Current Issue

• Interdecadal Change of Winter Snow Depth on Tibetan Plateauand Its Effect on Summer Precipitation in China
• 2011 Vol. 30 (4): 843-851. 
• Abstract ( ) PDF (1076KB) ( )
• A set of consecutive and long-recorded observational snow depth data with 51 observation stations are obtained through choosing, removing and interpolating original observation data in the Tibetan Plateau during 1961-2006. Using the monthly precipitation and temperature data at 160 stations in China during 1951-2006, which was collected by National Climate Center, through calculating the correlation coefficient, significance test, polynomial trend fitting, composited analysis and abrupt change test and so on, the interdecadal change of winter snow on Tibetan Plateau and its relationship to summer precipitation and temperature in China, and to tropospheric atmospheric temperature, the general circulation and the East Asian summer monsoon under the background of global warming are studied.

• Contrast of Diurnal Variations of Summer Precipitationbetween the Tibetan Plateau and Sichuan Basin
• 2011 Vol. 30 (4): 852-859. 
• Abstract ( ) PDF (974KB) ( )
• The hourly summer (from June to August) precipitation data at two automatic weather stations during 2006-2008 and the TRMM (Tropical Rainfall Measurement Mission) Multi-Satellite Precipitation Analysis (TMPA) during 2002-2008 in the Tibetan Plateau and its neighboring region are used to explore the diurnal variation of summer precipitation. There is a marked difference between the diurnal variation of precipitation in the Tibetan Plateau and that of Sichuan Basin. The peak times of precipitation in a day are, on average, different for the two regions, showing a propagating characteristic from the central Plateau to eastern basin. Usually, the convective systems tend to generate over the central Plateau in the afternoon, strengthen in the evening and move eastward to the eastern edge of the Plateau at night, resulting in the frequent ‘Night Rain’ in the Sichuan Basin. There are corresponding diurnal variations in the horizontal vorticity, vertical velocity and other relevent meteological elements. Therefore, the ‘Night Rain’ in the Sichuan basin is a result of the Tibetan Plateau effect on the diurnal cycle of convective systems. This process is similar to a convective propagation when a diurnal signal over land is spread out over the adjacent oceans in a tropical coastal area.

• Numerical Simulation of Diurnal Variation of SummerPrecipitation in Sichuan Basin
• 2011 Vol. 30 (4): 860-868. 
• Abstract ( ) PDF (1237KB) ( )
• A regional climate model (RegCM3) has been applied to simulate the summer precipitation in Sichuan basin during 1991-2004. The station rain-gauge data and NCEP/NCAR reanalysis data are used to evaluate the performance of the model to simulate the diurnal cycle of precipitation, especially the formation of mid-night maximum rainfall. The results show that the RegCM3 can simulate well the spatial distribution and diurnal variation of averaged precipitation in Sichuan basin. The orography forcing is related to the formation of mid-night maximum rainfall. The low-level eastly wind encounters the mountain slopes on the west side of the basin and a convergence center appears on 850 hPa in summer. The low-level temperature and humidity gradually increase at afternoon, which leads to the reinforcement of the unstable layer. In the mean time, the convective activities are enhanced, and reach their maximum at night, which finally results in the mid-night maximum rainfall.

• Trend of Snow Cover Fraction in East Asia in 21thCentury under Different Scenarios
• 2011 Vol. 30 (4): 869-877. 
• Abstract ( ) PDF (1046KB) ( )
• Using the snow cover fraction(SNC) output by 8 WCRP CMIP3climate models under SRES A2, A1B and B1 scenarios, the trend of SNC in East Asia in future is analyzed. Results show that SNC is likely to decrease in East Asia continent， where SNC decreases the fastest in spring(MAM), then winter(DJF) and autumn(SON), and the slowest in summer(JJA), under the same scenario. In spring and winter, the SNC decreases faster in Qinghai-Xizang Plateau than in northern East Asia, while in autumn there is little difference between them. As for different scenarios, SRES A2 has the largest decrease trend, then A1B, and B1 has the least trend. The decrease of SNC is mainly caused by the changes of surface air temperature and snowfall, but they have different contributions to SNC trend in different regions and seasons.

• Homogeneity Test of the Total Solar Radiation Data Series and FurtherResearch on Climatological Calculation over Xinjiang
• 2011 Vol. 30 (4): 878-889. 
• Abstract ( ) PDF (1282KB) ( )
• The invalid and missed data were interpolated in the sequence of monthly solar radiation and percentage of sunshine at 12 radiation stations of Xinjiang, then all were examined by the homogeneity test approach and adjusted accordingly month by month, based on the monthly homogeneous percentage of sunshine sequences and history metadata files from 105 meteorological observation stations, adopting controlled teston the data quality (such as logical test),spatial correlation test of station-by-station, spatial consistency check and objective test, such as Potter, etc. After that, the best climatological formula of calculating solar radiation was studied. The results were revealed as follows: (1) The monthly percentage of sunshine sequences are homogenous except for Urumqi and Ili radiation stations where disconnected points exist in several monthly time series. On the other hand, the monthly radiation time series disconnect only in Urumqi, Ili, Altay, Harmi, Hotan stations, where the discontinuityhappened mostly in winter half year, possibly caused by the increase in the aerosol of air, but the relocation is primary at Urumqi station. The discontinuity phenomenonis the most serious at Hotan and Altay stations. (2) It is the best to calculate coefficients a and b with single month and single station adopting the formula like Q=Q0(a+bS), which could lead to the mean absolute error from 3% to 8% at a single station. (3) Coefficients a and b are of obvious apparent spatial distributions and seasonal variation characteristics according to the radiation climatology formula based on the astronomical radiation constant. Coefficients a and b are of obvouis and steady reverse correlations except for Ili. (4) Based on the monthly mean percentage of sunshine at 105 meteorological stations and Kringing-interpolated coefficients a and b, the calculation shows that the yearly total solar radiation is higher in East and South of Xinjiang than in West and North and the lower center locates in the Tianshan Mountains. Zonal distribution of the total solar radiation is the most typical in autumn, secondly, in winter, which turn to latitudinal distribution in spring, it appera vortex in summer when the little discrepancyappears in the Junggar and Tarim Basins.

