Current Issue

• Evaluation on Forecasts of a Cold Wave in China and Its Eurasian Cold Air Activity by CFSv2 System in November 2015
• WEI Zhigang;ZHU Xian;DONG Wenjie;LIU Yajing;CHEN Guangyu;LIU Yujia
• 2019 Vol. 38 (4): 673-684.  DOI:10.7522/j.issn.1000-0534.2019.00014
• Abstract ( ) HTML PDF (31671KB) ( )
• The operational forecast data of the second generation climate prediction system (CFSv2) with the length of 9 months and the NCEP/DOE reanalysis data from National Centers for Environmental Prediction (NCEP), and the global daily highest and lowest surface temperature data from the NOAA Climate Prediction Center (CPC) in the USA are selected, the forecasts of the CFSv2 system to a cold wave process occurred in China from 21 to 27 November 2015 are evaluated. The results show that the CPC data with high resolution and the NCEP/DOE data with coarse resolution are both very clear to show the evolution characteristics, temperature drop and temperature anomaly of this cold wave process. The temperature drops caused by the cold wave occurred mainly in the eastern part of China, and in the north of the Caspian Sea and the Black Sea at the same time. The temperature drops is also evident in the Arctic Ocean coast of northern Asia. The temperatures between Siberia and the eastern part of China are obviously colder than usual, the temperatures in Western Europe and the Iranian Plateau are lower, and the temperatures in other regions of Eurasia, especially in the north, are higher. The CFSv2 has certain abilities to forecast the whole temperature drops and temperature anomalies of this rapid freezing cold wave for 0, 5, 10 and 15 d in advance, but the prediction ability is poor 20 d in advance. On the whole, the CFSv2 can predict the spatial distribution of temperature drops better than the temperature anomalies, but the absolute errors with the observed values of temperature drops are greater than that of the temperature anomalies. The temperature drops from the CFSv2 forecasts are obviously low than the ones from the observation by the cold wave in North China, South China and nearby areas, but higher in Siberia, Mongolia and Northeast China. In addition, the temperature drops from the CFSv2 forecasts in the north of the Caspian Sea and the Black Sea is also obviously low than the ones from the observation. The temperature anomalies from the CFSv2 forecasts are obviously low than the ones from the observation by the cold wave in the whole Eurasian land area, but higher in the surrounding ocean area and the adjacent coastal area.

• Interannual Variations of Siberian High during Boreal Winter and Its Influence on East Asian Temperature
• ZHU Hongxia;CHEN Wen;FENG Tao;WANG Lin
• 2019 Vol. 38 (4): 685-692.  DOI:10.7522/j.issn.1000-0534.2018.00116
• Abstract ( ) HTML PDF (12902KB) ( )
• The dominant interannual variations of Siberian high (SH) during Boreal Winter in north Asia region (40°N-60°N, 80°E-120°E) are analyzed using empirical orthogonal function (EOF) decomposition based on NCEP/NCAR monthly mean sea level pressure data from 1979 to 2017. The results show that the first EOF mode present a uniform variation over the whole region, the second mode exhibit a north-south seesaw relationship in seal level pressure change, and the third mode show a west-east seesaw relationship. In addition, the principal component time series of the three dominant modes all indicate significant interannual changes. Further analysis of the relevant atmospheric circulation pattern and East Asian temperature anomaly associated with the first mode show that the atmospheric circulation is characterized by changes in sea-land pressure gradient and related changes in East Asian trough strength and subtropical jet intensity. When SH is in negative phase, East Asia is warmer than usual, on the contrary East Asia is colder when SH is in positive phase. The second mode of SH is closely related to changes in Arctic Oscillation (AO) and North Atlantic Oscillation (NAO), where the height field shows a quasi-positive pressure north-south annular mode. When SH is strong in the north and weak in the south, the circulation pattern is similar to the AO positive phase, weakened temperate jet stream lead to warmer condition in the northeastern part of East Asia, but when SH is weak in the south, the northeastern part of East Asia is colder. The atmospheric circulation associated with the third mode mainly occurs in the local area of Eurasia, and also has a certain relationship with the North Atlantic Oscillation (NAO). When SH is strong in the east and weak in the west, the east part of East Asia is warmer and the southwest part is colder. When SH is weak in the east and strong in the west, the northeastern part of East Asia is colder and the southwest part is warmer.

