Current Issue

• The Influence of Atmosphere to Passive Microwave Retrieval of Snow Depth over Qinghai-Tibetan Plateau
• LIU Jinjun;FU Yunfei;LI Rui;WANG Yu;FU Yuyun;HU Jiheng
• 2018 Vol. 37 (2): 305-316.  DOI:10.7522/j.issn.1000-0534.2017.00050
• Abstract ( ) HTML PDF (10234KB) ( )
• The microwave at low and moderate frequencies (e. g., 18.7 and 36.5 GHz) has good transmittance through the atmosphere, therefor in most algorithms for satellite passive microwave (PMW) remote sensing snow parameters, ignoring the effect of atmosphere and the upwelling microwave brightness temperature at the top of atmosphere (TOA) were directly used to retrieve snow parameters on ground. There are few systematic analysis on the errors introduced by ignoring atmosphere effects. In this paper, we investigated the influences of atmosphere to the PMW retrieval of snow depth over Qinghai-Tibetan Plateau (QTP). We used the upwelling brightness temperature on TOA (TB_TOA) measured by the Advanced Microwave Scanning Radiometer-EOS (AMSR-E) as the main input data. The Moderate Resolution Imaging Spectroradiometer (MODIS) cloud product (MYD06_L2) and National Centers for Environmental Prediction (NCEP) FNL reanalysis data (including atmosphere water vapor, atmosphere component and land surface temperature) were used as the ancillary data. The effect of water vapor and non-rainy cloud were corrected and the upwelling brightness temperature at the plateau surface (TB_SRF) were derived based on microwave radiation transfer model (MWRT) calculation. We then estimated the snow depths of SD_TOA and SD_SRF over QTP using these two TBs, respectively. By comparing the two TBs and two SDs, the effect of atmosphere and cloud on PMW remote sensing snow depth were investigated. Through case analysis and nearly 10 years of statistics, we found that:the atmosphere effect on TBs at low frequency microwave 18.7 GHz is weak while TB_TOA at 36.5 GHz are significantly warmer than TB_SRF. Without considering such effect, the snow depth over QTP would be underestimated (SD_TOA < SD_SRF). The underestimations are common in multiple cases and significant at multi-year mean scales, therefore should not be neglected. The absolute error (SD_TOA-SD_SRF) is approximately 2~3 cm. In the region with relative shallow snow, the relative error is up to 50%~80%. While in the region with relative deep snow, the relative error is 10%~20%. The error has strong negative correlation with liquid cloud water path (R=-0.45) with sensitivity of -0.047 cm·(g·m^-2)^-1. The error is not sensitive to ice cloud and even weaker to column water vapor. Snow extent retrieved from MODIS (MYD10CM product) has better correlation to SD_SRF than that to SD_TOA. This imply that corrections of the influence of atmosphere can improve the accuracy of satellite PMW retrieval of snow depth over QTP.

• Diagnosis and Simulation on the Relationship between Snow Depth over Qinghai-Tibetan Plateau and Summer Precipitation in Eastern China
• LI Yan;YAN Jiahai;ZHANG Dongfeng
• 2018 Vol. 37 (2): 317-324.  DOI:10.7522/j.issn.1000-0534.2017.00040
• Abstract ( ) HTML PDF (6636KB) ( )
• Snow cover over Qinghai-Tibetan Plateau (QTP) is an important component of climate system in East Asia.Its depth shows strong inter-annual variability.It is understood that the variation of snow depth over QTP is strongly associated to the action of Asian monsoon.Summer precipitation is a constituent of the Asian monsoon, which has been used as an indicator of Asian summer monsoon activity.We employed climate diagnosis and numerical simulation method to test the mechanism that how the winter-spring (from December-to-May) snow depth anomaly over QTP effects the following summer (from June-to-August) precipitation distribution in eastern China.Firstly, this study used a remote sensing dataset with 25 km horizontal resolution and gridded (0.5°×0.5°) precipitation data from 1980 to 2010 to analysis the relationship between winter-spring snow depth over QTP and the following summer precipitation change over eastern China.Then, we setup sensitivity experiments with a regional climate model (RegCM4.1) to test the possible mechanism.The results show that:(1) Based on the snow depth data and the gridded precipitation data, there is a "-+-+" summer precipitation distribution pattern with latitude change (north to south) over eastern China in less winter-spring snow years, while there is a "+-+-" pattern in more winter-spring snow years.(2) The sensitivity experiments simulations show that a "+-"and "+-+" summer precipitation patterns from north to south in eastern China with the forcing of the less snow cover in winter-spring and spring over QTP, respectively.If there is more snow in winter-spring and spring over QTP, the following summer precipitation will present a contrary spatial distribution.(3) The simulations also show that anomaly of winter-spring snow depth over the Plateau can influence atmospheric circulation and lead to the anomaly of following summer precipitation in eastern China.The snow depth anomaly in spring plays a more important role than that in winter in effecting on summer precipitation and atmospheric circulation over eastern China.Although the paper has tried to explain how the snow cover over QTP effecting the following summer precipitation in eastern China, the climate anomaly is dominated by the combination of multi-impact factors.Moreover, the condition parameters in the sensitivity experiments are different from the actual situation.Hence, some difference exists between the simulation and observation data.Short-term climate prediction is a very difficult scientific question in atmospheric sciences, further study about the relationship between the abnormal atmospheric signal and the following climate effecting is needed to improve the skill of short-term climate prediction.

