by RCP8.5 is significantly more than the other two cases.In addition, the study finds that under the background of global warming, if the average precipitation in wet season in a certain area of the Sichuan Basin decreases, and the extreme precipitation threshold must be reduced, but the opposite is not necessarily true.Only when the average precipitation increases by more than 10% will the threshold of extreme precipitation in that area increase.

• Comparative Analysis of Xinjiang Mountain Flooding Simulation and Threshold based on Different Data
• Liancheng ZHANG;Xingjie YU;Weiling SHAO;Jingli ZHANG;Xingyi TONG;Yuanpeng LI
• 2020 Vol. 39 (1): 80-89.  DOI:10.7522/j.issn.1000-0534.2019.00008
• Abstract ( ) HTML ( ) PDF (4382KB) ( )
• In this paper, the flooding events in boerbosong basin is studied using observed flood depth data, digital elevation map （DEM） data, land use type data, hourly precipitation data, quantitative precipitation estimation(QPE) data, et al.FloodArea model was utilized to simulate the flood process of the study area on 25 August 2013, 28 June 2015 and 17 June 2016.The spatial and temporal distribution characteristics are analyzed based on the precision test of the measured data.Then the relationship between surface rainfall and submerged depth was established, and the critical rainfall corresponding to the four flood levels in the study area was determined.It is also found that the submerged depth is increasing, which can be divided into three stages: accumulation period, stable growth period and fluctuation uplift period.Through precision verification, the flooded depth derived by FloodArea model is higher than observation, while QPE and R-QPE (revised quantitative precipitation estimates data）data are lower than that observed.The above three data simulation results absolute error of the investigation points（borborzon and Tal village） is 0.46 m, 0.78 m, 0.35 m and 1.35 m, 1.44 m and 0.65 m respectively.R-QPE data can simulate the flood depth with the best accuracy and can reflect the flood situation of the basin.Through correlation analysis, the correlation between the surface rainfall of the cumulative aging for 7 h and the simulated flood depth is the best, with the correlation coefficient reaching 0.989.On this basis, the relationship between surface rainfall and submerged depth is established.The relationship between surface rainfall and flood depth was obtained according to mountain flood disaster grade, the cumulative aging of 7 h surface rainfall at the early-warning point can obtain the threshold values of four levels of critical rainfall causing disasters: level 4 is 6.25 mm, level 3 is 23.61 mm, level 2 is 49.64 mm and level 1 is 75.67 mm respectively.

• Performance Tests and Evaluations of Northwest Rapid Update Cycle Prediction System
• Xianyu YANG;Jun WEN;Guangshan NIU;Dayong WANG;Jianglin LI;Jinlei CHEN
• 2020 Vol. 39 (1): 90-101.  DOI:10.7522/j.issn.1000-0534.2019.00010
• Abstract ( ) HTML ( ) PDF (7304KB) ( )
• To explore the operational performance of northwest high?resolution Rapid Update Cycle (RUC) system, the operational forecasts during 2^nd June to 6^th July of 2012 were verified and evaluated.The Northwest RUC predictive results were interpolated to the nearby observation site using the bilinear interpolation method.Statistical methods were used to calculate mean error (ME) and root mean square error (RMSE) of geopotential height field, temperature, wind direction and wind speed at 500 hPa and 700 hPa, then the score of TS, deviation (BIA), T score (ETS) fair and true skill score (TSS) were calculated to evaluate the quantitative precipitation predicted in 24 hours.The results are as follows: (1) there were systematic positive deviation for height field prediction, temperature field prediction, and wind speed predication at 500 hPa and temperature at 2?meter height, the 24?hour average of ME were 0.17 gpm, 0.63 ℃, 1.19 m·s^-1, 1.49 ℃, respectively.Height field prediction and temperature field prediction at 700 hPa showed systematic negative deviation, the 24?hour average of ME was -0.41 gpm, -0.11 ℃, respectively.(2) Except for wind speed and wind direction, other elements forecast effect in 24?hour were better than the forecast effect in 48?hour of the model, which match to the prediction performance.The 24?hour average of RMSE of geopotential height field and temperature at 500 hPa were 1.32 gpm, 1.37 ℃, respectively, and the value of 48?hour of RMSE were 1.56 gpm， 1.53 ℃, respectively.The 24?hour average of RMSE of geopotential height field and temperature at 700 hPa was 1.21 gpm, 1.40 ℃, respectively, and the value of 48?hour of RMSE were 1.38 gpm， 1.94 ℃, respectively.The 24?hour and 48?hour average of RMSE of temperature at 2?meter were 3.06 ℃, 3.30 ℃, respectively.(3) The TS score, ETS score and TSS score of quantitative precipitation were almost have the same large value center at different precipitation grade in 24 hours.It means the precipitation forecast effect was comparatively good near the center region of the large value.The heavy rain and rainstorm forecast effect was better in the southeastern of Northwest area.From the BIA score, the model forecasted less light rain events than observed, but forecasted more moderate rain and heavy rain events than observed in the south of Qinghai and north of Sichuan.