• Analysis on Response of Vegetation Index to Climate Change and Its Prediction in the Three-Rivers-Source Region
• ZHU Wenhui;MAO Fei;XU Ying;ZHENG Jun;SONG Lixue
• 2019 Vol. 38 (4): 693-704.  DOI:10.7522/j.issn.1000-0534.2018.00105
• Abstract ( ) HTML PDF (15777KB) ( )
• To analyze the response of NDVI to climate change and its time-lag effect in multi-time scales, synthetic data NDVI detected by NOAA-AVHRR, monthly observed data of precipitation and temperature from 1989 to 2008 were used in this paper. On this bases, we built NDVI prediction models to forecast trends of NDVI under different emission scenarios in the future. Results showed that:(1) NDVI high value areas existed in southeastern and eastern Three-Rivers-Source Region, and gradually become lower to West-north direction. Months from April to August were growing seasons for vegetation, when NDVI reached maximum in August. (2) Variations of NDVI in spring, summer, autumn displayed an obvious positive phase with temperature and precipitation excluding the summer precipitation; correlation features in spring and autumn were especially remarkable; the response of NDVI to temperature was higher than that to precipitation. Time-leg effect of NDVI in the current month showed most significant correlation feature with the last month's temperature and precipitation. (3) Under the background of Three-Rivers-Source Region's climate warming and slightly increasing precipitation from 2006 and 2050, average NDVI increased significantly, slower in the first decade, and faster in the next three decades with large growth rate. Distribution of NDVI was essentially constant in spatial, and increasing centers with high-intensity and large-range under RCP8.5 scenario were much prominent than that under RCP4.5 scenario. Years of 2016-2035 were rapid growth phase with increasing center of Lancangjiang source region under RCP4.5 scenario. Periods of 2016-2025 and 2036-2045 were rapid increasing time with high variability center of yangtze river source region under RCP8.5 scenario. Location of high variability center in coming multi-decades shifted from north to south in Three-Rivers-Source Region under both scenarios.

• Observations of Soil Moisture Influence on Surface Energy Dynamics and Planetary Boundary Layer Characteristics over the Loess Plateau
• MA Yingsai;MENG Xianhong;HAN Bo;YU Ye;Lü Shihua;LUAN Lan;LI Guangwei
• 2019 Vol. 38 (4): 705-715.  DOI:10.7522/j.issn.1000-0534.2019.00036
• Abstract ( ) HTML PDF (2749KB) ( )
• Based on the observational data of land surface processes and disastrous weather observation and research station in Pingliang area of Gansu Province during the summer (June, July and August) of 2016-2017, the effects of soil moisture on surface radiation, surface energy distribution and the development of atmospheric boundary layer in Pingliang area under dry, medium and wet conditions were quantitatively analyzed. And then, according to the general soil moisture change trend, the soil moisture was further divided into dry-medium sections(0.158~0.22 m³·m^-3)and medium-wet (0.179~0.325 m³·m^-3) sections and the correlation between soil moisture and Bowen's ratio, sensible heat flux and latent heat flux was analyzed to explore the possible physical mechanism of soil moisture affecting precipitation by affecting surface turbulent energy distribution and the development of atmospheric boundary layer. The results show that:(1)Soil moisture has a relatively small impact on albedo, and has a significant impact on Bowen's ratio, mainly affecting sensible and latent heat changes, that is, affecting the process of surface energy distribution. With the increase of soil moisture, latent heat increases, sensible heat decreases and Bowen ratio decreases significantly. The change of soil moisture has a significant impact on net radiation, mainly on net long-wave radiation. With the increase of soil moisture, net short-wave radiation increases slightly and net long-wave radiation increases significantly. (2)Inter-zonal analysis of soil moisture showed that the influence of soil moisture on latent heat flux and boundary layer height was greater in the dry and middle sections (0.158~0.220 m³·m^-3) than in the middle and wet sections (0.179~0.325 m³·m^-3). That is to say, the change of surface flux and the development of atmospheric boundary layer are more significant when the soil is dry. The results of quantitative analysis of the observations are consistent with the theoretical mechanism, which shows the reliability of the observed data and the data can provide an important data basis for the simulation of the numerical model in the Loess Plateau region.

• Analysis on Evolution Characteristics and Influencing Factors on Evapotranspiration of Zoige Wetland
• MU Wenbin;SUN Suyan;MA Weixi;HAN Yuping
• 2019 Vol. 38 (4): 716-724.  DOI:10.7522/j.issn.1000-0534.2018.00150
• Abstract ( ) HTML PDF (8810KB) ( )
• Evapotranspiration is an important part of the hydrological process of wetland, which influences the hydrological ecosystem of wetland. Zoige Wetland is taken as the study area. Based on the daily meteorological observation data of 6 meteorological stations 1963-2013 which are within and outside the Zoige Wetland, the potential evapotranspiration (ET0) of each site and the wetland is estimated based on the Penman-Monteith formula recommended by FAO, respectively. The spatial and temporal evolution characteristics of ET0 are analyzed from the perspectives of tendency, mutation and periodicity, and the relationship between ET0 and its main influencing factors is discussed. The result shows that the tendency of seasonal and interannual ET0 in Zoige Wetland is presented as an increasing trend on the time scale, especially in summer, autumn and interannual scale; in terms of spatial scale, it exhibits an increasing trend to varying degrees, and this trend of ET0 is very significant among the whole region in autumn, and run through the east and west in the interannual scale; meanwhile, Zoige Wetland showed a more obvious trend of warming and drying. For the mutation of ET0, the mutation years of spring, winter and annual scale ET0 were all around 2002, while the mutation occurred in summer and autumn around 1988 and 1997, respectively. For the periodicity of ET0, the main period of ET0 in spring, summer, autumn and the interannual scales may be 28 years, and 22 years in winter. In addition, the first major influencing factor of ET0 is temperature in spring, autumn, winter and interannual scales, while the sunshine hours in summer; among different stations, the first one is relative humidity, which are the most obvious in Zoige and Hongyuan stations in winter. The study is expected to provide a scientific basis for further exploring the climate and ecological environment changes in the Zoige wetland.