• Phenomenon of Vortex Self-Organization of Several RainstormProcesses in Northwest Region of China
• 2011 Vol. 30 (4): 890-900. 
• Abstract ( ) PDF (1461KB) ( )
• Based on the vortex self-organization dynamics method, several rainstorm processes in Northwest China were analyzed, the obtained results are as follows: (1) Most of cloud clusters produced heavy rainstorm experience the process from the non-organized to organized and from irregular to regular clouds; (2) The precipitation clouds cause the rainstorm of Gansu Province which generally united by two to four little clouds about 35 km×35 km, the combination time of 110 km×110 km clouds is 3~4 h, the time of 200 km×200 km clouds is 9~10 h, The clouds of more than 220 km×220 km are not self-organizing success; (3) The TBB centers are successful in sell-organizations which generally are about 220 K; (4) TBB center of cloud clusters in Gansu Province is about 220 K , the intensity of TBB is weaker than the clouds in southern China, and the convective system of Gansu Province move faster; (5) Precipitation cell are basically located in dense with TBB contours, and on the western side of TBB contours are more intensive, relatively east sparse. The analysis shows that the vortex self-organization is an important reason cause heavy rainfall in arid and semi-arid regions and an important basis to improve the physical mechanism of the development of rainstorm.

• Dynamic Diagnosis and Mechanism Analysis of Yellow RiverCyclone Induced Bohai Storm Tide
• 2011 Vol. 30 (4): 901-912. 
• Abstract ( ) PDF (1929KB) ( )
• Using the digital 6.7 μm satellite water vapor image and NCEP/NCAR 1°×1° reanalysis data, the synoptic and dynamic processes of Yellow River cyclone induced Bohai storm tide is diagnosed based on the dry intrusion and potential vorticity theories. The result shows that the storm tide occurred during the adjustment of Eurasia mid- and high-latitude circulations, east moving and development of unstable low tough and the rebuilding of East Asian trough. Northerly gale wind induced by strongly developed Yellow River cyclone forced the sharp increase of tide over Bohai tide sharply bloomed. Dry cold air from tropopause with high potential vorticity intruded into lower level troposphere shown as dark area in vapor image, when the dry cold air encountered with warm moist and wet air from low troposphere, it was distorted into an axe-shaped dry air area which manifested a strong horizontal deformation. Then the cyclone rapidly strengthened when it moved to the area with bigger potential vorticity from upper to lower levels. It followed by the mature of cyclone when the spiral structure can be found in the dry and wet area. In the center of cyclone where the dry air with lower θw superposed the warm air with higher θw, which increased the potential instability. The mechanism of rapid intensification of cyclone can be shown as follows: Firstly, the downward intrusion of dry air into low level; secondly the reduction of static stability of atmosphere and augmentation of absolute vorticity; finally, the quick development of cyclone. The isallobairc gradient, pressure gradient, downward propagation of upper level momentum and divergence of super-low-level jet all contributed to the gale wind during the Bohai storm tide.

• Synthetic Diagnostic Analysis on a Rainstorm Process CausedInteraction of MCC and Meso-β Scale Severe ConvectiveCell in Mid- and Lower-Reaches of Yellow River
• 2011 Vol. 30 (4): 913-928. 
• Abstract ( ) PDF (2269KB) ( )
• Using the satellite image data, Doppler radar data， the conventional observation data, the surface intensive observationdata and NCEP reanalyzeddata, the large-scale environment field and mesoscale influence systems of the floodingrainstorm process in common boundary of Shanxi and Henan on July 29～30, 2007 is analyzed. The results show that the rainstorm is caused by MCC, the meso-β scale severe convection cloud clusters, as well as MCC and the meso-β scale severe convection cloud cluster merger.The low jet stream and northeast wind at boundary layer are one of the triggeringmechanisms for generation and development of MCC. The secondary circulation circleis generated when the air current is clockwise rotation to provid the dynamic conditions for the generation and development of MCC. The generation of the secondary circulation circle has the meso-α scale in downstream when the air current the counterclockwise rotation which is of the impediment and the stabilization tothesecondary circulation circlein upstream. The high pressure of surface mesoscale moves to the south triggeredthe generation and developmentof MCC in the shear line, it is located in thefront ofthe mesoscale high pressure. The severe precipitation of MCC brings triggered the meso-β scale severe convection cell development in the shear line that located at the upstream of MCC. The cyclone perturbation, the motion trendof thesmall high-pressuretongue, as well as the generation of mesoscale low pressureon the surface pressure field, has the instruction function to the developmentof meso-β scale severe convective cell.

