Current Issue

• Study on Surface Process Parameters and Soil Thermal Parameters at Shiquanhe in the Western Qinghai-Xizang Plateau
• Xingbing ZHAO;Changwei LIU;Bing TONG;Yubin LI;Linlin WANG;Yaoming MA;Zhiqiu GAO
• 2021 Vol. 40 (4): 711-723.  DOI:10.7522/j.issn.1000-0534.2021.00017
• Abstract ( ) HTML ( ) PDF (4029KB) ( )
• The land surface processes of the Qinghai-Xizang Plateau have important effects on regional and global weather and climate through its thermodynamic and mechanical forcing.Due to the harsh natural environment， the western Qinghai-Xizang Plateau lacks the land surface process parameters based on field measurements.Thus， the land surface process models usually use empirical or default parameters， which leads to great uncertainty in the simulation of this area and reduces the performance of weather and climate models coupled with land surface process models.With the data collected from June 2015 to January 2017 at Shiquanhe （32.50°N， 80.08°E， 4279.3 m above sea level） in the western Qinghai-Xizang Plateau， the conventional meteorological characteristics were analyzed and the land surface parameters， such as aerodynamic roughness， thermal roughness， surface albedo， and heat capacity， thermal conductivity， thermal diffusivity， and water flux density of soil， were estimated.Results show that （1） the wind speed was relatively low and the annual value was 2.17 m·s^-1， and westerlies were dominant with the annual westerly wind frequency 59.2% and showed little season variation at Shiquanhe.The seasonal variation of air temperature， solar radiation and specific humidity were obvious.The difference between the maximum temperature and the minimum temperature could reach 47.1 K， and the maximum daily difference was 22.40 K.The average specific humidity was 2.6 g·kg^-1， lower than in the easter or central Qinghai-Xizang Plateau.The monsoon could affect Shiquanhe area approximately in late May， and then brought most of the annual precipitation during June to September.The surface albedo was affected by soil moisture and had weak seasonal changes， with an average of 0.20， which is equivalent to deserts and Gobi.（2） The aerodynamic roughness and zero-plane displacement were affected by the distribution of ground features in directions， and the average were 5.58×10^-2 m and 0.44 m， respectively.The thermodynamic roughness length or the excess resistance to heat transfer （kB^-1） varied with the atmospheric stratification， and the atmospheric stratification of the boundary layer at Shiquanhe was mainly unstable.The performances of thermodynamic roughness parameterization schemes were different.Compared to other parameterization schemes the mean kB^-1 calculated by the Z95 scheme agreed best with the value calculated with observation under unstable stratification.（3） The annual average soil heat capacity， thermal conductivity， thermal diffusivity， and water flux density were 0.95×10⁶ J·m^-3·K^-1， 0.24 W·m^-1·K^-1， 2.73×10^-7 m²·s^-1， 0.12×10^-5 m·s^-1， respectively， which were relatively consistent with the observations in the desert and Gobi.

• Integration and Sharing for Meteorological Data of the Land-atmosphere Systems over the Qinghai-Xizang Plateau
• Anyuan XIONG;Aixia FENG;Mei GAO;Feng GAO;Zhiqiang ZHANG;Wenchun HE;Weiqiang MA;Fanglin SUN;Wenhua ZHANG;Na LIU;Yufei ZHAO;Yuanyuan LIU;Donghui CHEN;Heping YANG;Di YANG
• 2021 Vol. 40 (4): 724-736.  DOI:10.7522/j.issn.1000-0534.2020.00079
• Abstract ( ) HTML ( ) PDF (5661KB) ( )
• Sparse observations over the Qinghai-Xizang Plateau is one of the key factors hindering research our ability to gain deep understanding of the region and its effects.The land-atmosphere observations and their related analysis products made in the last a few decades in the region were integrated by the National Meteorological Information Center together with the Chinese Academy of Meteorological Science， the Institute of Qinghai-Xizang Plateau Research and the Northwest Institute of Eco-Environment and Resources of Chinese Academy of Sciences， leading to a long-term， multiple-element and integrated land-atmosphere dataset.The integrated database and sharing platform was also developed.This paper introduces the related observations and data products， including the long-term operational measurements of the China Meteorological Administration， data from the four atmospheric experiments conducted over the Qinghai-Xizang Plateau， part of long-term observations implemented by the Chinese Academy of Sciences and some products produced in scientific research projects.The techniques on the combination and standardization of the multiple datasets are described.It presents a highly valuable data resource for the scientific research and applications in dealing with various earth issues in the region.

• Prediction of Precipitation in the Southern Qinghai-Xizang Plateau during the Flood Period Based on the Interannual Increment Approach
• Shaoge DENG;Yijia HU;Tingzhen Lü;Wei YAN
• 2021 Vol. 40 (4): 737-746.  DOI:10.7522/j.issn.1000-0534.2020.00047
• Abstract ( ) HTML ( ) PDF (2710KB) ( )
• The researches on the precipitation prediction in the southern Qinghai-Xizang Plateau during the flood period are few and difficult.To solve this problem， the correlation between the year-to-year increments of precipitation and those of 88 atmospheric circulation indices， 26 oceanic indices and 16 other indices released by the National Climate Center from 1981 to 2010 were analyzed.The optimal combination of predictors was selected for the precipitation prediction by using the stepwise regression method.Based on these predictors， a physically-based statistical forecast model was established.Independent sample return tests from 2011 to 2019 were carried out to evaluate this forecast model.The results showed that the accuracy of the model was very high.The prediction of precipitation year-to-year increment and anomaly are correct with the same sign like the observation in 8 years out of 9 years.The RMSE of precipitation anomalies was 13%.The years with relative bias within ±15% are 8 years out of 9 years.Thus， this model can improve the forecasting capability of precipitation in the southern Qinghai-Xizang Plateau during the flood period.At last， the physical mechanism of the predictors affecting precipitation during the flood period was explored based on the monthly NCEP/NCAR reanalysis data and the NOAA sea surface temperature data.

