Current Issue

28 June 2011, Volume 30 Issue 3   
  • Analysis on Mechanism of Anomalous Variation of TropopausePressure over Tibetan Plateau in Summer
  • ZHU Bao-lin-;GUAN Zhao-yong;LU Chu-han;PENG Ni;TIAN Yong-li
  • 2011 Vol. 30 (3): 559-567. 
  • Abstract ( ) PDF (1443KB) ( )
  • Using the monthly mean data from NCEP/NCAR reanalysis, the building tropopause pressure index and the selected years of 1992 and 1998 which are respectively the highest and lowest year of tropopause pressure anomaly over Tibetan Plateau to contrast and analyze, the mechanism of anomalous variation of tropopause pressure over Tibetan Plateau in summer is investigated. The results are summarized as follows: (1) Over Tibetan Plateau, the variations of tropopause pressure have been found well correlated with respectively the anomalous temperature and geopotential height in both troposphere and stratosphere. The anomalous tropopause pressure correlates well with the anomalous surface temperature over Tibetan Plateau. In 1992(1998), the surface temperature is anomalous low (high), tropopause pressure over Tibetan Plateau is anomalous high (low). (2) Over Tibetan Plateau, the correlation of tropopause pressure and OLR is positive. Furthermore, for further diagnosing the circulation fields between 850 hPa and 200 hPa and the whole troposphere vapour field, it is found that the anomalous high tropopause pressure in 1992 is corresponding to the anticyclonic divergence in low level wind field and the cyclonic convergence in upper wind field, and coupled with divergence of the whole troposphere vapour fields and the South Asia high weakens at the same time. While in 1998, the case is just opposite to 1992. These facts indicate that the anomalous convection results in the significant difference of tropopause pressure over Tibetan Plateau in 1992 and 1998. (3)Furthermore, the vertically integrated heat budget anomaly is also responsible for explaining the tropopause pressure anomaly over Tibetan Plateau in 1992 and 1998.
  • Link between Perennial Snow Cover Variations and ClimateChange in Qomolangma Nature Preserve from 1975 to 2000
  • CHU Duo-;LABA Zhuo-ma;LA Ba;PUBU Ciren
  • 2011 Vol. 30 (3): 576-582. 
  • Abstract ( ) PDF (794KB) ( )
  • The perennial snow cover changes in Tingri County of core zone of Qomolangma Nature Preserve(QNP) were studied and the relationships with main climate variables (temperature, precipitation) are analyzed using the GIS spatial analysis and three times Landsat data from 1975 to 2000. Results showed that perennial snow cover in Tingri county reduceed by 7.49%, 105.35 km2 from 1975 to 2000, which mainly occurred on the edge of Mt. Qomolangma and its surrounding high mountains. Around 70% of reduceed areas were situated from 5 000 to 6 000 m above sea level. Driving forces of snow cover retreat is temperature and precipitation and particularly, on the background of globe climate warming, the temperature in QNP increase higher than Tibet Autonomous Region. China and global is the main driving force. Perennial snow cover in Tingri decreased from 1407.19 km2 in 1975 to 1283.60 km2 in 1992. In 1975, the perennial snow cover in Tingri is 10.08 % of total county land area while in 1992 it decreased to 9.20%. The total perennial snow cover deceased 123.59 km2 from 1975 to 1992. From 1992 to 2000 the perennial snow cover slightly increased with 18.24 km2 of net increase from 1283.60 km2 in 1992 to 1301\^84 km2 in 2000. Analysis on climate change indicate that the temperature from 1970 to 2000 was continuously increasing with 2.59 ℃ on average in 1970s, 2.64 ℃ in 1980s and 3.12 ℃ in 1990s. The general trend of precipitation is that annual rainfall was decreasing from 1970s to 1980s with 318.5 mm in 1970s and 258.3 mm in 1980s while it was consecutively increasing after 1993 with 310.6 mm on average in 1990s.The spatial distribution of perennial snow cover change in Tingri is that most decline in snow cover from 1975 to 2000 occurred on the edge of Qomolangma mountain and its surrounding high mountains. The most increased snow cover from 1992 to 2000 is mainly distributed in the southeastern part of study area where relatively low altitude.
  • Ensemble-Based Four-Dimensional Variational AssimilationUsing Hybrid Samples
  • SHAO Ai-mei;QIU Xiao-bin;QIU Chong-jian
  • 2011 Vol. 30 (3): 583-593. 