• Snowfall Identification and Evolution Trend in Xilin River Basin
• WANG Fei;ZHU Zhongyuan;HAO Xiangyun;HAN Dongdong;WANG Huimin;WANG Qiong
• 2019 Vol. 38 (4): 725-733.  DOI:10.7522/j.issn.1000-0534.2018.00119
• Abstract ( ) HTML PDF (4251KB) ( )
• Based on the dual temperature threshold method, the precipitation and temperature data of four national meteorological stations in Xilin River Basin from 1969 to 1979 were used to calculate the relationship between the snowfall ratio and the daily average temperature, and the critical temperature of snowfall discrimination in the Xilin River Basin was determined, and the snowfall identification index equation was fitted.. According to the critical temperature and identification equation, the snowfall of each station in the basin was estimated from 1980 to 2016, and the Mann-Kendall test was used to test the snowfall of 1969-2016 to find the typical mutation point of snowfall in the basin. A simulation scheme for temperature and precipitation changes was established for the boundary, and their contribution to the change of snowfall was quantified. The results showed that the snowfall identification method combined with the critical temperature and snowfall identification equation can better estimate the snowfall at each station in the Xilin River Basin, and the correlation coefficient is above 0.89 with an error of less than 4%. The trend of estimated snowfall between the stations in the basin is inconsistent in the Xilin River from 1980 to 2016, and the snowfall in the whole basin shows a trend of increasing eastward and decreasing westward. According to the results of Mann-Kendall mutation test, the typical mutation point of the basin was taken in 1980. and the simulation scheme of temperature and precipitation change was established. It was concluded that the temperature increase had a negative contribution to the snowfall change during the snowfall period, and the increase of precipitation contributed positively to the snowfall. The combination of temperature and precipitation will promote the increase in snowfall.

• The Simulation of Extreme Precipitation over Hunan Province based on the Statistical Downscaling Method of Transform Cumulative Distribution Function (CDF-t)
• ZHOU Li;LAN Mingcai;CAI Ronghui;HUANG Juan;JIANG Zhihong
• 2019 Vol. 38 (4): 734-743.  DOI:10.7522/j.issn.1000-0534.2018.00122
• Abstract ( ) HTML PDF (8081KB) ( )
• Intensify, frequency and duration of Extreme Precipitation would increase in the future under a warming climate. Especially for Hunan where is sensitive to the climate change. Based on the CMIP5 historical simulations datasets, the ability of the CMIP5 models in simulating the spatial pattern andinterannual variability of extreme precipitation over Hunan province are evaluated using the statistical downscaling method of transform cumulative distribution function (CDF-t) combined with four extreme precipitation indices. The results show that due to the low resolution of GCM models, characteristics of extreme precipitation related to the terrain and atmospheric circulation over Hunan were not exactly reproduced. There are great differences between patterns, and the model sets have relatively poor simulation results. CDF-t statistical downscaling can improve CMIP5 simulation of extreme precipitation in Hunan by establishing the functional relationship between large-scale variable CDF and the same regional variable CDF. As far as the spatial structure is concerned, this method can greatly improve the spatial structure ability of the model to simulate the heavy rain days (R10) and the continuous five-day maximum precipitation (R5d), and shows a high consistency between the models, especially the effect of R10 improvement is the most remarkable. Compared with the observation, the spatial average absolute error in Hunan area reaches 2.18 d, which is lower. The absolute error before scale is reduced by 45.46%. As far as time variability is concerned, this method can greatly improve the time variability ability of model simulation R90P and R5d. After scaling down, the IVS value decreases from 2.2 and 1.5 to 0.3 and 0.6 respectively.

• Statistical Analysis of the Characteristics of the Southwest Vortex with/without the Existing of Typhoons
• FAN Jiao;CHEN Keyi
• 2019 Vol. 38 (4): 744-755.  DOI:10.7522/j.issn.1000-0534.2018.00108
• Abstract ( ) HTML PDF (6376KB) ( )
• The characteristics of the southwest vortexes are analyzed under the condition of the presence or absence of typhoons by using the 700 hPa and 850 hPa synoptic maps at 08:00 and 20:00 (Beijing time, the same after)provided by the China Meteorological Administration (CMA) and the daily four times ERA-INTERIM reanalysis data with 0.75°×0.75°spatial resolution provided by the European Centre for Medium-Range Weather Forecasts (The European Centre for Medium-Range Weather Forecasts). The generated numbers, moving paths, life periods and precipitating impacts are analyzed based on the 149 southwest vortexes that generated from June to August between 2010 and 2017, and the characteristics of the southwest vortexes with the presence or absence of typhoons are also analyzed. The results show that the annual variation of the southwest vortex generating frequency with the presence or absence of typhoons is small, but the year with greater generating frequency difference like 2017 exists. Generally, the southwest vortexes mainly occurred in June and the vortexes impacted by typhoons are mostly generated in August. According to the characteristics of the moving paths, the southwest vortexes can be categorized into the local type and the moving types, and the moving types are further classified into the eastward moving type, the northeastward moving type and the southeastward moving type. Among them, the eastward moving type counts the most while the southeastward moving type occurs the least. The differences of the annual variation among the three moving southwest vortex types are small under the condition of the existence of typhoon and the intensity difference is less than that under the condition of the absence of typhoons. The local southwest vortex type is very different in annual variation under the condition of the presence or absence of typhoon, and the monthly variations of the four vortex types are various whether typhoons exist or not. The numbers of the southwest vortexes with different life periods decreased with longer maintaining time. The southwest vortexes always produce plenty of rainfall and the intensities of the precipitation produced by the moving southwest vortexes are greater when typhoons exist.