• Variation of the Winter Extreme Cold Events in the Northern Hemisphere and its Relationship with Arctic Sea Ice in Autumn
• Dongdong YANG;Lujun ZHANG;Shu ZHOU;Huazhao WANG;Weijia ZHOU;Yuan LI
• 2020 Vol. 39 (1): 102-109.  DOI:10.7522/j.issn.1000-0534.2019.00020
• Abstract ( ) HTML ( ) PDF (2886KB) ( )
• Based on daily surface temperature from European Centre for Medium-Range Weather Forecasts and monthly sea ice concentration from National Snow and Ice Data Center， the days of monthly extreme cold events were calculated by the climate percentile method， and then the correlation of winter (November to subsequent February) extreme cold events in the northern hemisphere and Arctic sea ice in autumn (form September to November) during 1979 -2016 was analyzed.The possible mechanism of the influence of autumn Arctic sea ice on extreme cold events is discussed through the selected typical years.The results show that the variations of autumn sea ice area in the key region (Beaufort、 Chukchi、 Barents and Kara sea) has a significant relation to winter extreme cold events in the northern hemisphere.The events in northern Asia have a significant negative correlation with autumn sea ice area in the key region， while Qinghai-Tibetan Plateau、 northern Africa and northeast North America have a positive correlation with autumn sea ice area in the key region.Through the analysis of the atmospheric circulation in the winter of typical example， it is found that when the sea ice in the key region is abnormally less in the autumn， the Siberian high pressure and the north winds of its east is strong in winter， resulting in low temperatures and more extreme cold events in northern Eurasia； The Icelandic low pressure is strong in winter and the abnormally southwest winds of its south bring warm air from low latitudes to the northern Africa， resulting in high temperatures and fewer extreme cold events in northern Africa； An abnormal anticyclone is mainly located near Greenland， and its downdraft is not conducive to the formation of extreme cold weather， resulting in relatively few extreme cold events in northeast North America.

• Sub-seasonal Scale Oscillations of Winter Temperature in China and the Relationship with Interannual Anomalies
• Wenhui LI;Guirong TAN
• 2020 Vol. 39 (1): 110-119.  DOI:10.7522/j.issn.1000-0534.2019.00053
• Abstract ( ) HTML ( ) PDF (7929KB) ( )
• Based on the daily averaged temperature data of 756 stations in China,we analyze the basic sub?seasonal characteristics of winter temperatures in China and study the interannual anomalies of winter temperature caused by sub?seasonal oscillations,by using the Rotated Empirical Orthogonal Function（REOF）and power spectrum analysis methods.The results show that:(1) There are regional differences in the sub?seasonal oscillations of winter temperature in China.The sub?seasonal scales of winter temperatures in southern,western and eastern have 10~20 days and 20~60 days oscillations,but the 10~20 days oscillations in the southern and eastern China are more pronounced than in the western China.(2) The intensity of the main oscillations of 10~90 days,10~20 days and 20~60 days in winter has obvious interannual variations.The interannual variations of the oscillation period in the northwestern,central,and southern China are similar.The interannual variations of the oscillation period in northern and northeastern China are similar,and the interannual variations of the oscillation period in southwestern China and Yunnan province are similar.(3) The sub?seasonal oscillations of winter temperatures in China are closely related to the interannual variations of winter temperatures.There are significant winter temperature anomalies corresponding to the regional main oscillation strength year.And there is a negative correlation relationship between the low?frequency variation and the winter temperature anomalies.

