Current Issue

• Relationships between Thermal Anomalies over the Qinghai-Xizang Plateau and Tropical Indian Ocean in May with Summer Rainfall in Xinjiang
• Tianzhu WANG;Yong ZHAO
• 2021 Vol. 40 (1): 1-14.  DOI:10.7522/j.issn.1000-0534.2020.00003
• Abstract ( ) HTML ( ) PDF (8920KB) ( )
• Based on the sea surface temperatures （SSTs） data provided by the National Oceanic and Atmospheric Administration （NOAA）， reanalysis data provided by the National Center for Environmental Prediction （NCEP）/National Center for Atmospheric Research （NCAR）， the surface sensible heat flux calculated at 149 stations in May over the Qinghai-Xizang Plateau （QXP） from 1979 to 2017， and the monthly precipitation data at 81 stations in Xinjiang provided by the Xinjiang Meteorological Information Center， the concurrent and individual effects of thermal anomalies over the tropical Indian Ocean （IO） and the QXP in May on summer rainfall in Xinjiang are analyzed.The results show the thermal anomalies in in May have good heating persistence with summer sensible heat （SH） and summer SSTs over the QXP and tropical IO.The singular value decomposition （SVD） analysis indicates the SH over the eastern QXP （divided by 90E） in May has a good negative correlation with summer rainfall in northern Xinjiang and southwest Tarim Basin （TB）， and the SSTs over the tropical IO have a good positive correlation with summer rainfall in western TB.When only considering the heating effects over the QXP， the strengthened （weakened） SH over eastern QXP is corresponded to less （more） summer rainfall in the northern Xinjiang and southwest parts of the TB.When only considering the heating effects over the tropical IO， the warmer （colder） SSTs are corresponded to more （less） summer rainfall over the TB.When corresponding to stronger SH in the QXP and warmer SSTs over the tropical IO in May， the northern Xinjiang （TB） receives less （more） summer rainfall.When corresponding to weaker SH in the QXP and colder SSTs over the tropical IO in May， less summer rainfall occurs over the western TB and northeast Xinjiang and the remaining regions receive more summer rainfall.When the SH is weaker （stronger） over the QXP and the SSTs are warmer （colder） over the tropical IO， the subtropical westerly jet shifts south （north） over central Asia， anomalous south （north） wind prevails over Xinjiang and more （less） water vapor is transported into Xinjiang from the IO.Above all are contributed to more （less） summer rainfall over Xinjiang.

• The Analysis of the Cloud’s Radiative Forcing Effect over Qinghai-Xizang Plateau Based on MODIS and CERES Data
• Guangcan CHEN;Hanlu LI;Yunfei FU
• 2021 Vol. 40 (1): 15-27.  DOI:10.7522/j.issn.1000-0534.2019.00107
• Abstract ( ) HTML ( ) PDF (12904KB) ( )
• Accurate estimation of cloud radiation effects on the Qinghai-Xizang Plateau is essential for analyzing the near-surface sensible heat flux.The weighted average method was used to merge the data of MODerate-resolution Imaging Spectroradiometer （MODIS）， CloudSat Profiling Radar （CPR）， and Clouds and the Earth’s Radiant Energy System （CERES）.The discrepancy between the visible and infrared channel， cloud parameter， and the radiative forcing （RF） in two cases （May 5， 2017 for cloudy， August 2， 2017 for cloudless） were analyzed base on the merged data.The results show that the atmospheric longwave RF at the top of the atmosphere （TOA） in the cloudless case is 108.3 W·m^-2， in the cloudy case is 104.5 W·m^-2.The atmospheric longwave RF at the TOA on the Tarim Basin is 200.7 W·m^-2 in the cloudless case.It indicates that longwave RF is strongly influenced by surface thermal conditions.The results also show that there exists a little discrepancy between the deep and the shallow cloud at the cloud top height.The shortwave RF of the deep cloud in ??the cloudy case is more than twice that of the shallow cloud.This ratio is much larger than that of the longwave.It indicates that shortwave RF is more sensitive to cloud thickness.Finally， not only the relationship between the longwave radiation and infrared signal but also the relationship between the shortwave radiation and visible signal were simultaneously analyzed.The results show that they both have a strong correlation （correlation coefficients exceed 0.95）， indicating the signals of the visible channels measured by MODIS can be used to estimate the shortwave radiation at the TOA， while the signals of the thermal channels can only be used to estimate the longwave radiation at the TOA at the cloudy condition.

