Current Issue

• The Characteristics of Raindrop Spectrum in Different Altitude Region on the Eastern Slope of Qinghai-Xizang Plateau
• Shanshan LI;Xiaofang WANG;Rong WAN;Guoping LI
• 2020 Vol. 39 (5): 899-911.  DOI:10.7522/j.issn.1000-0534.2019.00086
• Abstract ( ) HTML ( ) PDF (9652KB) ( )
• Using raindrop spectrum data observed with four DSG5 precipitation phenomenon instruments deployed at different altitudes in western Sichuan Plateau from June to August 2018， the raindrop number concentration， several microphysical parameters and falling velocity at different regions with high altitude and steep terrain were compared and analyzed.The results show that： The average raindrop spectrums at different altitudes are in good agreement with the Gamma distribution， while completely different characteristics of raindrop spectrum are found between weak and strong rainfall types.For the weak rain types， with increasing altitude， the raindrop number concentration of small particles （D<1 mm） increases and medium diameter particles （1 mm<D<3 mm） decreases slightly.The number concentration N_w increases and the average diameter （D_m） decreases with altitude.For the strong rain types， with increasing altitude， the raindrop number concentration of small and medium particles decreases and larger particles （D>3.25 mm） increases significantly.The number concentration N_w decreases and the average diameter （D_m） increases rapidly.The medium rain types are found to be the conversion phase of raindrop numbers between small and large particles.The falling velocity observed at higher altitude locations is greater than lower altitude in all types of rainfall.

• Characteristics and Causes of Surface Sensible Heat Trend Transition in Central and Eastern Qinghai-Xizang Plateau
• Lu ZHANG;Hui WANG;Xingdong SHI;Dongliang LI
• 2020 Vol. 39 (5): 912-924.  DOI:10.7522/j.issn.1000-0534.2020.00050
• Abstract ( ) HTML ( ) PDF (7086KB) ( )
• In this paper， the Piecewise Linear Fitting Model （PLFIM） of climate change was used to analyze the characteristics of the trend transition of the surface sensible heat flux at 70 stations on the Qinghai-Xizang Plateau （hereinafter referred to as plateau） from 1982 to 2018 and the possible causes of the trend change were analyzed from the following aspects： the response rate of the plateau temperature to the warming of the northern hemisphere and the background of atmospheric circulation.Results show that： （1） there is a trend transition from weakening to strengthening in the annual mean surface sensible heat flux on all four climatic zones of the plateau around 2000； the earliest turning point is in 1999 occurred on the Ⅱ zone （the eastern part of plateau）， followed by the Ⅰ （the northern part of plateau） and Ⅳ zones （the southeastern part of plateau） are in 2000， the latest turning point is in 2002 occurred on the Ⅲ zone （the southwest part of plateau）； the Ⅱ and Ⅲ zones are the key areas with the trend transition of surface sensible heat flux， and the change of the surface sensible heat flux on the Ⅱ zone is mainly caused by the increased of surface-air temperature difference which due to the rapid increase of the ground temperature， while on the Ⅲ zone， the change of the surface sensible heat is mainly affected by the ground wind speed， and the increase of surface wind speed after 2000 plays an important role in the trend transition of the surface sensible heat flux； （2） in pre-2000 epoch （1982-2000）， the mid-latitude westerly jet is weaker and the jet axis is southward in the northern hemisphere； meanwhile， the temperatures in the north （south） part of the plateau to the high （low） latitude are abnormally higher （lower）， and the meridional temperature gradient and pressure gradient are decreased， these cause the plateau wind speed to decrease continuously during this period， however， the background of the atmospheric circulation is reversed in post-2000 epoch （2000-2018）， which alleviates the decreasing trend of the plateau wind speed and causes it to gradually turn into an increasing trend， thus induces the trend transition of the plateau surface sensible heat in this period.