• Numerical Simulation on the Influence of Bohai Sea to a Squall Line Process
• TAO Ju;YI Xiaoyuan;ZHAO Haikun;ZHANG Wenlong
• 2019 Vol. 38 (4): 756-772.  DOI:10.7522/j.issn.1000-0534.2019.00035
• Abstract ( ) HTML PDF (3396KB) ( )
• To investigate the impact of sea surface to a squall line over Bohai sea in the evening on 25 July 2016, which developed over sea、moved slowly and had a long life, Weather Research and Forecasting (WRFV3.8) model is used. This squall line develops over sea, moves slowly and has a long life time. The control runs and a sensitivity experiment is designed. Results show that:(1) WRF model can simulate the formation process of the squall line reasonably. East wind blowing from the sea is the key factor of convection before the system goes into the sea. In enhancement phase of squall line in Bohai Sea, the north wind and the southwest wind converge at sea and form the strong convergence zones, leading to the reorganizing and developing of squall line. North cold air goes down south and triggers the release of unstable stratification energy, providing energy for convection. The pulsation of the southwest low level jet has a positive effect in the development of the system. Strong vertical wind shear in the deep and low level creates a favorable environment for squall line to forming and developing into linear convection; (2) Smooth Bohai Sea surface strengthens the wind near the ground. Southwest wind enhances after going into the sea, strengthening the convergence with north ground wind, and making the convection more active. This effect also hinders the movement of convergence and slows down the speed of squall line moving southward; (3) Bohai Sea surface has less sensible heat and latent heat exchange than land surface at daytime, turbulence activity in sea surface is weak. Latent heat exchange of Bohai Sea is higher, but boundary layer height is lower, that is not conducive to the enhancement of low vertical wind shear, hindering the development of squall line.

• Impacts of Urban Surface on a Heavy Rainfall in Xi'an
• ZHOU Linfan;ZHANG Shuwen;LI Shaoying;LI Yanlin;WANG wenqiang
• 2019 Vol. 38 (4): 773-780.  DOI:10.7522/j.issn.1000-0534.2018.00117
• Abstract ( ) HTML PDF (15092KB) ( )
• On August 3, 2015, a heavy rainfall occurred in Xi'an with floods and heavy losses. To better investigate the rainfall, highly temporal and spatial resolution radar data, mesoscale WRF model and its 3DVAR assimilation system were used. After assimilating the radar data, the precipitation area and intensity were improved, and the TS (True Shooting) and ETS (Effective True Shooting) scores of 10~25 mm precipitation increased respectively by 0.188 and 0.187 compared with no data assimilation. Then two experiments with and without urban surface (CITY and NoCITY) were carried out to explore the impact of urban surface on forecast of precipitation. In CITY, the average convective available potential energy (CAPE) increased and the convective inhibition energy (CIN) reduced, low-level wind speed became smaller, and vertical gradient of the pseudo-specific temperature was larger and the atmospheric became more unstable than those in NoCITY. The urban surface enhanced precipitation over the urban area; if the urban surface was substituted by a cultivated land, the precipitation area would shift southward approximately 0.2 latitudes.

• Analysis of Precipitation Forms Characteristics in Heilongjiang Province based on Snowfall/Precipitation Ratio
• HOU Bingfei;JIANG Chao;SUN Jianxin
• 2019 Vol. 38 (4): 781-793.  DOI:10.7522/j.issn.1000-0534.2018.00103
• Abstract ( ) HTML PDF (8636KB) ( )
• The precipitation form (snowfall, rainfall or fleet) have greatly influenced a large number of ecological processes, such as surface runoff, energy flow, and material circulation processes. Obviously, precipitation form is very sensitive to temperature changes. To discuss the effects of climate change on precipitation form, a dataset including average daily rainfall and temperature data of 27 stations from 1960 to 2015 in Heilongjiang province was employed to analyze the long-term change in annual snowfall and snowfall/rainfall ratio. The results indicate that:The annual mean snowfall in Heilongjiang province experienced a sharp growth with 34.3% increase after a break which occurred around the year 2003. The long-term increase rate was 3.3 mm per decade. On the contrary, no significant change was observed in annual mean rainfall in Heilongjiang province. Trend tests showed a 7.6% per decade significant increase in snowfall/rainfall ratio in Heilongjiang. The main characteristic of change in snowfall spatial distribution was consistent upward trend except Huma station, but the amplitude of eastern parts was larger than the western ones. Otherwise, rainfall variation spatial pattern was differed among regions. In general the changes in the southern part were more strongly than the northern. The variation of fleet presented a distinct trend of decreasing from east to west. There was a large difference in fleet between the two sides of The Changbai-Hinggan mountains, presented as a sharp decline from the eastern part of the mountain to the western. The difference in spatial distribution between snowfall/rainfall ratio and snowfall was mainly reflected in the areas where rainfall was significant decreased, such as the western foot of Changbai mountains, where the rain shadow effect was extremely strong. The common impacts of delayed origin date and advanced end date resulted in the snowfall season range evidently shortened about 18 days in the last 56 years. The reason may be attributed to a significant temperature rise in Heilongjiang province. The spring warming should be considered as a major role rather than autumn because of the higher temperature variation, especially the increase in minimum temperature. There was no significantly change observed in average annual snowfall days. The amplitude changed in snowfall frequency in the northern was larger than the southern. Consistent with the snowfall growth, an increased trend of snowfall intensity was found in Heilongjiang, with a changing rate of 0.8 mm per decade. In the context of global warming, higher snowfall rate phenomenon was observed in Heilongjiang province.

