Plateau Meteorology

Current Issue

28 February 2018, Volume 37 Issue 1   
  • Impact of Assimilating the New Radiosonde Data on Qinghai-Tibetan Plateau on Summer Rainfall Forecast over Southern Xinjiang
  • YU Xiaojing;DU Juan;WANG Minzhong;XU Hongxiong;HE Qing
  • 2018 Vol. 37 (1): 13-27.  DOI:10.7522/j.issn.1000-0534.2017.00034
  • Abstract ( ) HTML PDF (49729KB) ( )
  • Using the radiosonde data of the three newly-built stations (Shiquanhe, Shenzha and Gaize) on the Qinghai-Tibetan Plateau (QTP) in the third Tibetan Plateau Experiment of Atmospheric Sciences (TIPEX), employing the Weather Research and Forecasting (WRF) model and the Gridpoint Statistical Interpolation (GSI) system, two summer rainfall processes occurred in Southern Xinjiang in 2015, in the background of double-body (Process Ⅰ) and one-body (Process Ⅱ) of the South Asia High (SAH), respectively, were selected to conduct the data assimilation sensitive experiments, in order to assess the impacts of assimilating the new radiosonde data on the QTP upon summer rainfall forecasts over Southern Xinjiang preliminary.In the terms of the analysis increments, the initial fields of the two processes were improved after assimilating the new radiosonde data, and the Process Ⅱ was more significant, which might be related to stronger southerly airflow and the effect of upper and lower courses.The centers of increment on the high and middle levels occurred in the middle and west of the QTP, corresponding to the Shenzha and Shiquanhe, respectively.Then the increments decreased to the surrounding regions, and showed weak positive or negative increments over the Southern Xinjiang.Although the new radiosonde data on the QTP are above 600 hPa, the meteorological fields in the low levels were also affected through dynamic readjustment.The increment centers of the divergence and humidity presented in the southwest of the QTP, while it changed little over the Southern Xinjiang.The adjustments of the meteorological fields and main effect systems became remarkable gradually with the model integrating.As a result, the subtropical long wave trough got deepened, the south jet over the Southern Xinjiang strengthened, the low pressure systems on the 500 hPa weakened, and the divergence and humidity changed obviously over the Southen Xinjiang.However, over the precipitation centers in the west of the Southen Xinjiang, the divergence and humidity varied little relatively.The precipitation forecasts showed that the Threat Score of the small thresholds increased remarkably, which meant the forecast capacity of the rainfall area were improved to some extent.Moreover, the result of heavy rainfall were affected little, which also agreed with the variation of the meteorological fields.
  • Characteristics of Surface Sensible Heat Flux over the Qinghai-Tibetan Plateau and Its Response to Climate Change
  • XIE Jin;YU Ye;LIU Chuan;GE Jun
  • 2018 Vol. 37 (1): 28-42.  DOI:10.7522/j.issn.1000-0534.2017.00019
  • Abstract ( ) HTML PDF (22873KB) ( )
  • Using the conventional meteorological observation data of the Qinghai-Tibetan Plateau (QTP) offered by the China Meteorological Administration (CMA), the average daily sensible heat flux from 1981 to 2014 was calculated on the basis of 85 stations which have continuously better data and the CHEN-WENG heat exchange parameterized scheme.The characteristics of seasonal average and annual average sensible heat flux and the connections between them and climate factors which include surface temperature, air temperature at 1.5 m, wind speed, precipitation and sunshine duration were analyzed by using the methods of Mann-Kendall test, empirical orthogonal function (EOF), and Pearson correlation.The results showed that both seasonal average and annual average sensible heat flux had risen after falling for more than 20 years since 1981 and the time of change happened earlier in winter and spring than in summer and autumn.The decline of sensible heat flux between 1981 and 2003 was mainly caused by the decrease of land-air temperature difference and the average wind speed, while the raise between 2004 and 2014 was mostly due to the significantly increase of land-air temperature difference, and not all stations had the same pace in decrease or increase.The stations which increased mostly locate in Qinghai province.In addition, the correlations between the sensible heat flux and climate factors are obviously temporal and spatial different.Almost the whole stations are significantly influenced by the surface temperature with positive correlation with sensible heat flux, while other climate factors are probably tend to have a better correlation with sensible heat flux in the growing season than in the whole year, especially in summer when the sensible heat flux mostly has a negative correlation with the precipitation and a positive correlation with wind speed, air temperature at 1.5 m and sunshine duration.
  • Spatial-temporal Changes of the Near-surface Soil Freeze-thaw Status over the Qinghai-Tibetan Plateau
  • YANG Shuhua;WU Tonghua;LI Ren;ZHU Xiaofan;WANG Weihua;YU Wenjun;QIN Yanhui;HAO Junming
  • 2018 Vol. 37 (1): 43-53.  DOI:10.7522/j.issn.1000-0534.2017.00043
  • Abstract ( ) HTML PDF (3338KB) ( )
  • Based on the surface soil daily minimum temperature and air temperature datas from 87 meteorological stations over the Qinghai-Tibetan Plateau (QTP), the trends of the near-surface freeze-thaw status and its correlation with air temperature, altitude and latitude was analyzed by using the linear regression method and correlation method.Using Mann-Kendall method to test the abrupt change and discuss the spatial variation characteristics of the near-surface soil freeze-thaw status over QTP.The results show that the near-surface soil freeze-thaw status changed significantly on QTP in recent 36 years.The first date of the near-surface freeze was delayed by about 26 days, or at a rate of 0.72 d·a-1, and the late date of the near-surface freeze was advanced by about 14 days, or at a rate of 0.40 d·a-1.The number of duration days and freeze days of the near-surface freeze decreased about 41 and 33 days respectively, and the rate of change was 1.13 d·a-1 and 0.93 d·a-1, respectively.The trend of the near-surface soil freeze-thaw status was same overall QTP, while in some areas was slight differences.The central and eastern region of QTP, the first date of the near-surface freeze was earlier and the last date was later than other regions.However, there was a contrary variation in the southeast region.It may be the lower elevation of the stations and it had the higher air temperature all years.For the change rate of the near-surface soil freeze-thaw status, the eastern part of QTP changed the fastest, the western was moderate and the stations that changed slower scattered in central and southern regions.The temperature had a significant effect on the near-surface soil freeze-thaw status, but air temperature had a certain lag effect on soil freeze-thaw cycle.And the near-surface soil freeze-thaw status was great significantly correlated with altitude.With decreasing elevation, the first days of the near-surface soil freeze was delayed and the late days was advanced, and the numbers of duration days and freeze days of the near-surface soil freeze were significantly decreased.