• Large-Scale Circulation Characteristics and Influence Factors of Winter Precipitation Anomaly in the Northern Tibet
• Ji NIMA;Zongjian KE;Lijuan CHEN;Yangzong CIREN
• 2021 Vol. 40 (1): 28-36.  DOI:10.7522/j.issn.1000-0534.2020.00011
• Abstract ( ) HTML ( ) PDF (3218KB) ( )
• Precipitation and snow cover data in weather observation site in Tibet， NCEP/NCAR reanalysis data and sea surface temperature data from NOAA are used to analyze the large-scale circulation and influence factors resulting in precipitation anomaly in winter in the Northern Tibet.Results show that there is a periodic variation with 2~4 years in winter precipitation in the Northern Tibet， and 3 years period is the strongest.In more rain years， a west-negative and east-positive spatial distribution of geopotential height anomaly at 500 hPa level is shown over the mid-high latitudes of the Eurasian continent from the Ural Mountains to the Lake Baikal nearby.The path of cold air influencing China shifts west.Geopotential height at 500 hPa level over the Tibetan Plateau shows negative anomaly.The Middle East jet stream （MEJS） is stronger than normal.The southern branch of westerly flow around the Tibetan Plateau is stronger than normal， and the southern branch trough is more active.Winter precipitation in the Northern Tibet is closely related to the strength of MEJS.The correlation coefficient between them is up to 0.61.Further analysis shows that the phase of arctic oscillation （AO） has an impact on the path of cold air.Positive phase of AO is conducive to west path of cold air affecting the Tibetan Plateau.Meanwhile， The MEJS is stronger and southern than normal.In addition， warmer sea surface temperature in the central and eastern tropical Pacific is conducive to a stronger and southern MEJS.The synergetic effects of AO and ENSO phase play a key role in the precipitation anomaly in winter in the Northern Tibet.

• Vertical Gradient Changes of Temperature and Precipitation in the Sygera Mountains， Southeastern Qinghai-Xizang Plateau
• Lun LUO;Zeng DAN;Liping ZHU;Hongbo ZHANG
• 2021 Vol. 40 (1): 37-46.  DOI:10.7522/j.issn.1000-0534.2019.00123
• Abstract ( ) HTML ( ) PDF (3052KB) ( )
• Investigating the spatiotemporal patterns of temperature lapse rates and precipitation gradients can contribute to a better understanding of the physiological and ecological mechanism controlling the altitudinal zonality of plants and animals in the Sygera Mountains， and can also provide reliable parameters for future hydrological modelling in basins of the region.The regression analysis between air temperature and elevation and between precipitation and elevation is conducted based on the daily air temperature and precipitation （from April to October） observations from 11 meteorological stations in the Sygera Mountains.The results show that： （1） The multiyear average annual air temperature lapse rate of the Sygera Mountains has relatively small interannual variation （from 2013 to 2018） with the averaged lapse rates as 0.71， 0.55 and 0.60 ℃·（100m）^-1 for the western， the eastern and the both slopes， respectively.（2） As for seasonal variation， the air temperature lapse rate is relatively steep in winter and spring， and relatively shallow in summer and autumn.As a whole， the air temperature lapse rate of the Sygera Mountains is relatively shallow during the monsoon season （from June to September） under the strong influence of the Indian monsoon， and this is consistent with the findings in other parts of the Tibetan Plateau where similar impacts from the Indian monsoon can be observed.（3） The comparison between slopes shows that the temperature lapse rate of the western slope is always steeper than that of the eastern slope in the same period， which could be linked with the less precipitation of the western slope compared with the eastern slope.（4） The correlation between annual precipitation （from 2013 to 2018） and elevation on the western slope is not statistically significant， whereas the correlation is indeed significant for the eastern slope， with the multiyear average annual precipitation gradient as 10.5 mm·（100m）^-1.（5） In terms of the comparison of the precipitation gradients between the monsoon and the non-monsoon periods， the situation is very complex.On the western slope， the precipitation increases with the elevation in the non-monsoon period， but does not show obvious trend with elevation in the monsoon period.On the eastern slope no obvious trends of precipitation with elevation are found in either the monsoon or the non-monsoon periods.There is an elevation band with relatively low precipitation in the middle-elevation area of the Sygera Mountains in both the western （3035~3698 m） and the eastern slopes （3326~3390 m）.However， it should be noted that in the high-elevation areas the precipitation consistently increases with elevation for the both periods and the both slopes.