• Relationship between 0℃ Isotherm Height and Precipitation and Disastrous Weather in Flood Season over Hexi Corridor
• LI Yanying;CAI Ying;ZENG Ting;ZHANG Aiping;YANG Jiping
• 2019 Vol. 38 (4): 794-803.  DOI:10.7522/j.issn.1000-0534.2018.00069
• Abstract ( ) HTML PDF (2113KB) ( )
• In order to provide reference for the forecast of disastrous weathers, based on daily sounding data at 07:00 (Beijing time, after the same) and 19:00 from May to October at four stations of Dunhuang, Jiuquan, Zhangye and Minqin over Hexi Corridor during 2006-2015, the variation characteristics of 0℃ isotherm height as well as its relationships with dry-wet, precipitation and disastrous weather were analyzed. The 0℃ isotherm height is most closely related to the daily extreme temperature, 0 cm minimum ground temperature; the higher the extreme air temperature and ground temperature is, the higher the 0℃ isotherm height is, and the best correlation is between the 0℃ isotherm height and 0 cm minimum ground temperature at 19:00, the coefficient of which is greater than 0.95. The value of temperature and dew difference (T-Td) is inversely correlated with daily precipitation, daily minimum air temperature and 0 cm minimum ground temperature, but is positively correlated with the daily temperature range, and the maximum correlation coefficient is greater than 0.7. The 0℃ isotherm height over Hexi Corridor was 3300~5000 m, the atmospheric pressure was 680~560 hPa, the T-Td was between 10~17℃, the height was low and wet in morning, but which was opposite at night. In dry and wet weather contrast, dry weather 0℃ isotherm height was high, obvious morning-evening variation and higher at 19:00, while the morning-evening variation of T-Td was obvious and more humid at 07:00 in wet weather. When precipitation occurred, the 0℃ isotherm height was 3000~4800 m, the atmospheric pressure was 750~570 hPa, T-Td < 8℃, and T-Td < 6℃ at 07:00; in day-night variation, low 0℃ isotherm height occurred at 07:00 in nighttime rainfall, while which occurred at 19:00 in daytime precipitation. In different precipitation levels, the maximum values of T-Td from light rain, to moderate rain and heavy rain were 2℃, 5℃ and 9℃, respectively. Thunderstorm 0℃ isotherm height was 3600~4900 m, the pressure was 660~560 hPa, T-Td ≤ 7℃. In gale and sand-dust weather, 0℃ isotherm pressure was 700~540 hPa, sandstorm 0℃ isotherm height at 07:00 from July to September was higher 300~500 m than that of gale and sand-dust, which was above 5000 m from July to August. When sandstorm occurred, it was dry at 07:00 but wet at 19:00 when T-Td < 5℃, so sandstorm in flood season often occurred in the precipitation afternoon. In daily maximum temperature ≥ 35℃ high temperature weather, 0℃ isotherm height was 4600~5300 m, the pressure was 570~530 hPa, T-Td ≥ 13℃.

• The Physical Mechanism and Strong Precipitation in Northeast China Analysis during Typhoon "Lionrock" Merging into Extratropical Cyclone Process
• LIU Shuo;LI Deqin;SAI Han;TIAN Li;ZHAO Ming
• 2019 Vol. 38 (4): 804-816.  DOI:10.7522/j.issn.1000-0534.2018.00109
• Abstract ( ) HTML PDF (43192KB) ( )
• Based on conventional ground data, typhoon best track from Shanghai Typhoon Institute, sounding data, black body temperature equivalent (TBB) of FY-2 meteorological satellite from National Satellite Meteorological Center, and high-resolution NCEP/NCAR global reanalysis data, the physical development mechanism and strong precipitation mechanism in Northeast China during typhoon Lionrock (1610) merging into extratropical cyclone process was analyzed. The result indicated that symmetric tropical cyclone cloud system developed into asymmetric baroclini cloudsystem, and finally evolved into mature extratropical cyclone cloud system. Meanwhile, Lionrock entered into the strong vertical wind shear environment gradually, and typhoon vortex circulation, water-vapor transfer and vertical movement showed remarkable asymmetric and vertical westward tilt feature. Furthermore, warm-core structure was destroyed, water-vapor transfer gradually went away from typhoon circulation. Under the interaction between upper and low-level jet, extratropical cyclone appeared obvious frontogenesis for the positive vertical vorticity advection, which enhanced the development of extratropical cyclone. Under the co-effect of Lionrock and extratropical cyclone, enhanced dynamic, water vapor and energy transport caused by development cyclone, was the main reason for the heavy rain in northeast China. It was found that precipitation in Northeast China mainly occurred in warm advection, high value of thickness gradient had good direct a indicative function. It was also found that heavy precipitation was influenced by strong upper levels divergence and low levels convergence of dynamic and water vapor, meanwhile corresponded to strong temperature advection and vertical upward motion. Long time duration of rainfall and ending slow, was related with weak dry cold air intrusion from high to low level slowly. The precipitation process was sustainability, with relatively strong convective precipitation occurring locally.