  • The Case Study in Causes and Environmental Fields Analysis of Departure Plateau Vortex Accompanying with Induced Southwest Vortex
  • GAO Wenliang;YU Shuhua
  • 2018 Vol. 37 (1): 54-67.  DOI:10.7522/j.issn.1000-0534.2017.00020
  • Abstract ( ) HTML PDF (49139KB) ( )
  • By using NCEP/NCAR FNL reanalysis data, historical weather graphs and Qinghai-Tibetan Plateau and shear line year books, the observational facts of sustained departure Qinghai-Tibetan Plateau Vortex (SDPV) accompanying with influenced Southwest Vortex (SWV) during year 1998 to 2013 were analyzed, and a long time lasting case study of SDPV with induced SWV was analyzed by using synoptic and diagnostic methods.The results show that the SDPV and SWV moving in same direction is mainly caused by the SWV, which is induced and controlled by SDPV, and their main moving direction is east or north-east in the joint active processes of them.The SWV induced by SDPV generated under the south-west air flow in the southeastern portion of the SDPV circulation on 500 hPa, with weaker air flow along longitude side.The SWV accompanying with the SDPV will be stronger while the SDPV is stronger and be influenced largely by the SDPV.When SDPV is moving out of the Plateau, the positive vorticity air flow is downward to lower level and to be superposition with the low troposphere positive vorticity region which is going with cyclonic bend, and this will strengthen the cyclonic vorticity and thus generates the SWV.The force rising effect of the positive vorticity advection along with the altitude over the southwest vortex area is another important factor of the SWV induced by the SDPV.The accompanying between SDPV and SWV is closely related to the plateau vortex area, the positive vorticity advection of the southwest vortex area and the plateau vortex area, and the positive vorticity advection along the basin vortex area.
  • The Connection Between the Precipitation and Water Vapor Transport over Qinghai-Tibetan Plateau in Summer Based on the Multiple Datasets
  • XIE Xinru;YOU Qinglong;BAO Yuntao;MENG Xianhong
  • 2018 Vol. 37 (1): 78-92.  DOI:10.7522/j.issn.1000-0534.2017.00030
  • Abstract ( ) HTML PDF (22814KB) ( )
  • In this study, the monthly precipitation data set at 113 stations during 1979-2014 over the Qinghai-Tibetan Plateau (QTP) provided by the National Meteorological Information Center, had been compared with 4 gridded precipitation data sets (APHRO, CMAP, GPCP, GPCC) and 8 reanalysis data sets (NCEP1, NCEP2, MERRA, ERA_Interim, ERA20c, 20CRv2, JRA55, CFSR).Compared with the observation, it was found that the AHPRO and GPCP can capture the spatial and temporal patterns of the summer precipitation over the QTP during 1979-2007 and 1979-2014, respectively.For the climatology of water vapor, the southern boundary is the main moisture source over the QTP in summer with the dominant channel in the lower layer.Meanwhile, both the western and northern boundaries are also the moisture input over the QTP, with the main channels in the middle layer and the lower layer, respectively.Furthermore, the water vapor output over the QTP is through the eastern boundary by means of its middle layer.Generally, QTP is a moisture sink in summer, and the moisture is convergent over it, to which moisture advection term makes the greatest contribution, while wind divergence term has a diverse effect.In addition, ERA_Interim and NCEP1 showed better ability to delineate these characteristic, however, MERRA was the worst.By comparing multiple datasets, it was shown that MERRA and ERA_Interim can better depict the water vapor transport condition over the local QTP and peripheral area, respectively.Exploring relationship between the precipitation variability over the southeastern QTP and the atmospheric circulation, we picked out the high and low value years according to precipitation index.By conducting the synthesis analysis on them, it was shown that the moisture from the western boundary was the most sensitive to climate change and the decrease of net income in dry years was greater than the increase of net income in wet years, and ERA_Interim and MERRA can represent the water vapor transport condition at different boundary and levels in dry years and wet years better, respectively.Conducting the synthesis analysis on the integrated water vapor transport, it was revealed that there is a zonally orientated anticyclone anomaly across the Indian subcontinent and the Bay of Bengal, and the strong westwards water vapor transport at its northern edge attributes to the excessive precipitation over the southeastern QTP.