• Response of Runoff to Extreme Climate Change in the Upper Reaches of the Heihe River
• Wenju CHENG;Haiyang XI;Jingtian ZHANG
• 2020 Vol. 39 (1): 120-129.  DOI:10.7522/j.issn.1000-0534.2019.00017
• Abstract ( ) HTML ( ) PDF (2409KB) ( )
• In order to deeply understand the correlation mechanism between runoff change and extreme temperature and precipitation indices in the upper reaches of Heihe River, the article use the daily temperature, precipitation data of Qilian, Tuole, Yeniugou meteorological stations and daily runoff data of the Yingluoxia hydrological station in the upper reaches of the Heihe River from 1960 to 2014, by means of trend analysis, correlation analysis, multiple regression analysis and principal component analysis to analyze the trends of climate indices and extreme hydrological events, and the correlation relationship between extreme climate indices and runoff, and the hysteresis effect of extream flooding on precipitation in the upper reaches of the Heihe River.The results show that： (1) The temperature indices characterized by low temperature in the upper reaches of the Heihe River shows a downward trend, and the extreme temperature indices indicating high temperature shows an upward trend.Extreme precipitation events showed a slight increase.Extreme flooding showed an increasing trend, and extreme low water showed a significant decreasing trend, which was consistent with the increasing trend of total runoff in the upper reaches of the Heihe River.(2) The correlation between extreme precipitation indices and extreme flooding is significant, indicating that precipitation in the upper reaches of the Heihe River is the main factor affecting runoff.(3) The response of the flood to the precipitation of the Qilian station has a lag of 1~2 days, Based on the preliminary analysis, it is concluded that the time and spatial difference of precipitation in the upper reaches of Heihe River and the difference of river network density in the east and west branches are the leading factors to produce hysteresis response.

• Comparative Study on Atmospheric Environment Effects of Cases of Dry and Wet Southwest Vortices in Sichuan Basin
• Wanlu ZHAO;Xinyuan FENG;Shigong WANG;Qiufang SU;Bin LUO;Yunsong DU;Jingjing HAN;Yuling HU
• 2020 Vol. 39 (1): 130-142.  DOI:10.7522/j.issn.1000-0534.2019.00052
• Abstract ( ) HTML ( ) PDF (9014KB) ( )
• For the rarely researches that the atmospheric environment effects of Southwest Vortex(SWV), routinely observed meteorological data, air pollution monitoring data, atmospheric sounding data and Climate Forecast System Version 2 (CFSv2) products have been used to counted the number of SWV in winter and spring 2014 -2016 and the synchronous air quality grade with diagnostic and statistical methods in this study.It is found that SWVs developed in spring and winter are mostly dry low vortices due to the lack of water vapor.This type of SWV rarely induces precipitation and can easily cause air pollution weather in the Sichuan Basin.Based on those results, a dry and a wet SWV in Sichuan Basin in 2015 were selected for comparative study.The analysis of a severe air pollution over the Sichuan Basin from 29 December 2015 to 3 January 2016 suggests that a dry SWV was generated over Sichuan Basin on 30 December with weak intensity and small thickness.The foehn effect arising from the weak descending motion at the rear of dry SWV caused an intensive untouched?ground low?level inversion over Chengdu, generated a ‘pot cover’ effect that suppressed the diffusion of air pollutants, brought about an quite small maximum mixing depth and surface wind speed which presented an obvious stagnate synoptic status, gave rise to the concentrations of PM₁₀ and PM_2.5 of representative cities in basin were 398 and 268 μg·m^-3, respectively, which were the peak values during this heavy air pollution process.In contrast, the study found that, during August 16 -17, 2015, the strong upward movement and heavy precipitation resulted from the wet SWV produced the extremely favorable effects of atmospheric diffusion and wet deposition, rapidly and effectively reduced the concentration of pollutants, which was opposed to the environmental effect of the dry SWV that aggravating atmospheric pollution.