• The Mesoscale Characteristics of Extreme Rainstorm in the Eastern Region of Helan Mountain
• Yuying CHEN;Yang SU;Yin YANG;Suzhao ZHANG;Jing YANG
• 2021 Vol. 40 (1): 47-60.  DOI:10.7522/j.issn.1000-0534.2020.00012
• Abstract ( ) HTML ( ) PDF (13602KB) ( )
• Using high-resolution multi-source data such as the hourly precipitation of automatic weather stations in the past 10 years， Yinchuan CD radar， Temperature of Black Body of FY-2 satellite， radiosonde data and ECMWF reanalysis data （0.125°×0.125°）， the mesoscale characteristics of six extreme rainstorms in the Eastern Region of Helan Mountain were analyzed based on the classification of mesoscale systems.The rainstorm dominated by linear convection system is deep convection， while the rainstorm dominated by nonlinear convection system is mixed convection.The results show that： （1） The low-level southeast jet enhances and triggers meso-micro scale rainstorm systems in the eastern slope of Helan Mountain at night， leading to the extreme rainstorms are convective rainstorms with short-time heavy rainfall.The rainstorm is mainly concentrated in the eastern slope of Helan Mountain especially centralizes in the mouth of shanhong ditch with remarkable characteristics of night rain.（2） All the extreme rainstorm environment fields meet the three basic conditions of convective rainstorm.Low-level southeast jet at 700 hPa transports warm and moist flow to heavy rainfall areas， which promotes the atmospheric static instability， dynamic， thermodynamic and topography lifting trigger mechanism.There is no obvious low-level jet at 850 hPa in the rainstorm dominated by deep convection system.Vapor source is the Bay of Bengal.Limited water vapor transport condition but lower atmospheric stability is more favorable to convective rainstorm.However， the path of low-level jet at 850 hPa coincides with low-level southeast jet at 700 hPa in the rainstorm dominated by mixed convection system.Moisture transport from the Bay of Bengal， the South China Sea， the Yellow Sea and the Bohai Sea are the source of the extreme rainstorm.The more moisture transport contributes to sustained rainstorm.（3） Extreme rainstorm is mainly divided into convective precipitation in the warm zone of front， frontal convective precipitation and stratiform precipitation of frontal zone.Convective precipitation in the warm zone of front mainly occurs in the mountain areas， and its trigger mechanism is topographic uplifting.Frontal convective is triggered by warm and moisture flow lifted on the cold surface， and it could occur in plains and mountains.The movement of convective system is consistent with lower wind field.It propagates along mountain in the mountain areas but along the low-level jet in plains.Usually the movement of convective system is parallel to the direction of propagation.However， when the lower level dominated by east wind in the mountain areas， it moves approximately perpendicular to the direction of propagation with obvious train effect.（4） There is a weak cold air in linear convective rainstorm， and the types of rainstorm are mainly convective precipitation in the warm zone of front and frontal convective precipitation.Convective system propagates along the mountain and form the linear zonal echo with high degree of organization， its movement could be parallel or perpendicular to the direction of propagation.It develops strongly and maintains a long time in front of the mountain affected by topographic uplift.So the rainstorm has features such as the short duration， the small range， the great rainfall intensity and the intermittent precipitation.Cumulative rainfall of 3~4 h of rainstorm accounted for about 85% of the total amount of the process， and the area mean rainfall is much smaller than heavy rain magnitude， which reflects the feature of topographic strong convective rainstorm.（5） Cold air is active in nonlinear convective precipitation.It is dominated by frontal convective precipitation and stratiform precipitation of frontal zone.Convective system propagates along the mountain in the mountain areas and along the jet stream axis in plains， forming the nonlinear echo.It moves parallel to the direction of propagation in plains while its movement could be parallel or perpendicular to the direction of propagation in the mountain areas.Convective system moves quickly with weak intensity and low degree of organization.Rainstorm has features such as the long duration， the large range， the small rainfall intensity， the continuous precipitation and the large cumulative rainfall.The area mean rainfall is close to or equal to the heavy rain magnitude.It has the remarkable characteristic of mixed precipitation.（6） The precipitation intensity is positively correlated with CAPE amplification， echo intensity， duration of strong echo， echo tops and vertically integrated liquid， but negatively correlated with TBB.Correlations are clearer in rainstorm dominated by linear deep convection.The positive correlation between precipitation intensity R and echo intensity Z is the most significant when the echo intensity is more than 40 dBZ （R=3.67×10^-8×Z ^5.222+4.835）.

• Diagnosis of Dynamic and Thermal Mechanisms of Two Rainstorm Processes by the Warm Front Frontogenesis North of the Subtropical High
• Li REN;Ning ZHAO;Meiling ZHAO;Yanmin YANG;Yue XU
• 2021 Vol. 40 (1): 61-73.  DOI:10.7522/j.issn.1000-0534.2019.00111
• Abstract ( ) HTML ( ) PDF (5935KB) ( )
• Based on the conventional meteorological observational data， automatic observational precipitation and 1°×1° NCEP FNL reanalysis data of time resolution of 6 hours interval， two heavy rain processes occurred on 1 August 2017 and 2-3 August 2018 in Heilongjiang province by the warm front frontogenesis north of the subtropical high are diagnosed with dynamic diagnosis method and synoptic method.The major conclusions are as follow： There are typhoons during the two warm front rainstorm， which cause the position of subtropical high to the west and north.The southwest low level jet outside the subtropical high transports a large amount of warm moist air with high momentum to the north.The two rainstorm processes are closely related to the high and low air jet.In the process of "0803"， the low-altitude jet stream is stronger， and the rainstorm area is located in the ascending branch of the vertical secondary circulation formed by the coupling of low-altitude jet stream and low-altitude jet stream.Before the rainstorm， the atmosphere is characterized by convective instability.The interaction of convergence uplift and secondary circulation updraft triggers convection and releases unstable energy， resulting in heavy precipitation.During the process of "0803"， the atmosphere is shown as convective stability during the rainstorm.The condition symmetry instability of the middle layer in the frontal region is beneficial to the enhancement and maintenance of precipitation intensity.In this process， the frontal intensity is greater， and the upward movement formed by frontal convergence is broader， resulting in heavy precipitation in a larger range.The release of latent heat of condensation over the rainstorm area will cause the generalized high potential temperature region to extend downward， and the wet baroclinic property of the middle and lower layers will increase significantly.The moisture divergence flux and the moisture vertical helicity can well describe the process of heavy precipitation.The strong precipitation area corresponds to the positive region of the moisture divergence flux and the negative region of the moisture vertical helicity.