  • Research of the Vertical Structure of Summer Convective Precipiation Cloud over the Qinghai-Tibetan Plateau by C-FMCW Radar
  • RUAN Yue;RUAN Zheng;WEI Ming;GE Runsheng;LI Feng;JIN Long
  • 2018 Vol. 37 (1): 93-105.  DOI:10.7522/j.issn.1000-0534.2017.00025
  • Abstract ( ) HTML PDF (14168KB) ( )
  • During the Third Qinghai-Tibetan Plateau Atmospheric Scientific Experiment Ⅲ, the precipitation clouds in Nagqu, Tibet was continuously detected with C-FMCW radar from July to August 2014.The dataset gained was then analyzed, as a consequences of which, 37 convective clouds is obtained; further, 13 characteristic parameters were extracted, including Convective Index (difference of updafts and downdrafts, CI), the maximum cloud top(Hctop), the maximum height of 35 dBZ (Hz35), the maximum reflectivity (Zmax), etc.The cluster analysis method was applied for categorization of all these characteristic parameter in terms of deep and shallow convective cloud.From which, it is found that the parameters of Hctop and Hz35 are most favorable for the classification, with a similarity of more than 0.8 to that of CI.In addition, the parameters of CI, Hz35 and Hctop, which are in possession of relatively excellent consistency, were employed for a cluster analysis, then the 37 clouds were identified as 9 deep convective precipitation clouds and 28 shallow convective precipitation clouds.For the deep convective clouds, the maximum of CI is up to 33 m·s-1, as well as maximum Hctop of 12.5 km and Hz35 of higher than 5 km(above ground level, hereinafter the same).While, for the shallow convective precipitation clouds, the average of CI and Hctop are 14 m·s-1and 2.5 km, respectively.In the deep convective clouds, a steady layer similar to the Bright Band often appeared at the height of about 0.8~1.5km, which is however not applicable to the shallow convective clouds.Based on the C-FMCW radar, it is believed that the horizontal distribution of the deep convective clouds was mainly manifested as organizing multi-monomer into convective precipitation system, and shallow convective clouds showed a distribution like individual scattering popcorn.The 9 deep convection clouds resulted in a accumulated ground rainfall of 82.7 mm, accounting for 28% of the whole rainfall of the very two months, and sometimes it was accompanied by hail.On the contrast, all 28 shallow convective clouds only generated an accumulation of ground rainfall of 28.7 mm, which is far less than that of the deep convection rainfall contribution.
  • The Variation of Effective Radiation in Qinghai-Tibetan Plateau Based on the CERES Satellite Data
  • YU Han;ZHANG Jie;BAI Hanbing
  • 2018 Vol. 37 (1): 106-122.  DOI:10.7522/j.issn.1000-0534.2017.00045
  • Abstract ( ) HTML PDF (18534KB) ( )
  • As an important component of surface radiation balance, effective radiation plays an important role in radiation balance, energy balance and atmospheric circulation. Based on the effective radiation and other relevant parameters of Aqua/CERES satellite products from 2000 to 2015, the spatial and temporal distribution of effective radiation and its factors of the Qinghai-Tibetan Plateau (QTP) were analyzed under two different conditions, which is all-sky and clear-sky. The following conclusions were obtained:The effective radiation of the western region of QTP is larger than the southeast. Because of the regional differences of effective radiation, QTP was divided into four climatic regions by using the EOF method, which is the west edge (region Ⅰ), the midwest hinterlandn (region Ⅱ), the northeast (region Ⅲ) and the southeast (region Ⅳ), The trend of effective radiation is consistent with the upward long-wave radiation with increased (reduced), but the effect of the change of the atmospheric counter radiation on the effective radiation showed different trends in different seasons and regions. The cloud reduces the effective radiation by increasing the atmospheric counter radiation. Over the past decade, the impact of cloud on the surface of the effective radiation was weakened. There is a positive correlation between the upward long-wave radiation and the surface temperature. Atmospheric counter radiation has a positive correlation with the atmospheric temperature and the relative humidity at 500 hPa. It is mainly cold advection and less relative humidity in the midwest hinterland of QTP (region Ⅱ), but in other three regions, it is mainly warm advection and high relative humidity. These factors like cold (warm) advection or relative humidity affect effective radiation by impacting on the atmospheric counter radiation. The results can provide a reference for understanding the diabatic heating characteristics and the influence mechanism of QTP.
  • Applicability Evaluation of Merged Soil Moisture in GLDAS and CLDAS Products over Qinghai-Tibetan Plateau
  • CUI Yuanyuan;QIN Jun;JING Wenqi;TAN Guirong
  • 2018 Vol. 37 (1): 123-136.  DOI:10.7522/j.issn.1000-0534.2017.00035
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  • The temporal and spatial variations in soil moisture play an important role in the water and energy cycle on the Qinghai-Tibetan Plateau (QTP). In-situ soil moisture observation at 0~10 cm layer from the automatic soil moisture monitoring stations around the QTP and the 3rd QTP Atmospheric Scientific Experiment (TIPEX Ⅲ) were firstly put into use to test and verify two land surface model products, i. e. GLDAS-NOAH(Global Land Data Assimilation System) and CLDAS-V1.0(CMA Land Data Assimilation System Version1.0) by calculating the correlation coefficient and bias between model product and in-situ soil moisture observation. The two merged products were better in the four sites of Ando, Nagqu, Nierong and Sta-ave (Kobayashi alpine meadow), while in Bangor (Grassy alpine grassland), Jiali (Subalpine evergreen leaves Shrub) and Biru (Subalpine evergreen leaf shrubs), the quality of the merged data performed less well, and the Ali station (Dwarf shrub desert) was the site with the largest deviation between the merged data and the in-situ soil moisture data. There was a significant diurnal variation of the quality of soil moisture products and the worst performance of model products shows during 14:00 to 20:00 (Beijing Time). And their performances on simulating the temporal distribution in 2014 were all superior to that in 2013. From June to August, the two models had a good consistency with the in-situ soil moisture data. The quality in 2014 of the two merged products had an advantage over the quality of 2013, and the quality of the two merged products had the lowest score in the middle and the late of August and mid-October in 2013. By further analysis, it is found that when the precipitation intensity increased sharply, the quality of the two merged data became worse. For the two merged products, the quality in the QTP decreased from southeast region to northwest region. Compared with GLDAS, the quality of CLDAS was raised more remarkable improvement in southeastern Sichuan province and Xinjiang region. In addition, the two merged products were in good agreement in northeast Sichuan province.
