Current Issue

28 April 2008, Volume 27 Issue 2   
  • Study on H2O and CH4 Distributions and Variations over Qinghai-Xizang Plateau Using HALOE Data
  • BI Yun;CHEN Yue-juan;ZHOU Ren-jun;FANG Ming-hui;XU Li
  • 2008 Vol. 27 (2): 249-258. 
  • Abstract ( ) PDF (1506KB) ( )
  • The H2O and CH4 data observed by HALOE in UARS satellite from 1993 to 2004 are used to analyze their distributions and variation features in stratosphere over Qinghai-Xizang Plateau, and compare with those in the same latitudes. Finally the trends of the H2O and CH4 in stratosphere over Qinghai-Xizang Plateau are also analyzed. The results show that the H2O mixing ratio decreases with height in upper troposphere quickly reaches a minimum near the tropopause and the bottom of stratosphere; and then it increases with height in stratosphere. The characteristic of vertical distribution of CH4 shows that it always decreases with height from 140 hPa to 1 hPa. The mixing ratio of H2O and CH4 in summer is higher than that in winter in upper-troposphere and lower-stratosphere. There is obvious difference between the mixing ratio of H2O and CH4 over Qinghai-Xizang Plateau and those over the same latitudes, especially in upper-troposphere and low-stratosphere. Vertical motion caused by the thermodynamics of the Qinghai-Xizang Plateau influences the distribution of H2O and CH4 significantly, and troposphere and stratosphere exchange is active over Qinghai-Xizang Plateau. Relation of H2O and CH4 is consanguineous in middle and upper stratospheres, this is because a principal source of stratosphere H2O is from the oxidation of CH4. The trend analyses show that the H2O mixing ratio decreased from 1993 to 2004 and CH4 mixing ratio decreased near tropopause before 1998 and after 2001. In middle stratosphere, the H2O mixing ratio increased before 2000 and then decreased after 2000; the CH4 mixing ratio decreased before 2000 and then increased after 2000.
  • Soil Moisture Retrieval Based on ENVISAT/ASAR Data
  • ZHANG Tang-tang;WEN Jun;Rogier van der Velde;WEI Zhi-gang;LIU Rong;LIU Yuan-yong;LI Zhen-chao
  • 2008 Vol. 27 (2): 279-285. 
  • Abstract ( ) PDF (1963KB) ( )
  • Using the ENVISAT/ASAR AP mode VV polarization observation data at a low incidence angle and ground measured soil moisture collected from the land surface process experiment Loess Plateau of, which was conducted in the summer of 2005(LOPEX05), an algorithm for estimating the land surface soil moisture over LOPEX05 area was developed. The validated results indicate that the average difference soil moisture between the estimated from microwave remote sensing and ground measurements is less than 0.02 cm3·cm-3, the maximum difference is less than 0.04 cm3·cm-3. And the developed algorithm was applied to the surface soil moisture mapping, the results show that it is potential to monitor drought on the agricultural fields over the Chinese Loess Plateau, when the land coverage mixed with small farm fields and the imagery data resolution are taken into accounted. However big differences are not acceptable for surface soil moisture estimation over the steep slope region, the edge of mesa and building groups region. Thus, further work on surface soil moisture retrieval will be investigated in the future.
  • The Relationship between Mobile Mesoscale Convective Systems over Tibetan Plateau and the Rainfall over Eastern China in Summer
  • HU Liang;LI Yao-dong;FU Rong;HE Jin-hai
  • 2008 Vol. 27 (2): 301-309. 
  • Abstract ( ) PDF (933KB) ( )
  • The relationship between mobile MCSs over Tibetan Plateau and the summer rainfall over China is studied by using the Deep Convection Tracking Database from ISCCP, reanalysis data from NCEP/NCAR, precipitation data from 138 stations. The spatial and temporal distribution characteristics of mobile MCSs over Tibetan Plateau are also analyzed. The paper describes the possible mechanism of mobile MCSs over Tibetan Plateau influencing the rainfall in China by comparing the differences between the geopotential heights and wind fields for the strong and weak years of mobile MCSs generation over Tibetan Plateau. The results show that most of the mobile MCSs over Tibetan Plateau in summer come from southeast of Tibetan Plateau, their generation times have evident diurnal cycle characteristic, and they could move or propagate to most of Chinese east-middle and South Asia region. It is found that there is significant correlation between mobile MCSs over Tibetan Plateau and the rainfall over China. The distribution of correlation coefficient presents to be four zonal bands, which is "-+-+" from south to north, just like the regular pattern of rainbands over China. The intensity of South Asia High, West Pacific Subtropical High and Northeast Cold Vortex are suggested to play their roles on the environment, thus effecting the generation of mobile MCSs over Tibetan Plateau and rainfall over China.