• Analysis on the Causes of Development and Evolution of the Yellow River Cyclone Rainstorm Process
• Yale ZHANG;Xiaoding YU
• 2021 Vol. 40 (1): 74-84.  DOI:10.7522/j.issn.1000-0534.2019.00103
• Abstract ( ) HTML ( ) PDF (10405KB) ( )
• On 19-21 July 2016 North China experienced an extreme rainfall event， which is characterized by wide influence range， large accumulated rainfall， long duration and locally large rainfall intensity.In terms of the rainfall amount， it is the most severe rainfall event since August 1963.The intensity and duration of rainfall in Hebei province and Beijing exceeded that of "7.21" in 2012.The characteristics of the weather system development， the path of the Yellow River cyclone are analyzed with the data of ground automatic station， satellite and NCEP data.The deep low vortexes over North China， the westerly trough associated with the low vortex， the subtropical high and the Yellow River cyclone induced by the low vortex are the direct influencing systems of the rainstorm.Because of the blocking of the subtropical high， the cyclone moved very slowly.Additionally， the path appears counterclockwise rotation twice during the movement.It is found that the surface cyclone center always moves along the warm advection in the middle and lower layers and the region with large differential vorticity advection in the lower and upper layers.Meanwhile the positive feedback generated by the latent heat release and the vercital movement， guides the cyclone moving to the place where the vertical movement is strong.The latent heat plays an important role in the growth of low level potential vorticity， which is beneficial to the generation of cyclone.At the same time， the high-altitude vortex is coupled with the low-altitude system， and has a positive feedback effect with the warm advection over the surface cyclone， which leads to the rapid development of the surface Yellow River cyclone.The dry zone in the dark region of water vapor in satellite water vapor image has the characteristics of high vortex， which is analyzed by combining it with the high level potential vortex field， which is helpful to judge the development and evolution of high-altitude dynamic characteristics in the water vapor image， and provides reference for the monitoring of extratropical cyclones.

• A Numerical Simulation Study of the Southwest Vortex Mechanism during the "6·30" Heavy Rain Event in Sichuan and Chongqing
• Chengzhi DENG;Yu ZHAO;Fanyou KONG;Danhua ZHAI;Qiang LI;Yue HE
• 2021 Vol. 40 (1): 85-97.  DOI:10.7522/j.issn.1000-0534.2019.00106
• Abstract ( ) HTML ( ) PDF (11931KB) ( )
• The Southwest Vortex weather event that brought extremely heavy rainfall in regions across Sichuan and Chongqing from 29 June to 2 July 2013 was analyzed using datasets from intensive automatic weather stations， NCEP reanalysis （1°×1°） and WRF-ARW numerical simulations.This extremely heavy rainfall episode could be classified into three stages， with the primary precipitation process occurred in the second stage that was closely associated with the Southwest Vortex development.The analyses revealed that： （1） The Southwest Vortex in this case， after emerged， exhibited enhance-weaken-enhance pattern， with vorticity intensification during morning and midnight on 30 June， respectively， peaked in the second period.（2） Low-level convergence was the primary origin of positive vorticity throughout the Southwest Vortex life cycle.Mid-level convergence and vertical transport of vorticity increased significantly during the second intensification period of the Southwest Vortex.（3） The low-level convergence was maintained by negative non-equilibrium dynamic forcing， mainly attributed to Laplace term of potential height.（4） Diabatic heating intensified ahead of Southwest Vortex’s intensification.The positive feedback between the two might be a key mechanism for the development of the Southwest Vortex.Sensitivity experiments using WRF model simulations with latent heating from microphysics and sensible and latent heat fluxes from the surface turned off produced weaker Southwest Vortex and precipitation.

• Difference Analysis on Influence of EP and CP El Niño of Precipitation in Yunnan in Winter
• Jianqin ZHOU;Hongming YAN
• 2021 Vol. 40 (1): 98-108.  DOI:10.7522/j.issn.1000-0534.2019.00124
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• There are few analyses on the effect of different types of SST changes in the equatorial Pacific Ocean of precipitation in Yunnan in winter.Based on daily precipitation observation data of 125 stations in Yunnan and NECP reanalysis data from 1981 to 2017， the authors analyze the differences influence of eastern Pacific （EP） and central Pacific （CP） El Ni?o of precipitation in Yunnan in winter by Partial correction， Composite analysis.It was found that the rainfall in most areas of Yunnan in winter will be more than annual year in EP El Ni?o year， but there was no obvious unusual of rainfall in CP El Ni?o year.With deep study on the physical causes of two types El Ni?o events affect winter precipitation differences， results demonstrate that： Firstly， in the EP El Ni?o year， the Walker circulation has an unusually strong downdraft in the western Pacific， the West Pacific Subtropical High （WPSH） is stronger， and the position is westward than normal.The Hadley circulation has an abnormal updraft at 20°N， which offer an advantage for water vapor transport and convergence enhance in Yunnan.At the same time， the ridge developing between the Balkhash Lake and Baikal in the middle and high latitudes which leader to cold air move south and invade Yunnan along the east side of the plateau.Meeting of cold and warm air in Yunnan causes heavy rain in winter.Secondly， in the CP El Ni?o year， the intensity of downdraft of the Walker circulation in the western Pacific is weaker than EP El Ni?o year.The WPSH is stronger and the position is westward than regular ones but weaker and eastward than EP El Ni?o year.The Hadley circulation has a downdraft at 20°N， which against the water vapor transport and convergence enhance in Yunnan.Meanwhile， the circulation in the middle and high latitudes result no obvious cold air move south and influence Yunnan.So， except the rainfall-days is less than normal in eastern of Yunnan， there is no obvious effect on precipitation in winter in Yunnan in CP El Ni?o year.

