Current Issue

• Simulation on Afternoon Convective Precipitation Triggered by Soil Moisture over the Qinghai-Tibetan Plateau
• LUAN Lan;MENG Xianhong;Lü Shihua;HAN Bo;LI Zhaoguo;ZHAO Lin;LI Ruiqing
• 2018 Vol. 37 (4): 873-885.  DOI:10.7522/j.issn.1000-0534.2018.00008
• Abstract ( ) HTML PDF (30254KB) ( )
• This study designed sensitive experiments using WRF model and used CTP-HI_low framework to investigate the influences of soil moisture change on triggering and inhibiting the afternoon convective precipitation over the Qinghai-Tibetan Plateau. The results show that WRF model can reproduce the spatial distribution of the precipitation over the Qinghai-Tibetan Plateau. In addition, there are some improvements of the precipitation simulation over the west part of the Qinghai-Tibetan Plateau when soil moisture decreases. In general, the statement of large scale atmospheric circulation dominates the occurrence of the afternoon convective precipitation process, especially in the middle, southwestern and northeastern part of the Qinghai-Tibetan Plateau. The large scale atmospheric circulation caused the triggering and inhibiting afternoon convective precipitation events account for about 60%~90% of the total number of the triggered and inhibited precipitation events. According to the results of the simulation, when soil moisture decreases, there are more positive feedback cases than negative feedback cases between soil moisture and afternoon convective precipitation which means the decreasing of the soil moisture inhibits the occurrence of afternoon convective precipitation in most cases. However, relative smaller proportion of the cases is the decreasing soil moisture that triggers the afternoon convective precipitation which is the negative feedback. The amount of convective precipitation triggered by the negative feedback process accounts for larger proportion in the northwest part which is the arid part of the Qinghai-Tibetan Plateau. It has the center value up to 80% or more. The mechanism of negative feedback is that the decreasing soil moisture increases the surface sensible heat flux which influences the distribution of sensitive heat flux over the Qinghai-Tibetan Plateau. The increased sensible heat flux contributes to the development of the boundary layer which makes the air parcel easier to reach the level of free convection and the occurrence of afternoon convective precipitation. By comparing the values of CTP and HI_low between control and sensitive experiments in different years, to some extent, there are differences between these two years. It means that soil moisture can influence occurrence of afternoon convective precipitation through its influences both on the surface energy and the atmosphere humidity.

• Numerical Simulation of the Effect of Soil Moisture on a Case of Plateau Vortex over Qinghai-Tibetan Plateau
• ZHANG Huan;FAN Guangzhou;ZHANG Yongli;LAI Xin
• 2018 Vol. 37 (4): 886-898.  DOI:10.7522/j.issn.1000-0534.2018.00004
• Abstract ( ) HTML PDF (26654KB) ( )
• Using the National Centers for Environmental Predication Final Analyses (NCEP-FNL) reanalysis data, the temperature of brightness blackbody (TBB) data from FY-2E meteorological satellite, and the Climate Prediction Center morphing technique (CMORPH) precipitation data, the effect of soil moisture on a plateau vortex occurring from 16 to 17 August 2014 over Qinghai-Tibetan Plateau were analyzed on the numerical simulation for a control experiment and four sensitivity experiments by employing the WRF model (version 3.8.1). The results show that the vortex center, the vortex intensity and the vortex precipitation at 500 hPa were simulated in the control experiment successfully. The soil moisture plays a key role in the intensity and precipitation of the vortex, however, it has no significant influence on the nature and moving path of the plateau vortex. Meanwhile, the soil moisture mainly influences the vortex by changing the surface latent heat flux and the surface sensible heat flux. When the soil moisture increases, the surface latent heat flux increases, and the instability of the air in middle and low atmosphere increases as well, which provides energy for the development of convective systems and increases the convective precipitation, leading to the strengthening of vortex intensity by increasing the release of the condensation heating. On the contrary, the intensity and precipitation of the plateau vortex are both weakened. In the paper, the change of the surface sensible heat flux has little effect on the formation of vortex, hence we just considered its impact on the convective precipitation. When the soil moisture increases, the surface skin temperature gets lower, the surface sensible heat flux decreases and the planetary boundary layer height (PBLH) decreases, thus increasing the moist static energy per unit mass of air, which increases the convective precipitation. Otherwise, the convective precipitation decreases.

• Spatial-temporal Variability of the Snow Depth over the Qinghai-Tibetan Plateau and the Cause of Its Interannual Variation
• BAO Yuntao;YOU Qinglong;XIE Xinru
• 2018 Vol. 37 (4): 899-910.  DOI:10.7522/j.issn.1000-0534.2017.00099
• Abstract ( ) HTML PDF (19784KB) ( )
• Based on daily snow depth observation data from National Meteorological Information Center and atmospheric circulation data from JRA55 reanalysis, the spatial-temporal variability of snow depth over the middle east area of Qinghai-Tibetan Plateau (QTP) in early winter (November to subsequent January) and late winter (February to April) during 1961-2013 was analyzed. The circulation patterns and water vapor conditions affecting the snow depth anomalies and its interannual variations over the QTP were analyzed. The results show that, interannual and interdecadal variations of snow depth over the QTP is significant. Spatial distribution of snow depth is uneven, the interannual variability of snow depth increases with the increases of altitude. Changes of the snow depth are consistent with the region in early and late winter. Trend of snow depth are not obvious in both early and late winter during 1961-2013. Snow depth increases significantly before 1996 and decreases insignificantly after 1996. The interannual variability of snow depth in early winter is likely to be dominated by interannual variations of both Arctic Oscillation (AO) and geopotential height near the QTP. In late winter, the interannual variability of snow depth is likely to be dominated by the geopotential height near the QTP and adjusted by interannual variations of AO. When snow depth over QTP is significantly positive, geopotential height anomaly from Arabian Sea to eastern QTP is negative, causing the animation of southern branch trough, westerly jet to the southern side of the plateau strengthens, increasing the water vapor flux in front of the trough. Meanwhile, the subtropical high moves northward and becomes strong, increasing the water vapor flux in its peripheral areas. Strengthening of the Lake Baikal ridge leads cold air southward and meet with warm and humid air from low-latitudes in the eastern plateau, which is conducive to more snowfall and more snow depth over the QTP.