• Characteristics of Water Vapor Transport over the Low-Latitude Highlands and its Effect on Yunnan Climate
• Yunxia WAN;Hongming YAN;Yan JIN;Qiyang PENG
• 2020 Vol. 39 (5): 925-934.  DOI:10.7522/j.issn.1000-0534.2019.00082
• Abstract ( ) HTML ( ) PDF (3114KB) ( )
• Using the monthly reanalysis data of NCEP/NCAR and the monthly precipitation of 124 meteorological stations in Yunnan， based on the various statistical methods， the horizontal variation and the vertical variation of water vapor transportation over the low-latitude highlands are studied.The results are shown as following： （1） the resources and the paths of the vapor transportation influencing the low-latitude highlands exist obvious seasonal differences.In the wintertime， the source of water vapor transportation over the low-latitude highlands is from westerly wind belt transportation， but from the tropical ocean water vapor transportation in the summertime.（2） The seasonal differences of the water vapor budget at different levels are significant.In the wintertime， the water vapor inflow mainly from the western boundary but from the southern boundary in the summertime， and the water vapor outflow from the northern boundary in all seasons.The monthly fluctuation of the water vapor budget on the eastern boundary is the largest and the property of water vapor budget sometimes is converted.（3） The water vapor budget decreases with the increasing of the height at the different boundaries in different seasons.The water vapor transportation flows in Yunnan at the western and southern boundary in all seasons.It exits obvious vertical and seasonal differences for the water vapor budget at the eastern and northern boundary.For the water vapor importation layer at the eastern boundary， it is deeper in autumn and winter than that in spring and summer.At the interannual scale， the variation of water vapor budget in winter and spring is relatively simple but complex in autumn and summer.The water vapor outflows at the eastern and northern boundary but inflows at the western and southern boundary in winter and spring.The interannual variation of water vapor budget is very complex in summer and autumn and the interannual difference of water vapor budget at each boundary is significant.There is a significant positive correlation between Yunnan summer precipitation and the net water vapor budget.The water vapor transportation brought by transequatorial airflows from the southern hemisphere turning north near 80°E-90°E and Somali cross-equatorial airflow has significant impact on summer drought and flood in Yunnan.

• Diurnal Variations and Causes of Warm Season Precipitation in Qinling and Surrounding Areas
• Hongfang ZHANG;Liujie PAN;Haoming CHEN;Lu HAO;Xi ZHANG
• 2020 Vol. 39 (5): 935-946.  DOI:10.7522/j.issn.1000-0534.2019.00067
• Abstract ( ) HTML ( ) PDF (12406KB) ( )
• Based on three sources（automatic weather station observation， retrieve precipitation of satellite and weather radar） precipitation fusion data， the ERA5 reanalysis data from European Centre for Medium-range Weather Forecasts（ECMWF）， the diurnal variation of warm season precipitation and its probable cause over Qinling and surrounding areashas been revealed.Results show that diurnal variations of precipitation on both sides of Qinling in the warm season were significantly different， affected by the topography， diurnal peaks of precipitation amount and precipitation frequency in the southern Qinling occurs at night and the north occurs at afternoon.The spatial distribution of long and short duration precipitation is significantly affected by the large terrain， the frequency of short-term precipitation in the southern Qinling is very high， but the precipitation intensity is relatively small， while the frequency of short-term precipitation in the northern Qinling is low but the intensity is very large.Mountain winds and the southwest warm and humid updraft air of terrain trough affected by the Tibetan Plateau over played is an important reason for the frequent occurrence of night rains in the southern Qinling.Affected by the valley wind circulations during the day， the updraft airweakened in the front of the terrain trough， itmakes the daytime precipitation less.The local heating of Loess Plateau， updraft and downdraft air intersection around 700 hPa， which causes the heavy rainfall more frequent in the northern Qinling in the afternoon.

• Analysis on the Causes of an Extreme Rainstorm in the Eastern Xinjiang
• Xiaocui ZHUANG;Boyuan LI;Rong QING;Ruqi LI;Yunhui ZHANG;Songzhu BAI
• 2020 Vol. 39 (5): 947-959.  DOI:10.7522/j.issn.1000-0534.2019.00081
• Abstract ( ) HTML ( ) PDF (11743KB) ( )
• By using FNL reanalysis data， the routine observation data， the regional automatic station data， FY-2G data， Analysis of extreme rainstorm environmental field characteristics in eastern Xinjiang on July 31， 2018， and compared with the research results of torrential rain in Xinjiang and southern China.The results are as follows： The extreme rainstorm were in the stable two ridges one trough large-scale circulation background； It caused by elevated convection； The rainstorm zone were located in the right side of southwest jet stream inlet region in high altitude， the Confluence area on the 500 hPa from southwest stream before central Asia low vortex and south airflow From western Pacific subtropical high on the west side， front convergence zone of southeast low level jet stream outlet zone on the 700 hPa and the overlapping area of the negative variable temperature area behind the cold front on the ground map； Central Asia low vortex of 500 hPa， low level jet of 700 hPa and its anterior convergence area， strong frontal zone 800~600 hPa that the elevated convection were triggered； Strong convergence and high level strong divergence nearby the lower troposphere 700 hPa， it provides dynamic triggering conditions for the development of elevated convection， so that SW Warm and Wet Air Flow in the Front of Central Asian Low Vortex and water vapor bypasses and crosses the Qinghai-Xizang Plateau， from the Arabian sea， Bay of Bengal， South China Sea and Western Pacific and Convergence and concentration rapidly in rainstorm area， and constantly being lifted to the sky， it provides sufficient water vapor condition for extreme rainstorm.The extreme rainstorm in this region is quite different from that in other parts of Xinjiang； There were also significant differences between the elevated convection system in south China.