  • Abstract ( ) PDF (1279KB) ( )
  • The ensemble-based 4DVar approach with SVD technique (SVD-En4DVar) may be subject to significant uncertainties due to the size of forecast ensemble. Especially, the less ensemblesize will cause more truncation errors when the analysis variables are expressed as a linear expansion with the leading singular vectors extracted from an ensemble of the perturbed forecasts. In order to improve assimilation skills by increasing sample members but without addition computational costs, a hybrid sample analysis scheme is developed. In this scheme some time-invariant samples are added to the flow-dependent samples obtainedby the short-range forecasts over the analysis time window. The static samples can be produced by two approaches. In the first approach, the initial pseudo random fields with a specified statistic structure are added directly to the background field in 4D space without operating by the model integration. In the second approach, the static samples are obtained by integrating the model over the first analysis time window with the initial fields superposed the pseudo random fields on the initial background field. This implies that the partial flow-dependent samples yielded in the first assimilation circle will be used as the static samples in the subsequent circles. The numerical experiments on the different sample structures are tested with the shallow-water-equation model and Lorenz-96 model with 80 variables. When only large size of static sample ensembleis used, the better assimilation skills can be found in the shallow-water-equation model but not for Lorenz-96 model. However, two models perform well when hybrid samples are used. For the same computation costs, the hybrid sample analysis scheme can obviously improve assimilation accuracy and the second approach for statically sampling is better than the first one.
  • Analysis on the Effect of the Transient Eddy on UralBlocking High in 2008
  • XU Hui;JIN Rong-hua
  • 2011 Vol. 30 (3): 600-606. 
  • Abstract ( ) PDF (861KB) ( )
  • A rarely and large-scale snowfall event with severe freezing occurred in the southern China, during the period from the middle ten days of January to the first ten days of February 2008, whose key causes are the anomalous atmospheric circulation in the mid-higher latitudes, especially the unusual development and maintenance of the Ural blocking high(hereafter UBH). The effect of the transient eddy on the development and maintenance of a blocking high(BH) in the mid-higher latitudes is analyzed, taking the blocking process in 2008 as an example, based on the following three factors: (1) the transient eddy forcing on the meridional and zonal flows, (2) the transient eddy momentum transport, and (3) the transient eddy heat transport. The results show that the transient eddy strengthens, via forcing the mean flow, the anticyclonic currents surrounding the BH, and thus favour the development and maintenance of the BH. On the other hand, despite the continuous conversion of the mean kinetic energy of the zonal flow change into the transient eddy kinetic energy in the BH area, the continuous conversion of the mean kinetic energy of the zonal flow change into the transient eddy kinetic energy in the westerly area in the northern part of the BH to cause the maintenance of the westerly jet and, as a result, leads the BH to develop and maintain. In addition, the strong transient eddy heat transport in the area causes the temperature gradient in this area to weaken, which is, to some extent, able to lead the mean westerly flow to weaken and thus favour the development and maintenance of the BH.
  • Albedo Characteristics in Different Underlying Surfaces in Mid-and Upper-Reaches of HEIFE and Its Impact Factor Analysis
  • SUN Jun-;HU Ze-yong;XUN Xue-yi;PENG Wen;L Bin;XU Li-jiao
  • 2011 Vol. 30 (3): 607-613. 
  • Abstract ( ) PDF (848KB) ( )
  • Using the observed data at six automatic stations in the mid- and upper-reaches of HEIFE from June 2008 to May 2009, the seasonal variations of albedo on different underlying surfaces are analyzed. The influences of solar elevation angle, soil moisture, and precipitation on albedo are also studied in this paper. The impact of snow cover on the albedo at Yakou station is discussed. Meanwhile, the soil moisture data are also related to albedo to discuss its influence at Huazhaizi station. The results show that the solar elevation angle in different seasons has different effect on albedo, while its impact is also different on different underlying surfaces. Solar elevation angle on snow surface has the greatest impact on alebdo, and the second is the forest land cover. At herbage and farmland stations, the solar elevation angle has greater impact on albedo in summer than that in winter. By analyzing the observed data, the surface soil moisture has a significant impact on albedo. Although sporadic rain can not infiltrate into the ground, it can still cause albedo decrease in a short time because of increasing the surface soil moisture. The different intensity of precipitation has different effect on albedo. According to the average annual albedo, the sequence of albedo at six stations are alpine meadow>desert>herbage>farmland>thin grass>forest, respectivily.
  • Features of Drought-Flood Coexistence in West and East ofSichuan-Chongqing Basin in Midsummer and Its RelatingBackground of Atmospheric Circulation
  • ZHOU Chang-yan;LI Yue-qing;BU Qing-lei;PENG Jun
  • 2011 Vol. 30 (3): 620-627. 