  • The Relationship between Kunming Quasi-stationary Front and Yunnan-Guizhou Plateau Terrain
  • DUAN Xu;DUAN Wei;XING Dong;ZHANG Yanan
  • 2018 Vol. 37 (1): 137-147.  DOI:10.7522/j.issn.1000-0534.2017.00032
  • Abstract ( ) HTML PDF (3381KB) ( )
  • Using ground meteorological observation data from 1961 to 2010, ERA-Interim reanalysis data from January 10 to February 15, 2008 and December 10 to 20, 2013 and terrain elevation data of digital elevation model(DEM), the relationships of Yunnan-Guizhou Plateau topography, position of Kunming quasi-stationary front(KQSF) and meteorological elements near the front were analyzed. The main results are as follows:(1) The Yunnan-Guizhou Plateau is divided into the eastern and the western in Wumeng Mountains (103°E). The KQSF present frequency is 61.5% in the eastern area of Yunnan-Guizhou Plateau, the frequency of the western region is 38.5%. Most of the activity of cold air is blocked in the eastern area of Yunnan-Guizhou Plateau. Only a small part of the strong cold air activity can across Wumeng Mountains, and get into the western area of Yunnan-Guizhou Plateau. The effect of plateau topography on cold air activity is significant. (2) There is a good correlation between the advance (retreat) of KQSF and the temperature and pressure field before (after) the frontline. The stronger the cold air mass after KQSF, the weaker the warm air mass before KQSF, the KQSF position is more westerly. On the contrary, the KQSF position is more easterly. The significant correlation is mainly reflected in the western area of Yunnan-Guizhou Plateau. The effect of terrain reduced the correlation in the western area of Yunnan-Guizhou Plateau. (3) Blocking effect of plateau topography makes cold air activities moving slowly, or even stagnation and leads to the formation of quasi stationary front. Uplift effect of plateau topography results in the formation of clockwise secondary circulation in local low layer, leading to the emergence of the inversion layer. Once the lifting effect is weakened when the cold air passes over the plateau, the inversion layer will disappear. (4) The zero line of zonal wind can describe the front position and the cold air mass thickness, which illustrates that the distribution of KQFS is quasi-North-South. And characteristics of cold air path is from east to west. (5)The potential height after front can indicate the thickness of the air mass. In the eastern part of the Yunnan-Guizhou Plateau, the frontline position depends on the thickness of the cold air mass. In the eastern part, the frontline position depends on contrasted dynamics between the cold and warm air mass.
  • The Northwest Arid Areas in Summer Sunny Day, Cloudy Day Boundary Layer Structure and Land Surface Process Comparison Analysis
  • DU Yibo;ZHANG Qiang;WANG Kaijia;ZHANG Hongli
  • 2018 Vol. 37 (1): 148-157.  DOI:10.7522/j.issn.1000-0534.2017.00042
  • Abstract ( ) HTML PDF (4467KB) ( )
  • Based on the sounding data of Dunhuang field observation in the summer of 2006, the structure of the atmospheric boundary layer on the sunny and cloudy days in the desert area of Northwest China had been studied. In addition, the corresponding land surface processes were investigated as well. Conclusions were drawn as follows:The convective boundary layer and the stable boundary layer on the sunny and cloudy days of northwest desert are more developed than those in central and eastern of China. In contrast, the boundary layer of sunny days is very different from that of the cloudy days in the structure and land surface processes, the height of convective boundary layer is up to 3.5 km in sunny days, while the height of the stable boundary layer is about 1 km, The maximum daily height of cloudy days for the convective and stable boundary layer is about 2.5 km and 0.2 km respectively. In addition to the boundary layer height, the specific humidity of northwest desert on cloudy day and sunny day shares the different characteristics. Sunny specific humidity with height range is greater than the cloudy day, the cloudy day starts from the ground surface up to 200 m, appearing the weaker counter humidity Phenomenon, but sunny days do not appear the phenomenon. The difference between the boundary layers are mainly caused by the thermal and dynamic factors on sunny and cloudy days. First of all, in different background weather, the solar radiation and the heat flux conversion rate lead the heat convection to be different, the solar radiation and sensible heat flux of the sunny days are stronger and greater than that of cloudy days; Secondly, the speed of the near ground level wind in sunny days is higher than that of cloudy days, This dynamic action in turbulent form also provides a certain dynamic background for the development of boundary layer height in sunny days, which is greater than that of cloudy days. The convective boundary layer is greatly affected by land surface thermodynamic factors in the early stage of the development, without the limitation of the stable boundary layer, it will develop rapidly. In addition, the temporal development in the diurnal variation of the net radiation, surface temperature and sensible heat flux exist a hysteresis quality, it is related to the transformation and transmission of energy.
  • Characteristics of Environment Condition and Cloud Microphysics during Heavy Wet Thunderstorms at Guanzhong in Mid Summer
  • ZHANG Yabin;HUANG Lei;MAO Dongyan;YANG Rui
  • 2018 Vol. 37 (1): 167-184.  DOI:10.7522/j.issn.1000-0534.2017.00041
  • Abstract ( ) HTML PDF (40455KB) ( )
  • Spatial and temporal distribution of cloud-to-ground (CG) flashes and mesoscale characteristics of two heavy wet thunderstorm processes with most CG lightning in the last 10 years at Guanzhong, which occurred respectively on August 11-12, 2010 (the "0811") and August 15-16, 2011(the "0815"), were analyzed by using NCEP reanalysis, CG lightning, satellite, Radar and WRF data. The results show that heavy wet thunderstorms at Guanzhong occurred favorably under the circulation background of two-through and one-ridge in Eurasia mid-high latitude, and Shaanxi province is controlled by the stable West Pacific Subtropical High. Low level shear line is the directly influence system. During thunderstorm, cold advection on upper levels and moist barotropic potential vorticity move southward, the energy frontal zone over northern Shaanxi move southward and invade the unstable stratification environment over central and southern Shaanxi. The low-level warm tongue over southwest of Shaanxi extend to the northeast. With unstable stratification increasing and high humidity at the early stage, the unstable energy at Guanzhong increases significantly with CAPE (Convective Available Potential Energy) above 3 000 J·kg-1. The vertical ascending motion is strong and deep. Aforementioned characteristics provide favorable environmental conditions for strong wet thunderstorm. The West Pacific Subtropical High develops strongly and westward, unstable stratification with dry air at high levels and wet at low levels, high temperature and humidity near surface layer, obviously CAPE, relatively high altitudes of vertical