• Temporal and Spatial Distribution Characteristics of Short-time Heavy Rainfall during Southwest Vortex Rainstorm in Sichuan Basin
• Qiang LI;Xiuming WANG;Guobing ZHOU;Yaping ZHANG;Yue HE
• 2020 Vol. 39 (5): 960-972.  DOI:10.7522/j.issn.1000-0534.2019.00096
• Abstract ( ) HTML ( ) PDF (9541KB) ( )
• Based on the hourly precipitation data of 123 meteorological stations in Sichuan Basin from May to September 1980 to 2012 and 96 short-time heavy rainfall （SHR） days of southwest vortex rainstorm， the spatial-temporal distribution characteristics of SHR are investigated in the process of regional southwest vortex rainstorm.The results show that larger cumulative frequency and precipitation amount of SHR mainly occur at from 21:00 （Beijing time， the same below） to 08:00 the next day， and the larger values are located in western and southern Sichuan Basin.The proportion of stations with more than 50% SHR in the total precipitation is 51%.It is obvious diurnal variation characteristics of SHR events frequency and precipitation.The main starting periods of SHR events is happened from 21:00 to 08:00 the next day.The ratio of frequency and precipitation accounted for the total is 73.8% and 81.4% respectively， and the peak value appears at 04:00.The duration of rainfall are mostly more than 10 hours（10~17 hours）， which account for 63.1% of the total events， and the peak value occurs in 14 hours.In spatial distribution， the larger frequency and precipitation stations of SHR events with long duration （7~18 hours） are mainly located in the western basin.It is obvious asymmetry characteristics of SHR events.The asymmetry of precipitation in the western and southern basin is more obvious than that in the northern and eastern basin.

• A Preliminary Study on Statistical Characteristics and Mechanism of Backward-Propagating Thunderstorms in Shaanxi
• Qiyuan HU;Nan WANG;Pingyun LI;Jing YUE
• 2020 Vol. 39 (5): 973-985.  DOI:10.7522/j.issn.1000-0534.2019.00099
• Abstract ( ) HTML ( ) PDF (5700KB) ( )
• Based on Doppler Radar products and observation data in Shaanxi from 2012 to 2016， the standard for the backward-propagating thunderstorm survey in Shaanxi was established.The temporal and spatial distribution characteristics of 48 backward-propagating thunderstorm processes in 5 years were statistically analyzed.It indicates that backward-propagating thunderstorms tend to emerge between 14:00 and 18:00 （Beijing Time） from June to August in area of Shanbei and northern Guanzhong.The disasters are mainly short-term heavy rainfall.The new echo survives 1 to 2 hours， while its center can develop to be the strongest at 10 to 30 minutes.According to the moving direction， the new echo pattern can be categorized into three types： Forward-propagation along advection （type 1）， continuous backward propagation （type 2） and low movement （type 3）.Typical processes are selected for analysis.The results show that type 1 thunderstorm occurs in the unstable environment of upper-level cold vortex and lower-level shear line， which is triggered by coordination of ground convergence line and the dew point front.The convective movement develops along the convergence line and the dew-point front， and eastward advection develops reversely， which forces the thunderstorm propagates backwards.After regeneration， the strong environmental wind and the weak vertical wind shear cause the thunderstorm to move forward with the advection.The propagation of type 2 thunderstorm is closely related to the movement of gust front.The gust front in the front of cold pool on the ground forces warm moist air to ascend near the ground convergence line to generate a new thunderstorm.The thunderstorm propagates along the intersection of the moving gust front and the ground convergence line.Type 3 thunderstorm occurs where the upper-level trough leans forwards.In this structure， the ground convergence line and the significant dew point front trigger the generation of a storm cell， and the strong vertical wind shear strengthens its maintenance.The storm tends to move towards the unstable layer on the northwest side of the dew-point front， which shows characteristics of backward propagation.However， this self-propagation is offset by eastward advection， resulting in stable and low movement.