  • Abstract ( ) PDF (888KB) ( )
  • Based on the monthly precipitation data from 160 stations in China during 1951-2004 and NCEP/NCAR monthly reanalysis data, the features of drought-flood coexistence in the west and east of Sichuan-Chongqing basin the midsummer and its relating background of atmospheric circulation are studied, the main conclusions are as follows: The annual precipitation in the west of the basin in the midsummer had a decrease trend from 1951 to 2007, especially after 1990s; while the precipitation of the east of the basin had no obvious changeduring this period. The frequent rain pattern are both the drought in the west, flood in the east of it and less precipitation in the whole basin, especially after 1990s. The rain pattern of more precipitation in the whole basin has the lowest frequencyin 57 years. When flood in the west and drought in the east of basin appear, the precipitation are obviously less in the mid- and lower-reaches of the Yangtze River, and more in South China, the irrigation area in Yellow River section of Inner Mongolia and North China. When drought in the west and flood in the east of the basin appear, the precipitation are obviously more in the mid- and lower-reaches of the Yangtze River, and less in South China, the irrigation area in Yellow River section of Inner mongolia and North China. In the midsummer of flood years in the west and drought ones in the east of the basin, the South Asia high is strong and far north, and obviously strengthens and extends eastward over north to the Yangtze-Huaihe basin, Yellow Sea and Japan Sea. On 500 hPa that is associated with the circulation pattern that two ridges 1ocated in Ural and the east of Asia, respectively, and a trough between the lakes Balkhash and Baykal, and also with thenorthward displacement of the western Pacific subtropical high(WPSH). In the midsummer of drought ones in the west and flood ones in the east of the basins, the South Asia high is weak and southwards, and it obviously weakens and shrinks westward over north to the Yangtze-Huaihe basins, Yellow Sea and Japan Sea. On 500 hPa the meridional circulation pattern prevails in the middle-high latitudes of Eurasian continent, and also with thesouthward displacement of the WPSH.
  • Applicability and Potential of the Different PrecipitationData in Mainland China
  • LV Shao-ning-;WEN Jun;LIU Rong
  • 2011 Vol. 30 (3): 628-640. 
  • Abstract ( ) PDF (1518KB) ( )
  • The analysisandreanalysis precipitation data could compensate the shortage of surface observational data. This is especially important for the relevant meteorology and hydrology researches. In this paper, 7 kinds of analysisandreanalysis grid-precipitation data were compared and analyzed to the real precipitation data collected from 621 surface observation stations in the mainland China. The results showed that the applicability was distinctive in different regions. In western part of mainland China, the bias between grid-precipitation data and surface observation was above 50% and accumulated sampling error ratio was beyond 30%. In eastern part of mainland China, the bias between grid-precipitation data and observations was about 10% and accumulated sampling error ratio was below 30%. In general, the products retrieved from satellites remote sensing data performed better than that calculated by using numerical models because of the types of local raining system and the shortage of observation data. It was proved that both numerical models and inversion methods would cause system errors and deviated the normal distribution in reanalysis grid-precipitation data. In the future, the surface observation data, satellite remote sensing technology and numerical models should be synthesized to improve the applicability and potential of the grid-precipitation data.
  • Circulation Anomalies during Weather Process of Electric WireFreezing in Southwestern China
  • QU Qiao-na;LI Dong-liang;YANG Xuan;LIU Yu;GUO Yue-ming
  • 2011 Vol. 30 (3): 641-650. 
  • Abstract ( ) PDF (1547KB) ( )
  • The 12 icing processes and 8 no-icing processes were selected from the freezing data at Erlang station in Sichuan in January from 2002 to 2008, and the same icing date (11~19 January) in 2008 and 2005 were taken. Using NCEP/NCAR reanalysis grid data, the circulation features of the icing and no-icing processes were analyzed. The results show that, in icing process in Southwestern China, 500 hPa height anomaly field is ‘north-higher and south-lower’; There is a maximum negative center of strong cold air around Baykal Lake and the cold air can extend to the Southwest China; the vapor source is mainly the southwest air from Arabian Sea, Bay of Bengal and southeast air from South China Sea. The wind, temperature and humidity profiles in Erlang area on 24~29 January 2008 have obvious features. They are inversions between 750 hPa and 650 hPa, small diurnal range temperature, relative humidity over 80%, wind direct change on 750 hPa, cold air at the low level and warm air above 750 hPa, that is, deeper trough or plateau shear line activities above 750 hPa. Further studies indicate that there is a maximum zone of dew-point temperature gradient along southern Gansu-Central Sichuan-Yunnan, because winds converge around it, cold and warm air also confluence here. With the conditions of circulation and atmospheric stratification, the electric wire freeze in Southwestern China can been well known and the prediction of such weather events can been improved.
  • Tendency Change of Cloud Cover over Northern Chinaand Its Relation with Regional Climate
  • WU Wei-;WANG Shi-gong
  • 2011 Vol. 30 (3): 651-658. 