• Numerical Simulation of Impact Factors of Urban Haze in Nanjing Area
• 2011 Vol. 30 (4): 929-941. 
• Abstract ( ) PDF (1367KB) ( )
• Air pollution process in Nanjing on 7 January 2005 induced by typical weather condition was simulated with the modified Nanjing University City Air Quality Prediction System (NJU-CAQPS). The contribution ratios of urban anthropogenic heat source, urban buildings and various anthropogenic heat sources to the concentration of several main pollutants and the impacts of the anthropogenic heat sources on visibility distribution were analyzed. The result shows that in main urban district, the daily average surface visibility reduced below 8 km, and the hourly surface visibility is less than 10 km for 18 h in one day; this condition should be considered as a heavy haze process. The industrial point source dominates mostly the daily average surface concentration of SO2, its peak value is above 110 μg·m-3; mobile source contributs the most to the daily average NO2 surface concentration, its peak value is above 70 μg·m-3; area and point sources have the significant contribution to the daily average surface concentration of PM2.5, the peak value is more than 100 μg·m-3 and 45 μg·m-3, respectively. Due to the anthropogenic heat source release, the lower layer temperature air increased and wind converged, the vertical speed over urban district increased, all these lead to the decreases of surface concentration of SO2, NO2, PM2.5 in urban district, the surface visibility increased correspondingly, and the area of regions over where visibility less than 10 km has decreased 20.2 km2. The horizontal wind speed over urban district decreased because of the building distribution, so that mass of pollutants concentrate over urban area and upper drift to the urban district, and in this district the concentration of various pollutants obviously increased. The concentration of fine particles (PM2.5) has increased 10 μg·m-3, comparing with the case without building effects. The comparison also showed that the ground visibility could decrease by a maximum of 2 km, the duration of visibility below 10 km increased by 2 hours, and the area of regions with haze increased by 134.2 km2 when the simulation concerned about the effects of buildings rather than not.

• Simulation Study on Microphysical Process of Freezing-RainEvent in Southern China during the Early 2008
• 2011 Vol. 30 (4): 942-950. 
• Abstract ( ) PDF (1280KB) ( )
• A case of freezing-rain weather in southern China during the early 2008 was simulated by the model MM5V3.7. The simulated results show that there are two obvious water vapor channels during the freezing-rain process, and the ascending motion is significant. Over the freezing-rain areas, there are the accumulation of cloud- and rain-water, especially the former on the lower-level, but with less snow flake and a little ice crystals on mid- and upper-levels. Comparing with the freezing-rain area, over no freezing rain areas the supercooled water has larger volume, but it is mainly on the lower level, and there is no graupel, snowflake is much less on the upper level. The main reason is that the updraft over the ice rain area is weak, and the vapor in the air is not saturated. In the rainfall area, the ice-phase rainfall is just above the 0 ℃ line, and rain water is just below 0 ℃ line. But in the ice rain area, the ice-phase particles do not fall to the 0 ℃ line, and the top of rain water is not against the line neither. The cloud physics of ice rain belongs to liquid-phase warm rain mechanism. The reasons of caused huge severe disaster are not only just the ice rain, but the desublimation effect of the rime and vapor. Just because the combined icing action of glazed and fog frosts led to the severe disaster, but the ice rain amount was not big during the ice rain process.

• Analyses on the Structure Characteristic and FormationMechanism of the Rainstorm Related to a Cold VortexSystem over Northeast China
• 2011 Vol. 30 (4): 951-960. 
• Abstract ( ) PDF (1617KB) ( )
• Using the encrypt observational data and NCEP/NCAR reanalyses data, the development and structure of a rainstorm event related to a cold vortex system over northeast China during 20～24 July 2006 were investigated. The formation mechanism is numerically simulated using the mesoscale model MM5. Observations show that there are two upper-level jets over the top-troposphere during the evolution of the cold vortex, one stretching southward from high latitude and another from Subtropical Westerly Jet System (SWJS), which converge over Northeast China. Cyclonic vorticity is reinforced by the SWJS, make cold trough being cut off and develop eastward. During the development stage of the cold vortex system, low level convergence occurs between the southeast jet and northwest wind.The heavy rainfall mainly takes place in the ascending air of the convergence area of the northeast of the cold vortex. At the mature stage of the cold vortex, a deep cold core is located below 300 hPa, above is a warm core. The strong wind area distribute on the edge of the cold vortex, while no apparentwind in the cold core. The topography experiment shows that the cold vortex system retreat at the decrease stage after the remove the terrain of northeast China. The high potential vorticity (PV) stream from the high level tropopause insert the lower level, which characterize by its cold-dry air incursion. High PV stream overlay at the low equivalent potential temperature, which means cold-dry air incursion has high PV characteristic. Positive PV anomaly of high tropopause overlay with positive anomaly of (-θ/p) of low level, which strengthen the new born cyclone and intensify the cold vortex .