• Analysis of a Rare Autumn Rainstorm behind Cold Front in Xi’an
• Damei GUO;Liujie PAN;Yueqin SHI;Qiyuan HU;Linrong WU;Jiahuimin LIU;Jianling TAO
• 2020 Vol. 39 (5): 986-996.  DOI:10.7522/j.issn.1000-0534.2019.00097
• Abstract ( ) HTML ( ) PDF (9295KB) ( )
• Conventional observation data， radar data and EC-thin data （0 25°×0 25°） are used to analyze an autumn rainstorm behind a cold front before the ending of a consecutive rain on 27 September 2017 in Xi’an.Results show that the rainstorm locates 300~400 km back from a cold front on surface， where the temperature is rather low， unfavorable for the accumulation of warm and moist energy.Meanwhile， the northerly wind on 700 hPa and 850 hPa brings no water vapor.However， westerly trough on 500 hPa provides a favorable background circulation for the rainstorm.Through analyzing saturated pseudo equivalent potential temperature and geostrophic absolute momentum， the mechanism of this rainstorm is considered conditional symmetric instability.The cold front slopes gradually from south to north.A southerly wind on 700 hPa brings warm moisture from the periphery of the Western Pacific Subtropical High over to the south of Shaanxi.The airflow is forced upward by the cold front to the conditional symmetric unstable area above Xi’an， which results in inclined convection.In the strongly baroclinic atmosphere， a moderate vertical wind shear is favorable to the geostrophic absolute momentum with a small slope.On middle and upper level， the warm and humid airflow makes the saturation pseudo-equivalent potential temperature have a large slope， thus conditional symmetric instability are formed.The precipitation emerges as paralleling belt echoes on radar， which is parallel with vertical wind shear vector from 0 to 6 km.There is a good correspondence among the conditional symmetric unstable area， the upward sloping motion and the echo height.

• Spatial Analysis of Annual Precipitation Lines of 800 mm in the Eastern Monsoon of China
• Yanjun CHE;Xiaochun GUAN;Shijin WANG;Rong WU
• 2020 Vol. 39 (5): 997-1006.  DOI:10.7522/j.issn.1000-0534.2019.00094
• Abstract ( ) HTML ( ) PDF (4239KB) ( )
• Precipitation is a complex natural event that exhibits significant variability in both time and space.As global climate change， the temporal and spatial characteristics of terrestrial precipitation have changed.In the Eastern Monsoon Region of China， annual precipitation line of 800 mm is an important geographical boundary.For example， it is reference line/geographical boundary between southern and northern China and between rivers that freeze and do not freeze， respectively.Based on the dataset of 0.5°×0.5° grid of China's ground precipitation during the period of 1961 -2015， spatial distribution and gravity-center in terms of the annual precipitation line of 800 mm in the Eastern Monsoon Region were calculated using spatial analysis of Geographic Information System （GIS） and time series analysis.Periodic characteristic and long changed trend were also analyzed in terms of the gravity-centers of precipitation line of 800 mm， using several methods， i.e.linear regression， Ensemble Empirical Mode Decomposition （EEMD）， and Mann-Kendall （MK）.The results showed that： （1） Annual precipitation line of 800 mm in the Eastern Monsoon Region of China was extended from northeast to southwest in space， and the fluctuations of the annual precipitation lines in both of Huanghuai Plain and southeastern Tibetan Plateau were stronger.（2） The spatial gravity-centers in terms of annual precipitation line with 800 mm were distributed in Sichuan Basin during the period of 1961 -2015.（3） Changes of gravity-center of the annual precipitation line of 800 mm were relatively complex in different time-scale.However， there were significantly moving trends in longitudinal direction and latitudinal direction in terms of the annual precipitation line of 800 mm， i.e.moving to east in latitudinal direction and moving to south in longitudinal direction， respectively.（4） Based on the methods of EEMD and MK， there were no significant characteristics of period and abrupt in spatial change for the annual precipitation line of 800 mm in terms of longitudinal direction and latitudinal direction， respectively.We also found that spatial distribution of those precipitation lines were significantly affected by atmospheric circulation， local climate change， and topography.In addition， annual changes of those gravity-centers in terms of annual precipitation line of 800 mm were mainly resulted from changes in El Ni?o-Southern Oscillation （ENSO）， while decadal changes of that were mainly affected by changes in Pacific Decadal Oscillation （PDO）.

• Application of an Improved Radar Data Assimilation Scheme in Heavy Rain Forecast in Meiyu Period
• Juxiang PENG;Yuanfu XIE;Zhaoping KANG;Hongli LI
• 2020 Vol. 39 (5): 1007-1022.  DOI:10.7522/j.issn.1000-0534.2019.00091
• Abstract ( ) HTML ( ) PDF (14647KB) ( )
• The radar data assimilation is practical for enhancingthe accuracy of numerical weather prediction in precipitation， yet few systems have correct and practical results.This research used a Space and Time Multiscale Analysis System （STMAS） in assimilating radar radical velocity and reflectivity factor， to compare with the previous Local Analysis and Prediction System （LAPS） results in the initial wind field， water vapor condition， weather prediction， precipitation， and radar reflection.The case study in the Mei-Yu event， in Wuhan on 5 July 2016， showed that the STMAS method provides a better initial condition in the wind field， water vapor condition and hence improved precipitation prediction.First， when assimilating the radar radical wind velocity， STMAS added the continuity equation as a strong constraint， which significantly improves the dynamic field in the initial condition.Second of all， STMAS saturated the water vapor when assimilating the radar reflection higher than the threshold， which provided more water vapor to the initial condition.This process can increase the instability， and trigger the convection.The last and the most important part is that， since the STMAS method helped to improve the initial condition， the patterns of the high altitude in the forecast is more realistic， which lower the bias of the prediction of precipitation in location and strength， especially in the prediction of the strong event which is larger than 100 mm.

