Current Issue

• Application of C Grid to the p-σ Nine-Level Regional Climate Model
• LIU Peng;QIAN Yong-fu
• 2008 Vol. 27 (2): 231-238. 
• Abstract ( ) PDF (1055KB) ( )
• C grid scheme designed in this paper has been applied to the p-σ nine-level regional climate model, and the impacts of C grid on the p-σ nine-level regional climate model have been studied by simulating the January and July mean climatic fields in East Asia and the rainfall during the summer in 2003. The model results show that the capability of C grid model has been improved, and the improvement of the simulated air temperature and wind in the lower troposphere is more remarkable than in the middle-upper troposphere. The model of C grid can simulate the precipitation in East China much better, and it has a good capability to simulate the rainfall during the summer. The improved simulations of wind field induce the improvement of the capability to simulate the rainfall;this work has established a good base for the further development of the regional climate model.

• Analysis on Simulation of Characteristic of Land Surface in Western Qinghai-Xizang Plateau during Frozen and Thawing
• WANG Cheng-hai;SHI Rui;ZUO Hong-chao
• 2008 Vol. 27 (2): 239-248. 
• Abstract ( ) PDF (1136KB) ( )
• Using CAMP/Tibet CEOP-EOP3 observational data at Gaize station in the western Qinghai-Xizang Plateau from October 2002 to September 2003, the land surface characteristics in the western Qinghai-Xizang Plateau were simulated by an improved land surface model CoLM(Common Land Model). The model reproduced surface thermal and moisture features. The simulated result indicated that, in western Qinghai-Xizang Plateau, the sensible heat flux dominates the surface heat energy balance, the latent heat flux is less, especially, in frozen season(arid), the latent heat flux is almost equal to zero. But during the thawing season(wet) in western Qinghai-Xizang Plateau, the latent heat flux can't be ignored. When thawing occur, it is also transition time from arid season to rain/wet season(that is late of May), the changes of surface layer soil water phase frequently happen as result of thawing, these processes contribute to the latent heat flux. At same time, the Bowen ratio is decreased. The change of surface heat fluxes(sensible and latent heat) are associated with the precipitation and land surface frequent frozen-thaw.

• 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.

• Simulation Analysis on Land Surface Process of BJ Site of Central Tibetan Plateau Using CoLM
• LUO Si-qiong;Lü Shi-hua;ZHANG Yu;HU Ze-yong;MA Yao-ming;LI Suo-suo;SHANG Lun-yu
• 2008 Vol. 27 (2): 259-271. 
• Abstract ( ) PDF (1967KB) ( )
• Using the Common Land Model of NCAR and nearly two-year observed data of BJ site during CEOP Asia-Australia Monson Project on the Tibetan Plateau(CAMP/Tibet, 2001-2005), the simulation and other related research work of land surface process in Tibetan Plateau have been done. The difference of the surface energy flux between the in situ observation data and the simulation results were discussed. The results indicate that the model closely captures the pattern of USR, ULR and Rn. The bias of simulated radiation occurred during winter. The bias of soil heat flux is small during summer half year. From the observed vertical profiles of soil temperature and soil moisture, the impact of soil parameterization scheme in Common Land model on soil temperature and soil moisture simulations were analyzed. The simulation result of upper layer soil is better than lower layer soil. The simulated shallow soil temperature is well. The model underestimates the liquid water content in frozen soil.

• Analysis on Turbulent Flux in Complex Underlying Surface Conditions
• YANG Sheng-peng;Lü Shi-hua;CHEN Yu-chun;AO Yin-huan;JIANG Xi
• 2008 Vol. 27 (2): 272-278. 
• Abstract ( ) PDF (1644KB) ( )
• Using the methods of spectral analysis and energy balance closure the quality of turbulent data collected from the filed experiment conducted in the Gaolan Mountain in summer of 2006 and in winter of 2005 was analyzed. The results show that the energy spectra and cospectra were in agreement with the "-2/3" and "-4/3" scaling law corresponding in inertial sub-range. The energy imbalance was found in all observational sites. The energy balance ratio(EBR) was 66% and 94% in the afforestation soil and in the bare soil in the summer sites, and the corresponding value was 62% and 84% in the winter sites, which showed that the EBR in bare soil was better than that in afforestation soil. The diurnal variation of energy balance closure and surface energy budget were also discussed.

• 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.

• Numerical Simulation of Heating Effect of Mountain Peak
• AN Xing-qin;HU Yin-qiao;Lü Shi-hua;ZUO Hong-chao
• 2008 Vol. 27 (2): 286-292. 
• Abstract ( ) PDF (1007KB) ( )
• The existed results of analyzing data and theory research have already revealed that heating effect of mountain peak is the main factor of forming inverse temperature of Lanzhou in winter daytime. The meso-scale model MM5 has been used to study the characteristics of temperature and circumfluence structures of Lanzhou daytime. The simulated results show that, in winter daytime, the Gaolan peak is a hot source for ambient atmosphere after sunrise and air temperature above the Gaolan peak is relatively hotter than that of valley city. Therefore the inverse temperature of the valley city has come into been by the cool air above the city and the hot air which transported from the Gaolan Mountain by circumfluence. The simulations verify and make a supplement for observation data and theory analysis.