• The Model Analysis of Lightning Charge Structure Characters and Attributions over Qinghai-Tibetan Plateau
• GUO Fengxia;WANG Manfei;HUANG Zhaochu;LI Yang;MU Yijun;LIAN Chunhao;ZENG Fanhui
• 2018 Vol. 37 (4): 911-922.  DOI:10.7522/j.issn.1000-0534.2018.00002
• Abstract ( ) HTML PDF (15021KB) ( )
• To further recognize the particularity of thunderstorm over Qinghai-Tibetan Plateau (QTP), this paper has analyzed the primary attribution of charge distribution, and also predicted the microphysics and electrification occurring on 13 August 2003 in QTP, using a three-dimensional dynamics-electrification coupled model. The charging parameterization included both the graupel/hail-cloud/ice inductive charging mechanism and the graupel/hail-ice non-inductive charging mechanism. The charging processes between other large and small particles are small, so they were ignored in this study. The results indicated that the characteristics of thunderstorms in QTP are unique. The life period of the thouderstorm is short, and the positive cloud-to-ground flashes occur frequently. The updraft and downdraft are weaker, and solid precipitation is more than liquid precipitation. Cloud top of thunderstorms are low and warm cloud area is small. Meanwhile, the height of solid small particles (ice crystals, snow) is low. The solid large particles (gravel, hail) distributed widely and mainly grounded. The thunderstorms in QTP displays a vertical tripole charge structure, then transforms into dipole distribution during dissipate stage. total charge density shrinks, while the peaks of charge center is higher. The main positive charge center is located at 7~9 km (-40~-30℃), and the main negative charge center is located at 4~7 km (-10~0℃). The lower positive charge center is located at 2~3.5 km. And all the charge areas are uplifted with convection. The lower positive charge center occupies widely and it lasts a long time. The tripole distribution is referred to as non-inductive collisional separation between ice-phase microphysics. The main positive charge center is mainly formed by ice crystals, the main negative charge center and lower positive charge center are mainly formed by snow and graupel. The weakening of the non-inductive collisional charging mechanism between graupel and ice makes the lower positive charge center dissipate. The dipole one results from the precipitation of graupel particles. Because of the smaller warm cloud thickness, high effective liquid water content in mixed area, and lower the tropical tropopause, the overlap area of graupel and hail distribution is larger, so the lower positive charge is wide and last for a long time.

• Variation Characteristics of the Surface Turbulent Flux and the Components of Radiation Balance over the Grassland in the Southeastern Tibetan Plateau
• LI Hongyi;XIAO Ziniu;ZHU Yuxiang
• 2018 Vol. 37 (4): 923-935.  DOI:10.7522/j.issn.1000-0534.2017.00097
• Abstract ( ) HTML PDF (3769KB) ( )
• Based on field observations of the grassland over Nyingchi area in the southeastern Tibetan Plateau for the period from 20 May to 9 July 2013, the variation characteristics of the basic meteorological elements, the surface turbulent flux and the components of the radiation balance over the grassland in Nyingchi area under different weather changes were analyzed, and the relationships among these variables and their features under typical sunny day and cloudy day were analyzed emphatically in this paper. The results show that:(1) The change trends among each meteorological elements are match well with each other, the variation of the relative humidity is correlated with that of the precipitation, but that those of the air temperature, ground temperature and wind speed are anti-correlated with that of precipitation; During the observation period, more latent heat than sensible heat is exchanged, sensible heat flux is definitely higher during the days without rain, but latent heat flux is lower, things are the opposite in the precipitation period; The variation of the sensible heat flux is consistent with that of the total solar radiation (DR), and the variations of the reflective solar radiation (UR), the long wave radiation from the earth (ULR), the net radiation (Rn), the surface albedo and the soil heat flux are also correlated with the DR, but that of the long wave radiation from the atmosphere (DLR) is anti-correlated with the DR. (2) The analysis results of the typical sunny day and the typical cloudy day show that the diurnal variation amplitude of sensible heat flux and latent heat flux in sunny condition is larger than that in cloudy condition, during the daytime, the sensible heat flux and the latent heat flux in the typical sunny day is significantly greater than that in the typical cloudy day, except the downward long wave radiation, the other components of the surface radiation balance in the sunny day are much larger than that in the cloudy day; At night, the upward long wave radiation, the net radiation and the soil heat flux in the sunny day are smaller than that in the cloudy day. (3) The maximum value of relative humidity appears in the morning, and the lowest value occurs in the afternoon; The minimum value of wind speed appears in the morning and the maximum value appears at noon, and the values in the sunny day are mostly greater than that in the cloudy day. As a result, the sensible heat flux, latent heat flux, soil heat flux, each components of radiation balance and basic meteorological elements over the grassland at Nyingchi area in the southeastern Tibetan Plateau all have very close coordinated variation relationships with weather changes, the correlation coefficients between these variables are high, and these variables fit well with each other. It shows that this boundary layer observation data has high reliability, and this experiment observed data can provide important data basis for numerical model to simulate the surface-to-air exchange process over Nyingchi area in the southeastern Tibetan Plateau.

• Dynamic Snow Melting Process and Its Relationship with Air Temperature in the Hinterland of Sanjiangyuan Region in Qinghai-Tibetan Plateau
• ZHANG Juan;XU Weixin;WANG Li;ZHOU Huakun
• 2018 Vol. 37 (4): 936-945.  DOI:10.7522/j.issn.1000-0534.2018.00001
• Abstract ( ) HTML PDF (1857KB) ( )
• The data of 30 mins snow depth and air temperature in winter half year during 2013 to 2014 derived from the field automatic observing site in the hinterland of the Sanjiangyuan Region in Qinghai-Tibetan Plateau were used in this study. We mainly analyzed the relationship between snow depth and air temperature in the time level of half hour based on one long snow melting period with 16 days in this area from 21 February to 1 March in 2014. The melting process of snow in this area is characterized by slow first and fast later. It was found that snow melting is slow while snow depth above on 10 cm, but it was changed obviously when snow depth is less than 10 cm and snow depth melting will more remarkable along with more low snow depth. During the snowmelt period, the snow depth drops rapidly at 10:00 (Beijing time, the same as after) -11:00 and 14:00-15:30. In this area, the relationship between snow depth and air temperature show a weak correlation before 9:00, the correlation becomes obvious after 9:00 and it is gradually stronger after 10:00 until 18:00. The time from 13:00 to 14:00 is a main period contribute to snow melt in a day. The advance lag analysis showed that the temperature within 240 mins before the melting period would significantly influence the change of snow depth. We found that the decrease of snow depth can be observed even though at -12℃ in this area.