• Variation of the Snow Disasters under Global Warming and Its Relationship with General Circulation over Tibetan Plateau
• HUANG Xiaoqing;TANG Shuyi;CIWANG Dunzhu
• 2018 Vol. 37 (2): 325-332.  DOI:10.7522/j.issn.1000-0534.2017.00038
• Abstract ( ) HTML PDF (5124KB) ( )
• By using the daily snow data, monthly precipitation and monthly mean temperature data of 19 meteorological stations in high altitude pastoral areas of Tibet plateau from October 1979 to April 2013, and based on the snow disaster index of snow depth and snow last days, the climate change characteristics of different grade snow storms and the impact of changes in temperature and snowfall of snow storms were analyzed.The results show that the period from November to the next February is the high incidence of snowstorms in the Tibetan plateau and the disasters are very severe, with the big probability of moderate or above snowstorms occurring throughout the year, which accounts for 54% of the total number of stations; The snow disaster change showed a decrease trend since 1979, but there exists a decadal variability, which is characterized by higher volatility in 1980-1997 and show a significantly reducing trend since 1998-2007, since then up slightly, the point mutation is in 1999 and 2008; The correlation between temperature and snowstorm is higher than that of snowfall, the temperature is significantly warmer, but the snowfall changes are not obvious, so the temperature plays a decisive role in the snowstorm climate change.The relationship between the atmospheric circulation system and the snow disaster was analyzed, and it is concluded that it is prone to snow disaster when the west wind belt and the eastern hemispheric vortex become stronger and the east Asian trough and the subtropical high become more west, and vice versa.The variation trend and mutation point of the western wind belt south branch trough and the eastern hemispheric vortex are very consistent with the change trend and mutation point of the snow disaster in the Tibetan plateau, which is a possible cause of the snowstorm changes in the Tibetan plateau.

• Analysis of Vertical Temperature Gradient Characteristics and Its Causes over Qinghai-Tibetan Plateau and Its Surroundings
• CHENG Yixuan;FAN Guangzhou;ZHANG Yongli;LAI Xin
• 2018 Vol. 37 (2): 333-348.  DOI:10.7522/j.issn.1000-0534.2017.00057
• Abstract ( ) HTML PDF (34439KB) ( )
• Based on the ERA-Interim monthly mean reanalysis data of temperature field, wind filed and vertical velocity field from 1980 to 2015, the characteristics of Qinghai-Tibetan Plateau (QTP) temperature gradient (T_G) and its causes were studied. The results show:(1) The decreased degree of the temperature in the major region of QTP decreases faster with the rise of the altitude than that in the surrounding areas, and the temperature on both sides of the plateau decreases lower with the rise of the altitude. (2) The change degree of T_G in the lower troposphere in the steep terrain area at the edge of QTP is greater than that in the surrounding areas, and T_G in the upper-middle troposphere is in horizontal uniform distribution. (3) The decreased degree of the temperature in the non-plateau region decreases with the rise of the altitude, which is slightly higher than that in the plateau region; In winter and spring, T_G in the both regions is sensitive to changes in external factors. (4) The initial cause analysis revealed that at the edge of plateau region in the lower troposphere, the stronger the effect of the non-adiabatic heating (cooling), the smaller (larger) the T_G, and the smaller (larger) the reduced degree of the temperature decreased with the rise of the altitude; In the upper-middle troposphere, the stronger the effect of non-adiabatic heating (cooling) in some regions of the plateau, the larger (smaller) the T_G, and the larger (smaller) the reduced degree of the temperature decreased with the rise of the altitude; The non-adiabatic heating (cooling) is the main factor that causes the temperature to decrease slowly (quickly) with the rise of the altitude in the whole atmosphere of the plateau.

• Variability of NDVI with Elevation and Precipitation in Yarlung Zangbo River Basin
• LIU Xiaowan;PENG Dingzhi;XU Zongxue
• 2018 Vol. 37 (2): 349-357.  DOI:10.7522/j.issn.1000-0534.2017.00048
• Abstract ( ) HTML PDF (2875KB) ( )
• Spatial discrepancy of vegetation is mainly derived from terrain abnormality and uneven distribution of precipitation. Yarlung Zangbo River basin, situated in the Tibetan autonomous region with great altitude difference, was selected as the case study. With use of moving t mutation test, tendency value computation, Pearson correlation analysis method, spatial and temporal pattern of NDVI and its relationship with elevation and precipitation in the Yarlung Zangbo River basin were investigated by combining the datasets of NDVI, precipitation and elevation within 0.25°×0.25° pixels. The results show that:(1) distribution of NDVI heavily depends on elevation and the relationship between NDVI and elevation is apparently negative with tendency value of -0.000 18 m^-1. NDVI of pixels less than 3 003 m and over 5 843 m exhibited in linearly reduction with the elevation increase, while the magnitudes of NDVI in pixels with elevation between 3 003 m and 5 843 m greatly differ with the fitted NDVI using elevation; (2) According to three elevation bands divided by 3 767 m and 5 051 m, the magnitude extent of NDVI are 0.65~0.88, 0.17~0.49 and 0.09~0.24, respectively; (3) Vegetation growth within 12 months can be grossly divided into three phases including February to May, June to September and October to next January; (4) An increasing tendency was detected in NDVI over 5 051 m, and there was a decreasing tendency in NDVI from June to September at pixels located between 3 767 m and 5 051 m, however at less than 3 767 m, NDVI are generally of downward trend; (5) Variability of 32% NDVI are controlled by elevation, but that 51% NDVI are dominated by precipitation with the correlation coefficient over 0.7 mainly distributes between 3 003 m and 5 843 m (especially for the pixels with elevation over 4 010 m in them), and that the leftover 17% NDVI primarily depend on other factors. The findings are expected to provide an insight for local ecological protection and water resources management and be a reference for relevant studies in similar areas.