• Weather Classification and Circulation Configuration of Easterly Wind-Blown Snow in the Mayitas Wind Area
• Junlan ZHANG;Xia YANG;Juanjuan WEI;Chao MA;Chunlei ZENG
• 2020 Vol. 39 (5): 1023-1032.  DOI:10.7522/j.issn.1000-0534.2019.00105
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• The 10-minutes observation data and conventional ground and upper-air observation data for the temperature and precipitation， maximum wind speed and wind direction， minimum visibility， etc.of the Mayitas traffic station and Laofengkou station in Tacheng area of Xinjiang during 2015 -2018 were selected.The 15 easterly wind-blown snow weather cases in the Mayitas wind area were analyzed.It was found that the cold front easterly wind-blown snow mostly occurred， and the easterly wind-blown snow mostly appeared about 1 day after the snowfall ended.The easterly wind-blown weather circulation situation is divided into 2 types （reflow type and front decompression type） and 3 types （Horizontal trough to vertical， low trough east shift and mid-latitude fluctuations）， of which the reflux type of easterly wind-blown snow is the highest proportion.The three-dimensional spatial configuration of the reflow type and front decompression type of easterly wind-blown snow is a backward-inclined structure.The high-altitude is surrounded by high-pressure ridges near the north of Xinjiang， but the reflow type is westward and develops strong， and the front decompression type is slightly biased.The strength of the east is weaker； Although the ground pressure field is “east high and low west”， the Mongolian high pressure of the reflow type wind-blown snow weather is strengthened， and there is obvious positive pressure change； Mongolian high pressure intensity in the front decompression type does not change much.However， the thermal and low pressure in Central Asia is developing， the Maitas wind zone is in the significant decompression zone in front of the front.

• Characteristics of Solar Spectral Radiation and Long Wave Radiation over the Evergreen Broad-leaved Forest in the South of the Five Ridges
• Huan WANG;Zhigang WEI;Xian ZHU;Chenghai WANG;Wenjie DONG
• 2020 Vol. 39 (5): 1033-1044.  DOI:10.7522/j.issn.1000-0534.2019.00090
• Abstract ( ) HTML ( ) PDF (5083KB) ( )
• By using the radiation observation data from October 2015 to May 2018 at Zhuhai Phoenix Mountain land-air interaction and carbon flux observation tower which represents the typical secondary evergreen broad-leaf forest underlying surface around cities and villages in the South of the Five Ridges of China， statistical analysis were carried out on the characteristics of total and spectral solar radiation， long-wave radiation and net radiation.The results show that the diurnal variations of total and spectral solar radiation are the regular sinusoidal curves with highest values at noon in the typical clear days while the diurnal variations are serrated in the cloudy days.In the typical clear days， the upward long-wave radiations increase first and then decrease during the daytime and generally reach the maximum after noon， the downward long-wave radiations do not change obviously during the day， but often change violently at night.In the cloudy days， the downward long-wave radiations emitted by atmosphere are very close to the upward long wave radiations emitted by the underlying surface， but the diurnal variations of both are very small.The net radiations are positive during the daytime but negative at night.Their diurnal variations are similar to the ones of the downward total solar radiations during the daytime and similar to the ones of the upward long-wave radiations at night.The solar radiations and long-wave radiations are the largest in summer， followed by autumn and spring， and the smallest in winter.The average ratios of the near infrared radiation， visible radiation and ultraviolet radiation to total radiation are 51.2%， 43.0% and 5.8% respectively during the observation period.The ratios of the visible and ultraviolet radiation to total radiation are both the largest in summer and the smallest in winter， while the ratio of near infrared radiation to total radiation is the smallest in summer and the largest in winter.These results can provide a basis for the improvement of land surface process model in the South of the Five Ridges.

• Comparative Study of Boundary Layer Characteristics between Valley Basin and Gentle Hillside in Semi-Arid Region in Winter
• Chuang QIN;Ying WANG;Meng HUANG;Bo LI;Xuechao LI
• 2020 Vol. 39 (5): 1045-1057.  DOI:10.7522/j.issn.1000-0534.2019.00089
• Abstract ( ) HTML ( ) PDF (9846KB) ( )
• In this paper， the characteristics of atmospheric boundary layer over two types of topography， Xigu District， Lanzhou （complex topography） and Lanzhou New District （flat terrain）， were simulated by WRF model， the discrepancies between the two types topography on surface wind field， temperature， theta profile， surface flux and atmospheric boundary layer height were analyzed to discuss the effect of topography on the atmospheric boundary layer.The results indicated that： Characteristics of the underlying surface have a considerable influence on the atmospheric boundary layer.Rough underlying surface in Xigu District results in a lower near-surface wind speed than that in Lanzhou New District， this is also the main reason why the daytime momentum flux in the valley basin of Xigu District was significantly stronger than that of Lanzhou New District.Compared with the homogeneous near-surface flow in Lanzhou New District， the near-surface flow field in the valley basin of Xigu District was highly complicated.Thermal effect of solar radiation in the daytime over dry underlying surface in Lanzhou New District was more efficient than that on river basin in Xigu District， which leads to higher maximum boundary layer height in Lanzhou new area.