  • Abstract ( ) PDF (844KB) ( )
  • The spatial and temporal characteristics of the cloud cover over six regions of Northern China are systematically investigated based on the daily data of cloud cover and precipitation at 333 observation stations in the region to the north of 35°N from 1960 to 2005. The correlation between the total cloud and low cloud covers with the precipitation is discussed. Linear variational trends of the total cloud and low cloud covers and precipitation from 1960 to 2005 were analysed. The results show that: The cloud cover decrease in the east of Northern China and increase in the northwest China; precipitation in the northwest and northeast of China increase in the region to the north of 35°N and reduce trend in the east; precipitation in the northwest and northern part of northeast of China obvoiusly increase in the recent years, which appears drought trend. Analysis on the correlation between cloud cover with precipitation and temperature show that there is a significant negative correlation between the total cloud and low cloud covers with temperature. It is found that correlation between the low cloud cover and temperature is positive, but notable positive correlation with precipitation. This indicates that the total cloud cover maybe is a important factor to restrict the change of temperature in the Northern China, while the low cloud cover is an important factor of precipitation.
  • Changes of the Seasons in Mainland China under Global Warming
  • ZHANG Shi-xuan;ZHANG Lu;SUN Shu-peng;FENG Guo-lin-
  • 2011 Vol. 30 (3): 659-667. 
  • Abstract ( ) PDF (1060KB) ( )
  • Using the daily observational data of surface air temperature, pressure, relative humidity and precipitation at 752 stations in China from 1961 to 2008, and the non-linear similarity method, the spatial-temporal characteristics of four seasons in China are investigated under the background of global warming and division of season index. Results indicate that in the majority of the country, the length of summer has extended and the length of winter has shortened. In particular, the lengths of summer, autumn, spring have increased 2.8, 4.7, 2.6 days, respectively since the 1960s. However, the length of winter has shortened by 5.6 days since the abrupt climate change in the middle of 1980s. These changes in the lengths of seasons are linked to the changes in the starting dates of seasons. Averaged across the whole country, the starting dates of autumn and winter have been delayed while spring and summer in China have started earlier; this phenomenon is especially obvious since 1980s.On the other hand, the changes in the seasons exhibit apparent seasonal and regional differences under the background of global warming. The most significant changes occured in winter, then summer, autumn and spring are less.They are more significant in the north than the south where the trend of local changes in Heilongjiang, Xinjiang Provinces and south China are the most significant.
  • Analyses on Precipitation Characteristics in the YangtzeRiver Delta City Belt Based on the Satellite Data
  • ZHAO Wen-jing;ZHANG Ning;TANG Jian-ping
  • 2011 Vol. 30 (3): 668-674. 
  • Abstract ( ) PDF (980KB) ( )
  • Based on TRMM data, the urbanization effects on precipitation in the Yangtze River Delta region are analyzed, combined with the underlying surface types data from the MODIS satellite, the USGS topographic data, and the NCEP reanalysis data. The results indicate that: (1) The Yangtze River Delta region is a precipitation center comparing with its surrounding area. It indicates that the urbanization may be a critical impact factor of increasing precipitation in the Yangtze River Delta region. (2) A significant precipitation minimum locates in Tai Lake Basin which suggests that large water bodies can dramatically decrease the local precipitation. (3) The increase of precipitation over the Yangtze River Delta region exhibits marked seasonal variations, which is the most remarkable during summer monthes. (4) The urban effects on precipitation are closely related to the characteristics of the background wind field. The rainfall center is located in the leeward area of the city group, especially for Shanghai, where the maximum of increasing precipitation is about 60~70 km downwind of the urban center. (5) The urbanization leads to the strengthening in the intensity of precipitation, rather than the rainfall frequency in the Yangtze River Delta urban region.
  • Automatic Detection of Heavy Fog and Cloud-Fog Separation Technologyin City and Coastal Area of Eastern China Based on MeteorologicalSatellite Remote Sensing Image
  • ZHOU Hong-mei;TANG Xu;GE Wei-qiang;LIU Dong-wei;BAI Hua;YANG Ying-min
  • 2011 Vol. 30 (3): 675-682. 
  • Abstract ( ) PDF (911KB) ( )
  • Heavy fog may bring enormous disaster to the national economy in the coastal cities, so there is an urgent need for real-time monitoring and precise analysis of area, distribution and location of the fog. In this paper, a practical methodology for automatic detection of fog and cloud-fog separation technology based on meteorological satellite remote sensing images is developed, such as FY-2C/D and MTSAT, assisted by polar orbit satellite data. The characteristics of the spectral channels for the detection is outlined with consideration of the available meteorological remote sensing data, as well as the live ground visibility and some other weather observation data. Using the synchronous or quasi-synchronous observation data, the spectrum and reflective characteristics of clear, could, and fog pixels in the visible light and infrared bands of the images on the same ground surface are analyzed. The relative relationship between the reflectivity of surface, cloud and fog on the visible light band of the images is then established for the automatic detection. The method of dynamic threshold is first used to getting approximate fog area and then based on this, many powerful technologies of detecting fog are adopted for separating fog and cloud, such as differential box counting, morphology fractal analysis, zonal tracking detection, template feature analysis and infrared character analysis. The average relative error of recognized fog area by above mentioned remote sensing methods is 21.03%, which have been verified by ground observation data. The result of fog detection is good, as well as in service application.