• Study on Energy Partitioning and its Environmental Factors of Four Types of Typical Underlying Surfaces in North China
• XueYuan REN;Qiang ZHANG;Ping YUE;Jin Hu YANG;XinYang YAN
• 2021 Vol. 40 (1): 109-122.  DOI:10.7522/j.issn.1000-0534.2020.00008
• Abstract ( ) HTML ( ) PDF (6332KB) ( )
• Surface energy balance and distribution are the result of the interaction of vegetation， climate and other factors.The study of energy， especially the distribution of turbulent flux and its influencing factors， is of vital importance to regional water resources management， and is also of great significance for guiding scientific agricultural production.North China has a vast territory， a variety of vegetation types crisscross distribution， and the land surface process is more complex.Water vapor and precipitation caused by summer monsoon activities will change the underlying surface water， thermal characteristics and solar radiation forcing characteristics， which makes the factors affecting the characteristics of surface energy distribution more complicated.The study of surface energy balance and distribution process in this region is helpful to further understand the productivity and climate change of its ecosystem.Therefore， this paper analyzed the observation data of "Cooperative observation experiment in North China"， and finally selects four vegetation types in north China， meadow， desert grassland， corn farmland and semi-arid grassland， which represents the vegetation types in the north of China to a certain extent.Based on a deep understanding of the characteristics of surface energy distribution， the effects of environmental factors on energy distribution are discussed.The results show each component of surface energy on a typical underlying surface presents a unimodal change trend， with obvious diurnal characteristics.Surface energy is uneven on each underlying surface.The energy closure of the above four typical underlying surfaces is 71%-91%， of which the semi-arid grassland is the largest and the corn farmland is the smallest.From the ratio of each energy component to net radiation， the net radiation of desert grassland and semi-arid grassland heats the atmosphere mainly in the form of sensible heat， and the percentage of sensible heat flux to net radiation is 29% and 36%， respectively.Alpine meadow and corn farmland latent heat flux is dominant， accounting for 42% and 37% of the net radiation， respectively.Among the meteorological factors affecting the Bowen ratio which is the water and heat comprehensive parameters of each underlying surface， the semi-arid grassland is affected by the ground-air temperature difference （R^{\mathrm{2}}=\mathrm{0.64}） and vapor pressure deficit （R^{\mathrm{2}}=\mathrm{0.56}）， while the corn farmland is mainly affected by the ground and air temperature difference （R^{\mathrm{2}}=\mathrm{0.52}）.The Bowen ratio of the desert grassland is influenced by the ground-air temperature difference （R^{\mathrm{2}}=\mathrm{0.37}） and average wind speed （R^{\mathrm{2}}=\mathrm{0.23}）.In addition， there is a significant exponential relationship between Bowen ratio and NDVI， and decreases with the increase of NDVI.

• Seasonal Variation Characteristics of Extreme Temperature Index and Its Influence on Circulation in Hedong Area of Gansu Province in the Past 30 Years
• Hao HUANG;Bo ZHANG;Shangqian MA;Tao HUANG;Bin MA;Yanqiang CUI;Xiaodan WANG
• 2021 Vol. 40 (1): 133-144.  DOI:10.7522/j.issn.1000-0534.2019.00118
• Abstract ( ) HTML ( ) PDF (5632KB) ( )
• Based on the daily temperature data of 61 meteorological stations from 1988 to 2017， the spatial and temporal variation characteristics of the seasonal extreme temperature index in Hedong region of Gansu province in the past 30 years were analyzed， and the influence of ENSO and AO on the extreme temperature index in Hedong region was analyzed.The results showed that in the past 30 years， the daily temperature range （DTR）， the number of warm night days （TN90p） and the number of warm day days （TX90p） in each season increased， while the number of cold night days （TN10p） and the number of cold day days （TX10p） decreased.The change of extreme temperature index in Gannan Plateau is the most significant among different regions， and Spring is the season with the most significant change of each extreme index， which is also an important factor that makes the variation trend of DTR in Hedong region different from that in the whole country.The DTR increased after the abrupt change in 1992， the average temperature changed in 1996 -1997， and the rest of the extreme temperature index changed in 1997.The changes of the extreme temperature index before and after the abrupt change in itself and the mean temperature year reflected the trend of regional warming.El Ni?o affects the increase of DTR in winter， La Nina affects the increase of TX10p days in winter in Hedong region， and high temperature events are more likely to occur in summer in Hedong region when AO is in positive phase.