• The Impact of Temperature Change on China's Summer Cloud Water Content
• Juju LIU;Tianjiang LI;Wei WEI
• 2021 Vol. 40 (4): 747-759.  DOI:10.7522/j.issn.1000-0534.2020.00044
• Abstract ( ) HTML ( ) PDF (8962KB) ( )
• Based on the 1979 -2016 ERA-Interim reanalysis data provided by the European Centre for Medium-Range Weather Forecasting （ECMWF）， and by using correlation analysis， singular value decomposition（SVD） method and synthesis analysis， the temporal and spatial characteristics of summer atmospheric water cycle variables and temperature， and the impacts of temperature on cloud water content in four regions of China are analyzed.The results show that： The spatial distribution of cloud water content in summer in China decreases from southeast to northwest.There is a positive correlation between cloud water content and temperature in Qinghai-Xizang Plateau， and a significant negative correlation in other areas of China.The warming in the northwest China weakens the water vapor transported by the westerly belt and maintains the anomalous anticyclone in eastern Mongolia.The warming in the north China maintains the anomalous anticyclone in northeast Mongolia and the anomalous cyclone in southeast coastal， and withdraws the Northwest Pacific subtropical high （subtropical high） to the east.The warming in both the northwest and northern China weaken the 200 hPa westerly stream， the water vapor transport and the updraft are weakened， and thus the cloud water content reduced.The warming of the southern China maintains the anomalous anticyclone in the Yellow Sea and the anomalous cyclone in the South China Sea， and making the subtropical high withdraw eastward and the 200 hPa westerly jet move northward， which are not conducive to water vapor transport and updraft， and thus reduce the cloud water content.The warming of the Qinghai-Xizang Plateau strengthens the south branch of the westerly jet and the anomalous cyclone in the western part of the plateau， causing the subtropical high extend west-northward and the westerly jet and the South Asian high strengthened.These intensify the water vapor transport and convergence on low level， which further increase the cloud liquid water content in Qinghai-Xizang Plateau.

• Characteristics of Long-Cycle Abrupt Drought-Flood Alternations in Southwest China and Atmospheric Circulation in Summer from 1961 to 2019
• Yingsi WANG;Tiangui XIAO;Xuefeng DONG
• 2021 Vol. 40 (4): 760-772.  DOI:10.7522/j.issn.1000-0534.2020.00067
• Abstract ( ) HTML ( ) PDF (8853KB) ( )
• Using the daily precipitation observation data of 121 stations in the southwest China from 1961 to 2019， the southwest China is divided into three regions： southwest I， southwest II， and southwest III， according to the REOF positive anomalies of precipitation， and analyzes the characteristics of abrupt drought-flood alternations of these districts.The results show that there are obvious regional differences and similarities in the abrupt drought-flood alternations in summer in Southwest China.There are fewer severe abrupt drought-flood alternations in region I and some strong abrupt drought-flood alternations mainly occurred before 2000.And there was a relatively obvious interdecadal oscillation in the abrupt drought-flood alternations index in region II from 1961 to 1990， more drought-to-flood events occurred from 1961 to 1970.What’s more， there are more flood-to-drought events occurred from 1971 to 1980.Then the intensity of abrupt drought-flood alternations from 1980 to 1990 was more pronounced.Smaller， it gradually turned into an interannual oscillation after 1990.The overall abrupt drought-flood alternations index in region III was relatively low.It has obvious interannual oscillations from 1975 to 2000.But after 2010， the abrupt drought-flood alternations events showed an increasing trend.Further research on the atmospheric circulation characteristics of typical abrupt drought-flood alternations years in each region found that during the drought period of the three regions， at mid-to-high latitudes， high-altitude westerly winds were strong and zonal air currents prevailed.At mid-low latitudes， the western Pacific subtropical high was stronger to the west， the South China Sea-Pacific and Indian Ocean-Bay of Bengal water vapor transport was weak， and sinking air currents prevail in the lower layers， resulting in less precipitation.The circulation situation during the flooding period in the three regions is complex.During the flooding period in region I， the mid-high latitude circulation presented a "-+-" zonal wave train， the Ural Mountains high pressure ridge deepened， the western Pacific subtropical high was northeast and east， the water vapor transport in the Bay of Bengal was enhanced， the upward movement was enhanced， and the precipitation was more frequent.While during the flooding period in region II， the mid-high latitude circulation presented a "-+" zonal wave train， the Okhotsk high pressure ridge strengthened， the western Pacific subtropical high was northeast and the southern branch trough was obvious， and the water vapor transport in the Pacific and Indian Oceans enhanced.So that the precipitation is on the high side.However， during the flooding period in region III， the mid-high latitude circulation presented a "+-+-" zonal wave train， the Ural high pressure ridge and the Baikal low pressure trough strengthened， the western Pacific subtropical high was northeast and the Gulf of Bengal-Indian Ocean water vapor strengthened， and precipitation was more frequent.