• Comparison of Four Methods for Calculating Surface Fluxeson Alpine Grassland at Naqu
• YAN Xiaoqiang;HU Zeyong;SUN Genhou;XIE Zhipeng
• 2018 Vol. 37 (2): 358-370.  DOI:10.7522/j.issn.1000-0534.2017.00067
• Abstract ( ) HTML PDF (10204KB) ( )
• The near-surface layer gradients observed data of wind speed, temperature and specific humidity combined with the radiative and soil heat fluxes have been widely applied in estimating the surface-air turbulent exchange over decades. However, different methods may produce significant differences and errors in their results. In this paper, the observational data of automatic weather station (AWS) and eddy correlation system (EC) from Naqu Station of Plateau Climate and Environment in the Norther Tibetan Plateau from September 2013 to August 2014 were used to calculate turbulent fluxes by the eddy covariance, the aerodynamic method, the combination methodand the mass transfer method and analysis the consistency and difference among the calculated results. The results show that the characteristics of turbulent fluxes calculated by different methods have obvious differences. The combination method satisfies the energy balance relationship. However, the turbulent fluxes appear to be abnormally unstable during the morning and evening. The turbulent fluxes calculated by the aerodynamic method have the highest correlation with the turbulent fluxes calculated by the eddy correlation method. But when the atmospheric stability parameter is close to zero, the calculation result is unstable. When the difference between the surface temperature and the air temperature is less than zero, the flux data calculated by the mass transfer method show obvious divergence. But this method is simple in principle and suitable for field stations which have few observation instruments and incomplete meteorological observation stations. The mean deviation of the turbulent flux calculated by the aerodynamic method and the combination method is smaller, while the average deviation of the turbulent flux calculated by the mass transfer method is larger. The results of this study provide reference for the use of these methods. Besides, the results of this study provide a reasonable basis for the establishment of long time flux series. Finally this study will help us to understand the interaction between the surface and the atmosphere.

• Applicability Analysis of Soil Moisture from Multiple Substitute Data in Qinghai-Tibetan Plateau
• WANG Jing;QI Li;WU Zhiwei;SHI Xiaohui;HE Jinhai
• 2018 Vol. 37 (2): 371-381.  DOI:10.7522/j.issn.1000-0534.2017.00074
• Abstract ( ) HTML PDF (12612KB) ( )
• There is not any reliable long-time observed dataset to reflect the characteristics of soil moisture change, in this paper we comprehensively refer to several observation datasets, and assess the applicability of multiple substitute data to the Qinghai-Tibetan Plateau (QTP). The results show as following:(1) The observation dataset shows that the changes of the soil moisture in the surface, middle and deep layer have a good consistency, and the correlation coefficient between different layers are mostly above 0.8. (2) The SSM/I satellite retrieval dataset has a positive correlation with every site's observation data, as the correlation coefficients are all above 0.5 in the southeast, middle and north of QTP, and the standard deviations (SD) are both close to the observation SD in southeast and middle of QTP, so the SSM/I RETRIVALS should be a first-rate substitute data for studying the variation characteristics of soil moisture in QTP. (3) The spatial distribution of spring soil moisture in QTP is characterized by a large southern margin and a decline from southeast to northwest, and the general soil moisture of QTP has an obvious linearly increasing trend. After removing the linear trend, there are two large standard deviations areas in east and west QTP, and the soil moisture has great continuity from spring to summer in both areas which can be used to predict summer rainfall in China.

• Applicability Study of SR-50A Ultrasonic Snow Depth Sensor for Snow Measurement in Tibetan Plateau
• CHU Duo;BIANBA Ciren;ZHA Zhu;DEJI Yangzong
• 2018 Vol. 37 (2): 382-393.  DOI:10.7522/j.issn.1000-0534.2017.00037
• Abstract ( ) HTML PDF (5969KB) ( )
• Snow depth is one of main surface meteorological observation elements and currently is mainly measured by manual observation. Due to poor real-time performance, it is difficult to meet requirements of emergency meteorological service and response. Previous study indicated that ultrasonic technology has excellent potential for snow depth measurement. Therefore, the SR-50A ultrasonic snow depth sensors developed by Campbell Scientific Company were installed from September 2013 to November 2014 at 4 meteorological stations where have often heavy snow and are prone to snow disaster and key regions of snow accumulation in Tibetan Plateau. In this study, the applicability evaluation of SR-50A snow depth in these stations was made using daily 12:30 intensive and 08:00 (Beijing Time) manually observed snow depth as ground truth data. The following are results. (1) Mean biases between SR-50A and manual snow depth are within ±2 cm. SR-50A sensors are more suitable for the measurement of higher snow depth since the larger the depth of snow, the smaller the mean root-mean-square error and the higher the observation precision. (2) SR-50A shows a good performance for monitoring snow depth in Tibetan Plateau. There is a very good agreement and highly significant linear correlation between manual and SR-50A sensor observation for snow depth. The correlation coefficients at 4 stations range from 0.81 to 0.97. (3) Wind scour, local solar radiation condition, environmental temperature and surface feature will cause spatial variability of snow cover at observation sites through wind blowing and snow melting, and manual observation in the study is not taken just adjacent to sensor installation, which are main factors resulting in these biases.

• Simulation of the Response of Qinghai Lake Thermal Conditions to Climate Change
• SU Dongsheng;HU Xiuqing;WEN Lijuan;ZHAO Lin;LI Zhaoguo
• 2018 Vol. 37 (2): 394-405.  DOI:10.7522/j.issn.1000-0534.2017.00069
• Abstract ( ) HTML PDF (7847KB) ( )
• Lake is a very sensitive indicator to climate change. There are thousands of lakes on Qinghai-Tibetan Plateau, about 1 200 of them have an area larger than 1 km², but few observation data of lakes are available, which makes the thermal condition of plateau lakes under the background of climate warming far from well understood, at the same time, most of the studies on plateau lakes focused on short-term research. In this study, the China Meteorological Forcing Dataset developed by Institute of Tibetan Plateau Research, Chinese Academy of Sciences (ITPCAS), MODIS LST data and buoy observation data were used to analysis the applicability of Freshwater Lake Model (Flake) at Qinghai Lake and reveal the response of thermal condition of Qinghai Lake to climate change. The results show that Flake have good abilities to capture the thermal characteristics of Qinghai Lake and have a good simulation to the seasonal variations of the lake surface temperature. But some positive deviation was found in summer and autumn (especially in nighttime), part of the deviation was caused by the bias of forcing data, after a simple correction to temperature and wind speed of the forcing data, the deviation of the simulation result was partly reduced. The comparison and analysis of interannual variation trend and correlation between lake surface temperature simulated by Flake and meteorological factors of ITPCAS forcing data from 19892012 found there is a warming trend in lake surface temperature, which have a positive correlation with air temperature and downward longwave radiation, and a negative correlation with wind speed, indicating that the air temperature warming plays a key role in lake surface temperature increase. The simulation of inner lake thermal condition revealed that the mixed-layer temperature of Qinghai Lake presents an increase trend almost all the year round, which is most obviously in May and June. For the bottom of the lake, the increase trend only happens in May and December, it is also the seasonal overturn period of the lake, and a decrease trend happens from June to October when the lake is in stratification period. This pattern may caused by the increase of stratified stability due to the temperature increase of the up-layer water in stratification period.