• Analysis on Severe Convection Rain and Snow WeatherProcesses in Dalian in Spring of 2009
• 2011 Vol. 30 (4): 961-968. 
• Abstract ( ) PDF (1314KB) ( )
• There was the latest spring snowfall weather process on 15 April 2009. The rain and snow weather processes of severe convection are analyzed using the conventional observation data, automatic meteorological station data, MM5 model, radar data and so on.The results show that the circulation background of the severe convection event is composed of many parts which include 200 hPa jet stream, 500 hPa cold trough, vapor transportation in middle-low levels and surface cold front. In addition, the dry and cold air of middle level overlay the humid and warm air at lower level to make for instability stratification. On the dynamical uplift of front, more abundant vapor transportation at lower level overlay the cold air to be favorable for the severe convection snow and rain occurring. Otherwise, the temperature inversion of lower level and instability energy with obvious uplift results in instability precipitation. The much meso-β scale convection cloud clusters in the cold front cloud system is direct mesoscale system. In the echo of Doppler radar, the high intensity in different shapes, ‘S’ style zero rapidity line, and also ‘Bulls-eye’ in different levels can all indicate the instability stratification positioning and the cause of meso- and micro- scales of convection convergence system. The analyzed temperature show that the incursion of cold air at upper level induces a large range of temperature decrease over middle-lower levels and surface, which is direct reason of convection event.

• Flow Pattern Configuration and Physical Quantity Diagnostic Analysisof Heavy Snowstorm Process in Shanxi on 11 November 2009
• 2011 Vol. 30 (4): 969-981. 
• Abstract ( ) PDF (1994KB) ( )
• Using the conventional and unconventional meteorological observation data, flow pattern configuration, the physical diagnosis of the satellite and radar data for the heavy snowstorm process occurred in Shanxi region from 9 to 12 November 2009 were comprehensively analyzed. The results showed that the durative heavy snowstorm weather process presented against backgrounds of two kinds of circulation, which influenced by 3 middle-α scale snowstorm cloud systems during the heavy snowstorm, the occurring, developing and moving of the heavy snowstorm cloud system were closely linked with 700 hPa shear line and jet flow in low altitude. The analysis results indicate that the three jet flows from northeast, southwest and westwards below 400 hPa were strong and prosperous, and turn around with altitude, which is the main characteristic of the rare heavy snowstorm process flow pattern configuration. The atmosphere stratification below 200 hPa was in instable status and wet layer thickness reaches 200 hPa, the vertical distribution of divergence presented obvious symmetrical structure of convergence in lower level and divergence in upper level, the water vapor convergence quantity below 400 hPa was a fold increase in the period of heavy snowstorm. This kind of configuration of the physical quantity field accelerated the convergence of wet air in lower level and their raising upwards movement, and which provides the advantageous condition for the occurring of snowstorm and heavy snowstorm. The snowfall is positive proportion to the divergence field, the high-low divergence and convergence intensity of vapor flux field, and the wet layer thickness against the background of two kinds of circulation. The increasing of divergence variability has perfect corresponding relationship to the appearing of the snowstorm peak value, and it is an initial lead of 12～18 h.

• Study of Micrometeorological Characteristic in Typical TerraceRegion of Middle Loess Plateau in Winter
• 2011 Vol. 30 (4): 982-988. 
• Abstract ( ) PDF (795KB) ( )
• The micrometeorological characteristics in terrace region of Loess Plateau in winter are analyzed using the observation data from LOPEX (Experimental Study of Land Surface Processes in Chinese Loess Plateau). The results show that each component of radiation fluxes on clear day in winter has only half as much as that in summer. The surface is heated by atmosphere at most of time (from 17:00 to 09:00 of the next day). The average radiation is close to that on clear day. The sensible heat flux in winter occupy large proportion in surface energy which is an half of net radiation whether on typical clear day or average condition. The ratio of the latent heat flux is only 25% of the sensible heat flux and the soil heat flux is between the sensible heat flux and the latent flux. The turbulent exchange at nighttime in winter is very weak. The heat is transferred from atmosphere to surface in two third times of a day. Average value of albedo is 0.22 during the non-precipitation period time and that is 0.28, which is almost increasing 30%during the snowfall process. It needs 7 days when albedo restores to new quasi-equilibrium. The effect of the snowfall on albedo is very complicated, which is one of reasons that are difficult to predict albedo.

• Numerical Simulation of Influence of Fractional Vegetation Cover Changein the Source Water Region of Yellow River on Regional Climate
• 2011 Vol. 30 (4): 989-995. 
• Abstract ( ) PDF (799KB) ( )
• Based on AVHRR/NDVI of 8 km spatial resolution from 1997 to 2006, a fractional vegetation cover data were obtained, which has the same spatial resolution with Regional Climate Model (RegCM3). Using the derived fractional vegetation cover instead of the default fractional vegetation cover in RegCM3, the main climatologic elements in the source water region of the Yellows River were simulated. The results showed that, with considerating the fractional vegetation cover derived satellite in the model, the simulated monthly mean temperature is closer to the surface measurement; which isalso somewhat improvement to simulate regional precipitation. The influence of vegetation on the simulated sensible heat and latent heat fluxes are somewhat improved, and the simulated latent heat flux ismore accuracy than that of the simulated sensible heat flux.