• Stimulation Analysis on Differences and Force Effects of Gust Fronts in a Severe Convection Trigging Process
• Wendong HU;Kan YANG;Xiaohang WEN;Ying ZHANG
• 2021 Vol. 40 (4): 773-788.  DOI:10.7522/j.issn.1000-0534.2020.00058
• Abstract ( ) HTML ( ) PDF (16792KB) ( )
• In order to further explore the mechanism of severe convection triggered by gust front in arid northwest China， overcome the radar’s incapability to detect gust front， operational numeric model mesoscale WRF is applied to simulate a severe secondary convection which propagated reversely and triggered by three gust fronts in Northwest China arid area.Locally modified index is used to investigate the key factors of triggering mechanisms and comparison analysis between simulations and radar sounding data is conducted.The results show that： （1） The mesoscale WRF model relatively well reproduces the atmospheric backgrounds， but shows a limited capability to describe the convective cells and the gust fronts directly， and it is necessary to develop specific index to reveal the mechanism of convection trigging according to local meteorological situation.（2） MBI and TKE show mutual corroboration and demonstrate the differences between the 3 gust fronts and their trigging characteristics.The areas and intensities of the modified MBI high value regions are consistent with the characteristics of original convections， the out-flow edges align with the positions of the 3 gust fronts， and the core high value areas accord with the intensities of gust fronts.（3） Comprehensive conditions of the areas and intensities of MBI relating to 3 gust fronts， wind field at 850hPa and vapor diversities of surface characteristics， leads to the capability differences of 3 colliding points which trigger secondary convections， and reveal their severities and propagation behaviors.（4） Gust fronts force causes strong updraft of 1.74 m·s^-1， upraising the surface air over LFC.Orographic effect contributes 1.1% of uplift， enclosing press and directly force makes up 40.9% and 58.0% respectively.Extraordinary force and favorable vapor are keys to trigger this extreme violent secondary convection， while the gravity wave propagating east at low altitude of atmosphere is favorite to trigging.（5） The numeric simulation and MBI analysis suggest that this simple and practical index is able to depict gust front’s characteristics that are difficult for models to reflect directly.It can be expected to provide clues for seamless grid forecasting after further practice.

• Objective Identification and Variation Characteristics of Regional Heavy Rainfall Events in the East of Southwestern China
• Jie ZHOU;Junhu ZHAO;Yonghua LI;Xukai ZOU
• 2021 Vol. 40 (4): 789-800.  DOI:10.7522/j.issn.1000-0534.2020.00048
• Abstract ( ) HTML ( ) PDF (7856KB) ( )
• The regional heavy rainfall events （RHREs） were identified by using the Objective Identification Technique for Regional Extreme Events （OITREE） based on the daily precipitation data of 118 stations in eastern Southwest China （ESWC） from 1961 to 2018.The parameters related to OITREE method were determined.There are 246 RHREs in total in the ESWC from 1951 to 2018， of which 25 are extreme RHREs.The strongest RHRE occurred on 3-6 September 2004， detected by the comprehensive intensity.Further analysis shows that the duration of the RHREs in the ESWC is generally 2 days and the longest duration is 5 days.The cumulative intensity of RHREs is about 500~1000 mm， and the cumulative area is about 10×10⁴~20×10⁴ km².RHREs in the ESWC occur frequently from May to September， with the highest frequency of the RHREs in July， accounting for 31.7% of the total occurrence frequency.The plain areas in eastern Sichuan and western Chongqing are the center areas with the highest frequency and intensity of RHREs.During the past 58 years， the number of persistent RHREs in the ESWC shows a significant increasing trend at the rate of 0.57 times per decade.Also， the duration， the maximum impacted area and the extreme precipitation of the RHREs are all show a significant increasing trend at the rate of 1.2 d·（10a）^-1， 5.7×10⁴ km²·（10a）^-1 and 73.4 mm·（10a）^-1， respectively.

• Comparative Analysis of Convective Conditions and Triggering Mechanisms of Short-term Rainstorm in Xi'an on Two Consecutive Days
• Qiang ZHAO;Nan WANG;Xingxing GAO;Xiaoting CHEN
• 2021 Vol. 40 (4): 801-814.  DOI:10.7522/j.issn.1000-0534.2020.00053
• Abstract ( ) HTML ( ) PDF (11591KB) ( )
• Using conventional observation data， satellite cloud images， doppler radar data of Xi'an station and ECMWF reanalysis data （0.25°×0.25°）， the convective environmental conditions and triggering mechanism of two short-term rainstorms which occurred in Xi'an on 2 and 3 August 2015， causing flash floods and mudslides and resulting in railway interruption and casualties were comparative analyzed.Results show that atmospheric environment conditions are obviously different.Xi'an is controlled by subtropical high， has high temperature and humidity and ground temperature reaches 39 ℃， CAPE value is more than 2000 J·kg^-1.The decline rate of vertical temperature from ground to 850 hPa is close to superadiabatic state， which is very conducive to the triggering of convection on 2 August 2015.However， on 3 August 2015， Xi'an is located at the intersection of cold and warm air between the trough and subtropical high.There is a ground cold front moving southward in northern Shaanxi and air instability near surface layer decreases.Cold advection is stronger and ground temperature drops to 30 ℃， CAPE value is 800 J·kg^-1.The synoptic scale system forcing is stronger on 3 August， although the temperature and unstable energy are significantly lower than those on 2 August.From the perspective of triggering mechanism， the surface convergence line triggers convection in the afternoon of 2 August in Yan'an and produces cold pool in the process of moving southward.The gust front of outflow triggers new convection， due to the large water vapor content and sufficient energy around Xi'an area， short-term rainstorm is generated and hourly precipitation is as high as 47.2 mm.However， the rainstorm in the afternoon of 3 August is triggered by cold front.Strong frontogenesis area corresponds well with the low-level cold advection area， which locates in the near-surface layer to 850 hPa.Diagnosis result indicated that vertical movement from ground to 850 hPa caused by frontogenesis secondary circulation makes the air mass overcome convective inhibition energy and rise to the level of free convection， which makes unstable energy release and produces heavy precipitation.During the process of cold front moving southward， due to the blocking effect of Qinling Mountains， a jet stream is formed in the boundary layer along the northern foot of Qinling Mountains.Strong thunderstorms continuously generated along the jet stream and train effect formed during the strom moving eastward， which causes heavy rain in the mountains.