• Analysis of Energy Evolution Characteristics of Key Areas in Europe Affecting Decadal Extreme Drought in Yangtze-Huaihe River Basin during the Pre-summer Period
• Shimeng LIU;Jie ZHANG;Han YU
• 2020 Vol. 39 (1): 143-152.  DOI:10.7522/j.issn.1000-0534.2019.00004
• Abstract ( ) HTML ( ) PDF (5378KB) ( )
• Based on the global reanalysis data provided by the European Center for Medium?Range Weather Forecasts (ECMWF), this paper analyzes the time characteristics of the dynamic variability and kinetic energy budget of the European key area that lead to extreme drought in the Yangtze?Huaihe river basin during the pre?summer period by using the multiscale energy and vorticity analysis (MS?EVA).It is found that in the early summer when the kinetic energy of high?level in European key area had a tendency to increase, extreme drought events easily occurred in the Yangtze?Huaihe river basin.The kinetic energy here mainly comes from the energy conversion from synoptic?scale eddy, followed by the pressure work and vertical transport of kinetic energy; Buoyancy conversion and energy conversion from the mean flow are outputs of high?level kinetic energy.Some of the increasing upper?strata kinetic energy comes from eastward kinetic energy of the east coast of the North Atlantic and the southwestern continent of Europe, and these energy is transported upwards after convergence in Europe to transfer energy to the upper strata which can transfer energy to higher levels.At the same time, due to the increase of ground heating in the key area, the vertical wind shear increases, the baroclinic stability decreases and the pressure work increases, which makes the upper kinetic energy supplemented.During this period, the energy conversion from synoptic?scale eddy also increased due to ground heating.The net energy added in the key area converges in the Yangtze?Huaihe river basin by the westerly circulation, which helps to enhance the ridge above the ground and promotes the occurrence of extreme drought events.This result explores part of the causes of drought in the Yangtze?Huaihe river basin from the perspective of energy conversion and provides a basis for drought prediction.

• Study on the Influence of External Forcing Weakness on the Predictability of Initial Value in Lorenz Model
• Yiwei LI;Guangzhou FAN;Xin LAI
• 2020 Vol. 39 (1): 153-161.  DOI:10.7522/j.issn.1000-0534.2019.00061
• Abstract ( ) HTML ( ) PDF (5036KB) ( )
• To explore the predictability of the initial value of the Lorenz system constructed under different external forcings by adjusting the parameter value r that characterizes the external forcing in the Lorenz model， and using the explicit fourth-order Runge-Kutta method.It is concluded that the predictability of the initial value decreases and the error growth increases， so the forecast period is shortened， the forecast effect is worse， and the system is more sensitive to the initial value with the increase of external forcing.The correlation coefficient between the initial value and its superimposed small deviation has three sudden decrease with the increase of external forcing.In the picture of simulated Lorenz system motion trajectory， the strange attractor of the Lorenz system changes from one to two， and the surface around the strange attractor also evolves from one to two， and Chaos phenomenon appears.The variance of the X， Y， and Z values； the number of steps in which the X value and the Y value exceed one standard deviation show an upward trend with the increase of external forcing.The increase in external forcing also reduces the number of integration steps of differentiation and the first reversal used in the Lorenz system， and the parallel time of the two sets of data is shorter and shorter.By counting the number of integration steps in the error range in 5%、 10%、 20% of X， Y， and Z values， it is found that the error growth of the system increases with the increase of external forcing.It is no longer within a reasonable range， so the predictability of the initial value is reduced and the forecast period is greatly shortened.