• Numerical Simulation and Stage Structure Characteristics of a Plateau Shear Line Process
• LUO Xiong;LI Guoping
• 2018 Vol. 37 (2): 406-419.  DOI:10.7522/j.issn.1000-0534.2017.00046
• Abstract ( ) HTML PDF (31462KB) ( )
• Using the non-hydrostatic mesoscale WRF (Weather Reaserch Forecast) model, and combining with the National Centers for Environment Prediction Final Analysis (NCEP-FNL) data, the conventional observation data, the temperature of black body (TBB) data from the Fengyun-2F (FY-2F) satellite and the Climate Prediction Center Morphing Technique (CMORPH) precipitation data, the plateau transverse shear line process occurring from 29 June 2014 to 1st July was simulated, and the structural characteristics of precipitation, thermodynamic, water vapor and dynamic in the course of evolution were analyzed. The results show that the WRF model successfully simulated the precipition and precipition area caused by the Plateau shear line. During the shear line process, there are significant differences in the structural characteristics of different stages. It usually corresponds to the cloud sector of TBB < -20℃ nearby the shear line; with the developing of the shear line, the TBB decreases, and there are many convective activities centers of TBB < -60℃, corresponding to the main period of precipitation; TBB increases again during the weakening stage of the shear line and the precipitation goes to end. The plateau shear line has a thermodynamic structure of "warm south but cold north", the vertical distribution characteristic of high level stability and low layer instability appears during the development and maintenance stage of the shear line; the plateau shear line is the water vapor congregated zone, the change of water vapor flux divergence has a certain effect on the development of plateau shear line. Above the vertical direction of the nascent, developing and maintenance stage, there are positive vorticity and converge centers which both present a dynamic system of lower troposphere positive vorticity coupled with the high potential vorticity. The cyclonic shear is favorable for maintaining the positive vorticity of plateau shear line; lower level convergence and upper level divergence structure on divergence field is conducive to the development of vertical ascending motion of the shear line; and it is a characterstic signal of plateau shear line weakened that the converge zone begins to subside then disappear in advance of the positive vorticity does.

• Case Study on Shape Evolution of Plateau Shear Line: Structural Characteristics
• ZHAO Dajun;YAO Xiuping
• 2018 Vol. 37 (2): 420-431.  DOI:10.7522/j.issn.1000-0534.2017.00066
• Abstract ( ) HTML PDF (7710KB) ( )
• Using NCEP/NCAR 1°×1° FNL datasets, the CMA surface precipitation data and Qinghai-Tibetan Plateau and shear line year books, the dimensional structure characteristics and their causes of the plateau shear line S1019 were diagnosed which occurred on July 16-17, 2010. The results show, in its generative development period, there exist strong divergence area near the South Asia high ridge, and low level relative vorticity has developed rapidly in the aspect of scope and intensity. Overall, it shows a baroclinic vertical structural configuration. It appears a "warm and wet core" structure near the height of 300 hPa, the apparent heat source Q₁ and apparent moisture sink Q₂ both strengthening in the vertical direction, the Q₁ maximum value center lifted from 400 hPa up to 300 hPa while the positive extreme value of Q₂ decreased from 300 hPa to 600 hPa. In the decaying period, the divergence area decreased significantly near the top of 100 hPa along South Asia high ridge, it mainly appears wet and cold in the upper troposphere, the low level relative vorticity value decreases in the scope and intensity, the southwest vortex gradually moves out of the Qinghai-Tibetan Plateau area, the lower level completely controlled by the cold and wet air. When the precipitation tends to end, both the apparent heat source Q₁ and apparent moisture sink Q₂ reduce quickly.

• Validation of AIRS Retrieved Temperature and Moisture Products and Its Applicability for Boundary Layer Height Estimation in Loess Plateau
• CHENG Haiyan;YU Ye;CHEN Jinbei;YAO Dun;XIE Jin;LI Jianglin
• 2018 Vol. 37 (2): 432-442.  DOI:10.7522/j.issn.1000-0534.2017.00094
• Abstract ( ) HTML PDF (999KB) ( )
• Planetary boundary layer height (PBLH) plays an important role in turbulent mixing, convective activity, cloud formation, atmospheric pollutant diffusion and cloud/aerosol crimping. It is also the basic parameter for the study of atmospheric boundary layer, as well as important parameter for weather, climate and air quality modeling. Currently, radiosonde is the most widely used method for obtaining the planetary boundary layer temperature and humidity profile. However, most sites only launch the radiosonde twice a day (usually at 08:00 and 20:00, Beijing time), and these sites are inhomogeneously distributed. It is still very difficult to obtain the information on vertical profiles of temperature, humidity and planetary boundary layer height in areas where observations are sparse. In this study, the applicability of the temperature and relative humidity profile from the Atmospheric Infrared Sounder (AIRS) which have a global coverage and the feasibility of using AIRS temperature profile to determine the planetary boundary layer height over the Loess Plateau area were evaluated using radiosonde observation data obtained during the intensive observation periods in summer of 2012-2016. The results indicated that the correlation among the planetary boundary layer heights determined by six different methods are significant. The height differences among various methods are generally not more than 200 m, and the selection of critical Richardson number value has little influence on the determined planetary boundary layer height. On the other hand, AIRS retrieval products can well reflect the vertical variations in atmospheric temperature and moisture, with mean bias and root mean square error less than 1 K and 2 K for air temperature and they are not more than 10% and 20% for relative humidity, respectively. However, the error of surface air temperature between AIRS and radiosonde observation is relatively large, with the mean bias and the root mean square error being -1.68 K and 3.32 K respectively, which could affect the determination of the planetary boundary layer height. The comparison of planetary boundary layer height determined by using temperature profiles from the AIRS with that determined by using radiosonde through Parcel method shows that although the planetary boundary layer heights determined by AIRS temperature profiles are lower than that determined by radiosonde observations, it can reproduce the change of the planetary boundary layer height well. AIRS retrieval temperature profiles can be used to estimate planetary boundary layer height in the study area when radiosonde data are not available. The study will help enhancing the understanding of the planetary boundary layer over the Loess Plateau and provide modelers with information on planetary boundary layer characteristics that can be used to improve numerical model simulations.