  • Relationship of Northern Boundary of East Asian Summer Monsoon and Summer Precipitation in Eastern Part of China
  • LI Chun;HAN Xiao
  • 2008 Vol. 27 (2): 325-330. 
  • Abstract ( ) PDF (1032KB) ( )
  • In order to study the relationship of the northern boundary of East Asia summer monsoon and summer precipitation anomalies in the eastern part of China, a new northern boundary indices of East Asia summer monsoon is defined, using the latitude of 2 m/s southerly north of 20°N, which is the mean meridional wind over 105°~125°E at 850 hPa. The results show that the northern boundary of East Asia summer monsoon lies far north than normal before 1976 and far south after 1976, and has an obvious inter-decadal variability, and is close related with summer precipitation anomalies in the East part of China. Corresponding to the anomaly of East Asia summer monsoon northern boundary, the east Asia summer monsoon intensity, subtropical high in the northwest Pacific and warm low pressure over the Asia continent have also the relevant changes, their correlations are as follows: When the northern boundary of East Asia summer monsoon reaches far north than normal, the Asian continent warm low pressure in tropospheric lower layer, stronger;the East Asia summer monsoon, stronger;the ridge and northern boundary of tropical high in the northwest Pacific, far north;its area, bigger;the South Asia high, weaker, the dominant air flow is sinking and rainfall is less in the mid-and lower valley of the Yangtze River, while the dominant air flow is rising and rainfall is richer in North China, and vice versa.
  • Characteristic of Instable Energy Distribution in Cold Vortex over Northeastern China and Its Relation to Precipitation Area
  • CHEN Li-qiang;ZHANG Li-xiang;ZHOU Xiao-shan
  • 2008 Vol. 27 (2): 339-348. 
  • Abstract ( ) PDF (2043KB) ( )
  • Using 1 h rain data observed by AMS and NCEP/NCAR 1°×1° reanalysis data, according to circulation features of a typical case of cold vortex over Northeastern China, the process was divided into 3 phases which were called developing phase, mature phase and weakening phase, respectivly. The precipitation of developing phase was caused by moisture baroclinic instability on westerly frontal zone which belongs to regional mixing precipitation. The other precipitation phases were caused by convective instability, which was main convective rainfall. There is instable energy area within cold vortex in all phases, but it has obvious difference. The warm and moisture air transportations and convergences are key factor to the accumulation of instable energy, so the instable energy area is located in southeast of cold vortex far from center in developing phase, located in southeast of cold vortex near center in mature phase, and in weakening phase instable energy area is located in low trough which evolved from cold vortex. The instable energy brings different convective rainfall in different phases. CAPE and bigger vapor flux are the main elements to decide precipitation area in developing phase. Convective mainly occurs in overlapping area of CAPE and humid area in 925 hPa in mature phase. In weakening phase, convective is not only related to CAPE and relative humidity, but also to convergence line in lower troposphere.
  • Analyses on VHF Radiation of Cloud-to-Ground Flashes in Pingliang Loess Plateau
  • CAO Dong-jie;ZHANG Guang-shu;ZHANG Tong;WANG Yan-hui
  • 2008 Vol. 27 (2): 365-372. 
  • Abstract ( ) PDF (1726KB) ( )
  • VHF radiation characteristics of cloud-to-ground(CG) lightning flashes in Pingliang of Gansu have been analyzed using the data from a VHF radio receiver and a fast electric field antenna with time resolution of 0.1μs. It was found that the VHF radiation waveforms before the first return stroke are consistent well with the fast electric field change waveforms in time. The radiation waveforms in 300μs around the time of return strokes of negative CG flashes have been classified into three categories according to the VHF radiation and electric field variations, and it has been found that 90% of return strokes are belong to the type three, whose mean duration of VHF radiation is 600μs which is less than that of positive CG flashes. The peak value of VHF radiation appeared 10 to 100μs after the start of return strokes for negative CG flashes, with an average duration of about 45μs, but 10 to 260μs and 91μs for positive CG flashes, respectively. In generally, the peak value of VHF radiation intensity is larger during the first return stroke process than that during the stepped leader process, which may be related to that much stronger VHF radiation produced from branches in the main channel after the first return stroke.