• Frontogenesis and Moisture Characteristic Analysis on a Sudden Rainstorm at the Edge of Subtropical High
• QIU Guiqiang;ZHAO Guixiang;DONG Chunqing;WANG Xiaoli
• 2018 Vol. 37 (4): 946-957.  DOI:10.7522/j.issn.1000-0534.2017.00059
• Abstract ( ) HTML PDF (14843KB) ( )
• For the sudden rainstorm predicted with a large deviation by several operational models, which occurred at the edge of western Pacific subtropical high (WPSH) southwest of Shanxi province at night on 31 July 2010, the conventional observation, hourly precipitation, TBB data derived from FY-2E satellite and WRF model high resolution simulation results were used to analyze the evolution of rainstorm, frontogenesis and moisture characteristics. The results indicated that the sudden rainstorm was due to frontogenesis that caused by dry and cold air at the back of upper trough pushing the warm and moist air at the edge of WPSH. The meso-β circular convective system (MβCCS) led to the rainstorm directly. The formation and development of mesoscale-β vortex provided a favorable condition of moisture convergence to the maintenance of MβCCS. The surface cold front and nearby mesoscale convergence line triggered the convection develop. Frontogenesis diagnosis showed that the vertical structure of low-level convergence and middle-level divergence led to low-level horizontal frontogenesis and middle-level horizontal frontolysis in the troposphere. The strong ascending motion made the height of strong instability layer rise and thus led to strong middle-level vertical frontogenesis. The vertical and horizontal frontogenesis happened at the same time, but the vertical frontogenesis was an order of magnitude larger than the horizontal frontogenesis. The appearance of middle-and low-level strong frontogenesis and secondary circulation corresponded well with the time and the location of strong precipitation. In comparison, the tilting term contributed most to total frontogenesis, and the convergence term contributed least. The strength of middle-and low-level frontogenesis is beneficial to the rise of low-level moisture. In the process of frontogenesis, deep moisture saturation layer thickness and the water vapor content stretching to high-level have evident indication to the forecast of local strong precipitation. At last, the intensity and moving track of upper cold air and development of MβCCS are major points to determine the location of such type of rainstorm.

• Mesoscale Characteristics and Environmental Conditions of South Trough Squall-Line Hailstorm in Yunnan
• ZHANG Tengfei;ZHANG Jie;ZHANG Sidou;ZHU Li
• 2018 Vol. 37 (4): 958-969.  DOI:10.7522/j.issn.1000-0534.2017.00093
• Abstract ( ) HTML PDF (21771KB) ( )
• By using the automatic station, FY2E satellite, CG lightning and NCEP 1°×1° reanalysis meteorological data, mesoscale characteristics and environmental conditions of two spring squall-line hailstorms in Yunnan were analyzed under the influence of the south trough. The results show that the partial westerly jet before south trough not only provides water vapor condition for strong convective hailstorms, but also provide momentum condition for hailstorms through their mutual coupling action strengthens ascending motion. Hailstorms occur in the mutual coupling area of the partial westerly jet before the south troughs at 500 hPa and 700 hPa. The deep and strong jet stream in high altitude and the strong vertical wind shear can produce high wind on the ground through momentum transfer, on the other hand, in the production of convective instability, they can lead to the increase of baroclinicity in the middle and high layer, and strengthen the upward movement to promote the development of hailstorm, especially the strong vertical wind in the middle and low layer influences the organization and development of hailstorm. Hailstorms occur in areas where the vertical wind shear is greater than or equal to 3×10^-3 s^-1 between middle and low layer. When the 500 hPa low trough over the Qinghai-Tibetan Plateau moves to the southeast and leads the cold air southward in the north, the strong convective instability of upper cold and lower warm air is formed to provide convective instable conditions for the occurrence and development of hailstorm, because of the cold air intrusion on the middle layer and warm ridge domination under the common action of warm advection and surface radiation heating on the low layer. Hailstorms occur in the strong instable region of T_(850-500) ≥ 27 K. The south trough clouds continuously develop to squall-line hailstorms which influence Yunnan from the west to the east for about 12 hours. The strong convective instability of upper cold and lower warm air and the strong vertical wind shear lead to the formation of convective cumuliform clouds of the south trough, and the cold advection invasion of rear side in the middle level and the momentum down delivery function lead to further develop to comma clouds and arched squall lines, which produce TBB decrease and CG lightning increase, produce the sudden change of wind direction, the sudden increase of relative humidity, the sudden drop of temperature, and produce the strong convective hailstorm weather of intense thunderstorm, gale, hail and short-term heavy rain. While the strength of westerly jet and the size of strong vertical wind shear are the direct causes of two squall line hailstorm development difference.

• Diagnostic Analysis on a Heavy Rainfall Associated with the Northeast Cold Vortex and Atmospheric River
• SUN Yingshu;WANG Yongqing;SHEN Xinyong;ZHOU Yushu;DENG Guo
• 2018 Vol. 37 (4): 970-980.  DOI:10.7522/j.issn.1000-0534.2018.00005
• Abstract ( ) HTML PDF (10605KB) ( )
• Based on the FNL reanalysis and HYSPLIT model driven by NCEP GDAS data, this study examined a heavy rainfall associated with the northeast cold vortex (NECV) and atmospheric rivers (ARs) over the northeast China occurred on July 25, 2016. The results indicated that the heavy rainfall occurred in a favorable synoptic pattern, NECV, the Okhotsk blocking high, the low at the east of Japan, upper-and low-level jet played important roles in the process. There were two ARs that both originated from the Western Pacific and coupled with deep wet layers during this event. However, one of the two ARs flowed northward to the northeast China through the East China sea and the Yellow Sea and the other flowed northeastward through the South China Sea with considerable moisture. ARs provided favorable moisture condition for the heavy rainfall by entraining abundant moisture from tropical regions to mid-latitudes directly. The convergence of moist air from tropical origin and dry air from the circulation of NECV induced intense ascending motions in surrounding regions, which was the main dynamic uplift mechanism of the intense rainfall. Analysis of the trajectory tracking reveals that the most significant moisture sources of the heavy rainfall were the Western Pacific, the South China Sea, the Bay of Bengal and the Eurasia. Furthermore, the moisture within the lower and middle troposphere was mainly transported by the south atmospheric river and the southwest atmospheric river separately.