• Numerical Simulation of Diurnal Variation of Surface-to-air Exchange over the Grassland in the Southeast Tibet
• LI Hongyi;XIAO Ziniu;ZHU Yuxiang
• 2018 Vol. 37 (2): 443-454.  DOI:10.7522/j.issn.1000-0534.2017.00052
• Abstract ( ) HTML PDF (2986KB) ( )
• Based on the boundary layer observations of the grassland in Southeast Tibet for the period from 21 May to 9 July 2013, the WRF simulation capacity on the diurnal variations of sensible heat flux, latent heat flux, surface soil heat flux and each component of radiation balance over the grassland in Southeast Tibet before and after the South Asia summer monsoon burst was evaluated from perspective view of a typical sunny day and long-time average, respectively. This study is trying to find out the differences and similarities between simulation results and boundary layer observations. The results of the case simulation over a typical sunny day and the long-time simulation during the whole observation period all show that the model has a good performance in modeling the diurnal variations of sensible heat flux and latent heat flux, the simulating effect of sensible heat flux is better than that of latent heat flux. The simulating effects of sensible heat flux and latent heat flux are good at night-time, and in the daytime, the simulated values of sensible heat flux and latent heat flux are larger than the observed values. The simulated values of downward shortwave radiation and net radiation over the typical sunny weather day are all basically consistent with the observed values, but the simulated values of upward shortwave radiation are larger than the observed values at day-time. The long-time simulation results of downward shortwave radiation, upward shortwave radiation and net radiation basically agree well with the observed data at night-time, but in the daytime, the simulated values are significantly larger than the observed values. Both the typical sunny day simulated values and the long-time simulated values of long wave radiation from the atmosphere and long wave radiation from the earth are smaller than the observed values during the whole day. The long-time simulated values of surface soil heat flux are lower than the observed values in the morning and evening, but in the daytime, the simulated values are higher than the observed values. While the long-time average results and the sunny day results are similar, but without the disturbance of precipitation process, the analysis results on sunny weather conditions can more consistently reflect the diurnal variation characteristics of this region.

• A Simulation Comparison Study on the Climatic Characteristics of the South Asia High by the BCC Climate System Model
• DONG Min;WU Tongwen;ZUO Qunjie;GAO Shouting
• 2018 Vol. 37 (2): 455-468.  DOI:10.7522/j.issn.1000-0534.2017.00051
• Abstract ( ) HTML PDF (31399KB) ( )
• The simulation ability of BCC climate system model (BCC_CSM1.1) on climatic characteristics of the South Asia High is assessed by using the CMIP5/AMIP historical experiment output data. The results show that the BCC_CSM1.1 can pretty well simulate the mean state, ridge line position and the high pressure center of the South Asia High and their seasonal variation. The deficiencies of the model are the followings:The simulated height field is much weaker than observation, the model produced ridge line position is slightly more southward than observation in winter half year, the simulated high pressure centers have some differences in some months, for example, the simulated SAH center is more westward than observation in May, and in summer the dipole pattern of SAH center is also not well simulated. The weak simulation of SAH is related to many factors. It was found when the sea surface temperature is specified as observations, the error from AMIP run will reduce about 13%~15% compared with the results from coupled model. This means that the total error of the coupled model is mainly from atmosphere component. The improvement of ocean model would contribute only small part to total improvement. Comparing the error from T106 resolution model with that from T42 resolution model shows that the middle high resolution model has greatly reduced the simulation error of the SAH and global 100 hPa geopotential height field. To verify the effect of topography forcing on simulation results, some experiments with different topography of Qinghai-Tibetan Plateau were conducted. It is found the topography of Qinghai-Tibetan Plateau has significant influence on the strength of the SAH and global geopotential height field. The topography uprising of the Plateau could enhance the simulated SAH strength and global geopotential height field. This means that specifying the topography correctly would improve the model simulation results.

• Check Analysis of the Prediction of Northern Hemisphere Blocking in Summer by NCEP CFSv2
• ZHOU Ningfang;JIA Xiaolong
• 2018 Vol. 37 (2): 469-480.  DOI:10.7522/j.issn.1000-0534.2017.00036
• Abstract ( ) HTML PDF (19503KB) ( )
• Daily output data from 12-year retrospective forecasts by the National Centers for Environmental Prediction (NCEP) Climate Forecast System version 2 (CFSv2) was analyzed to understand the skill of forecasting summertime atmospheric blocking in the Northern Hemisphere and associated climate anomalies in East Asia. Prediction skills of sector blocking, sector-blocking episodes, and blocking onset/decay were assessed with a focus on the Ural mountains sector (10°E-70°E) and the Baikal-Okhotsk sector (110°E-180°) based on the hit rate, the false alarm rate, the bias score, and the HSS skill scores. Circulation and climate patterns in East Asia associated with blocking in the CFSv2 predictions were also examined. The CFSv2 captures the observed features of longitudinal distribution of blocking activity well, but underestimates blocking frequency and shows a decreasing trend in blocking frequency with increasing forecast lead time. Skillful forecast (if taking the hit rate of 50% as a criterion) can be obtained up to 7 days in both the Ural mountains (10°E-70°E) and the Baikal-Okhotsk (110°E-180°) sectors. When beyond two weeks, there are nearly little skills. The forecast skill of sector-blocking episodes is slightly lower than that of sector blocking in both sectors, and it is slightly higher in the Ural mountains sector than that in the Baikal-Okhotsk sector sector. Compared to block onset, the skill for block decay is slightly lower in the Ural mountains sector, and for both sectors, forecast skills of the block onset and the block decay tend to near zero when forecast lead time beyond 7 days. In both two sectors, a local dipole pattern at 500 hPa geopotential height associated with blocking and associated wave-train like patterns which are far away from the blocking sector can also well represented in CFSv2. The CFSv2 well reproduces the observed characteristics of local temperature and precipitation anomalies associated with the blocking over both sectors. Additionally, the CFSv2 also well reproduces the observed above normal precipitations over southern China when both sectors occur blocking, particularly in the Baikal-Okhotsk sector.