  • Analysis on a Typical Squall Line Case with Doppler Weather Radar Data
  • YAO Ye-qing;YU Xiao-ding;ZHANG Yi-jun;CHENG Hua;WEI Ming;LI Jin
  • 2008 Vol. 27 (2): 373-381. 
  • Abstract ( ) PDF (1832KB) ( )
  • A typical case of squall line occurred in Anhui Province on 24th August 2002 is analyzed, using the Hefei Doppler weather radar data, routine upper-air and surface data, and intense surface observation data. The synoptic background is featured by the southward invasion of mid-level troposphere dry and cold air behind the westward moving trough, lower level convergence, extreme unstable air and moderate vertical wind shear. The squall line produced high wind in a very large area, hail and heavy rain in some areas. The radar echo displays "bow" shape, with a clear outflow boundary(gust front) in front of it. Corresponding to the bow echo in reflectivity image, the velocity image shows significant mid-level radial convergence(MARC), indicating strong wind in surface afterwards. Furthermore, above the leading edge of the bow echo, there is a weak echo region and a echo overhang above it, and the strong echo extend up above the-20℃ level, implying strong updraft in the storms, favorable for the severe hail and heavy precipitation. The analysis also shows that the variation of the distance between the gust front and thunderstorm can, to some degree, indicate the future trend of the thunderstorm.
  • Multi-Time Scale Correlations between Climate Variations and the Arctic Oscillation in He'nan Province
  • SUN Wei-guo;CHENG Bing-yan;GU Wan-long
  • 2008 Vol. 27 (2): 430-441. 
  • Abstract ( ) PDF (2704KB) ( )
  • The cross spectrum analysis combining with the wavelet transform analysis method is adopted to study the time-frequency characteristics and multi-time scale correlations between the anomaly series of precipitation(ΔR), temperature(ΔT) and the Arctic Oscillation Indices(ΔIAO) in He'nan Province in summer and winter of the last 55 years. The results show that there are periodic variations of quasi-biannual, 4 a, 6~8 a, 11~22 a in the winter and summer ΔIAO, ΔR and ΔT. The significance of correlations between ΔR and ΔIAO in winter present on the syntonic periods at scales of quasi-biannual and 14~22a, and the cross-wavelet coherence of the positive correlation distributing in all time space on the interdecadal timescale is the highest. The winter ΔT and ΔIAO exhibits significant correlation at scales of 2~4 a and 6~10a and localization characteristics in time space are obviously. The significance of correlations between ΔR and ΔIAO is higher than the significance of correlations between ΔT and ΔIAO on the interdecadal timescale, but contrary on the interannual timescale. It shows that effects of the winter AO on the variations of precipitation and temperature in He'nan province are different. The significance of correlations between ΔR and ΔIAO in summer display on the syntonic periods at scales of quasi-biannual, 4~6 a, 6~8 a and about 16 a, and the most significant correlation present on the scale of 6~8 a. The cross-wavelet coherence of the correlations between ΔT and ΔIAO in summer is lower, only distributing in some of the time space on the interannual timescale. The effects of the summer AO on the variations of precipitation and temperature in He'nan province are indirect by changing the intensity of the East Asian monsoon.
  • Advances of Research on Polar Vortex
  • ZHANG Heng-de;GAO Shou-ting;LIU Yi
  • 2008 Vol. 27 (2): 452-461. 
  • Abstract ( ) PDF (978KB) ( )
  • Polar vortex is a deep system and moves around the polar region, which embodies the characteristics of the atmospheric activity in the high latitudes.It belongs to one of the most important systems in the atmospheric circulation and affects the synoptic and climatic changes.Usually, it cooperates mutually and reacts together with the circulation systems such as the subtropical high, blocking high, monsoon and so on.It affects the global synoptic and climatic changes in great degree.In this paper, research on climatic characteristics, influence, change mechanism and numerical simulation of polar votex are summarized.It play key role on breaking of planetary wave, stratospheric sudden warming and dynamic coupling between stratosphere and troposphere.It also observably impact the process of absorbing and transportation of the atmospheric chemical composition, for example the HNO3, O3, etc.However, the redistributions of these chemical compositions have great feedback on the polar vortex.Though many studies have been done on the vortex, in the aspect of climatic dynamics, there still are some problems which need further researches.