• Contrast Analysis of Two Warm-Sector Heavy Rainfall Processes under Weak Synoptic Scale Background in Hunan
• Jia TANG;Chengzhi YE;Minghui TANG;Lin XU;Weiwei HE;Wei FU
• 2021 Vol. 40 (4): 815-828.  DOI:10.7522/j.issn.1000-0534.2020.00062
• Abstract ( ) HTML ( ) PDF (12429KB) ( )
• Warm-sector heavy rainfalls under weak synoptic scale background in Hunan during April-September in 2008 -2019 are divided into strong southwest jet type and subtropical high type according to 500 hPa circulation situation， and then two different types of warm-sector heavy rainfall cases under weak synoptic scale background on April 30， 2018 （"4·30" case） and July 17， 2016 （"7·17" case） are analyzed.Results are as follows： （1）There are obvious seasonal differences between the two types of Warm-sector heavy rainfalls.Strong southwest jet and subtropical high occur in spring and summer， respectively.The strong southwestern jet type appears at any time of the day， and the frequency of precipitation at night increases.Diurnal variation of the subtropical high type is obvious， and the peak appears in the morning.The precipitation of strong southwestern jet type is distributed widely， and mostly occurs in the southern Hunan.When the southwestern jet moves northward to the middle-lower reaches of Yangtze River， heavy rainfalls also occur in northern Hunan.Precipitation of Subtropical type distributes dispersedly， and occurs in northwestern， northern， and southeastern of Hunan， with strong locality and obvious convection.（2）Rainstorm area of the "4·30" case is in lower-to-upper southwest wind， and occurs in Northeast Hunan under influences of convergence and updraft on south side of shear line， southwest jet and surface convergence line， belonging to the strong southwest jet type of warm -sector heavy rainfall.The "7·17" case is affected by weak shear in the middle and lower levels and surface mesoscale cyclone， under the control of subtropical high.Heavy rain occurs in the northwest of Hunan， belonging to subtropical high type of warm sector heavy rainfall.（3）The values of vertical helicity over the rainstorm area during "4·30" case are all negative， and there is a negative center in 700 hPa， which means that the shear line in 700 hPa causes strong upward convergence in rainstorm area， leading to this heavy precipitation.During "7·17" case， vertical helicity shows a structure of positive in upper level and negative in lower level， strong cyclonic rotatory convergence is the strongest in 900 hPa level， indicating that the heavy rainfall is caused by the mesoscale and small scale systems in the near surface level.Water vapor transport and convergence in "4·30" case are stronger than that in "7·17" case.Thermal instability energy in the lower level of the "7·17" case is larger， and thermal instability stratification is stronger than that in the "4·30" case.β-mesoscale convergence lines and γ-cyclones are the triggering mechanisms of "4·30 "and "7·17" cases， respectively.

• Analysis of the Heavy Precipitation Caused by Plateau Vortex in Northwest China Based on Satellite Data
• Dong WEI;Liwei LIU;Wenshou TIAN;Rui WANG;Xiaojun YANG;Chenrui LI;Junxia ZHANG
• 2021 Vol. 40 (4): 829-839.  DOI:10.7522/j.issn.1000-0534.2021.000021
• Abstract ( ) HTML ( ) PDF (7712KB) ( )
• Global Precipitation Measurement （GPM） satellites has been currently widely used in the study of convective systems at present.Limited by the orbital scanning mode of GPM satellite， it was difficult to capture complete severe convective systems with GPM orbital observation data in the eastern region of the Tibetan Plateau.In this study， the structure of a heavy rainfall system occurred over this region on 21 July 2018 has been researched by using GPM and FY-4A satellite data， ERA-Interim and NCEP-FNL reanalysis data in combination with ground observation data.The result indicates that although the number of convective cloud samples was 1/5 of the stratiform cloud samples， but averaged convective rainfall rate was 14 times larger than the stratiform rainfall rate and the contribution of convective rainfall to the total precipitation reached 75%.The contribution of convective rainfall is much higher than that of southern China heavy rainfall system.The top of the heavy rainfall system reached up to 15 km with a low core structure about 2 km above the ground， which was more obvious than that of similar strong convective systems in southern China.The convective cloud droplet spectrum and cloud particle radius differ widely.There was an obvious particle accumulation zone in convective cloud at the height of 2~5 km， which was significantly different from the stratiform cloud.In the early stage of heavy rainfall， precipitable water reached to 40 kg·m^-2 with relative humidity to 16 g·kg^-1.The heavy rainfall system triggered by plateau vortex and shear line at 700 hPa， consisted of a main stratiform precipitation cloud cluster and several scattered convective precipitation cloud clusters characterized by high precipitation intensity.Blocked by the high-pressure ridge， the quasi-stationary rainstorm cloud cluster took nearly 4 h from the initial stage to the strongest stage within 3 longitudes.The slow movement of heavy rain clouds led to local heavy rainfall in southeast Gansu.