• Comparative Analysis of Single-Moment and Double-Moment Microphysics Schemes in WRF on the Torrential Rainfall Event in North China During 1921 July, 2016
• KANG Yanzhen;JIN Shuanglong;PENG Xindong;YANG Xu;SHANG Kezheng;WANG Shigong
• 2018 Vol. 37 (2): 481-494.  DOI:10.7522/j.issn.1000-0534.2017.00026
• Abstract ( ) HTML PDF (17379KB) ( )
• Based on a general analysis, the torrential rainfall event in north China during 19-21 July 2016 is simulated by using the Weather Research Forecast modeling system. The effects of microphysics schemes, divided into two groups of nine single and seven double-moment schemes on rainfall area and intensity of precipitation were evaluated. The results show that the heavy rainfall event with low vortex characterized by high intensity, long duration and large amount. Simulation of most schemes present a rather good reproduction of rainfall. As time goes on, differenc-es between schemes are more obvious. The results of the double-moment schemes presented less simulation effect, compared to the results of the single-moment schemes in terms of rain mixing ratio, solid hydrometeor and vertical velocity. The double-moment schemes was much better than its contrary one. Overall, it was the SBU_YLin that provided the most successful simulation scheme on the torrential, and the simulation of rainfall area and intensity of the rainfall was close to the observations.

• Experiment and Verification of the Convective-Scale Ensemble Forecast Based on BGM
• MA Shenjia;CHEN Chaohui;HE Hongrang;LI Xiang;LI Yi
• 2018 Vol. 37 (2): 495-504.  DOI:10.7522/j.issn.1000-0534.2017.00073
• Abstract ( ) HTML PDF (18209KB) ( )
• Based on breeding of growing modes (BGM) method, an ensemble forecast experiment was tested for a strong squall line considering the highly non-linear feature and detailed forecast requirement in convective-scale weather systems. The probability matched mean (PMM) method was used to analysis contrastively the results of the ensemble forecast, and the effect of precipitation forecast was verified by the bias score and equitable threat score (ETS). The results indicate that BGM method applied to the convective-scale ensemble forecast could generate the rapid growth perturbations that represent atmospheric uncertainties. The results of the ensemble forecast were more accurate than the control forecast, the traditional ensemble mean (EM) method was more accurate on the smaller intensity forecast, and the PMM method was more skillful at forecasting the large intensity events. The results of the verification in precipitation forecast demonstrated that the EM method had the highest forecasting skill of the small magnitude precipitation. And the PMM method had obvious advantages in the forecasting techniques of extreme precipitation events. Convective-scale ensemble forecast can improve the forecasting skill of precipitation forecast, and provide a guidance for the high-impact convective weather events.

• Study on Characteristics of Qinghai-Tibetan Plateau Cirrus Based on Satellite Data
• XUE Xiaoning;DENG Xiaobo;LIU Guihua
• 2018 Vol. 37 (2): 505-513.  DOI:10.7522/j.issn.1000-0534.2017.00047
• Abstract ( ) HTML PDF (3203KB) ( )
• The Qinghai-Tibetan Plateau (QTP) is one of the climate sensitive zone in China. The cirrus of QTP was studied for investigating the distribution features based on the MYD06_L2 of MODIS cloud product data. There we analyzed the cloud optical thickness, cloud-top height, effective scale and probability distribution of cirrus. The results showed as follows:(1)The cirrus probability of occurrence is higher in March and April and lower in October to December. Nevertheless, it performed a double peak probability distribution pattern. According to our research, one peak period is in January to April, and the other is in July to August, the two lower periods occurred in May to June and September to December. (2) The probability distribution of cirrus cloud-top height produced significant change in June and October. The mean height of the cirrus cloud peak appears in the summer months from July to August, and the minimum value appears in the winter months from January to February. (3) The effective radius of the particles in the cirrus cloud is mainly distributed in a range of 5~40 μm, and the probability is greatest in 15~25 μm. The maximum mean radius of the particles in the cirrus cloud was detected in August to September and the minimum value appeared in December to February. (4) Cirrus optical thickness was ranged in 0~40 with the top probability between 0~10. There showed a similarity to cirrus effective particles scale, the maximum and minimum of optical thickness was August to September and December to February, respectively.

• Compare and Analyze FY-2G Cloud Products to Ground-Based Manual Observed Cloud Amount
• LI Ya;GUO Jianxia;CAO Yunchang;ZHOU Can;CHEN Yizhi
• 2018 Vol. 37 (2): 514-523.  DOI:10.7522/j.issn.1000-0534.2017.00027
• Abstract ( ) HTML PDF (10458KB) ( )
• In order to promote the layout of automated ground-based cloud amount measurements, the cloud fraction (CFR) and the cloud total amounts (CTA) measured by geostationary satellite FY-2G were compared to the manual cloud amount measured at surface stations to analyze the concordance rate and deviation between each other. China was selected as study area and five months (July and October of 2015 and January, April and July of 2016) were selected to represent spring, summer, autumn and winter. There are five times manual cloud amount measurement (8 h, 11 h, 14 h, 17 h, 20 h) per day at 838 stations in China. The satellite data within 5 km radius of these station's points were used to produce point's data corresponding the manual cloud amount observed data, where the inverse distance to power method was used to the CFR data and the regional average method was used to the CTA data. It is considered consistent when the difference of two data is less than 2 tenths of sky cover at the same times. The results showed that the data of the satellite FY-2G cloud products' are usually lower than that of the manual observed at surface and the CTA is more obvious than the CFR. Then four levels of sky covers were divided by the manual cloud amount for further study. The level one is clear sky that cloud amount is less than 1 tenths of sky, the level two is partly cloudy that cloud covers 2~3 tenths of sky, the level three is cloudy that cloud covers 4~7 tenths of sky, and the level four is overcast that cloud amount is more than 8 tenths of sky. The comparison between satellite data and surface observed data was conducted time by time in each level. The results indicated that the performance of CTA and CFR are not good enough in all levels of sky cover and all over the country. In average, CTA is better than CFR in the condition of clear sky and overcast sky, while CFR is better than CTA in clear sky and partly cloudy sky. For the exploration of the performance' spatial distribution, the west and southwest part of China suffer from scarce capacity, especially in Yunnan, Guizhou, Guangxi and Guangdong province. So, we should plan more automated ground-based cloud observation in west and southwest part of China. It is obvious that although the satellite cloud product' could help us know more spatial information of cloud, a certain density of ground-based observation is needed to correct and promote the satellite products for further applications.