motion center and convective cloud, above factors are important reasons for that heavy wet thunderstorms have more CG flashes than ordinary rainstorms. The accumulated areas of CG flashes are consistent with the high potential temperature areas at lower levels, which also mainly located near positive helicity that below 50 m-2·s-2. There is a significant difference between the distribution pattern of TBB and CG flashes at different stages of heavy wet thunderstorm. At the developing stage, the oval cold-cloud cap of MCS had expanded significantly, the high gradient area of TBB bended northward with anticyclone shape. Convective cloud tops did not match the accumulated areas of the aggregating and increasing CG flashes. At the mature stage, the accumulated areas of CG flashes were basically coincidence with the convective cloud tops, the density and frequency of CG flashes reached maxima. Meanwhile, the center temperature of TBB reduced below to -76℃ and reached minimum, positive CG flashes scattered near southwest of the areas that accumulated negative CG flashes and also reached the maximum frequency of whole process. At the dissipating stage, the CG flashes weakened and dispersed obviously and its accumulated areas gradually separated from the convective cloud tops, but positive CG flashes were relatively active. Snow and graupel mixing ratio at -20~-10℃ layers is an effective indicator to flash trend. There are positive correlations between the number of particles and the frequency of CG flashes. Snow particle areas are relatively continuous and around the flash. Graupel particle areas are relatively dispersed and closer to the center of CG flash areas. At the mature stage, the vertical distribution of snow particle ranged from 8 to 16 kilometers, while graupel ranged from 6 to 12 kilometers. Accumulated areas of above particles corresponded to areas with large vertical velocity. With the significant increase of convection and vertical ascending motion, average current of CG flashes and rainfall intensity are increased, and the snow particles have obvious correlation with CG flash activity. When the vertical ascending motion become weak, average current of CG flashes and rainfall intensity will become small and have obvious correlation with graupel. Rate of CG flashes peak when convective cloud develop to the highest altitude. After CG flash doubling, cold-cloud area reach to peak in the next 3 hours and the maximum rainfall happen subsequently.
  • Statistical Characteristics of Environmental Parameters for Hail over the Two-Step Terrains of China
  • CAO Yancha;TIAN Fuyou;ZHENG Yongguang;SHENG Jie
  • 2018 Vol. 37 (1): 185-196.  DOI:10.7522/j.issn.1000-0534.2017.00044
  • Abstract ( ) HTML PDF (4280KB) ( )
  • Based on the hourly hail observations of 671 stations and National Centers for Environmental Prediction (NCEP) Final Analysis (FNL) data from March 1 to September 30 during 2002-2010, the atmospheric environmental conditions for hail over the two-step terrain (shortly for first-step and second-step respectively) areas of China with altitude above sea level of 1 km as the dividing line were analyzed. The hourly hail data and NCEP FNL data were matched by employing a temporal-spatial matching method. Due to the close relationship between hail forming and the height of characteristic temperature layers, the samples were filtered by using height of 0℃ layer above the ground, and then the environmental parameters representing moisture content, instability, and triggers were carefully analyzed, and the scatter plots also were studied. The results show that the environmental moisture conditions, the instability and best convective available potential energy (CAPE) conditions favorable for hails over the two-steps were much different. The hails over the first-step always had stronger instability, more CAPE, more moisture, and stronger vertical wind shear. The main scopes of total precipitable water (PWAT) for hails over the first-step terrain was 15~41 mm, but for the second-step, it was 6~30 mm. Almost no hails reported as PWAT were greater than 56 mm over the two-steps. More than 50% hails over the two-steps occurred under negative best lifted index (BLI) environment. If characterized by best CAPE, the percentage was greater than 75%. No hail was expected when BLI is above 2.8℃ over the two-steps. If measured by the vertical temperature lapse rate (TLR), more than 50% hails happened under high TLR environments. The differences on environmental conditions favorable for hails over the two steps were revealed dramatically by the scatter plots and probability density of parameters. The results provide an objective basis for the subjective and objective hail potential forecasting over the two-step terrains in China.
  • Characteristics of Climate Change of Summer Rainstorm in Sichuan Basin in the Last 53 Years
  • CHEN Dan;ZHOU Changyan;XIONG Guangming;DENG Mengyu
  • 2018 Vol. 37 (1): 197-206.  DOI:10.7522/j.issn.1000-0534.2017.00022
  • Abstract ( ) HTML PDF (2177KB) ( )
  • Based on the observed daily precipitation data and NCEP/NCAR reanalysis data from 1960 to 2012, the temporal and spatial variation of rainstorm in Sichuan Basin were discussed, and the water vapor transport, atmospheric circulation and sea surface temperature anomaly in the west and east of the Basin were analyzed by using the composite anomaly, correlation analysis, wavelet analysis and so on. The main conclusions are as follows:The rainstorm frequency and rainstorm amount showed the opposite changes in the east and the west of Sichuan Basin, the rainstorm increased in the west and decreased in the east, there was a significant positive correlation between rainstorm precipitation and frequency. The rainstorm in the west of Sichuan Basin was extremely more in 1960s and 1980s, while abnormally less in 1990s and early 21st Century, which mainly existed a 6~7 years inter-annual oscillation period in 1960s and from the mid-1980s to the end of the 1990s. The rainstorm in the east of Sichuan Basin was obviously less in 1960s and 1970s, while abnormally more in 1980s, 1990s and early 21st Century, which significantly existed 8~9 years inter-annual oscillation period and 14~15 years inter-decadal oscillation period from the beginning of 1970s to the beginning of 1990s. When the West Pacific Subtropical High shifts northward and become stronger, the Western Pacific water vapor will be more easily transported to the west of Sichuan Basin. These lead to rainstorm in the west of Sichuan Basin. By contrast, when the West Pacific Subtropical High shifts southward, the Western Pacific water vapor will be transported to the east of Sichuan Basin; under the situation of blocking pattern in the west of Lake Baikal, the southward moving path of the cold air tend to the east, so the cold air and warm wet air converge in the east of Sichuan Basin, cause more rainstorm in the east of the Basin. The rainstorm in west Sichuan Basin shows significant negative correlation with the West Pacific Warm Pool and ENSO events. The relationship between rainstorm and sea surface temperature in the east of Sichuan Basin is much weaker than in the West.