  • Climate Zoning of Frozen Disasters in Yunnan Province
  • DUAN Xu;TAO Yun;DUAN Chang-chun;DUAN Wei;WU Xing-lin
  • 2011 Vol. 30 (3): 683-691. 
  • Abstract ( ) PDF (1101KB) ( )
  • Using the freezing samples and corresponding temperature, wind and relative humidity data of all stations in Yunnan Province from 1951 to 2007, the discriminant of freezing weather was founded by analyzing the generalizing ratios of freezing samples and freezing weather. Applying Cressman objective analysis method, the day-to-day temperature, wind and relative humidity data were interpolated into 1 km 1 km fine-grid from November 1958 to April 2007. In interpolation, meteorological factors changing with altitude was considered and terrain correcting unit was defined by the scanning radius area. On the basis of above works, the refined climate zoning of frozen disaster in Yunnan Province was obtained. The results indicated that: (1)The northeast of Yunnan Province is the most severe area of freezing weather, the northwest is the second severe area, the middle and southeast is lesser area. With the exclusion of higher latitude area, there is not almost freezing weather in southwest of Yunnan Province. (2)The total trend of freezing weather has been decreasing since 1958, especially in seven years of 21st century. Except for the total was above normal in 2005, the total was below normal in other six years. (3)The most severe districts of frozen disaster in Yunnan Province include Zhenxiong, Weixin, Zhaotong, Ludian and Wulianfeng mountainous area of Yongshan of the northeast of Yunnan Province. The second severe districts include the majority of Qujing of the east of Yunnan Province, the higher latitude area of Luxi and Qiubai of the southeast of Yunnan Province and Deqin, Weixi, Gongshan and the mountain area of them of the northwest of Yunnan Province. The other districts of the east and northwest of Yunnan Province are light frozen disaster area. The other districts where had taken place freezing weather are lighter frozen disaster area.
  • Analyses on Spatial-Temporal Distributions and Temperature-MoistureStructure of Freezing Rain in China
  • OU Jian-jun;ZHOU Yu-quan;YANG Qi;PAN Liu-jie
  • 2011 Vol. 30 (3): 692-699. 
  • Abstract ( ) PDF (896KB) ( )
  • The spatial and temporal distributions of the freezing rain in China is analyed using the surface observation data from January 2008 to April 2010. And then, the vertical structures of cloud and atmospheric temperature from sounding, for example, the relative locations of cloud top height and warm layers (T>0 ℃), are used to study the temperature and moisture structures and the type of formation mechanism of freezing rain. The results show that the freezing rain occurs mostly from November to March, with the highest concentration in January (accounting for 72% of the total number). Over 90% of all freezing rain occur the areas to the south of Yangtze River, leaving only a few to other regions. According to different formation mechanisms, freezing rain can be divided to two patterns: Warm rain mechanism (WRM) and ice-phase mechanism (I-PM). The WRM account for 72%, while I-PM only 27%, among of all freezing rain detected here. The cloud top heights of WRM are low (below 3 km), while those for I-PM are relatively higher(reaching 9 km); The temperature of ground(instrument shelter) is lower than 0 ℃; The thickness of I-PM warm layers is basically more than 1 km and their maximum temperatures are higher than 3 ℃. It is likely that formation mechanism of freezing rain is regionally variable, with I-PM almost solemnly dominates in regions to the north of 30°N, and two mechanisms both exist in regions to the south of 30°N. Affecting by topography, WRM occurs more often than the other in high-altitude areas.
  • Numerical Study of Topography Effect on Rainfall ReinforcementAssociated with Tropical Cyclone ‘Talim’
  • DONG Mei-ying-;CHEN Lian-shou;CHENG Zheng-quan;LI Ying
  • 2011 Vol. 30 (3): 700-710. 
  • Abstract ( ) PDF (1600KB) ( )
  • Using the synthesizer of NCEP/NCAR reanalysis data and Japan regional spectral modeldata, WRF V2.2 model is employed to investigate the topographic effect on the rainfall reinforcement associated with tropical cyclone ‘Talim’ (0513). The results show that Dabie mountains can impact rainfall obviously by shifting its center and increasing the intensity of rainfall reinforcement about 15%. However, there is no relation between the occurrence of rainfall reinforcement and the topography. Convergence line and meso-β vortex formation and development due to the terrain effect may strengthen the convergence to increase the intensity of rainfall reinforcement and shift its center to upslope of mountain. The centers tend to locate in the superposition region of the convergence line and terrain upslope. The higher terrain, the stronger low-level vorticity, convergence and upward motion will induce. During the period of rainfall reinforcement, the terrain forced vertical motion at the lowest model level accounted for total vertical motion of the weighting at 50%; terrain forcing has a significant impact on the ascending motion. Maxima of terrain forced vertical motion appear in east slope near mountain top, rainfall maxima situate between the top and maxima of terrain forced vertical motion.