• Characteristics about the Duration of Rainfall Processes in Summer in Inner Mongolia
• CHANG Yu
• 2019 Vol. 38 (4): 817-828.  DOI:10.7522/j.issn.1000-0534.2018.00114
• Abstract ( ) HTML PDF (32548KB) ( )
• Using the hourly precipitation data of 111 national stations during 1991 to 2017 and the daily precipitation data of 115 national stations during 1971 to 2017 in summer (from June to August) in Inner Mongolia, the characteristics about the duration of short-time strong rainfall processes(STSRP) and daily rainfall(light rain, moderate rain, heavy rain, torrential rain, excessive torrential rain, extreme torrential rain) processes were studied. The results show that:(1) The longest duration of STSRP is 38 hours and the duration about 3 hours percentage is most in Inner Mongolia. Duration within 12 hours of STSRP has maximum deviation at 16:00 (Beijing time, after the same) to 18:00, but duration more than 12 hours of STSRP has maximum deviation at 03:00 in Inner Mongolia. Furthermore, the longer the duration of STSRP, the lower the extreme value of the hourly precipitation in Inner Mongolia. Since 2010, the frequencies of STSRP have increased in Inner Mongolia. Frequencies of 4~6 hours and 7~12 hours of STSRP increase obviously. But frequencies of 1~3 hours of STSRP reduce evidently in Inner Mongolia. (2) The frequencies of light rain process and torrential rain process have decreased in Inner Mongolia. However, in recent years, the long duration rainfall process in the light rain process, the moderate rain process and the torrential rain process are extremely excessive. The first extreme torrential rain process occurred in 2017. In Inner Mongolia, the longest duration of the extreme torrential rain is 2 days, but the longest duration of other daily rainfall processes is 10~15 days. The longest duration of the heavy rain is 15 days. Lasted 1 day of the light rain process and the moderate rain process have maximum proportion, but lasted 2 days have maximum proportion about the heavy rain process and the torrential rain process. The extreme precipitation of the daily rainfall process is easy to occur in the first three day. (3) Spatial distribution about the frequency and extreme value of duration hours or days, as well as extreme value of accumulative precipitation of STSRP and daily rainfall processes increase from west to east, the highest value appear in the eastern part of Inner Mongolia.

• Analysis on the Feature and Formation Mechanism of the Continuous Rain in Autumn in Anhui since 1971
• HE Dongyan;WU Rong;TIAN Hong;DENG Hanqing;LUO Liansheng
• 2019 Vol. 38 (4): 829-844.  DOI:10.7522/j.issn.1000-0534.2018.00107
• Abstract ( ) HTML PDF (4945KB) ( )
• In recent years, the continuous rain processes in Anhui turned anomalously longer in autumn, which leaded to more serious disasters. So it is necessary to find out its variation feature and climate formation mechanism. Based on the meteorological observational data and NCEP\\NCAR reanalysis data, using statistical methods such as the linear trend estimation, the power spectrum, the penalized maximal F-test (PMFT), the rotated empirical orthogonal function (REOF), the correlation analysis and the synthetic analysis and et al, the continuous rain process in Anhui in autumn has been analyzed. The results show:(1) From 1971 to 2017, the continuous rain processes in the southern and mountain area were more then that in the northern, plain and hilly area, according to which Anhui could be divided into 4 regions:the Region Ⅰ covered the Huaibei plain, the Region Ⅱ covered the Huaihe river basin and the northern Jiang-Huai region, the Region Ⅲ covered the southern Jiang-Huai region, the eastern Yangtze River basin and the southeastern Yangtze River, and the Region Ⅳ covered the southern Anhui Mountain, the southern Dabie Mountain and the western Yangtze River basin. (2) The annual accumulative process days increased slightly in the Region Ⅰ but decreased in the Region Ⅲ and Region Ⅳ. The accumulative process days in the Region Ⅰ, Region Ⅱ and Region Ⅳ have mutated obviously since 2014, 2013 and 2015 respectively. Moreovr, there was an obvious periodic change about 4 years in the Region Ⅰ. (3) The vertical circulation was deeper when there were continuous rain processes in autumn. Weak cold air affecting frequently and abundant water vapor over Anhui were the two most necessary factors for the continuous rain occuring. The South China Sea was the main source of water vapor, while water vapor from the East China Sea was also important to the northern processes, and its transmission range determined the northern boundary of the northern processes. (4) The land surface temperature (LST) in the northern hemisphere could influence the continuous rain processes in autumn by effecting the atmospheric circulation. When LST in summer was cooler in the middle northern Africa and the northwestern Indian Ocean, the low pressure trough over the Balkhash Lake turned deeper and the subtropical high over the western Pacific turned more strengthen in autumn, and the conditions of the cold air and water vapor transmission were better, which benefited to the continuous rain processes occuring in the Region Ⅰ.