• Numerical Simulation of Effect of Loess Plateau Vegetation Change on Local Climate
• LIANG Ling;Lü Shi-hua;SHANG Lun-yu
• 2008 Vol. 27 (2): 293-300. 
• Abstract ( ) PDF (1719KB) ( )
• Using the meso-scale model MM5 and the observed data in June and July 2003, the temperature and humidity field over the Loess Plateau have been simulated. The results show that through the green-recover experiment the decrease of air temperature and sunface temperature in the local area is obvious, especially in the center of the vegetation changed area, the maximum value of air temperature decrease is 0.6℃, and in the nearby area it decreases too. But surface temperature changes more obvious than air temperature, and this situation mainly occurs in the daytime. At the night, the two both change little relatively, even surface temperature slightly increases. In the area where vegetation recovers, both air temperature and diurnal difference of surface temperature decrease, while air humidity evidently increases during the whole day, and it increases in the daytime more than at the night, however the impact range in the daytime is less than at the night.

• 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.

• Climate Characteristics of Water Vapor Transportation and Its Variation over Xinjiang
• SHI Yu-guang;SUN Zhao-bo
• 2008 Vol. 27 (2): 310-319. 
• Abstract ( ) PDF (1169KB) ( )
• Using the daily NCEP/NCAR reanalysis data from 1961 to 2000, the features of water vapor transportation of different layers over Xinjiang are analyzed. The results show that from surface to 300 hPa, 26114. 8×10⁸t water vapor(WV) input Xinjiang and 25647. 7×10⁸t WV export from Xinjiang per year, as a result, annual net WV earning quantity is 467. 1×10⁸t. Due to the terrain of surrounding mountains in Xinjiang, water vapor transportation quantity(WVTQ) of middle layer is the most, and WVTQ of the lower and the high layers is adjacent. In summer, WVTQ is the most occupying about 38% of all year, 23%~25% of all year in spring or autumn, and the least in winter. There are the almost similar decreasing trends of total WV inflow and outflow for annual average, spring, summer and autumn in the last 40 years, furthermore without distinct change trends since 1976, resulting that annual net WVTQ doesn't present the obvious change trends.

• Numerical Simulation of the Impact of Abnormity of Sensible Heat Flux in Northwest Arid Zone on Precipitation in China
• GAO Rong;DONG Wen-jie;WEI Zhi-gang
• 2008 Vol. 27 (2): 320-324. 
• Abstract ( ) PDF (1076KB) ( )
• The impact of abnormity of sensible heat flux from surface to atmosphere in spring and summer in Northwest arid zone on precipitation in China in summer has been simulated by using RegCM3 model of the up to date edition, the results showed that, after the sensible heat in Northwest arid zone has been increased, the temperature in low layer will rise, and the air density will decrease so that there has an anomaly of ascending motion in Northwest arid zone. The sinking motion is weaken in Northwest arid zone, which will lead to more precipitation in Xinjiang. The weak sinking motion in Northwest arid zone make that there has a stronger air pressure in high layer, so there has a anomaly of anticyclonic circulation, which leads to the weaken ascending motion and the precipitation decreases in Tibetan Plateau. And then it makes a center of anomaly of low air pressure in the mid-and low-reaches of Yangtze River and the north of Northeast China, so that there have anomaly of anticyclonic circulation and more precipitation. However, The precipitation is less in South China, Southwest China, southern of North China and Northeast 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.

• Teleconnection between Summer Extreme Precipitation Event of East Part of Northwest China and Pacific SSTA
• YANG Jin-hu;JIANG Zhi-hong;BAI Hu-zhi
• 2008 Vol. 27 (2): 331-338. 
• Abstract ( ) PDF (1689KB) ( )
• Using the height field, wind field of monthly mean NCEP reanalysis NOAA reconstruct sea surface temperature, daily precipitation data of 38 stations in east part of Northwest China in recent 50 years, and with SVD, composite analysis methods, the Pacific SSTA effect on extreme precipitation event of east part of Northwest China are researched. The result show that there are remarkable relations between winter Pacific SSTA and anaphase summer extreme precipitation event of east part of Northwest China, and equator middle-east Pacific Ocean is key area which affect to summer extreme precipitation event of east of Northwest China, when the winter SST occurs anomaly phenomenon in the equator middle-east Pacific Ocean, at first longitudinal and latitudinal departure circulation cells occur anomaly, then general circulation occurs adjustment, successively west Pacific subtropic high pressure also arise anomaly by PNA and WP from winter to summer, finally summer extreme precipitation event of east part of Northwest China occur anomaly phenomenon.