  • Analysis and Forecast of Heavy Snow in Shanxi Province
  • ZHAO Gui-xiang;DU Li;FAN Wei-dong;ZHANG Guo-yong;HU Zhi-xin
  • 2011 Vol. 30 (3): 727-738. 
  • Abstract ( ) PDF (1461KB) ( )
  • The main characteristics of heavy snow in Shanxi Province was comprehensively analyzed using basic data at 108 meteorological stations and conventional observation data from 1971-2008. The results showed that: (1)The heavy snow occurredmainly from October to next April, the most in March, the least in October. The heavy snowmainly occurred in local, while regional snow was less relatively. The interannual difference of number of heavy snow in Shanxi Provinec is significant. There were three abnormally more years and five abnormallyless years. There was an increasing trend overall. The average growth rate was 0.259 times per 10 years. There were the most numbers of heavy snow in the south, while the least in the middle. There was an slowly increasingtrend in the north and middle, while a decreasing trend in the south. (2)There were three influencing systems, and there was about 74% of blocking circulation on 500 hPa. (3)Diagnostic analysis showed that: There were two vertical structures about ascending motion above heavy snow area. The download of vortex advection was mainly dynamic factor that lead to strength of vertical motion and cause duration and increase of heavy snow. The maintain and increase of jet at low level was not only important ways about vapor transportation and addition, but also organizer of symmetric instability and triggering release of unstable energy. At the same time, it strengthenedmesoscale upward motion at low level. There occurreda moist cooling pad near the surface which made warm and wet air climb along it, made humidity increase, made it cool and saturate. (4)There is differentconfigeration under the influence of different system, and it will lead to different intensity, snow area, and occuring time.
  • Contrast Analysis on ‘010805’ and ‘080825’ HeavyRainstorm in Shanghai
  • CAO Xiao-gang;WANG Hui;ZOU Lan-jun;CHEN Yong-lin;ZHANG Ji
  • 2011 Vol. 30 (3): 739-748. 
  • Abstract ( ) PDF (1357KB) ( )
  • ‘010805’ and ‘080825’ heavy rainstorm in Shanghai are two most influential processes in the recent years. The same and different characteristics are presented by atmospheric circulation background, thermal, vapor, dynamic condition and satellite cloud images, leading to heavy rainfall. ‘010805’ heavy rainstorm was caused by tropical depression (for short 010805TD), while ‘080825’ heavy rainstorm was irritated by mid-latitude vortex shear, and landing typhoon NURI (0812) provided the plenty of vapor and energy for the heavy rainstorm. The two heavy rainstorm processes are affected by weak cold air from north and interactions among different air masses in middle and low latitudes play a significant role in the occurrence of heavy rainstorm. Southerly and south-east jets on the east side of slow-moving 010805TD continuously provided the vapor and energy for ‘010805’ heavy rainstorm and maintained the strength of 010805TD. Strong southwest low-level jet existed between the north-west sides of the western Pacific subtropical high and low-level shear, which provid the vapor and energy for downstream Shanghai. Convective instability energy accumulated 24 h before the start of ‘010805’ heavy rainstorm, but the convective instability energy rapidly accumulated 12 h before the start of ‘080825’, whose the atmospheric convective instability is stronger. Atmosphere over Shanghai became unstable before the starting of two processes, while K index rise up more than 36 ℃. Vapor transportation started 12~24 h before the starting of the two processes. Vapor in ‘010805’ heavy rainstorm was transported by southerly and south-east jets from East China Sea, while vapor in ‘080825’ heavy rainstorm was transported by south-west jets from South China Sea and south-west region of China. Both of the precipitable water of atmosphere were above 60 mm in the two heavy rainstorm processes of Shanghai. Their positive vorticity and updraft gathered in very narrow area over Shanghai, as illustrated the reason why heavy rainstorm occurred only in Shanghai from one side. Convective cloud cells have the characteristics of backward transmission. It is one of the reasons that mesoscale convective cloud cells rapidly strengthen to combin with bright cloud core occurred behind weakened convective cloud cell. The combination of cloud cells is also one of the reasons that suddenly accelerate the evolvements of mesoscale convective cloud cells.
  • Some Characteristics of Torrential Rain Events duringContinuous Drought Period in Beijing
  • LIAO Xiao-nong;WEI Dong;SHI Zeng-yun;XUAN Chun-yi
  • 2011 Vol. 30 (3): 749-759. 