• Analysis on the Atmospheric Circulation and Low-Frequency Oscillation Characteristics of the Two Persistent Heavy Snow Processes over Yangtze and Huaihe River Valleys
• TONG Jin;YE Jinyin;WEI Lingxiang
• 2019 Vol. 38 (4): 845-855.  DOI:10.7522/j.issn.1000-0534.2018.00118
• Abstract ( ) HTML PDF (11518KB) ( )
• Based on the surface observation data and NCEP/NCAR daily reanalysis data, the atmospheric circulation of the two persistent heavy snow processes over Yangtze and Huaihe River Valleys in January 2018 were analyzed, and the impact of synoptic system and low-frequency variation in high and low latitudes (Ural block high and southern branch trough) on persistent heavy snow processes were discussed. Results are shown as follows:(1) The two processes happened with persistent atmospheric circulation anomalies, for example, the polar vortex had a dipole-type distribution, and the blocking high pressure was steady and strong in middle-high latitudes, with cold high pressure over the plain, thus in favor of the southward advance of cold air. In lower latitude, the west Pacific subtropical high and southern branch trough were stable, which is very favorite to transportation of heat and moisture to Yangtze and Huaihe River valleys. Cold air from north and warm-mosit air from south converged to each other and then the favorite environment of heavy snow could appear. (2) The stable and strong Ural block high and the southern branch trough and their interaction played an important role in the two processes. (3) There were differences of the polar vortex、blocking high、southern branch trough、low-level moisture and vertical circulation between the two processes, leading to different features on snow area、intensity and type. (4) Stronger blocking high and deeper southern branch trough benefit the occurrence of persistent heavy snow. The variation between the index of blocking high and southern branch trough was high in those strong snow days, which had important implications for middle and long term forecast on persistent heavy snow. (5) The low-frequency oscillation period of 10~30 days was the most remarkable component of blocking high and southern branch trough and gave a good reference on weather forecast over two weeks.

• The Formation of an Unusual Two-belt Heavy Rainfall around Beijing-Tianjin-Hebei Area
• WANG Hua;LI Hongyu;ZHONG Jiqin;WU Jin;LI Ziming;WU Jiankun
• 2019 Vol. 38 (4): 856-871.  DOI:10.7522/j.issn.1000-0534.2018.00102
• Abstract ( ) HTML PDF (39526KB) ( )
• Heavy rainfall is one kind of extreme weather which is harmful to human beings. Since the formation mechanism of heavy rainfall is very complicated, it brings great challenge to weather forecasting and warning. An unusual double-belt heavy rainfall with high precipitation intensity and long-duration precipitation happened on July 1st 2013 around Beijing-Tianjin-Hebei area, under the synoptic background of northwards stretching subtropical high, southwards strengthening low-level jets, and eastwards moving upper trough. The formation mechanism and mesoscale characteristics of this case is analyzedbased on conventional observation, NCEP (National Centers for Environmental Prediction) reanalysis data, multi-type of intensive observation, and the variational radar data assimilation. The result shows that thosetworainfall belt promote mutually, although their formation mechanism and mesoscale evolution differ obviously. The south branch heavy rainfall belt occurred under the strengthened southwest warm and moist environment, with high convective instability and deep moist layers. The heavy rainfall is triggered, organized by the warm mesoscale convergence line and developed by MCC(Mesoscale Convective Complex). The radar echoes of the rainfall is characteristic of "train-effect" and backpropagation. It is a deeper warm-zone wet convection rainstorm with extremely high rainfall intensity, large amount of accumulated rainfall, and obvious mesoscale features. The location of rainfall belt and the extremely intensive precipitation core is dominated by the position of the surface convergence line and the mesoscale eddies. Propagating direction of the intense radar reflectivity is indicated by the cold pool outflow generated by heavy rainfall together with the maximum temperature gradient formed by the southerly warm and wet airflow. The north branch heavy rainfall belt is brought about by multi-cell echoes belt formed by shearline cloud system, under the influence of cold shear line and low-level low vortex. It sinstability energy is lower than that in the south branch heavy rainfall belt, but the upward motion is stronger thanks to the coupling action of the upper and lower synoptic systems. Intrusion of dry and cold air in middle layer forms an obvious θ_se frontal zone. It is a frontal convective system. Meanwhile, the terrain helps to enhance precipitation markedly. Various factors jointly make the case be characteristic of relative weak rainfall intensity, long-lasting precipitation and large area with heavy rain. The moving path of the low-level low vortex is well consistent with the location of the rainfall belt and heavy rainfall region. The easterly wind induced by warm-zone precipitation within the south branch heavy rainfall belt not only brings water vapor to the north branch rainfall belt but also the orographic lifting made by the Taihang mountain benefits the occurrence and development of those severe convection cells, which furtherly enhance the rainfall intensity of the north branch rainfall belt. On the other hand, the cold pool formed by severe convective rainfall accelerates the formation of surface mesoscale eddies, which cause intense convective radar echoesmergence and strengthen the rainfall again at the later stage of the south branch rainfall belt.