• Analyses of the Boundary Layer Characteristics by Intensive Sounding Observation Data at Jiulong Station in Summer for 9 years
• Ping LU;Yueqing LI
• 2020 Vol. 39 (5): 1058-1069.  DOI:10.7522/j.issn.1000-0534.2019.00098
• Abstract ( ) HTML ( ) PDF (7351KB) ( )
• Jiulong station located in the slope transition zone between Qinghai-Tibetan Plateau and Chengdu Plain， has regional characteristics in weather and climate because of terrain undulation and special geographical position.Based on the analysis of intensive sounding data in summer from 2010 to 2018， we obtained the following results： （1） The temperature of atmospheric boundary layer is the lowest at 08:00（Beijing Time， the same as after）， then at 02:00， and the highest at 14:00.On the contrary， the smallest specific humidity appears at 14:00 and bigger at 20:00 and 02:00.The diurnal variation amplitudes of temperature and specific humidity are large near surface layer， while small at 2 km above the ground.The corresponding vertical gradient is also large when surface temperature/specific humidity is high.The inter-annual variation of mean surface temperature is smaller at 14:00 than at 08:00， but annual variation at 2 km height is similar at surface layer， and is little fluctuation.The deviation of temperature/specific humidity in lower atmosphere is larger than that in the upper atmosphere， but the maximum deviation does not occur in the atmosphere closest to the surface.（2）The vertical wind shear appears in the boundary layer.The wind speed is the biggest at 20:00， then at 14:00， and the smallest at 08:00.The westward wind is dominant at 02:00 and 08:00， but the eastward wind at 14:00 and 20:00 in the boundary layer.The fluctuation range of maximum wind speed is the smallest at 14:00， and the biggest at 08:00； the difference of maximum wind speed is the smallest at 08:00， and the biggest at 20:00.（3） The boundary layer height is the lowest at 08:00 and the highest at 20:00.It mixes most fully at 14:00.（4） The maximum difference of mean surface temperature is 1.6 K， and its diurnal range is 6.7~9.3 K.The maximum difference of mean surface specific humidity is 2.66 g·kg^-1， and its diurnal range is 0.6~1.13 g·kg^-1.The mean surface pressure is the highest at 02:00 and the lowest at 20:00.Its diurnal range is 2~2.5 hPa， and the maximum difference is 3.19 hPa.The mean surface wind speed is the biggest at 14:00， smaller at 02:00 and 08:00， and its diurnal range is 1.9~2.9 m·s^-1.There is a positive correlation between precipitation and surface temperature/ specific humidity， and a negative correlation between precipitation and surface pressure/wind speed.

• The Evaluation and Analysis of Radiosonde Humidity Data Quality in CIMISS and GDAS Database
• Min HAO;Ruiwen WANG;Weihong TIAN;Xiaomin WAN
• 2020 Vol. 39 (5): 1070-1079.  DOI:10.7522/j.issn.1000-0534.2019.00075
• Abstract ( ) HTML ( ) PDF (6862KB) ( )
• As one of the indispensable data sources for weather forecast and numerical prediction， the sounding observation data plays an important role in scientific research and operation.The quality of data directly affects the accuracy of modeling prediction， so it is necessary to carry out data quality control for the data source to ensure the application of high-quality data in assimilation and model forecasting.The certificated data and effective tools are both needed for the data quality control.In this study， the data sets from CIMISS database of the operational numerical prediction system in China were compared with those from GDAS database of NCEP.The quality and deviation of CIMISS database， and the experimental results of the two kinds of data applied with GRAPES 4DVAR system were analyzed.The results showed that the deviation between the two data sets was obviously reduced after data quality control.Both the horizontal and vertical deviation between the actual assimilation analysis and the EC reanalysis fields were very small， and the precipitation score of the model prediction remained stable.These supported the reasonable availability of the sounding humidity data in the CIMISS database， and provided helpful information for further understanding on their quality.