• Analyses on Radiation and Energy Balance Characteristics in Miyun of Beijing
• 2011 Vol. 30 (4): 996-1004. 
• Abstract ( ) PDF (1107KB) ( )
• Based on the radiation and fluxes data observed at Miyun station in Beijing in January, April, August, October 2007, the radiation balance, albedo and energy balance under different types of synoptic conditions including clear and cloudy days on heterogeneous underlying surface are analyzed. The results shows that: （1） The energy balanceclosure(OLS) was 82%, 97%, 72%and 83% in January, April, August and October, respectively. The total energy balanceclosure was 76%. These indicated that the quality were good; （2） As the changing of mixed crop-forest underlying surface, the averageof upwardlong-wave radiation were 279.6, 381.5, 430 and 358.7 W·m-2 on clear day, in January, April, August, October, respectively. Therespond time to short-wave radiation was 0.5 h and 1.5 h in January and August, respectively. （3） The behaviorof albedo is complex as it is predisposed by both surface moisture and vegetation condition. The monthly averaged value of albedo on clear day in January is 0.183, 0.143 in April, 0.133 in August, 0.139 in October. The diurnal variation of albedo is asymmetrical. The albedo at Miyun station in August is lower than that at Gucheng station, which is 0.19. （4） On clear day, the components of energy balance showed standards daily cycle patterns. The primary distribution of energy is the sensible heat exchange in January, April and October, whilein August it is mainly used for latent heat exchange. Thecharacteristic of energy distribution on cloudy day is the same as that on clear day.

• Characteristics and Impact Factors of Ultraviolet Radiation in Guiyang
• 2011 Vol. 30 (4): 1005-1010. 
• Abstract ( ) PDF (575KB) ( )
• Based on the observation data of Guiyang in recent 6 years, the change characteristic of ultraviolet(UV) radiation is analyzed. The results showed that the maximum of hourly averageUV radiation is 21 W·m^-2(four-grade intensity), and the instantaneous maximum is 26.4 W·m^-2, strong UV radiation in 5 grade does not appear. Strong UV radiation period is long fromApril to September, and it can reaches 4 gradesat 10:00～15:00; Strong UVradiation at 13:00 occurrs most probably from April to September, especially in July and August, it reaches 52% and 51%,respectively. UVradiation is strong and stable in sunnyday, fluctuates obviously incloudy day and weak in rainy day; Monthly UV radiation at noon exceed10W·m^-2 under sunny and cloudy conditions, while only medium intensityappears from July to September under overcast condition; seasonalvariation trends under three weather conditions are similar, they are all weak in winter and strong in summer. Cloudiness, relative humidityand visibility have significant correlation tothe UV radiation in Guiyang.

• Analyses on Atmospheric Aerosol Optical Properties withLidar Data in Lanzhou Suburb
• 2011 Vol. 30 (4): 1011-1017. 
• Abstract ( ) PDF (742KB) ( )
• Based on the lidar from the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL), the data from January to April 2007 with clear sky and dust storm weather were selected to retrieve aerosol extinction coefficient (AEC) and aerosol optical depth (AOD). The results show that the AEC has high value in the low layer under 1 km, which is 0.01～0.1 km-1 ; the average AOD is below 0.5, the daily AOD has two peaks appearing at 12:00 and 20:00, respectively. The difference between heating and non-heating season is obvious. In dust storm, The AEC has high value under 6 km, with 0.1～1 km-1 ; the AOD is larger than 1; the peak value is 3.5; the lidar valid observation has below 2 km with the retrieve of AEC showing segments phenomena in strong dust storm process, and the AOD has good relation with PM10 surface concentration. The AOD correlation coefficient between lidar and sun photometer is 0.86.

• Characteristic and Diagnostic Analysis of High Temperatureand Drought in Tongren Area in 2009
• 2011 Vol. 30 (4): 1018-1026. 
• Abstract ( ) PDF (1332KB) ( )
• Using the daily precipitation and mean temperature data at 10 stations of Tongren area in 1961-2009, the daily precipitation and maximum temperature from 10 July to 9 September 2009 and NCEP 2.5°×2.5° reanalysis data, the circulation situation and physics of high temperature and drought in Tongren area from July to September 2009 were studied and discussed. The results show that: (1) the subtropical high over the western Pacific is located westward and relatively strong. (2) The cold air activity center is northward and the subtropical high maintain in 30°N.(3) The vapor transport is weaker to cause precipitation reduce. (4) The air current downward motion was stronger to cause the local temperature rise. (5) The summer water vapor transport zones of Bay of Bengal, south of South sea, East sea and Japan sea and Guizhou, east of Tibetan plateau, Hunan and Jiangxi are obvouis positive departure , the convection activity is weak.

• Climatic Changes of Rainfall and Rain Days in Yunnan Province
• 2011 Vol. 30 (4): 1027-1033. 
• Abstract ( ) PDF (818KB) ( )
• Climatic changes and the spatial/temporal features of annual, seasonal, and monthly rain days in Yunnan Province are investigated using the observational data at 30 stations in the period of 1959-2009. The results showed that the spatial distributionof multi-year mean rainfall in Yunnan Province is nearly consistent with that of rain days, the maximum rainfall appears in the southwest part of Yunnan, and the minimum, is in the middle and southeast parts of Yunnan, and so the rain day does in the same way. The rainfall change is no obvious in resent 50 years, but the rain days appear obvious decreasing trend, the trend coefficient is -0.475, which has passed the confident level of 99.9% and regression coefficient is -3.19 d·(10 a)^-1. The analysis of seasonal rain days showed that the temporal trends of seasonal rain days are all negative except for spring, and the trend coefficients at 30 stations all indicatenegative values in summerand autumn. The negative trend stations in four seasons passing the confident level of 95% are summer>autumn>winter>spring. Besides, there are 9 monthes in a year show negative trend stations which is more than half, particularly in June, August, Septemberand October, in general, the trend of rain days is negative.