• Effects of Climate Change on Characteristics of Dry-hot Wind in Hexi Region of Gansu Province
• Qi HOU;Bo ZHANG;Hang HE;Shuai Li
• 2020 Vol. 39 (1): 162-171.  DOI:10.7522/j.issn.1000-0534.2019.00063
• Abstract ( ) HTML ( ) PDF (4528KB) ( )
• Dry-hot wind is a kind of special disastrous weather which is combined by three meteorological factors with high temperature, low humidity and certain wind force.Based on the daily meteorological data of 23 meteorological stations in Hexi region of Gansu Province and surrounding areas during June and July from 1960 to 2017 and the national meteorological industry standards for spring wheat in the region, the characteristics of the climate resources in Hexi region in June and July and their effects on dry-hot wind were analyzed.The results show that: On the characteristics of climate resources change, the temperature rises obviously and the relative humidity rises first and then decreases during the occurrence period of dry-hot wind.The central region has the largest changes in temperature rise and relative humidity, and is most sensitive to climate change.On the occurrence characteristics of dry-hot wind, the interannual variation of dry-hot winds tends to decrease slowly and then increases rapidly.The influence range of dry-hot wind is enlarged, and the large area of dry-hot wind events are obviously increased.The dry-hot wind start date was abruptly changed in 1995, and then stabilized in early June, with an overall advance trend.In the period with less dry-hot wind, the start and end dates are unstable and the interval days are few, while in the year with frequent dry-hot wind, the interval days are more.The wavelet coefficient of dry-hot wind days correspond positively to temperature and potential evapotranspiration, but negatively to relative humidity.This correspondence is most obvious after entering the 21st century, and the correspondence between the number of dry-hot wind days and the potential evapotranspiration is the best.On the condition of occurrence, when the daily maximum temperature reaches 32 ℃, the probability of dry-hot wind disasters in the northwest of Hexi region is the greatest, and the overall risk probability decreases gradually from north to south.When the relative humidity is less than 30% at 14:00 (Beijing time), there is the highest probability of dry-hot wind disasters in Andun Basin, Dingxin and Minqin area of Hexi, and the probability of the risk gradually decreases from the lower elevation site to the higher site.

• Numerical Simulation of Wind Field in Complex Terrain based on CFD Downscaling
• Jiarong ZHANG;Xueling CHENG
• 2020 Vol. 39 (1): 172-184.  DOI:10.7522/j.issn.1000-0534.2019.00005
• Abstract ( ) HTML ( ) PDF (5976KB) ( )
• The traditional RANS turbulence parameterization scheme is modified on the basis of the Computational Fluid Dynamics model (Fluent), and the large eddy model (LES) turbulence scheme is selected, then the buoyancy model of temperature stratification is introduced, finally the modified Fluent model is obtained.The Weather Research and Forecasting model (WRF) and WRF coupled Fluent before and after modified are used to simulate the wind speed and direction of the 4 months from December 2010 to March 2011 in Jishan wind station in Poyang Lake region, Jiangxi and the evolution of the flow field and the temperature field near Jishan station in March 6, 2011.According to the comparison of the observation data, it is found that: After coupling Fluent, the better WRF simulation result of the wind speed and wind direction in Jishan station is obtained.Compared with coupling original Fluent (Example 1), WRF coupling modified Fluent (Example 2) can provide more accurate simulation result of the wind speed and wind direction at each height in Jishan station.The average error of WRF, Example 1 and Example 2 for the 4 months 70 m height average wind speed are 3.963, 2.727 and 2.224 m·s^-1 respectively.The Matching ratio to the observed wind direction rose of Example 2 is higher than Example 1 at 70 m height mostly.Example 2 not only can simulate the thermal buoyancy effect under the daytime unstable state and the spatial inhomogeneous and higher turbulent kinetic energy, but also can simulate the temperature inversion of the atmospheric boundary layer at night, while Example 1 can not.All the above results indicate that after the modification of Fluent model, the simulation result of the method that WRF coupled Fluent to the wind field near Jishan Station is improved.To sum up, this research provides a new method and basis for the prediction of the atmospheric flow field in the bottom of atmospheric boundary layer and the multiscale coupling simulation, and has also laid the foundation for the development and improvement of Fluent model in the future .