• Influence of Rossby Wave Excited by Arctic Osoillation on the Wintertime Extreme Precipitation in Yunnan under the Background of El Niño
• Jianmeng ZHENG;Yu YAO;Rui LI;Wancheng ZHANG;Ziming MA
• 2021 Vol. 40 (4): 840-852.  DOI:10.7522/j.issn.1000-0534.2020.00069
• Abstract ( ) HTML ( ) PDF (14584KB) ( )
• The daily average precipitation of Yunnan province on 8 January 2019 is 29.8 mm， which is the third extreme heavy precipitation in winter since 1961.The study showed that a tropical depression which developed over the warm surface of the South China Sea moved westward and then turned northward in the Bay of Bengal （BOB）， guided by the peripheral air flow of the western Pacific subtropical high （WPSH）.A Rossby wave train induced by the Arctic Oscillation （AO） propagated eastward to the BOB and formed the southern branch trough （SBT）.The southwesterly wind in the front of the SBT converged with the peripheral air flow around the WPSH and the tropical depression， forming an intense southwesterly jet， upward movement and moisture convergence from Myanmar to Yunnan.This circulation situation ultimately led to the wintertime extreme precipitation.The main conclusions are as follows.First， when AO is in its positive phase， the northerly wind of the Scandinavian ridge is intense and is able to reach as low as the Mediterranean Sea and North Africa， and then excites Rossby wave trains.One of the wave trains is at the mid- and low-latitudes embedded with Mediterranean-North-Africa trough， Pakistan ridge and the SBT over the BOB.The other is at mid- and high-latitudes embedded with Scandinavian ridge， Ural ridge and Mongolian ridge， forming a north-ridge-and-south-trough pattern around the Tibetan Plateau （Plateau）.Second， the eastward propagation of the wave train at mid- and low-latitudes can be influenced by the subtropical highs.The favorable location configuration of the peripheral air flows around the North Africa high and the WPSH can deepen the SBT， which makes the wave train induced by AO more obvious.Third， El Nino event tends to enhance the Arab Sea anticyclone， the WPSH， the southerlies over Indo-China Peninsula， the detour flow around the Plateau and the Mongolian ridge， and vice versa for La Nina event.Therefore， ENSO can modulate the influence of AO on Yunnan’s precipitation through its impacts on the systems mentioned above.

• Study on Snow Cover Characteristic of Extreme Rain-snow Event based on Intensive Observation Data
• Chengfang YANG;Yu ZHAO
• 2021 Vol. 40 (4): 853-865.  DOI:10.7522/j.issn.1000-0534.2020.00072
• Abstract ( ) HTML ( ) PDF (7048KB) ( )
• Diagnostic analysis has been performed to study the characteristics of snow cover and contributing factor of temperature in an extreme rain-snow event over Shandong Province during 5 -7 January 2020 by hourly precipitation measurement instrument， automatic weather stationintensive snow depth observation data and NCEP/NCAR 1°×1° reanalysis data.Main results are as follows： （1） The rain-snow process is an extreme weather event caused by Jianghuai cyclone with weak cold advection and severe precipitation.So snow depth has presented a challenge to forecasters.（2）The averaged snow-liquid ratio in Shandong Province is 0.46 cm·mm^-1， less than that average of all snowstorms produced by Jianghuai cyclone over the past 20 years.（3） Snow depth is related to configuration of temperature， relative humidity and vertical velocity in upper level.The environment temperature at the level where maximum ascending motion accompanied relative humidity larger than 90% is favorable to branch ice crystal growth， while that with large snow depth and snow-liquid ratio is favorable to hollow columnar ice crystal growth.Temperature under the cloud higher than 0 ℃ can decrease snow depth.（4） The relationship between surface temperature and snow depth shows that obvious snow cover can form with the temperature of most stations lower than 0.5 ℃ and ground surface temperature at 0 cm lower than 0.4 ℃.The impact of ground surface temperature occurs before snow cover forms.Snow surface temperature maintains about 0 ℃ in 2 h prior to or after the formation of obvious snow cover， similar to air temperature in other time.（5） Generally， snow-liquid ratio decreases with air temperature increasing， with air temperature lower than 0.4 ℃ when the snow-liquid ratio is larger than 0.5 cm·mm^-1 during snowfall.The analysis of this snowstorm event revealed that forecasting snow depth and snow-liquid ratio need to consider various meteorological conditions.

• Effect Evaluation of Artificial Rainfall Enhancement in the Shiyang River Basin of Hexi Corridor in the Latest 10 Years
• Peng CHENG;Qi CHEN;Youyan JIANG;Baozi LI;Han LUO
• 2021 Vol. 40 (4): 866-874.  DOI:10.7522/j.issn.1000-0534.2020.00074
• Abstract ( ) HTML ( ) PDF (2952KB) ( )
• The effect of artificial precipitation enhancement has always been a key issue and difficult problem of weather modification， and there is great uncertainty about how to accurately detect the effect of precipitation enhancement after operation from the change of natural rainfall.Shiyang River， which is located at the eastern end of Hexi Corridor in Gansu Province， is an important inland river in this region.It is the main source of local agriculture， ecology and drinking water.However， it is also one of the most densely populated inland river basins in China with severe shortage of water resources and extremely fragile ecological environment.Although the Shiyang River Basin lacks ground water resources， it has very abundant aerial water resources.The scientific development and utilization of aerial cloud water resources through artificial rain enhancement technology has become one of the effective measures to increase local water resources in the basin and alleviate drought.Since 2010， in order to ameliorate adverse ecological and hydrological changes， ground cloud seeding stations has been added from 22 to 71 in Shiyang River Basin， and the seeding operations has also been significantly increased.Therefore， a question of general concern is， what is the effect of the substantial increase in the scale of artificial precipitation？ To answer this question， and evaluate the effect of artificial rainfall enhancement after the increase in operation sites and operations， precipitation data of the Shiyang River Basin in the past 10 years （from 2010 to 2019） was collected.Some statistical test methods recommended by Centre for Weather Modification of China Meteorological Administration were adopted in the effect evolution of the increased ground seeding operations during 2010 -2019.As a means of certification， the ecological changing trend of runoff， vegetation normalization index， and vegetation coverage percentage were also analyzed in this paper.The results showed that the average relative artificial rainfall enhancement in the basin was about 17.5%， which passed the significance test of 0.1.The cloud seeding operations has increased precipitation by 33.7 mm and increased runoff by 0.34 × 10⁸ m³ per year.Cloud seeding in spring and autumn were more effective than in other seasons.The runoff of Shiyang River increased by 3.7% during the cloud seeding period， while the runoff in the contrast area showed a downward trend.The vegetation in the Basin has improved significantly since 2010 because of both artificial rain enhancement and natural precipitation rise.The preliminary results show that artificial rain enhancement has played a positive role in improving the ecological situation of the Shiyang River Basin.