• Characteristic Analysis of Structure and Lightning for ConvectiveSystem Produced Heavy Precipitation in Warm Sector of South China
• 2011 Vol. 30 (4): 1034-1045. 
• Abstract ( ) PDF (1568KB) ( )
• The fine density surface observation data, Doppler radar data, and cloud-to-ground (CG) lightning data in Guangdong region were utilized to study the characteristics of structure and CG lightning of two convective systems, which occurred within 24 hours over Zhujiang delta, South China. Results showed that： (1) the first convective system (occurred in morning) exhibits similarity to parallel stratiform MCS, the convective cells in the first system are organized by way of back-building, the vertical structure is similar to those of marine convective. While the second system exhibits similarity to trailing stratiform MCS, the vertical structure tend to those conventions over continent. (2) The characteristics of lightning are as follows: (I) The negative CG lightning predominate in the whole lifetime of convective systems for both the systems. (II) The percent of positive CG lightning gradually increases in its development stage, then decreases from mature to dissipation stages for the first convective system, while the percent of positive CG lightning gradually increases during the lifetime of the second convective system. (III) At the mature stage of the first convective system, the negative CG lightning occurs just behind of intense reflectivity at low level, positive presents its head. Lightning concentrates in intense reflectivity area (92.8% of lightning) and partly occur on the leeward side of intense reflectivity (7.2%). As for the second convective system, the positive and negative CG lightnings mostly overlap in the intense reflectivity area (78%), and partly occur in the stratiform area (22%). The possibility of occurrence of lightning in stratiform region for the second convective system is larger than that of the first convective system. More than 88% of CG lightning occurred in a region with reflectivity value equal or greater than 25 dBZ at the height of 6 km at the mature stage for both the systems. The characteristics of structure of convective system and its lightning are also discussed.Key words: Warm sector of South China; Structure of convection produced precipitation; Characteristics of cloud-to-ground lightning
  

• Revision of the Measured Value of Slow Antenna under the ComplexTerrain Condition of Qinghai-Tibetan Plateau
• 2011 Vol. 30 (4): 1046-1051. 
• Abstract ( ) PDF (642KB) ( )
• Using the synchronous slow electric field data at 7 stations of high precision GPS clock in Datong region of Qinghai Province in 2009, the electric field change are fitted based on the point dipole model, and nonlinear least square and exhaust algorithm methods, the field changes for 26 times of return strokes happened in 11 negative ground flashes during the field observation of 2009 were fitted, it aims to solve for the correction coefficients of slow antenna at different stations taking Mingde station as the standard, namely, how environmental factors, such as altitude and vegetation cover influence on the slow antennas at each station. At the same time, the locations of dipole moment and the moment center of the charges neutralized return strokes at each times are obtained with help of mean correction coefficients at each station. The results show that the antennas are amplified or shielded by environmental factors in varying degrees, and the correction coefficients of slow antennas are closely related to natural factors on the Plateau. The vertical component of the dipole moments neutralized by return strokes of the negative ground flashes are 11.6～66.0 C·km-1, the moment centers are 1.6 to 6.8 km.

• Stream Structure of a Convective Line with Leading StratiformPrecipitation during Meiyu Period
• 2011 Vol. 30 (4): 1052-1066. 
• Abstract ( ) PDF (2475KB) ( )
• A rear-fed leading stratiform mesoscale convective system(RFLS MCS)was observed in middle part of Hubei Province during Meiyu period of 2007. The stream structure feature of the RFLS on June 18, 2007 are analyzed using LAPS of ESRL(Earth System Research Laboratory), USA, and NCEP 1°×1° daily reanalysis data, operational observation and radar data. The horizontal reflectivity structure observed by radar is as follows: Astrong and narrow echo band is in the behind of convective line, and a sub-strong and broad echo area is frontof this convective line, there is a weak echo gouge between them. The convective cells sometime elongated and canted along the convective line.The RFLS systemon 18 June mainly consists of fourflow branches: Rear-to-front inflowat lower level, front-to-rear descending inflow and ascending flow which produce stratiform cloud anvil by tilting the rear-to-front flow in the middle and upper troposphere layer, rear-to-front flowat middle level. The RFLS system on 18 June has an overturning updraft during its early stages, and produce leading stratiform precipitation. In mature stages the vertical flow develops strongly， and the frontal stratiform echoes continue to strengthen. The line-perpendicular vertical wind shear in middle and lower troposphere layers increasing with time and the surface cold pool weakening or keeping changeless with time are the main causes for which this RFLS system updraft flow tilts frontward.