• Analysis of the Accuracy of TRMM 3B42 Rainfall Data in the Upper and Middle Reaches of Taohe River
• Lizhen CHENG;Meixue YANG;Xuejia WANG;Guoning WAN;Zhaochen LIU
• 2020 Vol. 39 (1): 185-195.  DOI:10.7522/j.issn.1000-0534.2019.00016
• Abstract ( ) HTML ( ) PDF (2796KB) ( )
• TRMM satellite products play an important role in analyzing the temporal and spatial changes of precipitation, and have become an important source of hydrometeorological research in no data or less data areas. Since 1997, TRMM products have already been applied in plenty of researches with its robust advantages of high spatial and temporal resolution, wide coverage, long time series (real?time update). The Version 7 TRMM 3B42 products were evulated from January 2006 to December 2016 over the upper and middle of Taohe River Basin in different time scale. The results showed that: (1) More than 60% of the rainfall events were captured by the TRMM 3B42 satellite in the study area and the FAR was only 12%, which indicated that the TRMM satellite has a better detection ability for rainfall events. While, FBI was 0.88, suggesting that TRMM products was slightly underestimated the observation. In addition, it showed good performance for detecting the occurrence of rain events with average equitable threat score (ETS) of 0.31. Comparison of the occurrence frequency and rainfall contribution rate of TRMM daily precipitation and measured data at each rain level, TRMM performed best on the moderate rain level, which was significantly consistent with the observation. (2) The value of CC at daily scale average was 0.64 and the differences between TRMM and observation precipitation were narrow, which indicated that the accuracy of TRMM was high at daily scale. Comparative analyses with daily, TRMM data at monthly scale exhibited the best performance with CC of 0.96, which is close to the “ruth value”. In the monthly error distribution, BIAS in warm and humid season were smaller than that in cold and dry season, and the effect was good. While, RMSE in cold and dry season were smaller than that in warm and humid season owing to the concentration of precipitation in summer and autumn. (3) The spatial distribution based on TRMM and actual precipitation indicated that there was a decreasing trend from southwest to northeast in this area, and TRMM data slightly overestimated the annual data. In addition, the changes in summer and autumn were consistent with that in annual precipitation. TRMM products has an advantage in continuous space distribution and the accuracy was better. Therefore, TRMM precipitation products is liable in the study area.