• Spatiotemporal Variation of Snow and its Response to Climate Change in Northeast China
• Xiaoyu ZHOU;Chunyu ZHAO;Na LI;Yan CUI;Xue YI;Mingyan LIU
• 2021 Vol. 40 (4): 875-886.  DOI:10.7522/j.issn.1000-0534.2020.00055
• Abstract ( ) HTML ( ) PDF (2862KB) ( )
• Based on daily meteorological observation data from 162 meteorological stations in Northeast China from 1961 to 2017， the spatiotemporal variation of snow and its relationship with climate change were analyzed.The results showed that： （1）The average annual snow days and accumulated snow depth were 75.3 d and 582.1 cm， showing a distribution of more high latitude and less low latitude， more mountains and less plains， with snow days reaching 140 d or more in the northern Daxinganling， Xiaoxinganling and Changbai Mountain areas， and the accumulated snow depth is deeper in places with more snow days.（2）The average snow onset date， end date and snow duration were 7 November， 1 April and 145 d respectively， with the snow onset date advancing from the northern part of the Daxinganling to the coastal areas of Liaoning； areas with early snow onset date also have later snow end date and longer snow duration， most areas of Heilongjiang exceeding 150 d.（3）The snow days and accumulated snow depth distributed in a single peak during the year， with the maximum value occurring in January， with the most occurring in late January； the maximum value of snow onset date and end date occur in November and March respectively， with the most occurring in early November and late March.（4）The annual snow days and accumulated snow depth increased at the rates of 1.88 d·（10a）^-1 and 71.94 cm·（10a）^-1 respectively， reaching a chronological maximum in the 2010s， the snow days and accumulated snow depth all tend to increase in autumn， winter and spring， with the most significant increase in winter.Of the 162 meteorological stations， more than 75% sites showed increasing trend for the snow days and accumulated snow depth， 86.4% stations’s snow onset date delayed， 98.1% end date advanced and 96.3% snow duration shortened.（5）The snow was more influenced by precipitation （effective snowfall） than by the average temperature； the snow onset date correlates better with the average temperature in November and the precipitation in October， and the snow end date correlates better with the temperature factor in February with the latitude increases and altitude rises， the snow days and the accumulated snow depth increase， with earlier snow onset date， later snow end date and longer snow period.

• Characteristics of the Winter Extreme Low Temperature Events in Ningxia and their Relationship with the Arctic Sea Ice Coverage Anomalies in Autumn
• Fan WANG;Qingquan LI;Yinchuan SUN;Dai WANG;Guangfen ZHENG;Xiaowei ZHU
• 2021 Vol. 40 (4): 887-897.  DOI:10.7522/j.issn.1000-0534.2020.00054
• Abstract ( ) HTML ( ) PDF (3018KB) ( )
• Based on daily maximum and minimum temperature in Ningxia of China， monthly sea ice concentration from the Hadley Centre of UK， monthly atmospheric reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research of US， and the East Asian Winter Monsoon Index and Siberia High Index from National Climate Center of China Meteorological Administration， the characteristics of extreme winter low temperature events in Ningxia and their relationship with autumn sea ice concentration in the key region of the Arctic from 1961 to 2018 were systematically studied.The results show that the frequency of cold day and cold night in winter in Ningxia has decreased significantly since 1960s.The intensity of extreme low temperature events generally tends to weaken， and the daily extreme low temperature increases obviously.The Arctic sea ice anomaly in autumn is significantly related to the sea ice anomaly in the following winter.The sea ice anomaly in autumn influences the atmospheric circulation in the following winter through the seasonal sustainability， and then affects the winter temperature.When the sea ice concentration is low in the Lapjev-East Siberian Sea and high in Greenland Sea in the previous autumn， the Siberian High Index and the East Asian Winter Monsoon Index become stronger， which is benefit to more extreme temperature events occurring in Ningxia in winter.The 500 hPa geopotential height Arctic-Eurasia-Aleutian region's "L" like phase wave pattern decreased the height difference between the Arctic and Eurasia in the mid-high latitudes， the mid-high latitude westerly airflow is weakened， and the zonal activity is weakened， that’s conducive to the cold air of the Arctic to the low latitudes.Correspondingly， the sea level pressure is high in Siberia and cold air is squeezed from the polar region to the middle and high latitudes in the Northern Hemisphere， which makes the cold air easy to reach in Ningxia and results in more extreme cold weather days there.