  • A Numerical Study of Impact of Topography on Intensity and Pattern of Sea Breeze Precipitation over the Hainan Island
  • WANG Ying;MIAO Junfeng;SU Tao
  • 2018 Vol. 37 (1): 207-222.  DOI:10.7522/j.issn.1000-0534.2016.00135
  • Abstract ( ) HTML PDF (23034KB) ( )
  • Sea Breeze is a common local circulation driven by differential heating between land and sea, which has been studied observationally, experimentally, theoretically and numerically for a long time. Previous studies have shown that sea breeze can be strongly influenced by complex inland topography, theoretically from dynamic and thermodynamic aspects. The studied area Hainan Island which has high occurrence of sea breeze also has special terrain characteristics, therefore the sea breeze is different from other coastal areas, and the sea breeze precipitation is one of the most important precipitation regimes in Hainan according to previous studies. In this paper, the sea breeze precipitation over the Hainan Island on May 31, 2013 was simulated by high-resolution numerical model WRF, the impact of topography on intensity and pattern of local sea breeze precipitation was studied by designing different topography experiments. The results show that, WRF model can simulate the surface wind and sea breeze precipitation intensity reasonably, and the time evolution of simulation and actual precipitation generally approaches well. With the continuous development of sea-breeze circulation, the timing and placement of convective precipitation as well as the sea breeze front almost move inland in phase, and the precipitation area mainly distribute in the front of Li Mu Mountain, which is located in the southwest of studied area. The rainfall structural characteristics are closely associated with the topography feature which is high and upright in the middle area while relatively lower all around in the Hainan Island, the dynamic and thermodynamic influence of terrain has alternate evolution in the whole process of sea breeze precipitation. During 11:00-16:00 BST, precipitation was mainly caused by single sea breeze front. The primary mechanism was thermal enhancement duing to the lower height of topography at this stage, and the sea-land thermal flux difference which essentially drive the development of sea breeze is more notable with higher terrain height. While during 17:00-21:00 BST, precipitation was mainly caused by the collision of eastern and western sea breeze front, with the inland propagation of sea breeze front, terrain blocking effect took dominant role as elevation increases gradually, but if the terrain height increases to a certain degree, the blocking effect can rapidly weaken sea breeze circulation and thus reduce rainfall intensity. Nevertheless, all the effects mentioned above depends on the inhomogeneous character of underlying surface, the combination of topography and vegetation can produce larger difference of the land surface energy distribution, and consequently lead to greater influence on local precipitation.
  • Study of the Stratiform Cloud Liquid Water Path Retrieval from the Millimeter Wave Radar Data
  • YAO Zhigang;YANG Chao;ZHAO Zengliang;WANG Lei
  • 2018 Vol. 37 (1): 223-233.  DOI:10.7522/j.issn.1000-0534.2016.00127
  • Abstract ( ) HTML PDF (9078KB) ( )
  • Clouds play an important role in the weather prediction and global climate changes. Cloud liquid water path (LWP) is one of the important cloud microphysical parameters. LWP can be extracted from the millimeter wave radar. To investigate the dependence of the LWP retrieval on retrieval methods and cloud particle spectrum assumptions and improve the LWP retrieval, based on the cloud particle spectrum parameters from the aircraft detection data over China, the retrieval experiments are carried out by using the ground-based millimeter wave radar data in Shouxian from AMF-ARM Mobile Facility in 2008. Based on different cloud particle spectrum parameter assumptions, a physical iteration method and a statistical regression method are respectively used to retrieve the stratiform cloud LWP. And the results are evaluated with the products from the collocated microwave radiometer products. It is shown that although the results are strongly dependent on the spectrum assumption of the cloud particles, the physical iteration method less depends on the cloud spectrum assumption than the statistical regression method. Overall, the retrieval results from the physical iteration method agree better with the radiometer based LWP than those from the statistical regression method. Particularly, the spectrum of the clouds from the aircraft based measurements over China favor the LWP retrievals. The further analysis indicates that the ignorance of the large size particles could lead to the overestimation of the LWP retrievals, which increases with the increase of the radar reflectivity. Finally, a spectrum parameter selection scheme based on different cloud characteristics is proposed. The results show that the new scheme can significantly improve the agreement of the LWP retrievals with the microwave radiometer results.
  • Applicability Analysis of Four Soil Moisture Reanalysis Datasets in China
  • ZHU Zhi;SHI Chunxiang;ZHANG Tao;WANG Jiaqiang
  • 2018 Vol. 37 (1): 240-252.  DOI:10.7522/j.issn.1000-0534.2017.00033
  • Abstract ( ) HTML PDF (18614KB) ( )
  • The exchange process of water, heat and momentum between land surface and atmosphere is called land surface process. Soil moisture is an important physical parameter in land surface process research, and also is an important index to verify the accuracy of hydrological process in land surface process simulation, which receives extensive attention from researchers in different fields. Although soil moisture is very important to climate and drought research, relevant researches are hindered by temporal and spatial limitation of soil moisture observation data, so soil moisture reanalysis datasets, which have advantages of global coverage, long time series and spatial and temporal continuity, are often used as alternative data in land-atmosphere interaction research. Because each reanalysis datasets use different numerical prediction models and assimilation methods, there are some data quality differences, especially quality inconsistency of various soil moisture reanalysis datasets, so it is essential to evaluate applicability of various soil moisture reanalysis datasets in China, which can provide beneficial reference to climate and drought research. The historical soil moisture observation data of China mainly originate from agricultural meteorological observation stations built by China Meteorological Administration, and these data are mainly kept in paper form, which have not been used wildly and effectively. In 2014, National Meteorological Information Center finished digitization and quality control work of historical soil moisture observation data, and developed the "China Agricultural Meteorology Soil Moisture Dataset (1981-2010) (V1.0)", which provides a newer and more reliable soil moisture observation data for soil moisture reanalysis datasets assessment. Using soil moisture observing data of 150 agricultural meteorology stations from "China Agricultural Meteorology Soil Moisture Dataset (1981-2010) (V1.0)" provided by National Meteorological Information Center, we compared and analyzed four soil moisture reanalysis datasets:CFSR, ERA-Interim, NCEP R-1 and NCEP R-2's applicability in China. The results show that:(1) In the aspect of spatial distribution, four reanalysis datasets can basically describe the spatial distribution of soil moisture in China, but NCEP R-1 reanalysis dataset has problems in western Qinghai-Tibetan Plateau soil moisture simulation; (2) In the aspect of time variation, CFSR can well describe time series of soil moisture, and NCEP R-2 has the worst performance over four reanalysis datasets; (3)In the aspect of seasonal cycle of soil moisture, in surface layer, CFSR and ERA-Interim are better, NCEP R-1 and NCEP R-2 overestimated soil moisture in simulation; In deep layer, except for NCEP R-1, other three reanalysis datasets can basically simulate the seasonal cycle of soil moisture.