• Mechanism Analysis of a Squall Line Upscale Growing Process in South China
• Lin WANG;Xinyong SHEN;Yong WANG;Chi ZHANG;Yongqing WANG;Xiaofan LI
• 2021 Vol. 40 (1): 145-158.  DOI:10.7522/j.issn.1000-0534.2019.00127
• Abstract ( ) HTML ( ) PDF (9606KB) ( )
• In this paper， in order to better investigate the process of squall line， the national automatic weather stations and CMORPH product at 0.1°×0.1° resolution、NCEP（National Centers for Environmental Precipitation） 1°×1° reanalysis meteorological data、regular observation data and high-resolution WRF numerical simulation data are used to analyze the dynamic and thermal environmental conditions of the upscaling growth process of a squall line in south China around April 13， 2016.Before the formation of the squall line， there is a upper-level jet stream in the upper troposphere.South China is located on the right side of the entrance of the upper-level jet stream.There is a weak height trough in the upper level， and the temperature trough lags behind the height trough， which is beneficial to the development of the height trough.There is a low-pressure system on the surface and There is convergence of airflow in the low level of south China， which enhances the lifting movement.The simulation results show that The WRF model successfully simulates the upscale process of squall line， and the precipitation and the falling area of the squall line are relatively close.At the same time， compared with the previous squall lines， the convective available potential energy during the upscaling phase is higher than the initial convection phase， but the convective available potential energy in the entire south China region is at a low and middle level.In addition to the influence of synoptic scale system， the cooperation of various mesoscale conditions is beneficial to the upscaling development of squall line.The triggering conditions are vertical wind shear， low potential vorticity （PV） and high temperature declining rate in the lower level， which provide certain unstable conditions and lifting conditions.Low-level wind field turning and wind velocity strengthening， changes in the direction of vertical wind shear， sufficient water vapor supply and deepening of the rear inflow enhance instability and vertical lifting motion， which are important conditions for promoting the upscale growing of meso-β-scale squall line.The cold pool is not obvious during the upscale growing， but the cold pool is important for maintaining the meso-α-scale squall line structure in the mature stage.

• Characteristics of Atmospheric Water Vapor Distribution and Transport during Summer over Shandong Province
• Na WANG;Weizong GU;Can QIU;Xiangxin MENG;fang ZHOU
• 2021 Vol. 40 (1): 159-168.  DOI:10.7522/j.issn.1000-0534.2019.00119
• Abstract ( ) HTML ( ) PDF (7561KB) ( )
• Based on monthly rain-gauge precipitation data and JRA-55， NCEP/NCAR reanalysis data， the climatology distributional and variational characteristics of whole atmospheric column precipitable water， precipitation conversion efficiency， water vapor flux and transport during summertime from 1962 to 2016 in Shandong Province were investigated； The correlativity between summer precipitation and both moisture fluxes and divergences， as well as the water vapor sources in above normal rainfall years， were discussed.Results indicate that： As for the climatology， averaged precipitation， precipitable water， and precipitation conversion efficiency are 401.2 mm， 3478.8 mm and 11.5%， respectively.The spatial-temporal evolutions exhibit more consistent for precipitation and precipitation conversion efficiency compared with that of summer rainfall and whole atmospheric column precipitable water， which are even opposite in some specific years or periods.The surface effective precipitation tends to be more influenced by meridional water vapor transport and regional moisture flux divergences.When the atmospheric precipitable water and water vapor transport are abundant， the regional moisture convergence is more favorable for the occurrence and development of precipitation in the southern part of Shandong， thus make the special climatology of both rainfall and precipitation conversion efficiency distribute as more rainfall in the southeast Shandong than that in the northwestern part.By comparison， the main source of water vapor in rainy years is transported from the Northwest Pacific by the easterly and southerly of the western North Pacific subtropical high， lead to strong convergence in the southeastern Shandong； While in the heavy rainy years， water vapor in the tropical Pacific and the Indian Ocean also transported by both tropical and middle-high latitude general circulation systems， the Philippine Anticyclone， cross-equatorial flow and westerly of an anticlockwise moisture flux center located in Outer Mongolia for instance， thus give rise to intensive convergence in the west and south part of Shandong.The Northwest Pacific， South China Sea， Bay of Bengal， and Okhotsk to Japan Sea are significant water vapor sources which could bring about more summer rainfall in Shandong.Besides， the essential cold-air activity area extends from Balkhash Lake to Baikal.When the upstream region of Shandong prevails westerly wind， an anomalous water vapor disturbance appeared and developed in a belt area from Xinjiang and the Qinghai-Xizang Plateau to Inner Mongolia is the main factor for precipitation anomaly arising from anomalous moisture transported by mean circulation.