• Simulation Research of Ice Cloud Microphysical Parameter Retrieval at 220 GHz
• Xia DING;Xingyou HUANG;Jing HE;Yiwei HUO;Haitao WANG
• 2020 Vol. 39 (5): 1080-1088.  DOI:10.7522/j.issn.1000-0534.2019.00071
• Abstract ( ) HTML ( ) PDF (2026KB) ( )
• A retrieval algorithm based on optimal estimation theory for ice cloud properties， including effective radius （r_e）， ice water content （IWC） and particle number concentration （N_T）， has been investigated with simulated radar reflectivity factor （Z_e） at 220 GHz in this paper.Four ice crystal habits， including spherical， hexagonal column， plate， and six-branch bullet rosette， are considered.Assuming a modified Gamma partical size distribution （PSD）， Look up table （LUT） has been build based on the scattering properties of spherical and nonspherical ice cloud particles at 220 GHz.Simulated Z_e in LUT represents the measured vector， corresponding r_e and IWC is taken as a priori x_a（r_ea， IWC_a）， then r_ere、 IWC_re and N_Tre are retrieved based on optimal estimation theory.If x_a equals the simulated true solution， the retrieval results seem nearly the same with the truth.When x_a is far from the truth， the algorithm still successfully find a solution close to the truth through several iterations because simulated radar measurement Z_e contains significant information of ice cloud properties， which indicate that the algorithm does not only rely on the a priori accuracy.The algorithm error analysis shows， as x_a getting closer to the true solution， retrieval error and iteration number became smaller， which demonstrate that a better a priori can improve the retrieval accuracy and speed up the convergence process.This algorithm is expected to be applied to the cirrus cloud microphysical parameter retrieval for Terahertz Cloud radar.

• Analysis of Environmental Conditions and Radar Monitoring Warning of Tornado in Eastern Henan
• Yiping ZHANG;Junping LIANG;Shuzhen NIU;Mingming CAO;Han LI;Di WANG
• 2020 Vol. 39 (5): 1089-1101.  DOI:10.7522/j.issn.1000-0534.2019.00101
• Abstract ( ) HTML ( ) PDF (11963KB) ( )
• Based on upper-air observation， ground observation， the CINRAD radar， NCEP/NCAR （1°×1°） reanalysis and other data， analyzed the weather situation， environmental conditions and radar monitoring characteristics of four tornado cases in Eastern Henan Plain in details， and discussed the causes of tornadoes during heavy precipitation.The results show that： （1） The four tornadoes mostly occurred in the high-level diffluence divergence， the middle midlatitude trough and the southwest warm and humid airflow at the edge of the subtropical high.Low-level jets， ultra-low-level jets and low-vortex， shear and ground low pressure convergence zone are the main influencing systems that facilitate the occurrence of local tornado during heavy rain.（2） The single-station sounding parameter is characterized by a nearly saturated deep wet layer， a small vertical temperature decline rate， an atmospheric precipitation of 5.6~6.7 cm， and water vapor is abundant.The convective available potential energy is quite different， while the K index is mostly at 30~43 °C.The height of -20 ℃ layer， 0 ℃ dry-bulb temperature （DBZ） layer， and 0 ℃ wet-bulb temperature （WBZ） layer are all higher， while the free convection level and lifting condensation level are low.Before tornadoes occurred， vertical wind shear of 0~6 km and 0~1 km is respectively 14~22 m·s^-1 and 12~14 m·s^-1.Physical quantity of the similar process synthesize the tornado-prone area in Eastern Henan is located in the abnormal large value area representing the key physical quantities of heat and water vapor.（3） On the radar echo maps， the tornado is mostly generated by the micro-super-cell on the strong echo band before the large-scale rainstorm echo， on the corresponding velocity maps， there are mesocyclones and tornadic vortex signatures （TVS） moving from the southwest to the northeast.The mesocyclones and TVS top height and rotation depth are mostly below 4km， and the bottom height is mostly below 0.5 km.（4） The monitoring rate of mesocyclone to tornado varies greatly from 29% to 75%， and the early warning time is basically 30~50 minutes.The TVS monitoring rate of the tornado can reach 50%~100%， but the advance time is shorter in 0~18 minutes.In addition to the strength of the tornado， the maximum shear value is also related to the monitoring distance.