• The Features of a Type of West-Low and East-high Heavy Rainfall in Shaanxi Province
• LI Bo;WANG Nan;JIANG Ming;HUA Dengxin
• 2018 Vol. 37 (4): 981-993.  DOI:10.7522/j.issn.1000-0534.2017.00100
• Abstract ( ) HTML PDF (9500KB) ( )
• By using the Multiquadric method and the WRFDA (WRF data assimilation system) module, various data including the temperature data detected from the Raman Lidar in XAUT (Xi'an University of Technology), the mini-meteorological station observation data in XAUT and the convectional observation data were integrated into the initial field of WRF (Weather Research and Forecasting model). And a high resolution numerical simulation on a heavy rainfall case occurred in Shaanxi province in April 2015 was carried out. The quality control on the simulation data was conducted by using the quantitative check method and qualitative check method, and the results showed that the model had well copied the heavy rainfall case. Based on the simulation data and observation data, a new method named synthetically analysis and classifying diagnosis technique was used to study the features and formation process of the heavy rainfall case. It was a type of west-low and east-high rainfall. The warm low in the east of Qinghai-Tibetan Plateau and the cold high in North China together caused the collision between the warm-wet air and the cold-dry air in south Shaanxi. The air was near to be saturated with a water vapor mixing ratio of 10.3 g·kg^-1, which was favorable of the rainfall, and the shear of wind speed triggered the heavy rainfall. Also, the features of the weather type of west-low and east-high, and the formation of the low and the high system were introduced respectively. The low located to the west of Shaanxi was closely related to the Qinghai-Tibetan Plateau. The air flowed over the Plateau and formed the weather type of the low-pressure to the east of the Plateau. On the other side, the high located to the east of Shaanxi was from the middle part of Inner Mongolia. The Mongolia High would move southeasterly to Hebei province and Beijing, and it would couple with the ridge of high pressure over the Eastern China. Thus, the weather type of the east-high was formed. Generally speaking, it was the closed high and closed low that together caused the heavy rainfall. In fact, the typical characteristic of the west-low and east-high was that the pressure around the rainfall center reduced together, instead of a situation of reducing-pressure in west part and increasing-pressure in east part. During the reducing-pressure process, the east station possessed a higher pressure than the west station. In the end, a type of conceptual model for the heavy rainfall in Shaanxi province was proposed according to this study.

• Monitoring of Conditions for Heavy Snowstorm in Northern Xinjiang Using Satellite Remote Sensing Data
• LIU Song;HUANG Fuxiang;YANG Lianmei;HAN Shuangshuang
• 2018 Vol. 37 (4): 994-1001.  DOI:10.7522/j.issn.1000-0534.2018.00055
• Abstract ( ) HTML PDF (28150KB) ( )
• Based on AIRS remote sensing datasets of air temperature and total column water vapor and the method of HYSPLIT backward trajectory analysis, the sources and transporting paths of various meteorological elements of two heavy snow processes in Urumqi during 10-12 December 2015 and 2-3 March 2016 were monitored and analyzed, which including cold air, warm air and water vapor, the differences between conditions and intensities of snowfall in winter and spring were also studied. The results show that:(1) Snowstorm in northern Xinjiang is an outcome of interaction of cold air, warm air and water vapor. (2) During two snowstorm processes, the transfer of water vapor has five sources of the Black Sea, the Caspian Sea, the Aral Sea, the Balkhash Lake and the Arabia Sea, the cold air mainly comes from the northern Europe, the Norwegian Sea, the Barents Sea and the Iranian Plateau, the sources and transporting paths of warm air and water vapor are generally same or closely related. (3) The snowstorm during 10-12 December 2015 is a record strong snowstorm process, the cold air of this process mainly comes from the northern Europe, the Norwegian Sea and the Iranian Plateau, the warm air and water vapor both come from the Black Sea and the Caspian Sea. The transportation of water vapor from the Arabia Sea is an important cause of torrential storm. (4) The snowfall during 2-3 March 2016 is a weak snowfall process in spring, the cold air of this process mainly comes from the regions of Nordic and West Siberia, the warm air mass and water vapor comes from the Northern Xinjiang and the Balkhash Lake respectively. Due to the lack of continuous water vapor supplement, the snowfall is short and weak. (5) By comparing the two different snowfall processes, the abundant and continuous water vapor is a main factor that determines the duration and intensity of snowfall.

• Comparison of Different Methods for Estimating Potential Evaporation in an Arid Environment
• JIAO Dandan;JI Xibin;JIN Bowen;ZHAO Liwen;ZHANG Jinglin
• 2018 Vol. 37 (4): 1002-1016.  DOI:10.7522/j.issn.1000-0534.2018.00048
• Abstract ( ) HTML PDF (5937KB) ( )
• The potential evaporation indicates the atmospheric evaporative demand under some specific conditions and is one of the key parameters involved in land surface process and hydrological cycle. Combined with the meteorological data and pan evaporation from 2015 to 2016 in the Linze Inland River Basin Research Station, Chinese Academy of Sciences, We selected a total of 10 methods derived from the well-known radiation-based, temperature-based, and combination methods to estimate the potential evaporation in the middle regions of the Hexi Corridor, northwest China. We compared and analyzed the differences of methods in an arid environment and the results were compared with the data from E601 and Φ20 evaporation pan. The principal results indicated that:(1) We analyzed the relationship between evaporation and meteorological factors and found that the main meteorological factors affecting the evaporation were vapor pressure deficit, net radiation and temperature. (2) We used two methods to calculate conversion coefficients of pan. The arithmetic mean method of the conversion coefficients of pan were 0.65 and the linear regression method of the conversion coefficients of pan were 0.62. (3) The differences of the calculated values are mainly due to the value of different aerodynamic terms and radiation terms. Every method is based on a specific regional and climatic background and the parameters are also calculated based on experience. The methods need to be corrected when used in other regions. In general, the combination methods are most applicable in this region, followed by the radiation-based methods, and the temperature-based methods have the worst applicability. (4) In the combination methods, the results of the FAO-56 method was the best and the fitting value of E601 evaporation pan was 1.02 (R² was 0.70), followed by the radiation-based, the results of the Doornbos-Pruitt method fit well with the Φ20 evaporation pan and the fitting value was 0.78 (R² was 0.85). These provide a reference for estimating evaporation simply and accurately with the help of evaporation pan. In addition, the Blaney-Criddle method and the Hargreaves-Samani method were also fit for calculating potential evaporation in this region. The above results provide support for the accurate estimation of evaporation in regions where the climatic data were insufficient. And they also provide a methodological reference for calculating potential evaporation in the arid or similar conditions to our study site.