  • Abstract ( ) PDF (1508KB) ( )
  • From 1999 to 2007, the mean annual precipitation has mainly been in negative departure. It is the longest drought period in Beijing area since 1960. Based on the analysis of the data from manual observation and AWS, some new statistical characteristics of torrential rain in Beijing are obtained. On the average, the cases of torrential rain became less during this period. Further more, the positive correlation between the number of the torrential rain case and mean annual precipitation is broken in some years. The local and short-lasting torrential rain events significantly increases. Besides, the ratio of the torrential rain events containing the short-lasting intense precipitation (10 mm per 10 min) goes up. And, the peak of the rainfall only appears in the early morning and the late afternoon. The torrential rain is more frequently observed in the south of Beijing city, but not in the southeast part. According to the synoptic analysis, one of the reasons causing the change of statistical characteristics is that cold air plays more important role in the torrential rain events during continuous drought. As the result, the precipitation is always convective. The study of short-lasting torrential rain shows that the meso-scale systems are mainly in the boundary layer and usually shallow. However, the severe convection clouds develop due to the unstable environment, which makes it possible that more rainfall is in the surface. From the conclusion of this research, the weather forecasters might get some new knowledge about the torrential rain in Beijing and then improve their forecast further.
  • Comparison and Assessment of the MODIS C005 andC004 Aerosol Products Over the China
  • WANG Hong-bin;ZHANG Lei;LIU Rui-jin;ZHANG Zhi-hui;CAO Xian-jie
  • 2011 Vol. 30 (3): 772-783. 
  • Abstract ( ) PDF (1265KB) ( )
  • Based on the differences between the MODIS C004 and C005 AOD products in long time series inChina and its surrounding areas, and MODIS aerosol products are compared and evaluated at three AERONET stations. The results show that: (1) The mean value of MODIS C004 AOD in the study region is 0.34, 0.32, with the standard deviation showing a significant spatial variability; there are small positive differences of most marine AOD by MODIS C005 compared to C004 and there are significantly negative corrected over land; the corrected value in different seasons and different areas are difference. (2) MODIS AOD products; the better agreement of C005 AOD with AOD of Xianghe sation than C004, but at Taihustationthere is not a significant change; At SACOL, because of the limitation of bright surface, MODIS AOD products are not better than others.(3) MODIS angstrom exponent product can not show the aerosol size information in quantitative measure, but it can be a qualitative parameter; there is a good linear relation between MODIS fAOD and AERONET fAOD, showing the MODIS fAOD can quantify the fine aerosol optical depth and study originate from anthropogenic combustion processes.
  • Research on Automatic Detection Algorithm of Downburst
  • TAO Lan;DAI Jian-hua-
  • 2011 Vol. 30 (3): 784-797. 
  • Abstract ( ) PDF (2067KB) ( )
  • According to the descent of storm core height and strong low-level divergence characteristic in the flow field of a downburst, an Automatic Detection Algorithm of DownBurst (ADADB) using the Doppler radar data has been developed. First, the storm core height has been calculated, according to storm cell identification and tracking results of the SCIT (Storm Cell Identification and Tracking) algorithm, meanwhile the radial velocity data of the lowest elevation has been handled to search the one-dimensional segment with divergent characteristics. Then, two-dimension identification technology has been applied to combine the one-dimension segments into a two-dimension divergent feature, also a kind of quality control method has be used to exclude the divergence field caused by other factors, thus to obtain the significant signal of downburst in the Doppler radar radial velocity field. Some simulated and real radar radial velocity data are used to verify the ADADB. The verifications show that this downburst automatic detection algorithm can detect the downburst with clear low-level divergence characteristic and to make warnings 6~12 min ahead.Key words: Downburst; Low-level divergence; WSR-88D Doppler weather radar; Radial velocity
  • Observation Studies on Characteristics of Raindrop Size Distribution ofTwo Typical Summer Thunderstorm Cases in the Pearl River Delta
  • LIAO Fei-;DENG Hua-;WAN Qi-lin-;QIAN Jia-xing;HUANG Hui-jun-;MAO Wei-kang-
  • 2011 Vol. 30 (3): 798-808. 
  • Abstract ( ) PDF (1354KB) ( )
  • Two typical summer thunderstorm cases initiatedby cold front and typhoon weather systems, which happened on 13 and 25 June 2008, respectively, are selected to study thunderstorm precipitation microphysics in the Pearl River Deltaof South China. Data of raindrop size distribution (RSD) and drop velocity spectrum observed by Parsivel present weather sensor are used to researchcharacteristics of thunderstorm RSD.The results show that the average cube root diameters of raindrops of the two cases are 1.14 mm and 1.18 mm, respectively, that are quite equal. Average number concentration of raindrop of typhoon precipitation is 1 082 m-3, and that in cold front precipitation is just 717 m-3, but the maximum instantaneous precipitation intensity of cold front is relative bigger. Correlation coefficient of rainwater content and precipitation intensity is quite high, while other physical features of RSD do not correlative well to precipitation intensity. Physical feature of RSD vary with the position of the observation station relative to the cloud cluster, and diameter and number concentration of raindrops are comparatively larger in convective precipitation than in stratiform precipitation, whichmeans rainwater content is mostly contributed by larger size raindrops. The types of RSD exhibit inhomogeneousfeature, and number concentration of different size raindrops, especially relative bigger size raindrops, varyin wide range. Spectrum width of RSD continuously keeps comparatively larger in the cold front, and the spectrumtype is bimodal or multimodal distribution in mature period of precipitation process. While in the typhoon precipitation , number concentration ofrelative small size raindrops vary obviously, and spectrum type of RSD keeps unimodal distribution during whole precipitation process.