• Case Study of Bow Echo, Severe Convective Storm and Merger ProcessⅠ: Taking Single Doppler Radar Data as a Case
• 2011 Vol. 30 (4): 1067-1077. 
• Abstract ( ) PDF (1875KB) ( )
• Using CINRAD/SA radar data in Jinan, combined with satellite, automatic weather station and other conventional data, the research about occurrenceanddevelopmentof a bow echo and severe convective stormwas studied in this paper. Bow echo and severe convective storms merged to form new bow echo, and it then developed by the process into comma echo. Firstly, Convective process tookplace under the background of horizontaltrough turning to vertical trough. The atmospheric environment existed large convective available potential energy(CAPE)and moderate-intensity low vertical wind shear. FY-2C satellite infrared images clearly showedthat the development andenhancement of bow echowere influenced by outflow boundary of neighbor cloud. At the same time, thetemperature, pressureand humidity observed from automatic weather station had strong changes within 20 min, obviously. Secondly, the result obtained from Doppler radar data indicated that it was a typical bow echo process, because the system evolved through a typical evolution of the bow echo at every stage, such as tall convective echoes, bow and spear-shaped stage, comma echo. Thirdly, the severe convective storm was in the warm area in front of bow echo about 75 km and moved slowly, with some characteristics of common storms. At last, during the stage about bow echo and severe convective storm merging, the bow echo was already in late comma-cloud system. With time going on, the supercell gradually closed to the neck of bow echo. After experienced short decrease, it strengthened rapidly and filled the weakened part of the bow echo. Supercell developed into bow echo withstrong rear inflow in the bow echo, and soon evolved into a comma cloud. The disastrous wind was produced at the rotating head of comma cloud.

• Case Study of Bow Echo, Severe Convective Storm and Merger ProcessⅡ: Analysis on Three-dimensional Wind Field Retrievedby Dual Doppler Radar
• 2011 Vol. 30 (4): 1078-1086. 
• Abstract ( ) PDF (1249KB) ( )
• Three-dimensional wind field structure of a bow echo and a severe convective storm and interaction between them were studied in this paper, using the dual-Doppler (located at Jinan and Binzhou) retrieved wind field. The variations of wind field during the stage of the bow echo and severe convective storm merging were also analyzed. The main results were as follows: Firstly, the cyclonic circulation and anticyclonic circulation located at the head and tail of bow echo, respectively. But the cyclonic circulation was stronger than anti-cyclonic circulation. In the comma stage of cloud, the echo intensity and main updraft weakened, but the cyclonic and anti-cyclonic circulation strengthened. Secondly, the strong sinking divergent flow generated from old convective storm in the stage of dissipation, promoted convective storm formation and development. In the strong echo zone of severe storm, the convergence center located at the lower level, corresponding divergent field at the upper level. Finally, during the stage between severe storm and bow echo, the bow in the later stage of comma cloud, had weak updraft at the front of itself. But at the same time, the severe storm was in the mature stage, with strong downdraft close to the side of the bow echo. When the severe storm and bow echo closed, weak updraft and strong downdraft airflow merged. This situation led to rapid weakening of bow echo and short-time weakening of severe storm. As the organized rear inflow invaded back in the bow, the warm and wet airflow in severe storm was uplift. So the storm was encouraged an developed more powerful.

• Simulation and Analysis of a Gust Front Process
• 2011 Vol. 30 (4): 1087-1095. 
• Abstract ( ) PDF (1723KB) ( )
• Using the mesoscale numerical model ARPS, a gust front produced by a severe mesoscale convective system happened in Nanjing on 29 June 2006 was examinedand simulated. Numerical simulation result and synoptic situation were analyzed. The analysis of synoptic situation showed that there was obviously temperature inversion layer in the surface layer, and the atmospheric humidity deepened when the process of convective system move closely to the station. Jet stream and vertical wind shear were observed in synoptic situation. Though the thin line echo of gust front was not simulated, but the convergence of cold air descending and outflow from a thunderstorm and environment flow were successfully simulated. The convergence position was just the position of gust front occurring. There were obvious the internal wind stream and temperature construction in the simulation.

• Echo Parameter Estimation Algorithm Verification and GroundClutter Suppression of Wind Profiler Radar
• 2011 Vol. 30 (4): 1096-1101. 
• Abstract ( ) PDF (701KB) ( )
• Aimed at the problems of that the echo information is given directly by the radar manufacturer and its estimated accuracy and precision still need to be verified, the echo signal simulation method is improved, and a practical verification system to validate the correctly of parameter estimation algorithm of a variety of radar echo is given. And then a method to removing ground clutter from wind profiler radar based on static wavelet transforms (SWT) is proposed. This method determines the best decomposition level by calculating the 2-order moment of the wavelet coefficients at all levels, and selects the threshold through the average of the two bands which are adjacent to the clutter band. The simulation results show the algorithm is valid.

• Preliminary Application of Phased Array Technology in Weather Radar
• 2011 Vol. 30 (4): 1102-1107. 
• Abstract ( ) PDF (629KB) ( )
• The State Key Laboratory of Severe Weather of CAMS and Nanjing Research Institute of Electronics Technologyhas developed the first S-band phased array weather of China. In order to reduce the radar scan cycle, the S-band phased array weather uses a transmitted wider beam in pitch and narrower in azimuth, and multi received beams to overlap transmitted beam. However, for using this scanning method and pulse compression, beam width and gain is changed with elevation, so the Probert-Jones weather radar equation should be corrected. The characteristicsof beam width and gain are analyzed. Based on the Probert-Jones weather radar equation, it givesthe weather radar equation of this phased array weather radar and the estimation parameters of reflectivity in different regions. It provides a theoretical foundationfor the calibrationand measurement of the phased array weather radar.