• Comparative Analysis of Pan Evaporation Trends between the Summer Monsoon Transition Region and Other Regions of China
• YANG Siqi;ZHANG Qiang;XI Xiaoxia;QIAO Liang
• 2018 Vol. 37 (4): 1017-1024.  DOI:10.7522/j.issn.1000-0534.2018.00006
• Abstract ( ) HTML PDF (907KB) ( )
• In this paper, Nanchang station, Dingxi station and Urumqi station were taken as representative stations of the summer monsoon region, the summer monsoon transition region and non-summer monsoon region. Based on the conventional observation data of Nanchang station, Dingxi station and Urumqi station from 1961 to 2010, the pan evaporation trends in different regions were compared and the reasons for their differences were analyzed. The results show that the pan evaporation trends varied greatly in different regions. The tendency rates of pan evaporation in Dingxi, Nanchang and Urumqi are 50.3, -150.7 and -206.1 mm·(10a)^-1, respectively. Besides, by analyzing the sensitivity of meteorological factors, it was found that the pan evaporation is sensitive with different meteorological factors in different regions. In addition, combining the trends analysis and sensitivity analysis of the meteorological factors, the main factors that cause the differences of pan evaporation trend in different regions are annual precipitation, average low cloud cover and average wind speed. Due to the latitude that the north edge of the monsoon reached was lower and lower in recent years, the trend of precipitation, average low cloud cover and average wind speed in monsoon transition zone are contrary with these in other regions of China. Thus, the pan evaporation trend in monsoon transition zone are opposite to the pan evaporation trend in other regions of China.

• Hydrogen and Oxygen Stable Isotopes Characteristics of Atmospheric Water Vapor during Growing Season in Alpine Wetland Ecosystem of Qinghai Lake
• WU Fangtao;CAO Shengkui;CAO Guangchao;CHEN Kelong;LIN Yangyang
• 2018 Vol. 37 (4): 1025-1032.  DOI:10.7522/j.issn.1000-0534.2017.00092
• Abstract ( ) HTML PDF (827KB) ( )
• Water cycle is a "belt" that connects all circles of the earth and various water bodies, and is of great significance to the evolution of the Earth's surface structure and human sustainable development. Hydrogen and oxygen stable isotopes as an important part of the water body, are sensitive to environmental changes and record the historical evolution of the water cycle. Hydrogen and oxygen stable isotopes of atmospheric water vapor can provide rich information for studying atmospheric water movement and its phase transition process. Based on the in-situ continuous observation data of the stable isotopic composition (δ¹⁸O, δD) of atmospheric water vapor in the growing season of the plant, the characteristics about hydrogen and oxygen stable isotopic and the correlation between atmospheric water vapor δ¹⁸O and the main environmental factors were analyzed. The results showed that the differences of δ¹⁸O as well as δD in the heights of 0.5 m and 1.5 m, 0.9 m and 1.9 m are small, and the seasonal variation trends of them are low in the middle stage of the growing season, while the early growth season and the latter is just the opposite. Precipitation, temperature, relative humidity, evapotranspiration and net radiation are the important environmental factors that affecting the change of δ¹⁸O in atmospheric water vapor, and there are interrelated and synergistic interactions among environmental factors relationship. The local meteoric vapor line equation MVL, which characterizes the correlation between local atmospheric water vapor δ¹⁸O and δD, deviates from the global meteoric water line (GMWL) by the influences of environmental factors, atmospheric water vapor sources and evaporation of water vapor in Qinghai Lake.

• Method Study on Identification of Radio-Frequency Interference Signal from Airborne Microwave Radiometer
• WANG Wan;LEI Hengchi;WANG Zhaoyu;GUO Xiaojun;NIE Haohao
• 2018 Vol. 37 (4): 1033-1041.  DOI:10.7522/j.issn.1000-0534.2017.00084
• Abstract ( ) HTML PDF (5995KB) ( )
• Radio-frequency interference (RFI) signals were found in the brightness temperature datas of G-band water Vapor Radiometer (GVR). It is necessary to identify and correct the interference datas for better use. Based on the analysis of the applicability of various RFI identification methods of GVR data, the RFI recognition and correction method for GVR was proposed according to the principle of GVR detection and calibration. This method is used to identify the RFI from GVR brightness temperature datas on November 20, 2016 and the results show that:(1)The method works well for identifying the RFI from the brightness temperature datas of GVR different channels; (2) RFI signals exist in multiple channels and have no regular distribution in spatial and temporal that brings great difficulties to determine the source of RFI; (3) In addition to a few signals exist in the form of isolated points, majority of RFI signals in the brightness temperature datas exist in the form of continuity points. The more the continuity interference points are, the worse the correction results are. The datas are recommended to be eliminated when there are many continuity interference points. The retrival results analysis of before and after correction of RFI from GVR datas show that most of the PWV (Precipitable Water Vapor) and LWP (Liquid Water Path) values are overestimated because of the RFI and the correction of individual channels, which has different effects on the retrival results.