• Analysis of Prediction Method for Rainfall and Superposition Rainfall
• Tao SHU;Tangjin YE;Junjie LI;Hao LI
• 2021 Vol. 40 (1): 169-177.  DOI:10.7522/j.issn.1000-0534.2020.00014
• Abstract ( ) HTML ( ) PDF (2078KB) ( )
• In order to obtain High-precision rainfall predictive value and Superposition Prediction， Wavelet Neural Network and NARX Dynamic Neural Network methods are used to provide prediction of rainfall trends， rainfall amounts， and also to analyze the error of the superposed predictive value of rainfall.The results shows that the Wavelet Neural Network provide accurately in analyzing the monthly rainfall multiple variation periods and the overall variation trend； as the error test value of NARX Dynamic Neural Network prediction model is 0.21%， the correlation coefficient R of regression renderings is 0.99993， and feedback and test error value are only 0.22% and 0.40% respectively； the errors of superposed prediction and test of rainfall are small， less than 2%， which can meet the requirement of continuous superposed prediction of rainfall.This method will provide high-precision predictive value of rainfall for the prediction of slope dynamic stability.

• The Verification of Gridded Surface Meteorological Elements Merging Product in China
• Jing SUN;Guangguang CHENG;Xiaoyu HUANG
• 2021 Vol. 40 (1): 178-188.  DOI:10.7522/j.issn.1000-0534.2019.00100
• Abstract ( ) HTML ( ) PDF (6654KB) ( )
• Independent and non-independent validations have been done to evaluate the merged 5 km resolution gridded products in China in 2018， including 2 m temperature， 10 m wind and 24 h accumulated precipitation.The non-independent validation shows that： （1） compared with the in situ station data， the 2 m temperature product has a warm bias： the monthly-averaged Root-Mean-Square-Error（RMSE） is around 1 ℃， and for the hottest（≥35 ℃） and the coldest（≤-20 ℃） days， the RMSE is above 1 ℃ and 2 ℃ respectively.（2） The 10 m wind product can precisely re-produce the wind within grade 0~2， but it will underestimate the wind speed within grade 3 and after， especially over grade 6.（3） the precipitation product will over-estimate the rainfall area when the rainfall is between 0 to 0.1 mm； and the RMSE and Mean-Error （ME） will increase along with the precipitation increasing， which is due to the under-estimation of the precipitation compared with the observation.Generally， the precipitation product merged from three sources （radar， satellite， and gauge） is better than that from two sources （satellite and gauge）.The independent validation shows that the monthly RMSE and ME of the 2 m temperature， 10 m wind and 24 h accumulated precipitation data are very similar to the non-independent validation.And the independent validation can point out the bias， which are discussed in the non-independent validation， more clearly.This is mainly because the in situ station data used in the independent evaluation are not merged in the product.To summary， the merged gridded products have small biases in ordinary days， and larger bias in severe weather like very hot and cold days， windy or rainy days.

• Distribution Characteristics of Winter Haze Days in Sichuan Basin And Their Relationships With Meteorological Conditions and SST
• Yu LUO;Zhenfeng MA;Xiaolan LI;Luyang XU;Bing DU
• 2021 Vol. 40 (1): 189-199.  DOI:10.7522/j.issn.1000-0534.2019.00117
• Abstract ( ) HTML ( ) PDF (7852KB) ( )
• Based on the data of meteorological stations and NCEP/NCAR reanalysis and the spatial and temporal variations of haze days in winter in Sichuan Basin， the characteristics of the meteorological conditions and the SST anomaly were analyzed， which influenced haze days in winter in Sichuan Baisn.Based on the SST critical areas， a prediction model of winter haze days was established and validated.The results showed that the number of winter haze days increased weakly， three urban agglomeration were haze-prone areas， the relationship between the number of haze days in winter and relative humidity， temperature and precipitation days in Sichuan Basin was significant.The more （less） winter haze days in Sichuan Basin corresponded to the circulation characteristics of weaker （stronger） Siberian high， lower （higher） in the North and higher （lower） in the South of the Eurasian mid-high latitude， weaker （stronger） East Asian winter monsoon， weaker （stronger） East Asian subtropical jet.More （less） winter haze days were associated with warming （cooling） SST development in the key areas of Northeast Pacific， Tropical Pacific and North Atlantic.The previous autumn SST anomaly in the key areas of Northeast Pacific， Tropical Pacific and North Atlantic was interannual prediction signal， which significantly influenced winter haze days in Sichuan Basin.