• Further Analyses of Causes of Duststorm Explosions in Jinchang on 5 May， 1993
• Minhong SONG;Zheng’an QIAN;Ying CAI
• 2020 Vol. 39 (5): 1102-1109.  DOI:10.7522/j.issn.1000-0534.2020.00030
• Abstract ( ) HTML ( ) PDF (2673KB) ( )
• To better know and understand the Jinchang duststorm case and other related ones worldside， the paper further analyzes and discusses these related duststorm processes， fully utilizing the satellite images， surface pressure curves， etc.The main conclusions are as follows： （1） Under the weather situation of cold front invasion from Northwest track， the duststorm was， firstly， induced by the Jinchang squall line in the front of the cold front； then about 40 minutes later the cold front in the rear catch speedy with the squall line and the storm strengthens again.Namely the duststorm is caused by both the dry squall line and cold front， and has never seen in Jinchang， China before.（2） Before the squall line forms there is occurring the signals such as strong thermal unstable and surface pressure falling rate.After squall line forms， there is occurring the features as the pressure rise peak， strong down drought in the near surface and narrow- and white-bright cumulus cold belt as well.Shortly， the squall line forms， induces the duststorm in Jinchang， and is reasonable also.（3） It seemly that the squall line can occur under any dry and wet arrangements.Certainly， the water vapor condition has partly impact of for strengthening （weakening） the squall lines in semidry-and wet-（dry-） arrangement.

• Analysis of Meteorological Conditions for a Typical Fog and Haze Event Over Eastern China in Winter of 2018
• Shuxue ZHOU;Xueliang DENG;Chuanhui WANG;Yeqing YAO;Heming DING;Kaiwei YANG
• 2020 Vol. 39 (5): 1110-1121.  DOI:10.7522/j.issn.1000-0534.2019.00085
• Abstract ( ) HTML ( ) PDF (10236KB) ( )
• A persistent and wide range fog and haze event happened in the eastern China during 23 November and 3 December 2018.Using air pollution observation， surface meteorological data， sounding data and ERA-Interim reanalysis data， meteorological formation mechanism of the pollution event was discussed in climate anomaly， surface weather condition and planetary boundary layer structure.The results show： （1） At 500 hPa， mid-high latitudes of Eurasia were dominated by zonal circulation and abnormal high existed at North China and Huanghuai regions， which leaded to cold air northward.Meanwhile， anomalous high at 700 hPa was found both at Sichuan Basin and north of Bay of Bengal， which smoothed latitude circulation and was unfavorable for more water vapor transported to eastern China.The anomalous southerly winds at 850 hPa and 925 hPa resulted in a weak East Asian winter monsoon and resisted cold air moving southward.All the circulation anomalies caused abnormal surface meteorological conditions （high temperature， high relative humidity， weak wind， low visibility） and provided a favorable climate background for air pollution formation.（2） The remarkable feature for the air pollution event was the joint role by regional transmission and the local stagnant meteorological situation.Different intensities of cold air had different effect for pollution level and area.In 24 and 27 November， regional transmission just can affect the north area of the Huaihe River with northerly wind under weak cold air.Then it was controlled by uniform pressure field and the ground conditions tended to be stable， which aggravated the pollution level.In 29 November， the cold air was strengthened and air pollution transportation could cross the Yangtze River.Then the ground was controlled by saddle field， showing the characteristics of low wind speed， high humidity and low visibility.Thus， this air pollution reached the peak value.（3） The structure of boundary layer can inhibit the vertical transport of air pollutants.During the development and peak stage of air pollution， there were inversion or isothermal layer and the whole layer is controlled by high humidity and breeze， which is not conducive to the vertical diffusion of pollutants.

• Advances in the Study of the Influencing Mechanism and Forecast Methods for Orographic Precipitation
• Shuixin ZHONG
• 2020 Vol. 39 (5): 1122-1132.  DOI:10.7522/j.issn.1000-0534.2019.00083
• Abstract ( ) HTML ( ) PDF (2865KB) ( )
• An overview of orographic precipitation （OP） is presented， including the experimental studies， physic mechanism and its forecasting methods.The effects of orographic dimension and geometry， water vapor condensation and atmospheric stability on OP are summarized， as well as the progress on the linear OP model， topographic parameterization and its forecasting methods.The current challenges of research on OP are summarized.The improvement of the research on the mechanism of OP and the forecasting methods need to further carry out a variety of topographic observation experiments and analysis of mechanisms based on multi-source data.Furthermore， a new simplified OP parameterization scheme （SOP） is evaluated based on a linear orographic precipitation scheme by considering both the sub-grid topographic blocking effects and the probability of atmospheric precipitation.The application of the SOP scheme is implemented based on GRAPES （Global/Regional Assimilation and Prediction System）.The results show that the SOP scheme could predict the extreme OP over the mountainous terrain and capture the weak precipitation over the lee side of the mountain.Seasonal experiments showed that the intensity and distribution of the simulated OP had some typical correspondences with surface observations over the mountainous terrain.The SOP scheme provides useful reference values for the precipitation forecast over complex terrain， and also help to better predict the OP especially when the model underestimate the precipitation from microphysics scheme over the mountainous terrain.Further researches are needed to study the interaction of the weather systems under multi-scale complex terrain， and to improve the theoretical technology of numerical model dynamics， physical process and data assimilation， so as to improve the understanding of influencing mechanism and forecast methods for orographic precipitation.