• Evaluation of the Minimum Temperature Forecast of 1~52 Days Based on DERF2.0 Model
• XU Yanyan;CHANG Jun
• 2018 Vol. 37 (4): 1042-1050.  DOI:10.7522/j.issn.1000-0534.2017.00090
• Abstract ( ) HTML PDF (937KB) ( )
• On the basis of the lowest temperature data for the average of 20 full sample of the National Climate Centre second-generation monthly Dynamic Extended Range Forecast operational system 2.0 (DERF2.0) from 1983 to 2013, the forecast capacity of the lowest temperature in mid-latitudes of China in march from 1 to 52 days was evaluated. The first ten days of the minimum temperature were more credible, and the shorter the forecast time was, the higher the credibility was, but over the 10 days, the credibility of the forecast was getting worse and worse by evaluating the absolute value of the absolute error (AE), root mean square error (RMSE) and correlation coefficient (R). In order to analyze the deep reasons of the model error, the data was decomposed by the ensemble empirical mode decomposition (EEMD). The high frequency component IMF1 and the trend item R were the main components, while the low frequency component IMF2 account for a small proportion in DERF2.0 data and observation data. The main reason for the decline in predictive ability after ten days was the decline in the predictive ability of the high frequency IMF1 by analyzing. In the DERF2.0 model, the variance contribution rate and observation data of the high frequency components of the high frequency components were generally low compared with the observed data. The contribution rate and observation data of the trend item R variance were higher than that of each year. The DERF2.0 model should focus on the study of high frequency disturbances to improve the ability of DERF2.0 in predicting the temperature changing process.

• The Characteristics of Ice Cloud Properties Derived from Satellite Data in Northwest China
• LIN Tong;ZHENG Youfei;LI Te;WANG Liwen
• 2018 Vol. 37 (4): 1051-1060.  DOI:10.7522/j.issn.1000-0534.2017.00088
• Abstract ( ) HTML PDF (15216KB) ( )
• The Northwest China probability distribution of ice cloud occurrence frequency, ice water content and ice cloud effective radius were presented based on DARDAR data coalesce from Cloud-Aerosols Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and CloudSat Satellite which come from A-Train Satellite formation during the period from December 2012 to November 2016, the distribution and vertical structures were discussed and analyzed. The results show that, the occurrence frequency of ice cloud is 55.1% over the last four years and the occurrence frequency of ice cloud in spring is mostly greater than 70% apart from the Midwest area of Hexi-Inner Mongolia, it has obvious seasonal variation. The amplitude of season variation is bigger in 2015 and 2016 than the first two years, and ice cloud occurrence frequency generally small in the desert area. The high occurrence frequency of ice cloud area is in the northeastern part of the Qinghai-Tibetan Plateau because of the special terrain; The occurrence frequency of ice cloud is both bigger in spring, autumn and winter but only smaller in summer at the northeastern of the Qinghai-Tibetan Plateau, because the warm and humid air from the Indian Ocean is blocked by the southern mountain of the plateau, which leads to a lower occurrence frequency of ice cloud in the northeastern of plateau in summer. The ice water content is almost has no ice water distribution above 13 km, ice water content in Northwest China is the biggest in summer and almost has no ice water distribution below 5 km because of the high temperature in summer that make ice cloud not easy to form in the lower floors, and the ice water content is generally smaller in autumn and winter. The difference of ice water content between different regions in northwest of China is relatively large; Ice cloud effective radius and ice water content had a similar trend in the whole of Northwest China area and five different sections, which are bigger in spring and summer and smaller in winter and autumn; Especially in summer, ice effective radius is generally larger, but ice cloud effective radius is relatively small in the numerical value of ice water content area 37°N-39°N because of the higher temperature in summer. The difference of the Ice cloud effective radius between different regions in Northwest China is relatively larger, the Ice cloud effective radius is minimum in The east seasonal wind areas of Northwest China and biggest in Northern Xinjiang and the midwest of Qilian Mountain-Qinghai area.

• Wind Power Prediction Method for Micro-scale Wind Farm Based on CFD and Kalman Filtering Integrated Correction
• LIU Lijun;LIANG Youjia
• 2018 Vol. 37 (4): 1061-1073.  DOI:10.7522/j.issn.1000-0534.2017.00098
• Abstract ( ) HTML PDF (5161KB) ( )
• As a statistical method, Kalman filter is often employed for power forecasting, but the method is not able to capture tails of wind power distributions.In this paper, a hybrid method, based on the combination of Kalman filter and a physical method using computational fluid dynamics (CFD), considered the factor of wind resource distribution and will be useful to improve the availability of micro-scale wind energy.It is of great significance to improve the utilization of wind energy at the micro-scale.Taking Nanqiu wind farm as the study area, which locates in the Loess Plateau of Gansu Province.SCADA was provided by China Huadian Corporation (CHD).Firstly, CFD method was used to simulate the wind environment and the characteristics of wind speed, and the results of CFD were then analyzed and the sub-regions of wind prediction were set up.Secondly, the predicted wind speed was corrected by Kalman filter, which was based on the simulation results by BJ-RUC model.Thirdly, after the adjustment with the Kalman filter method, the forecasting accuracy of wind speed was improved for the wind station and all the sub-regions.Finally, the effects of wind power forecasting were assessed and the correspond benefits were also evaluated, which based on the power generation capacity of the wind farm.The results showed that:(1) Wind speed of the airflow over the mountains reaches maximum.When mountain height increases, the wind speed values increases, the difference of wind speed is up to 2.78 m·s^-1; (2) The result of BJ-RUC model showed that the model could resolve the variation trend of wind speed, the accuracy of wind speed has better performs with accuracy rate over 90% from the initial accuracy 20%~30% by integrating Kalman filter and CFD method.Meanwhile, the accuracy of wind power forecast in micro-scale Loess Plateau is up to 80%, the wind speed and wind power forecasting accuracy has been significantly improved at the micro-scale complex terrain; (3) The capacity factor C_P is on average about 12.4%~16.8%, curtailment rates η is on average about 5.5%~17.5%, which affects the forecasting effect of wind power, so the power generation efficiency should be improved furtherly; (4) In addition, some uncertainty factors were also discussed in the paper, including data quality of SCADA, computational efficiency of CFD, policy decision of energy sector, and the way in which it effects characteristics and forecast of wind speed.