  • Generalised Variational Assimilation of Cloud-affected Brightness Temperature of AIRS Data based on the Constraint Terms
  • WANG Gen;ZHANG Jianwei;WEN Huayang;YANG Yin
  • 2018 Vol. 37 (1): 253-263.  DOI:10.7522/j.issn.1000-0534.2017.00023
  • Abstract ( ) HTML PDF (7328KB) ( )
  • Assimilated channel brightness temperature data from infrared sounders accounting for cloud effects has a positive effect on weather forecasting, especially in weather-sensitive areas. When cloud parameters including effective cloud fraction and effective cloud top pressure are considered in the simulation on channel brightness temperature of the infrared sounders, the deviation of brightness temperature follows strong Non-Gaussian. The classical variational assimilation requires the observational errors to follow a Gaussian distribution to apply the least-square principle. The least-squares method is sensitive to outliers; if the analyzed data contain gross errors, the parameter estimation is inaccurate. When processing the cloud-affected brightness temperature, cloud detection or assimilating specific channel brightness temperature with weight function peaks above the cloud top were needed. Useful data were lost through the cloud detection process to eliminate the so-called outliers. The outliers are not always harmful, which may represent new information, such as weather phenomena. At present, the quality control is generally based on a certain threshold value if the subjective uncertainty is too strong. If outliers persist after the quality control, the optimal parametric results obtained by the classical variational assimilation are meaningless. In this paper, Atmospheric Infra-Red Sounder (AIRS) brightness temperature channel which affected by cloud, were assimilated by generalized variation method from the constraint terms of Non-Gaussian model. It combines both the advantages of classical variational assimilation and robust M-estimators. Generalized one is coupled with quality control in the process of assimilation. The main idea is to use weighting factor of M-estimators to re-estimate the contribution rate of the observation items to the objective function in each process of objective function minimization based on the classical variational assimilation. The cost function contains the M-estimators to guarantee the robustness to outliers, thus to improve the assimilation results. Numerical algorithm steps of the generalized variational assimilation are as follows:Firstly, a channel set was formed by dynamically selecting AIRS channels based on the temperature Jacobian matrix in each field-of-view (FOV). Secondly, generalized variational assimilation of cloud parameters, which were input variables in radiative transfer model (such as, RTTOV), were involved in the variational minimisation iteration process, and were used to simulate AIRS brightness temperature of channel set. Assimilation experiment demonstrated that for high clouds, the Cauchy estimator inversion results are the best, whereas for the mid and low clouds, the Huber estimator provides the best results. However, the inversion results for temperature in the high level of model is worse using the Fair estimator, and, on the contrary, the inversion results for humidity are good. These results may reflect an inherent characteristic of Fair distribution. The assimilated results in cloud-affected brightness temperature are better by using generalized variation method than the classical method, but the former depends on selecting M-estimator weight functions. The preliminary results also demonstrated the potential application value of generalized variational assimilation.
  • An Algorithm of Recognizing Automatically MARC Signature Using the Doppler Weather Radar Volume Scanning Data
  • XIAO Yanjiao
  • 2018 Vol. 37 (1): 264-274.  DOI:10.7522/j.issn.1000-0534.2016.00143
  • Abstract ( ) HTML PDF (23604KB) ( )
  • Damaging downbursts on the ground are the most common weather phenomenon produced by severe convective storm. One of the challenges in the severe storm warning process is forecasting the initial onset of damaging winds. A prominent MARC signature is a Doppler radar-velocity based precursor towards forecasting the initial onset of damaging downburst in a strong storm system. The lead time from the initial identification of MARC signature to the first reports of severe wind damage is about 10~30 minutes. In this paper, an automatic recognition algorithm of three-dimensional MARC signature was proposed. First of all, the algorithm uses a two-dimensional, local, linear least squares (LLSD) method to calculate the radial divergences of radial velocities. Secondly, the algorithm uses storm cell radial convergence zone identification (SCRCZI) algorithm which is similar to SCIT algorithm to recognize three-dimensional radial convergence zone based on the radial divergent shear field. And lastly, the locations of storm cells identified using modified SCIT algorithm are used to remove those three-dimensional radial convergence zones unrelated to storm. The algorithm can well identify three-dimensional MARC signatures, including those radial convergence zones not characterized by a symmetric positive/negative velocity pair. The reflectivity and radial velocity evolution characteristics of a strong storm producing a downburst have been analyzed and MARC recognition algorithm has been tested using Wuhan Doppler weather radar observations. The results show that the algorithm is very efficient, the prominent MARC signatures were recognized in six volume scans including three volume scans before the divergence signature appeared in radial velocity image at the lowest tilt for the first time and subsequent three volume scans. In this process, the average height of MARC was 3.9 km, the average depth was 2.5 km, and the strongest magnitudes of MARC were located between 3.0 and 4.6 km, mean magnitudes of the strongest convergence is -58×10-4 s-1, the lead time from the initial identification of MARC to the first reports of the strong divergence signature at the lowest tilt was 18 minutes.