  • Evolution of Polarimetric Parameters in Typhoon ‘Morakot’
  • SHEN Jin;CHU Rong-zhong;ZHAO Guo;WU Zhong-yuan
  • 2011 Vol. 30 (3): 809-816. 
  • Abstract ( ) PDF (999KB) ( )
  • The information of typhoon ‘Morakot’(200908) were observed by the X-band dual polarization Doppler radar on August 6~10, 2009. According to the moving path of the typhoon and different parts of the typhoon access to radar observation area, the observations of typhoon are divided into three parts, namely the spiral rain band region, the eye wall of typhoon and post-typhoon rain band. The changes of polarimetric parameters and spatial distributions of the dominant water particles during all parts of the typhoon are analyzed. The results show that the shallow convection exists in every part of the typhoon. Cold water and wet snow exist in every part of the typhoon and there also has a small amount of graupel and hail particles in post-typhoon rain band. The characteristics of melting layer of typhoon are obvious on the high ZDR, low ρHV(0) layers and high KDP layer exists in all parts of typhoon. The particle size in the eye wall of typhoon is smaller than the other two parts. The statistic results of polarimetric parameter show that the vertical distribution of ZH, ZDR and ρHV(0) are significantly different in three parts, however, the distribution of KDP has not obvious change in the different parts.
  • Characteristics of Electrical Waveform of Narrow Bipolar Event
  • WU Ting;DONG Wan-sheng;LIU Heng-yi
  • 2011 Vol. 30 (3): 823-830. 
  • Abstract ( ) PDF (666KB) ( )
  • Using the multi-station electric field data from field test in summer of 2007, based on electrical waveforms of 148871 narrow bipolar events(NBEs) selected with a relatively loose criterion and with hand picking, characteristics of NBEs with opposite polarities comprising the pulse width, peak value of electric field and the isolation were analyzed. The result shows that waveforms of NBEs with opposite polarities have distinct differences. The average pulse widths of positive and negative NBEs are 6.42 μsand 5.46 μs, respectively, and the pulse width of positive NBEs has a higher chance to be extremely large, with the maximum of 19.76 μs. The average peak values of electric field of positive and negative NBEs are 403\^4 and 627.0 digital units, respectively, while that of 97 713 negative return strokes is only 256.7 digital units. Peak electric field of negative NBEs has a higher chance to be extremely large, with the maximum of 5 118 digital units, while the maximum of peak electric field of positive NBEs is only 3 347 digital units. Most of NBEs are clearly isolated with other discharge processes. 73.5% of NBEs occurred without anyotherdischarge process occurring with in 1 s after them, and 78.5% of NBEs occurred without any discharge process occurring within 1 s before them. The difference of characteristic of isolation of opposite-polarityNBEs is also obvious. 4.39% of positive NBEs occurred with other discharge processes occurring within 10 ms after them, while only 1.61% of negative NBEs occurred with other discharge processes occurring within 10 ms after them. Based on these differences and the difference of source height of opposite-polarity NBEs, differences indischarge processes of NBEs are preliminarily discussed.
  • Characteristics of Lightning Activities in Yangbajing Region of Tibet
  • WANG Jun-fang;CAO Dong-Jie;LU Hong;WANG Dong-fang
  • 2011 Vol. 30 (3): 831-836. 
  • Abstract ( ) PDF (631KB) ( )
  • The characteristics of lightning are analyzed using the data of fast and slow antennas in International Cosmic Ray Observatory of Yangbajing in 2009. It is found that the lightning activities mainly occurred from late June to early September with a single percent peak of 58.2% in August. The diurnal variations of lightning activities show that the most of lightning easily occur in the afternoon and the percent of lightning activity from 17:00 to 19:00 is 65.1%. The maximum flash rate is 9 fl·min-1and the average value is 1 fl·min-1. 14.6% of lightning are cloud-ground flash and all are negative cloud-ground flash. From cloud-ground flash analysis, it is found that 22.1% of cloud-ground flash just have one return stroke. The percent of only one stroke of lightning is 22.1%.For cloud-ground flash the geometric mean of discharge duration before the first return stroke is 122.2 ms, the geometric mean of interstroke interval is 32.1 ms and for 84.5% of cloud-ground flash the peak electric field amplitudes of subsequent return strokes is larger than that of the first return stroke.