• Change Characteristic of Yunnan Hail
• 2011 Vol. 30 (4): 1108-1118. 
• Abstract ( ) PDF (1147KB) ( )
• Using the monthly hail data(1961-2008) at 120 stations of Yunnan Province, the change characteristics ofspatial and temporal distributionsof Yunnan hail in the nearly 50 yearsand its response to global warmingwere analyzed. The results indicated that: (1)The Yunnan hail has obviously region distribution. From northwest to southeast, the spatial distribution of annual hail in Yunnan Province appears more-less-more-less. The distribution in summer hail is the same as in autumn, which the hail of northwest of Yunnan Province is more than other and the southwest is less. The distribution in spring hail is the same as in winter, which the hail of northwest and northeast of Yunnan Province are less than other, and from northwest to southeast, the number of hail is increasing.(2)The Ynnnan hail has obvious intermonthly change. There is hail happening in each month of a year in Ynnnan Province and mainly happens in February, March and April. With a view to the season distribution Yunnan Province belongs to typical spring hail region. With a view to the climate zone, north tropic zone, south subtropic zone, middle subtropic zone, north subtropic zone and temperate zone belongs to typical spring hail region,the most hail happens in April. Plateau climate zone belongs to typical summerhail region, the most hail happens in July. (3)In the recent 50 years, the hail change trend of the whole year and four seasons in Yunnan consistently reduced. The hail change trend of six climate zones also reduced. (4)There are obvious interdecadal changetrend in the annual and four seasons of Yunnan hail, and there are also obvious interdecadal changetrends in the six climate zones. (5)The response of Yunnan to climate warming is inconsistent in Yunnan. The hail in most areas of middle, west, south and southeast of Yunnan Province is very excellent relationship with climate warming. When the climate is warmer, the hail may decrease; and vice versa.

• Characteristic and Forecasting of Continuous Hail ShootingProcesses Caused by the North China Cold Vortex
• 2011 Vol. 30 (4): 1119-1131. 
• Abstract ( ) PDF (1985KB) ( )
• Using the conventional data, NCEP data, satellite data and Doppler radar data， 19 continuous hail shooting weather processes in the areas of Beijing-Tianjin-Hebei during 1975-2008 caused by the vortex in North China are analyzed. The distribution, formation, cloud feature, characteristic of the radar, weather forecasting model and the forecast focus of continuous hail shooting weather processes caused by the North China vortex are given. The result shows that there are mainly four weather situations which bring about continuous hail shooting weather processes: Deep vortex pattern, shallow cold vortex pattern, stepped trough and cold vortex pattern, transverse trough and vortex pattern. The continuous hail shooting caused by the North China vortex generally occur in a stable blocking circulation background. The vortex lingered in the northern part of North China and Mongolia for a long time. The 500 hPa cold temperature trough superimposed above 850 hPa warm ridge. Dry and cold northwest streams on the higher level overlapped on the low level warm and wet south-west streams, which caused a wide range of potential instability in Beijing-Tianjin-Hebei. The thermal and dynamic conditions strengthened in the afternoon. The cold front on the ground, mesoscale convergence line and dry line triggered the occurrence of hail weather. Different patterns of north vortex continuous hail shooting weather processes perform markedly different satellite images. The satellite images of the deep vortex pattern performs as the typical vortex cloud system, while the shallow vortex is easy to form a number of MCS. In the middle and northern parts of Hebei hail echo tends to strip echo and not easy to drop large hail, while in the southern Hebei there are more massive echo and multi cell echo or super cell echo, more likely falling large hail.

• Climatic Characteristic of Hail in Hebei and Its Relationto Circulation Anomaly
• 2011 Vol. 30 (4): 1132-1138. 
• Abstract ( ) PDF (852KB) ( )
• Using the hail and monthly average temperature observation data at 142 stations in Hebei Province and NCEP reanalysis data from 1961 to 2007, the spatial and temporal distribution characteristics of hail and variation rule with time and circulation features of more and less hail years are analyzed by the statistical analysis methods of Mann-Kendall test, wavelet analysis, and correlation analysis. The results show that day numbers of hail have obvious interannual variation, an abrupt change of day number of hail occur in 1994 and there are quasi-periodic variation of 20 and 11 years in day number of hail. The day number of hail in Hebei Province has obvious positive correlation with 500 hPa wind speed and obvious negative correlation with the temperature. Before and after the abrupt change, the difference of mean circulation from May to July is obvious. The significant areas are in eastern Inner Mongolia and nearby the Black Sea. The difference of mean circulation from May to July is also obvoius in more and less hail years. The significant areas are in Hebei Province and nearby Mediterranean. The circulation characteristics of more and less hail years in each month from May to July show that the differences of mean circulation in more and less hail years are not significant in May and the difference is significant in June and July. It is shown that hail is small scale weather and its appearance frequency is related to macroscale circulation. Therefore, the analyzed results can be used for hailfall climatic prediction.