• Air Quality and Health Risk Assessment of Capital Cities in Five Northwest Provinces of China in the Spring of 2018
• Danrui SHENG;Xiaohu WEN;Qi FENG;Jun WU;Jianhua SI;Min WU;Chuanqi ZHANG
• 2021 Vol. 40 (1): 200-208.  DOI:10.7522/j.issn.1000-0534.2019.00113
• Abstract ( ) HTML ( ) PDF (2179KB) ( )
• Urban air pollution and its impact on human health always receive high attention.This study analyzed the concentrations of PM_2.5， PM₁₀， NO₂， SO₂， CO and O₃ in the capital cities of five Northwest provinces in the spring of 2018 and evaluated the health risks posed by PM_2.5， PM₁₀， SO₂ and NO₂ using the health risk assessment model recommended by the US Environmental Protection Agency （USEPA）.The results show that PM_2.5 and PM₁₀ are main pollutants exceeding standards.Except Urumqi （The average PM₁₀ concentration in spring in Urumqi also exceeded standards）， the average concentration of PM_2.5 and PM₁₀ exceeded the national standard Grade Ⅱ in spring in the other four cities.The concentrations of SO₂， NO₂， O₃ and CO in the five cities were relatively low.The air pollution of all cities was mainly good to light pollution in the spring of 2018.The health risks of PM_2.5 and PM₁₀ in spring in the five cities were at acceptable risk level set by USEPA.The health risks of SO₂ and NO₂ did not exceed the acceptable risk values recommended by Sweden， Netherlands and other countries.SO₂ and NO₂ posed the smallest risks to the elderly （>60 years old） and the greatest health risks to children （<6 years old）.Children were more sensitive receptors.The spring health risks of SO₂/NO₂ for children （<6 years old） were about 1.2/1.3 times those for adults （18~60 years old）， 1.7/1.8 times those for people over 60 years old.The health risks of SO₂ and NO₂ for men and women of different ages were different.Women aged 6~17 or over 60 were at greater risks than even-aged men， while the risks of men under 6 years old or aged 18~60 were higher.

• A Preliminary Study on the Relationship between Atmospheric Electric Field and Atmospheric Pollutants in Beijing
• Jingxiao LI;Xuemeng CHEN;Yuexing CHENG;Rujian LI;Fan DONG
• 2021 Vol. 40 (1): 209-218.  DOI:10.7522/j.issn.1000-0534.2020.00006
• Abstract ( ) HTML ( ) PDF (5790KB) ( )
• Atmospheric electric field and air pollutant concentrations measured at Beijing Chaoyang Site in the years of 2014 and 2015 were characterized for the overall diurnal variations and features in the winter and summer half-years.The relationship between the electric field intensity and the concentration of the main pollutant factors and the meteorological factors in three types of pollution weather， including static and stable accumulation type， pollution compound type and dust type， were mainly studied.The results showed that： （1） The hourly averaged electric field varied between 0.45 and 0.72 kV·m^-1 on a diurnal basis， with peak values occurring at 03:00 （Beijing Time， the same as after） and 23:00， and troughs at 06:00 and 13:00.The correlation between electric field intensity and pollutant concentration was stronger in winter half year， especially with PM₁₀， PM_2.5， PM_1.0 and NO₂.（2） In the accumulation of locally emitted air pollutants， the electric field increased quickly with the rapid increase in pollutant concentrations.They exhibited similar variations.The electric field changed its sign to negative under high relative humidity.（3） The electric field or air pollutant concentrations showed no remarkable variations， nor did they follow each other in the condition of mixed-source pollution.On heavily polluted days when relative humidity was high， the correlation between electric field intensity and pollutant concentration was not strong.However， the correlation between electric field intensity and relative humidity was strong.（4） The electric field showed negative values during sand-dust events.This type of pollution was characterized by a rapid accumulation of air pollutants， which made the eclectic field to peak with a large absolute value followed by a quick drop in magnitude.The absolute value of the electric field was observed to decrease in the order of dust storm， blowing dust， and floating dust events.

• Statistics on the Characteristics of Metal Na Layer in MLT Region under the Condition of Thunderstorm Activities
• Xiangzhen KONG;Zhenfeng QIU;Yang ZHAO;Xinyi TAO;Wang JIN
• 2021 Vol. 40 (1): 219-228.  DOI:10.7522/j.issn.1000-0534.2020.00002
• Abstract ( ) HTML ( ) PDF (5291KB) ( )
• The thunderstorm activities in tropospheric and metal Na layer in Mesosphere and Lower thermosphere （MLT） area were analyzed using superposed epoch analysis （SEA）， combined with the lightning location data of WWLLN and Na density data of the radar metal of Haikou station.The response and variation characteristics of Na atoms density were analyzed under the trigger of lightning activities.The results are showed as following.（1） The density of Na atoms of the thunderstorm day in MLT region within 90~95 km above the ground was smaller than that of non-thunderstorm one.（2） Before and after the trigger time， the Na atoms density presented different activities.Using the SEA under the trigger of total lightning activities during the thunderstorm processes， density of Na atoms was decreasing obviously within 24 h after the trigger time， while it had only a bit augment before trigger.It had relation with the distance and position of lightning activities away from the station.（3） Under the control trigger of northeast lightning activities， density of Na atoms presented significantly enhancement.The density enhancement of Na atom occurred about -12~0 h before the trigger time， and it ranged from 85 km to 93 km above ground.The maximum of variation ratio of enhancement was at 87 km， and the peak of Na atoms density was at 91 km.Above the 96 km， there had no obvious augment in density.（4） The column density and median density of Na atoms presented obviously difference during the epoch -12~0 h with the epoch 0~24 h and epoch -24~-12 h.The Maximum of variation ratio was 36.1%.The results show that the factor of thunderstorm electric field or lightning activities should be considered for the change of Na atoms density in MLT region of low latitude.