• Simulation of Highly Resolved Wind Field on a Severe Cold Air Case over Zhoushan Sea-Crossing Bridge
• GU Tingting;LI Xiaoli;LIU Danni;PAN Yaying
• 2018 Vol. 37 (4): 1074-1082.  DOI:10.7522/j.issn.1000-0534.2017.00086
• Abstract ( ) HTML PDF (7272KB) ( )
• Based on the NCEP FNL reanalysis data, the TAPM model was used to simulate the severe cold air case with a high spatial resolution of 300 m×300 m over Zhoushan sea-crossing bridge from 24 to 27 November 2015.The results of simulation were verified with the observational data from traffic meteorological observation stations on the bridge.Thus, the temporal and spatial distribution characteristics of cross wind at different sections of Zhoushan sea-crossing bridge were analyzed.The results show that TAPM model has a good performance in simulating the evolution and distribution characters of wind fields over the Zhoushan sea-crossing bridge during the severe cold air event.The variation trends of wind speed, wind direction and cross wind speed in every hour are near to the observations, as well as the wind speed and the time when the maximum wind happens.However, the model underestimates the wind speed at the land station.During the process of this severe cold air, the strong cross wind mainly influences the middle section of Jintang bridge, the east section of Xihoumen bridge and Cezi isle, where the cross wind speed is higher than 11 m·s^-1.The duration time of the strong cross wind force scale over 6 is more than 33 hours.Although the mean wind speed from Taoyaomen bridge to Zhoushan sections is high, the cross wind speed is much smaller and only about 2~7 m·s^-1, the negative impact of the high cross wind is the least compared with other sections.What should be paid attention to is that the risk of cross wind will suddenly increase in the two curve road sections in the east-west direction of Jintang isle of the Yongzhou highway and the ramp between the Taoyaomen bridge and the Cezi isle, which may bring potential traffic hazard and requires additional driving attention.The research provides an effective and feasible way to improve the forecasting and warning of highly resolved wind field and provide better management for the Zhoushan sea-crossing bridge traffic safety.

• The Application of Intensive FY-2G AMVs in GRAPES_RAFS
• WAN Xiaomin;HAN Wei;TIAN Weihong;HE Xiaohuan
• 2018 Vol. 37 (4): 1083-1093.  DOI:10.7522/j.issn.1000-0534.2017.00089
• Abstract ( ) HTML PDF (12453KB) ( )
• Atmospheric Motion Vectors (AMVs) can supply plenty of useful information for numerical weather prediction.Statistical results demonstrate that the quality of intensive FY-2G Atmospheric Motion Vectors (AMVs) is best when the quality indicator (QI) is greater than 80.Therefor, it is necessary to evaluate intensive FY-2G AMVs for the analysis field and precipitation forecast in GRAPES (Global/Regional Assimilation Prediction System) at CMA.In this study, by using GRAPES_RAFS (Rapid Analysis and Forecast System), three contrast tests had been researched based on one rainstorm occurred from 2 to 3 July 2016.The results show that assimilation of intensive FY-2G AMVs have weak positive impacts on the 850 hPa wind and height analysis field.The 24 hours precipitation forecast results show positive contribution to rainfall intensity and location prediction when using intensive FY-2G AMVs.One-month experiments were conducted to examine the impact of assimilating intensive FY-2G AMVs, the results indicate that assimilating intensive FY-2G AMVs improves the wind analysis field, especially in high levels, and the precipitation forecasting scores for moderate rain to heavy rain are improved with using intensive FY-2G AMVs.

• Simulation of Lightning Induced Overvoltage on Transmission Line Based on FDTD
• GAO Jinge;MA Jingjin;MA Haipeng;PIAO Wen
• 2018 Vol. 37 (4): 1094-1101.  DOI:10.7522/j.issn.1000-0534.2017.00087
• Abstract ( ) HTML PDF (1209KB) ( )
• In order to provide scientific guidance for lightning protection design of transmission lines, the Agrawal model telegraph equation's time domain form was deduced as the theoretical foundation, and the Finite-Difference Time-Domain (FDTD) method was used as the computational method, the double Heidler function was used to simulate the base current of the return stroke channel, the improved linear attenuated transmission line (MTLL) return stroke model was selected to calculate the lightning induced voltage on the overhead transmission lines.The effectiveness of the above method is proved by comparative analysis.Then the influences of position, height and soil conductivity on lightning induced voltage were studied.The results show that the horizontal electric field component and the vertical electric field component in the lightning electromagnetic pulse are very important in the coupling mechanism.When the observation point moves from the midpoint of the line to the endpoint, the induced voltage decreases gradually, and the bipolar characteristics of the waveform become more and more obvious, this may be related to the attenuation of the path.The midpoint voltage and the forward voltage of the endpoint increase with the height of the transmission line.Therefore, the designer can reduce the line height to reduce the damage of lightning coupling voltage to the transmission line.With the decrease of soil electrical conductivity, the midpoint voltage increases, and the endpoint voltage decreases.In addition, the response of the scattering voltage component to the soil conductivity changes significantly, while the incident voltage component is not affected.

• Simulation Analysis of Lightning-Return Stroke ELF/VLF Ground Wave Propagation over Intermediate Ranges
• FENG Jianwei;HOU Wenhao;FAN Xue;WANG Lei;ZHOU Lei;XIAO Dong
• 2018 Vol. 37 (4): 1102-1109.  DOI:10.7522/j.issn.1000-0534.2018.00047
• Abstract ( ) HTML PDF (2201KB) ( )
• Lightning discharges can radiate electromagnetic waves over a wide frequency range from a few Hz to many tens of MHz, but most of the electromagnetic energy is radiated in the ELF and VLF bands.A new approximate method for lightning-radiated extremely low-frequency (ELF) and very low-frequency (VLF) ground wave propagation over intermediate ranges (within 1500 km) was presented in this paper.In our approximate method the field attenuation function was divided into two factors in frequency domain representing the propagation effect of the earth conductivity and curvature, respectively, and these two attenuation factors have more clear and simple expressions in frequency domain, which can be easily calculated by multiplying them rather than solving complex differential equation related to Airy functions.The method was validated by using Newton-Raphson root-finding method for propagation path with different earth conductivities, we found our approximate method could predict the field peak and waveform rise time with a satisfactory accuracy.The comparison results show that our new approximate method can predict the lightning-radiated field peak value over the intermediate range with a satisfactory accuracy within maximum errors of 0.2%, 3.3% and 8.7% for the earth conductivity of 4 S·m^-1, 0.01 S·m^-1 and 0.001 S·m^-1, respectively.So, the research result has solved it in a more efficient way.We also found that the earth curvature has much more effect on the field propagation at the intermediate ranges than the earth finite conductivity.For example, the lightning-produced field peak of ELF/VLF frequency propagating over a spherical-earth is just about 30%~40% of that propagating over a planar-earth at a distance of 1500 km, and 75%~80% for a distance of 500 km.we should pay more attenuation to the effect of earth curvature, for example, the current moment peak value predicted from the measured far field peak will be underestimated when using a far-field-current relationship at the assumed planar earth.