• Case Study on the Formation Mechanism of Two Types of Short-term Strong Rainfall Occurred in Gansu Province on 18 June 2013 and 19 June 2014
• XU Dongbei;GOU Shang;XIAO Wei;MENG Lixia;SHA Honge;DI Xiaohong;SHI Yanzhao
• 2018 Vol. 37 (2): 524-534.  DOI:10.7522/j.issn.1000-0534.2017.00056
• Abstract ( ) HTML PDF (30872KB) ( )
• By using "2014·06·18" and "2013·06·19" short-term strong precipitation observation and NCEP 1°×1°reanalysis data, the characteristics of the situation, the configuration of the weather situation, the dynamic thermal characteristics, cloud and radar features for different kinds of strong short-term rainfall were compared and analyzed, which happened in same season and similar climate background at the middle and south parts of Gansu Province. The results show that the formation mechanism have both similarities and significant differences. The rain intensity of the two processes is large, and the former occurred in the case of intense convergence of cold and warm air in the middle and lower level, which accompanied with obvious temperature frontal zone, frontogenesis and the ground cold front activity. It is a kind of short-term strong precipitation of baroclinic frontogenesis. The latter occurred in the strongly developed warm and moist advection in the lower level, the warm and wet advection played a leading role in establishing thermodynamic instability, it is a kind of short time strong precipitation of the warm advection force. The instability index showed that the unstable energy of the former was much larger than that of the latter, and there was convective inhibition, which was conducive to the development of strong convection. The thickness of the wet layer of warm advection forced short-term heavy rainfall was higher than that of oblique pressure front short-term heavy rainfall, and high-level vertical wind shear performance of the latter short-term heavy rainfall was much stronger. The image features of warm advection force was a banded cloud which was quickly move northward along with warm air on 19 June 2013. The image features of oblique pressure front was a comma cloud system which corresponding to the low-level herringbone shaped shear on 18 June 2014. The change and development of cloud system is closely related to the changes of situation field, which is an important reason for the development and changes of precipitation area. Radar reflectivity factor on 19 June 2013 showed that it was a mixed cloud-based mixed precipitation echo, and the echo gradient was small with low center of mass. Radar reflectivity factor on 18 June 2014 was a stratified cloud scattered block convection single echo, and the echo gradient was large with high center of mass, besides, the echo intensity can be developed to very strong. When the core area of the strong reflectivity of 50 dBz is close to 8 km, reached the height of -20℃ layer, and the echo top height reached 12 km at same time, there would be hail there.

• Temporal and Spatial Variation of Extreme Precipitation Events in Dunhuang and Surrounding Areas from 1958 to 2015
• LI Peidu;SI Jianhua;FENG Qi;ZHAO Chunyan;WANG Chunlin
• 2018 Vol. 37 (2): 535-544.  DOI:10.7522/j.issn.1000-0534.2017.00055
• Abstract ( ) HTML PDF (10740KB) ( )
• Dunhuang Yangguan in the south of Qilian Mountain, where the flood season comes from the floods of Subei, Aksai and the local floods every year, it had a disastrous floods in 2~3 years, meanwhile, the flood carrying debris flow to polluted the unique survival local water sources and caused the serious damage of water resources. Sub-daily rainfall extremes may be associated with flash flooding, particularly in mountain regions, but compared with extremes on daily timescales, they have been relatively little studied in mountain regions. In the recent decade, extreme precipitation events have let to numerous flash floods in and around the Duhuang region. Based on the daily precipitation data from 1958 to 2015 (the weather station of Qilian data from 1958 to 2013) of six weather stations in Dunhuang neighborhood, that is, Mazongshan, Dunhuang, Guazhou, Jiuquan, Yumen and Qilian, period characteristics and spatial characteristics of extreme precipitation events were analyzed by the Manner-Kendall mutation test, wavelet analysis and kriging interpolation in Dunhuang area which can provide the basis for water resources management and flood control and disaster reduction. The results indicated that the frequencies of extreme precipitation in Dunhuang, Guazhou, Jiuquan, Yumen and Qilian are all increasing in addition to the decreasing trend of Mazongshan. The annual rainfall increments of extreme precipitation are -0.063, 0.127, 0.072, 0.138, 0.104 and 0.638 d·(10a)^-1, respectively. In the extreme precipitation intensity mutation analysis, the UF statistic showed the trend of "V" type, namely, the trend of increasing first and then decreasing, The control periods of extreme precipitation intensity have 53-year, 22-year, 36-year, 56-year and 58-year time scale in Dunhuang, Guazhou, Jiuquan, Mazongshan, Yumen and Qilian according to the result of the extreme precipitation intensity wavelet analysis. Daily maximum precipitation, extreme precipitation and extreme precipitation intensity show the spatial distribution characteristics of gradient from west to east.