  • Comparison and Evaluation of Three Types of Wind Field Reanalysis Data in Coastal Zone of Liaoning Province
  • AO Xue;ZHAI Qingfei;CUI Yan;ZHOU Xiaoyu;YI Xue;SHEN Lidu;ZHAO Chunyu;LIN Rong
  • 2018 Vol. 37 (1): 275-285.  DOI:10.7522/j.issn.1000-0534.2017.00029
  • Abstract ( ) HTML PDF (6702KB) ( )
  • Using the comparison of the conventional observation data of 20 meteorological stations and the reanalysis data of ERA-Interim, JRA-55 and CFSR in coastal zone of Liaoning Province from 1981 to 2015, the adaptability of reanalysis wind velocity field in coastal zone of Liaoning Province were discussed. The results show that the correlation between the three reanalysis data and the observed data is significant, and ERA-Interim is the best. But the maximum hourly wind speed of ERA-Interim data is obviously smaller than the observed data. The spatial deviations of the three kinds of reanalysis data are obviously heterogeneous, what is smaller in Suizhong and Xingcheng but larger in Lushunkou. The absolute deviation of the maximum hourly wind speed of CFSR is less than 1, and the applicability is better. The wind speed of ERA-Interim data is close to that of observation data, and the deviation of maximum hourly wind speed and gale number at 14:00 (Beijing time, the same as after) was smaller than that at 08:00. The mean absolute error of maximum hourly wind speed in the three sea areas is not significant, which is between 1.5 and 3 m·s-1, and the error of gale number is significant. The error of Bohai Strait is relatively large, the northern part of Yellow Sea and the northern part of Bohai Sea are the least. The mean absolute error of wind speed of CFSR data is the smallest. The observed data of maximum hourly wind speed and the number of wind events were significantly decreased, the JRA and CFSR data showed a slow decreased trend, while the ERA data showed an increased trend. The interdecadal curve of ERA and JRA data fluctuated smoothly, which could not show the interdecadal variation trend of the observed data, the CFSR data is close to the observed value, but the trend is slower than that of the observed data. In point of the spatial distribution of long-term trend, CFSR data credibility is relatively better, JRA data is second, and the difference of ERA-Interim data is larger.
  • The Optical and Microphysical Characteristics of Dust Aerosol over a Typical Semi-arid Region in Loess Plateau
  • SHI Yingying;ZHANG Lei;TIAN Pengfei;LIU Hui;MA Qiang
  • 2018 Vol. 37 (1): 286-295.  DOI:10.7522/j.issn.1000-0534.2017.00024
  • Abstract ( ) HTML PDF (3564KB) ( )
  • Atmospheric aerosols regulate the balance of radiation budgets of the surface and atmosphere through direct, indirect and semi-direct effects, which affect regional and global climate change. In order to evaluate the aerosol radiation effects accurately, it is necessary to have a good understanding of aerosol optical and microphysical characteristics. At present, there is no sufficient understanding of the aerosol optical and microphysical characteristics over the typical semi-arid region in Loess Plateau. Based on the 2006-07-28 to 2012-08-10 sun photometer data from the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL), dust aerosol was determined by using a strict judgment, and then dust aerosol optical and microphysical characteristics were analyzed. The work has important scientific significance and application value. The main results are as follows:Spring has the highest (2.80) dust aerosol optical depth (AOD), which is mainly distributed from 0.3 to 0.8 (about 82%), with a daily average of 0.63±0.44, indicating that the largest number of dust days occur in spring. Ångström exponent with maximum and minimum in spring (0.002) and autumn (0.525), which is opposite in phase to AOD, ranges between 0.2~0.4 (about 56%) and has a daily average of 0.27±0.12, showing that dust aerosols are mainly large particle size. The coarse mode dominates the size distribution of the dust aerosol, and the spring concentration is the largest. Both total and coarse mode volume concentrations have similar annual variation to AOD and reach their maximum in April with the fine mode volume concentration changing very little. The aerosol total and coarse mode effective radius ranges from its maximum in spring to its minimum in autumn, and the amplitude of the fine mode particles is small. The real part of the refractive index with the change of the effective radius is higher in spring and winter while it's lower in summer and autumn, which indicates that dust aerosol has strong scattering. In opposite phase to imaginary part of refraction index, the single scattering albedo is larger in spring, but has a minimum value in February, so dust aerosol absorption is weaker than black carbon aerosol. The asymmetry factor reaches its minimum in spring, which indicates that dust aerosol has stronger forward scattering than other kinds of aerosols.
  • Impact of Aerosol Radiative Effect on Surface Ozone Peaks during Heavy Haze Events
  • LIU Shuyan;BAO Yunxuan;JIN Jianping;LIU Cheng;XU Jianming;LI Jianmin;HUANG Jianping
  • 2018 Vol. 37 (1): 296-304.  DOI:10.7522/j.issn.1000-0534.2016.00141
  • Abstract ( ) HTML PDF (1435KB) ( )
  • Aerosols attenuate solar ultraviolet radiation, and exert an important impact on surface ozone formation during heavy haze events. This observational analysis was combined with the simulations of TUV (Troposphere Ultraviolet and Visible radiation) model and NCAR MM model (Master Mechanism Box model, MM) to quantify the impact of aerosol radiative effect on surface ozone concentrations during a heavy haze event in Yangtze River Delta region of China from 1 to 10 December, 2013. The results indicate that regional transport, trapping effect of the stable boundary layer, and the secondary formation processes were responsible for the occurrence of the heavy haze event. During the heavy haze event, O3 photochemical reactions were significantly slowed down, daily peak values were substantially decreased while photochemical reactions proceeded slowly. O3 concentrations showed a slowly increasing trend with increasing aerosol concentrations due to the combined effect of the regional transport, the stable boundary layer, and the secondary aerosol formation processes. The TUV and MM model simulations were matched well with the observations. The surface-reaching ultraviolet radiation and ozone peak concentration were reduced by 63% and 83%, respectively, when the aerosol optical depth (AOD) was increased from 0.8 to 2.0 which indicated that heavy haze events may alleviate the surface ozone pollution.

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