• Classified Identification and Nowcast of Hail Weather Based on Radar Products and Random Forest Algorithm
• Xinwei LIU;Yingsha JIANG;Wubin HUANG;Yongjie PAN;Xia LI;Runxia GUO;Yuxia HUANG
• 2021 Vol. 40 (4): 898-908.  DOI:10.7522/j.issn.1000-0534.2020.00063
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• Hail is a kind of strong convective weather with high possibility to cause serious disasters， but it is hard to be early-warned and nowcasted accurately for present meteorological operations.This study pre-warns and now-casts the hail disastrous weather and its accompanying strong convective weathers based on C-band radar products and random forest （RF） algorithm， and gets the following results.In the training set （from 2008 to 2017）， the identification of the four types of hail disastrous weather （the hail， hail with strong wind， hail with short-time heavy precipitation， hail with strong wind and short-time heavy precipitation） using the RF model has a mean probability of detection （POD） of 90.2% and a mean false alarm ratio （FAR） of 11.1%.This indicates that the RF model developed in this study is generally ideal.Then the RF model is used in the independent testing set in 2018-2019， which shows that the mean POD and FAR of the model identification for the testing set is 72.8% and 34.7%， respectively.Among the four types of the hail disastrous weather， the hail with strong wind has the highest POD of 83.3%， while the hail with short-time heavy precipitation has the lowest FAR of 12.5%.Thus， the testing set has a lower POD and higher FAR compared to the training set， which is probably because the sample numbers of the testing set is lower.The RF model is then applied in the nowcast of hail disastrous weather in 15~60 min using the storm identification and tracking （SCIT） products.Results show that the RF model has a good performance for the nowcast of hail disastrous weather with a mean POD of 74.8%， mean critical success index （CSI） of 60.8% and mean FAR of 24.4%.Among the four types of the hail disastrous weather， the hail with strong wind has the highest POD and CSI for the forecast in 15~60 min， while the hail with short-time heavy precipitation has the lowest FAR.Furthermore， the POD of RF model is comparable to other hail identification system， but its FAR （<35%）is lower than that of other systems.Therefore， the random forest model can well classify， early-warn and nowcast the hail disastrous weather and its accompanying severe convective weather efficiently and automatically， and is suitable to be applied in the real weather forecast operations.

• Study of the Classified Identification of the Strong Convective Weathers Based on the LightGBM Algorithm
• Xinwei LIU;Wubin HUANG;Yingsha JIANG;Runxia GUO;Yuxia HUANG;Qiang SONG;Yong YANG
• 2021 Vol. 40 (4): 909-918.  DOI:10.7522/j.issn.1000-0534.2020.00075
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• Strong convective weather can cause serious disasters， but it is hard to be pre-warned and forecasted because of its abrupt occurrence and small scale.This study generates a model based on the LightGBM （Light Gradient Boosting Machine） algorithm using C-band radar products and in-situ observations， and identifies and classifies three main kinds of strong convective weather （hail， strong wind and short-time strong precipitation）.Evaluation results shows that， for the training set from 2011 to 2017， the LightGBM model has good performances with overall false identification rate of 4.9%.Among the three main kinds of strong convective weather， the short-time strong precipitation has the lowest false identification rate （6.2%）， while the hail has the highest false identification rate around 14.4%.The false identification rate for the non-convective weather is only 3.6%.Furthermore， the LightGBM has a mean probability of detection rate （POD） for three kinds of strong convective weather in the training set of 88.8%， mean critical success index （CSI） of 73.9% and mean false alarm ratio （FAR） of 18.8%.The short-time strong precipitation has the highest POD and CSI， and the lowest FAR as well.Then the LightGBM model is applied in an independent testing set in 2018.For the independent testing set， the model has an overall false identification rate of 7.0% for the three kinds of strong convective weather and the non-convective weather， and a mean POD of 86.4%， mean CSI of 64.3% and mean FAR of 29.0%.Similar to the training set， the short-time strong precipitation has the lowest false identification rate， the highest POD and CSI， and its FAR is the lowest as well， while performances for the thunderstorm and hail are similar.Therefore， the LightGBM model generated in this study is generally ideal， which early-warning three kinds of strong convective weather automatically for the first time， and is appropriate to be applied to the future auto-identify system of the meteorology operation.

• Correction of FY-4A Surface Solar Irradiance based on Probability Density Function Matching Method
• Lina XU;Yanbo SHEN;Zhong LI;Hu YE
• 2021 Vol. 40 (4): 932-942.  DOI:10.7522/j.issn.1000-0534.2020.00080
• Abstract ( ) HTML ( ) PDF (2127KB) ( )
• Fengyun-4A（FY-4A） satellite is the second generation of geostationary meteorological satellite for quantitative applications independently developed by China.FY-4A supports nowcasting and severe weather warning， regional and global numerical weather production（NWP）， climate application， environment and disaster monitoring and so on.The new generation of FY-4A geostationary meteorological satellite provides high spatial and temporal resolution earth observations of geosynchronous orbit in China.The hundreds of quantitative products include cloud and atmospheric products， surface products， weather products， radiation products and so on， which play a very important role in weather forecast and climate prediction.In this study， ground-based radiation observations are adopted as the benchmark to evaluate accuracy and radiation detection capability of FY-4A in Inner Mongolia.Basing on the result of evaluation， the probability density function matching method （PDF） is employed to established the correction model of FY-4A surface solar irradiance.Results show that： （1） The correlation coefficients show the obvious regularity not only on the spatial distribution but also on the seasonal distribution， that in winter are significantly lower than that in the other seasons and that in the east are higher than that in the west.In addition， FY-4A overestimates the radiation of in the lower value range and underestimates that of in the higher value range.The feature of non-independent systematic errors are obvious.（2） Aiming to adjust the systematic bias of the high resolution satellite-based surface solar irradiance （SSI） estimations over Inner Mongolia， The probability density function matching method is applied to adjust the satellite retrievals through matching their probability density function against that based on situ observations.One advantage of this technique is that it is capable of correcting retrieval errors that are range dependent.The PDF model established on a quarterly basis can reflect the characteristics of stable probability density distribution between ground-based observations and FY-4A， the accuracy and radiation detection capability of FY-4A are effectively improved.（3） By comparing the results of test， it can be concluded that after correction by the PDF model， the systematic errors are effectively reduced， the distribution characteristics are closely to the original errors， and the improvement of FY-4A surface solar irradiance in cloudy days is significant.The correlation coefficients improve from 0.37~0.91 to 0.83~0.96， the mean absolute errors decrease from 5.2~404.9 W·m^-2 to 5.3~139.1 W·m^-2 and the mean errors decrease from -150.7~305.2 W·m^-2 to -98.2~78.9 W·m^-2.So the study demonstrates that the PDF technique is effective way in correcting systematic bias of FY-4A SSI product.