• Influences of the Winter EI Niño Event on the Summer Precipitation in the Jiuquan Region of China in 2016
• DUAN Shengze;ZHANG Yinghua;GU Yu
• 2018 Vol. 37 (2): 545-552.  DOI:10.7522/j.issn.1000-0534.2017.00053
• Abstract ( ) HTML PDF (17489KB) ( )
• Using the China Meteorological Administration National Climate Center 160 stations monthly precipitation data and the index of WPSH, the China Meteorological Administration National Meteorological Center 2 479 national ground stations monthly precipitation data, the NCEP/NCAR monthly average 500 hPa height field, 700 hPa humidity ratio, 700 hPa wind field, the CPC Oceanic Niño Index (Niño3.4 area monthly average sea surface temperature anomaly), the NOAA ERSST V4 average sea surface temperature data, through the analysis of the precipitation and atmospheric circulation situation of this site, the influences of the EI Niño event on the summer precipitation in Jiuquan region of China in 2016 were studied. The results show:(1)2016 is the attenuation year that after the super EI Niño event reached its crest value. Influenced by its direct and indirect effects, in the summer of 2016, different levels of drought and waterlogging occurred in all parts of China. In general, waterlogging is more severe than drought. Located in the hinterland of northwest China, Jiuquan region had also a high response to it. Summer precipitation in Jiuquan region of China in 2016 was significantly more than the same period of other years. (2) The summer precipitation in Jiuquan region was positively correlated with the Nino3.4 index in winter of that very year. The stronger EI Niño in winter often more favorable for the summer precipitation in Jiuquan region in the same year. (3) The 2015/2016 EI Niño event had an impact on the water vapor conditions and the upward movement of Jiuquan area in the summer of 2016, more water vapor conditions and stronger ascending motion eventually led to the significantly higher rainfall.

• Construction and Climate Variation Analysis of Icing Weather Phenomenon Series over China
• YU Yu;REN Zhihua;MENG Xiaoyan
• 2018 Vol. 37 (2): 553-559.  DOI:10.7522/j.issn.1000-0534.2017.00071
• Abstract ( ) HTML PDF (7103KB) ( )
• Long term series of icing weather phenomenon during 1954-2015 were extracted from the ground observations covering more than 2 400 national level surface stations over China. Then several quality control procedures were carried out, such as meteorological elements inherent consistency check and statistical check by using 30-year climate normal. Especially, we paid much attention on the following two situations when checked the time series. The first one was that a part of national stations under the historical guidance for simplifying observation did not measured and recorded the icing weather phenomenon before the year of 1981, and the other one was that the annual icing days from hundreds of stations in several years before 1981 were less than their normal values with remarkable differences. The results showed that, 662 stations actually did not take the mission of icing weather observation in the whole of 6 328 years during 1954-1979, which were mainly distributed in Hebei, Jiangsu, Jiangxi, Henan, Hubei, Hunan and Shaanxi provinces. Before 1981 there were also other 1 453 years from 839 stations obtaining much less icing weather records when compared to the normal of 1981-2000. Based on the raw data and the quality controlled data, we calculated the national mean values of annual icing days during 1961-2015. It illustrated that the raw data had an upward trend with about 2.0 days for every decade while the quality controlled data showed a declined trend of -1.5 days per decade. The national mean annual days of daily minimum air temperature lower than -1℃ had a high correlation (0.92) with the quality controlled national icing day series, which indicated the decline trend of icing days was acceptable. The annual mean icing day of the stations to the south of Latitude 25°N and of the stations in Sichuan Basin were almost less than 10 while it was greater than 200 in the northwest of Heilongjiang, northeast of Inner Mongolia, and Qinghai-Tibetan Plateau. We also analyzed the variations of the icing duration over Northern China from 1971 to 2015 by choosing 708 stations which were all located to the north of Latitude 35°N with consecutive observations. The average value of annual icing duration of Northern China was about 149 days with a downward trend of -2.1 days per 10 years. The icing duration of 288 north stations significantly reduced in the past 45 years, and the starting dates of icing duration from 155 stations were delayed, while the ending dates of 144 stations were brought forward.

• Spatiotemporal Change of Drought at Various Time Scales Indicated by SPEI and SPI in Xijiang River Basin
• ZHANG Lijie;LI Jian
• 2018 Vol. 37 (2): 560-567.  DOI:10.7522/j.issn.1000-0534.2018.00013
• Abstract ( ) HTML PDF (2918KB) ( )
• In this study, the standardized precipitation index (SPI) and the standardized precipitation evapotranspiration index (SPEI) were used to analyze the spatio-temporal variability of drought and difference between SPI and SPEI performance in Xijiang River basin. The two indices were calculated by using the observations at 34 meteorological stations during the period from 1959 to 2016. The results showed that:(1) A significant increasing trend of drought severity and drought frequency were detected at 12-month time scale in most areas of Xijiang River basin. (2) Drought showed more frequently and across a wider area at 3-month time scale in spring and autumn, and the same thing happened at 12-month time scale after 2000. (3) Drought with the highest frequency and the most extensive area were in 1980s, 2010-2016, 1960s and 2000s were more than other decades, and it was fewest in 1970s and 1990s. (4) Generally, SPEI and SPI index indicated the similar results in evaluating drought at 12-month time scale. The SPEI index is lower than overall SPI index at 1-month、3-month and 6-month time scale, the difference is very large greater, especially in spring and winter.

• Formation and Structure of '4·20' Warm Sector Squall Line in Guangxi Province
• ZHAI Liping;NONG Mengsong;LAI Zhenquan;QI Liyan;LIU Risheng
• 2018 Vol. 37 (2): 568-576.  DOI:10.7522/j.issn.1000-0534.2017.00058
• Abstract ( ) HTML PDF (20136KB) ( )
• A warm area squall line occurred in Guangxi province on 20 April 2016, bringing strong wind and heavy rainfall. For insight into the formation mechanism of the warm sector squall line, the environmental conditions, formation and structure of the squall line were further analyzed by using varieties of observation data. The results showed that the stranded cold temperature trough ahead of upper trough was beneficial to strongly convective instability. Meanwhile, the lower strong warm and moist air advection played a leading role in establishing static instability. The diagram of T-lnP indicated that the environmental conditions of the southern part of Guangxi were more conducive to the development and organizational reinforcement of convection than that of the northern part. In addition, the cold pool outflow interacting with lower environmental wind field was the main mechanism for the squall line to develop and maintain. The squall line moved and developed toward the one hour katallobaric center ahead. Moreover, the squall line was given priority to dispersive transmission, along with a guiding streamline and the trailing stratiform cloud area.