• Comparisons of Cloud Top Parameter of FY‑4A Satellite and its Typhoon Application Research
• Linli CUI;Wei GUO;Weiqiang GE;Yafei YAN;Shuang LUO
• 2020 Vol. 39 (1): 196-203.  DOI:10.7522/j.issn.1000-0534.2019.00065
• Abstract ( ) HTML ( ) PDF (2729KB) ( )
• Clouds reflect the dynamic of atmosphere and the thermal processing. Parameters such as cloud top temperature and cloud top height are significant for diagnosing the intensity of weather system and convection development, and they are important roles in weather analysis, numerical forecast and aviation meteorology. Fengyun?4 (FY?4A) satellite is the second generation of stationary meteorological satellite independently developed by China. Compared with the Fengyun?2(FY?2) meteorological satellite, FY?4A satellite's performance has been significantly improved. For example, the observation channels has been expanded from 5 to 14, the observation time of the whole disk image has been shortened from 0.5 h to 15 min, and the maximum spatial resolution has been improved from 1.25 km to 0.5 km. Therefore, FY?4A satellite's products have been increased 160 times than FY?2 satellite's. As the first satellite of scientific experiments, FY?4A is mainly used to validate new technologies and develop new applications. In order to evaluated and analyzed the accuracy of FY?4A satellite's products during the period of typhoons processes near the coastal area of Southeast China in 2018, three main products have been compared with the polar orbiting meteorology satellite of American EOS/MODIS's products and the second generation geostationary meteorological satellite of Japanese Himawari?8's products, including cloud top height (CTH), cloud top temperature (CTT) and cloud top pressure (CTP). The results indicated that the cloud top parameters obtained from FY?4A satellite had a high linear correlation with MODIS and Himawari?8 products as a whole. FY?4A was highly linearly correlated with MODIS, and the correlation coefficient was above 0.98, and the overall mean bias was the smallest. Particularly, in the typhoon center and eye wall area with deep and dense cloud, the mean bias of inter?satellite results was obviously reduced. For example, FY?4 A differed from himawari ?8 by 0.78 oC in CTT, 30 m in CTH and 0.2 hPa in CTP at the center of typhoon, and the mean bias between FY?4A and MODIS or the mean bias between Himawari?8 and MODIS was also small. Therefore, the quality of FY?4A cloud top parameters is reliable; the precision of FY?4A satellite's cloud products is comparable to those of MODIS and Himawari?8 satellites, which is suitable for analyzing typhoon's deep cloud structure. The reason for the bias was initially analyzed as the influence of the existence of transparent thin cirrus clouds and small?scale clouds, which were related to the spatial resolution of different instruments, cloud detection ability of different instruments and cloud detection algorithm and so on.

• Analysis on Autumn Aerosol Optical Characteristics at Lanzhou with Sun-photometer
• Hui LIU;Ye YU;Dunsheng XIA;Suping ZHAO
• 2020 Vol. 39 (1): 204-212.  DOI:10.7522/j.issn.1000-0534.2019.00057
• Abstract ( ) HTML ( ) PDF (1735KB) ( )
• Aerosol optical properties including aerosol optical depth (AOD), Angstrom wavelength index (α), and atmospheric turbidity coefficient (β) were inferred from the ground?based solar photometer observation data in Lanzhou from September to November 2015.The distribution and variation of aerosol optical properties were analyzed.Types and distribution of aerosols were derived based on Angstrom range and graphical method.The results show that the average AOD_{500 nm} in autumn in Lanzhou City is 0.47±0.22.α _{440~870 nm} was the lowest in October (0.95±0.26) and the highest in September (1.21±0.14).β is the lowest in September (0.15±0.05) and the highest in November (0.28±0.12).The daily variation of AOD_500nm ranges from 0.27 to 0.52.During September and October 2015, AOD_{500 nm} mainly distributed between 0.2~0.6.In November, AOD_{500 nm} is concentrated between 0.4~0.8, indicating that the distribution of AOD_{500 nm} in Lanzhou in autumn is concentrated, and loading of aerosols increased from September to November.The wavelength index is mainly distributed between 1.0~1.4, 0.6~0.8, and 1.0~1.4 in September, October and November, respectively, with peaks between 1.2~1.4 and 1.0~1.2.Overall, aerosol in autumn is dominated by fine particle aerosols in Lanzhou.AOD_500nm is significantly correlated with β, and both aerosol optical depth and turbidity coefficient can characterize the degree of turbidity.The main types of aerosols in autumn are anthropogenic and mixed aerosols in fine particle mode.The hygroscopic growth of fine particle aerosol is the main reason for the high aerosol optical depth in autumn for Lanzhou City.