• Relationship between the Associated Background Circulations of the Winter Haze Days in Shaanxi Province and the Snow Depth in Eurasia
• Xin HUANG;Yuanfa GONG;Yabin ZHANG;Hui LIU;Na WEI
• 2021 Vol. 40 (4): 943-953.  DOI:10.7522/j.issn.1000-0534.2020.00081
• Abstract ( ) HTML ( ) PDF (11412KB) ( )
• Based on daily observations from ground-level stations， monthly NCEP/NCAR reanalysis dataset and JRA-55 snow depth dataset， the interannual variation characteristics of haze days in Shaanxi province and the variations reason were analyzed.According to the background of the height field circulations of winter haze days in Shaanxi province， the main circulations systems affecting the number of winter haze days in Shaanxi province were studied.Meanwhile， the impact of the snow depth in Eurasia on the number of winter haze days was discussed.The main conclusions were as follows： （1）The negative （positive） anomaly center of the atmospheric circulations at 500 hPa over the Ural mountains is the background circulation of the increase （reduction） of the haze days in Shaanxi province in winter.The meteorological conditions conductive to the increase （reduction） of the haze days in Shaanxi province in winter was characterized by the opposite phase of sea level pressure between the Mediterranean and central Asia to Siberia.（2） The increase （decrease） of the snow depth in Europe could build up some meteorological conditions conductive to the decrease （increase） of the haze days in Shaanxi province in winter.（3） The correlations between the snow depth in Eurasia and the number of winter haze days in Shaanxi province showed an inverse distribution between Europe and west Siberia， the correlation coefficient between snow depth index and haze days in Shaanxi Province was greater than 0.41， the positive （negative） snow depth index could cause the negative （positive） height anomaly of the circulations over the Ural mountains， which will lead to the weakening （strengthening） of the cold air moving to East Asia and the meteorological conditions conducive to the increase （decrease） of the haze days in Shaanxi province in winter.

• Different-scale Changes in Ozone Concentration and Meteorological Environment in Fenwei Plain
• Xiaohua ZHENG;Mingxing LI;Panxing LOU
• 2021 Vol. 40 (4): 954-964.  DOI:10.7522/j.issn.1000-0534.2020.00064
• Abstract ( ) HTML ( ) PDF (4373KB) ( )
• As an energy supply and urban agglomeration area in the central and western regions， the Fenwei plain in recent years has been facing more and more serious air pollution problem.It has become the third key area for comprehensive treatment of environmental issues after the region of Beijing-Tianjin-Hebei and the Yangtze River Delta.With the improvement of the atmospheric environmental management and the adjustment of energy structure， the seasonal composition of pollutants has changed substantially.Particulate matters such as PM_2.5 and PM₁₀ have been effectively controlled.However， the emission of ozone precursors such as volatile organic compounds and nitrogen oxides leads to a significant increase in the concentration of ozone near the ground.Based on the observations of surface atmospheric O₃ and precursors in 11 key cities across the Fenwei plain from 2015 to 2019， along with the meteorological monitoring data during the same period， this paper analyzed the characteristics of their temporal and spatial variations.The spatial agglomeration effect and cold-hot spot area were analyzed by using the Global Moran's I and Getis-OrdG_i^* methods.Using Kolmogorov Zurbenko （KZ） filtering method， the influence of emission and meteorological elements on the variations in O₃ concentration was investigated on different time scales.The results showed that： From the temporal perspective， the O₃ pollution overall was mild in recent five years， the rate over standard increased year by year with obvious seasonal variability； the highest rate appears in summer， followed by spring， and there was no over-standard phenomenon in O₃ alone in winter.Among them， the rate of exceeding the standard reached more than 20% from May to August， and more than 37% in June.The CO in precursors decreased year by year， but in NO₂ the annual difference was not significant.From the spatial perspective， the concentration of O₃ increased year by year.The high concentration occurred mainly in Yuncheng， Linfen， Luoyang and Sanmenxia， while the low concentration appeared mainly in Baoji， Xi'an and Xianyang， the core cities in Guanzhong region.Furthermore， the temporal variation in O₃ concentration is mainly caused by seasonal and short-term fluctuations of pollutant precursor emissions and meteorological conditions.The contribution rate of seasonal component is 40%， that of short-term component is 24%， and is only 5%~18% from the long-term component.Besides the significant negative correlation between O₃ concentration and air pressure， a significant positive correlation was observed between O₃ concentration and air temperature， sunshine and mixed layer height， respectively.In contrast， the lower the relative humidity， the higher O₃ concentration.However， the effects of precipitation and wind speed on different components are not consistent in various regions.