• Intensive Radiosonde Observations at 14: 00 in China Mainland and Their Impact Study on Mesoscale Numerical Weather Prediction
• WANG Dan;XU Zhifang;WANG Ruiwen;ZHANG Lihong
• 2019 Vol. 38 (4): 872-886.  DOI:10.7522/j.issn.1000-0534.2018.00121
• Abstract ( ) HTML PDF (37051KB) ( )
• Based on the intensive radiosonde observations at 14:00(Beijing time, after the same) during June of 2014, both Observing System Simulation Experiments (OSSEs) and Observing System Experiments (OSEs) have been carried out to investigate the impact of extra radiosonde observations on mesoscale numerical weather prediction model. The preliminary observation network design of intensive radiosonde has also been discussed in this paper. The results suggested that:(1) The intensive radiosonde has a positive effect on improving the accuracy of precipitation forecast, especially for precipitation forecast starts from 14:00. The forecast skills increases with the magnitude of precipitation. (2) In the observing system simulation experiment, the assimilation of intensive radiosonde can effectively adjust the dynamic, thermal structure and water vapor distribution in model's initial field. Meanwhile, assimilating actual intensive radiosonde can correct wind filed, but has a slightly negative contribution to temperature and humidity field at the low level of the model. Bias of humidity and temperature may be a possible reason. (3) The intensive radiosonde plays a fundamental role in numerical prediction system. GPS/PW(Global Position System/Precipitable Water) and other unconventional observations are not similar as intensive radiosonde data. Taking into account the cost of the intensive radiosonde balloon, setting the detecting height to 300 hPa and key area encryption is an economical approach in the future.

• Numerical Simulation Study on the Transport of Pollution from China to the Arctic Region
• QIU Jiyong;HUANG Qian;TIAN Wenshou;XIE Fei;LIU Xiaoran;WANG Feiyang
• 2019 Vol. 38 (4): 887-900.  DOI:10.7522/j.issn.1000-0534.2018.00088
• Abstract ( ) HTML PDF (33610KB) ( )
• Using NECP/NCAR FNL objective analysis data driven mesoscale model WRF, four numerical experiments were conducted to simulate the total amount of traced emissions from South China to the Arctic region, investigating the transmission characteristics and related mechanisms under different weather conditions in March, June, September and December of 2010. The simulation results show that the peak concentration of emissions transported to the Arctic region was the highest in December, reaching 44‱ of the total emissions, followed by September and June, about 7.5‱ and 7‱ respectively, and the lowest in March, which was only 0.105‱. The emissions from South China to Arctic need 3 days in December, need respectively 5 and 6 days in September and June, and takes 9 days in March. In addition, the peak levels of absolute concentrations of emissions emitted to the Arctic under different weather conditions are also different, the emissions were mainly from 850 to 700 hPa in March and from 400 to 200 hPa in September, and in June and December appear at 850~200 hPa. Further analysis found that the path of emission transport is mainly controlled by the circulation field, and the strong radial south wind and cyclone systems facilitate the transmission of emissions to the Arctic. The East Asian trough is an important reason for the transport of traced emissions to the Arctic in a short period of time.

• Analysis of Variation Characteristics of Atmospheric Self-purification Capability in the Main Urban Area of Chongqing from 1951 to 2018
• ZHANG Tianyu;ZHANG Dan;WANG Yong;CHEN Daojin;LI Yonghua;TANG Hongyu
• 2019 Vol. 38 (4): 901-910.  DOI:10.7522/j.issn.1000-0534.2019.00030
• Abstract ( ) HTML PDF (7326KB) ( )
• Based on the meteorological observation data from 1951 to 2018 and the environmental air quality monitoring data from 2014 to 2018 in the main urban area of Chongqing, the long-term trend of the atmospheric self-purification ability index in the main urban area of Chongqing and its influencing factors are calculated and analyzed, and the relationship between the atmospheric self-purification ability and the environmental air quality in the main urban area of Chongqing from 2014 to 2018 is discussed. The results show that the air self-purification ability is weak in autumn and winter in the main urban area of Chongqing, which is not conducive to the removal of atmospheric pollutants. In the past 68 years, the atmospheric self-purification capacity of the main urban areas has changed obviously in different stages. From the early 1950s to the early 1960s, it has increased, then it has continued to weaken, and in the 10s of the 21st century it has increased. Among the influencing factors, the correlation between ventilation volume and atmospheric self-purification ability index is very significant, and there are obvious negative and positive correlation between the number of days of light wind and the number of days of strong wind and atmospheric self-purification ability. The mixed layer thickness is positively correlate with the index of atmospheric self-purification capability. Atmospheric stability is the main factor affecting the mixed layer thickness. Precipitation contributes positively to atmospheric self-purification ability, and the number of days of precipitation is positively correlated with the index of atmospheric self-purification ability. The increase of days of precipitation after 2011, especially those of days above moderate rainfall, is the main reason for the enhancement of atmospheric self-purification ability in the same period. In addition, the study also shows that there is a significant inverse correlation between the atmospheric self-purification ability and AQI and PM2.5 concentrations in the main urban area on the daily and monthly scales, indicating that when the atmospheric self-purification ability is strong, the concentration of AQI and PM2.5 in the corresponding day and month is low, that is, the environmental air quality tends to be better.