• The Detection and Analysis of Dust Weather by Lidar and Microwave Radiometer in Xingtai
• HAO Jufei;YUAN Leiwu;LI Zhixia;QI Jiahui;SHI Hairui
• 2018 Vol. 37 (4): 1110-1119.  DOI:10.7522/j.issn.1000-0534.2018.00009
• Abstract ( ) HTML PDF (8584KB) ( )
• Based on aerosol lidar and ground-based multichannel microwave radiometer data, combined with backward trajectory model and other data, the high-altitude extinction coefficient, the depolarization ratio, the temperature and the humidity of Xingtai city were calculated and analyzed during May 3-5, 2017.The results showed that:The main reason for the increase of particulate pollutant concentration in Xingtai is the dust deposition which transported at a distance from the northwest, and the dust from northern Xinjiang is affected by cold front moving eastward, local winds also cause dust pollution from the ground to high altitude, and the increase in PM₁₀ concentration is much higher than that of PM_2.5.The sand dust that collected near the height of 2 000 m can form a strong value region with extinction coefficient greater than 1 km^-1.The average value of depolarization ratio of sand dust accumulation area is 0.252, and a clear sand dust boundary is formed in the region with lower average deviation ratio of 0.041, the strong value center of the extinction coefficient and the sand dust boundary of the depolarization ratio can be used to characterize the change of dust deposition.the ground temperature has increased when dust deposition or sand dust was caused by ground wind, The atmospheric humidity in the whole layer shows a steep downward trend before the concentration of terrestrial particulate pollutants increases sharply, and the atmospheric humidity of the whole layer is maintained at a low level, the concentration of the particle pollutant is in the high value fluctuation stage.

• The Correlation Analysis with Meteorological Parameters during Sand and Dust Weather Conditions in Recent Four Years in the Southern Margin of Taklimakan Desert
• MAO Donglei;CAI Fuyan;ZHAO Feng;LEI Jiaqiang;LAI Fengbing;XUE Jie
• 2018 Vol. 37 (4): 1120-1128.  DOI:10.7522/j.issn.1000-0534.2018.00010
• Abstract ( ) HTML PDF (1254KB) ( )
• Wind velocity (V), relative humidity (RH), air temperature (T) and solar radiation (SR) observed synchronously from 1 September 2011 to 31 July 2014 in shifting sandy land in Cele in the margin of Taklimakan Desert were adopted in this paper.Time periods, duration of sand-driving wind and the correlations among average wind velocity, air temperature, RH and SR were analyzed through the research methods of regression analysis, statistical and correlated analysis.In order to provide theoretical basis for predicting sand and dust weather, interaction mechanisms of meteorological elements during sand and dust weather were discussed.The results show that the frequency of sand-driving wind more than 0.5 hour during the time period of 12:00(Beijing time, after the same)-13:00 is highest during a day and which is accounted for 8.78%, the frequency of sand and dust weather in the time period of 10:00-18:00 is accounted for 57.94% of the whole frequency.The frequency trend increases from morning and then decreases to night, and the changing trend is almost same with air temperature in daily change.The duration time from 2 hours to 2.5 hours of sand-driving wind is highest, which is accounted for 13.62%.The average monthly wind velocity is synchronously changing with average monthly air temperature during in shifting sandy land with significant linear correlation, while the changing trend for average monthly RH and average monthly air temperature is reverse.It shows significant correlations at the level of 0.01 between average wind velocity difference, temperature difference and RH between vertical distances, and it shows significant positive correlations at the level of 0.01 between average wind velocity and duration time of sand-driving wind.It shows significant negative correlation between average wind velocity, average wind velocity differnce in vertical distances and RH differences in vertical distances, and it shows significant negative correlations between average air temperature and average RH at the level of 0.01.It shows a significant negative correlation between average air temperature difference and average wind velocity difference in vertical distances, and the significant positive correlation is shown between average air temperature difference and average RH difference in vertical distances.Except for average wind velocity at the height of 0.5 m, the correlations are all significant between SR and rest meteorological parameters.The sand-driving winds in the seasons of spring and summer are dominant, the prevailing wind directions of sand-driving wind are mainly WNW and W wind directions in shifting sandy land in Cele, and the sand prevention measures should be strengthened in the orientation with W and WNW directions in oasis periphery.

• Statistical Characteristics of Low Visibility at Nanjing Lukou Airport Based on AWOS Data
• MU Xiyu;XU Qi;ZHOU Linyi;TAO Xing;HUANG Anning
• 2018 Vol. 37 (4): 1129-1142.  DOI:10.7522/j.issn.1000-0534.2017.00095
• Abstract ( ) HTML PDF (4775KB) ( )
• Based on the minute-level ground observation data from Lukou airport from 2011 to 2016, the temporal distribution characteristics of low visibility weather and the relationship between other meteorological factors and visibility were analyzed.The thresholds of weather factors in low visibility weather were established in order to get the early warning indexes of low visibility weather.It is found that in case of visibility lower than 2 000 m, the monthly average relative humidity are more than 90%, indicating that the low visibility of Lukou airport is mainly caused by the fog.Lukou airport visibility shows a obvious seasonal and sub-seasonal change, showing a double-peak and double-valley structure, April and July-August for the two peaks, June and December-January for the two valleys.The formation of this feature is closely related to the temperature, humidity and stratification of the surface atmosphere.Visibility distribution has a very obvious diurnal variation, with the lowest visibility in the morning and early morning, the highest visibility in the afternoon.The largest diurnal variation of the visibility happens in autumn, and the longest possible distribution of the low visibility happens in winter.It was found that the relationship between visibility and meteorological elements is complex and does not show some linear relationship.By analyzing the different levels of low visibility weather corresponding to the temperature, temperature dew point difference and the level of wind speed range, found that the temperature is different in different months, the temperature dew point difference and the level of wind speed is more stable.