• 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.

• Environmental Streamline Field and Dynamic Analysis of a MCC in Huaihe Valley
• JING Xi;JING Yu;LI Ming-juan;WANG Ming-xue;DU Ji-wen;LI Dong-liang
• 2008 Vol. 27 (2): 349-357. 
• Abstract ( ) PDF (2319KB) ( )
• Using the satellite cloud image and various synoptic data of upper level wind data, the large-scale environmental field and physical quantity, a mesoscale MCC and rainstorm event of Huaihe valley on July 2, 2006 are diagnostically analyzed. Results show that MCC is the direct cause of rainstorm; dry invasion from north in mid-level of troposphere played an important role in developing process of MCC; the triggering system of MCC was provided by the southward frontogenesis of over North China cold air in lower-level of troposphere with southwest stream ascending upon the front in lower-mid level of troposphere. Dynamic situation for generating and maintaining MCC derived from coupled lower-upper jet streams and formation of synoptic-scale longitudinal indirect secondary circulation. Energy field features in lower level of troposphere, vertical shear of wind velocity, total index, and change of dry invasion area in rear of bow echo are all indicative to the development of MCC.

• Analyses on Lightning Temporal and Spatial Characteristics in the Severe Convective Weather in North China
• LIU Dong-xia;QIE Xiu-shu;FENG Gui-li;WU Shu-jun
• 2008 Vol. 27 (2): 358-364. 
• Abstract ( ) PDF (1748KB) ( )
• Based on the lightning location detection(DF) data, Doppler radar data and synoptic information, the lightning characteristics of a typical mesoscale convective system in the north of Shandong Province on August 1^st, 2005 are presented. It is found that the negative lightning(-CG) is predominant to positive lightning(+CG) during the whole lifetime of thunderstorm. The maximum flash rate is 260 flashes in per five minutes. The comparison of location of lightning activity and radar echo shows that-CG usually cluster in the intense echo region with high reflectivity(>40 dBz), while +CG usually disperse in the weak echo such as stratiform region or cloud anvil. The lightning flash changes with different echos, the maximum lightning flash rate occurred in the echo within 45~55 dBz. A good correlation is observed between the cloud height of 30 dBz and lightning flash rate, and validates the exponential relationship between them.

• 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 24^th 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.

• Experiment of Rainfall Estimation Using X-Band Dual-Polarized Doppler Weather Radar
• MA Xue-qian;DONG Wan-sheng;CHU Rong-zhong;WEI Zhi-gang
• 2008 Vol. 27 (2): 382-391. 
• Abstract ( ) PDF (1256KB) ( )
• Using X-band dual-polarized Doppler Weather Radar and RG3-M automatic gathering rain gage, two that had consistent moving direction were observed in the strictly and scientifically designed Pingliang field experiment. We make use of the data testing the ability of radar rainfall estimation. The experimental results indicated that the filtering of raw radar data will affects the radar accuracy of rainfall estimation directly, and especially obvious for R(Kdp) and R(Kdp, Zdr). And after filtering, the further spatial smoothing of data is necessary. We developed a measuring method which retrieves radar rainfall estimation parameters using gage, this method improved the radar ability to measure rainfall in different districts and raindrop size distribution situations;simultaneity showed that the partial attenuation effects at X-band are very severe. The experimental result may be taken as an important reference for the next generation rainfall radar.

• The Impact of Variations of Underlying Surface and Vegetation Index on Numerical Simulation of Dust Emission
• ZHANG Tai-ren;SONG Zhen-xin;WANG Jin-yan;LI Zi-zhen
• 2008 Vol. 27 (2): 392-400. 
• Abstract ( ) PDF (2085KB) ( )
• The mechanism of impacts of leaf area index and the change in vegetation coverage on the process of dust emission is analyzed in this paper. In an integrated numerical simulation and forecast system of dust storms, the leaf area index in a simulated region is grouped into 0, 0.5, 3.0 and the measured value of satellite inversion. The results show that the leaf area index influences the numerical simulation of sand storms. The change of dust concentration calculated with the leaf area index of satellite inversion lies between 0~0.5. Meanwhile, the data of vegetation coverage is divided into 0, 0.2 and the measured value of satellite inversion. The dust concentration is the highest while the coverage rate of vegetation is 0, and the dust concentration is low when the rate is 0.2.

• Observation and Analysis of a Dust Storm in Minqin
• YUE Ping;NIU Sheng-jie;ZHANG Qinag
• 2008 Vol. 27 (2): 401-407. 
• Abstract ( ) PDF (1508KB) ( )
• The vertical temperature, specific humidity and wind speed of the atmosphere boundary layer at Minqin base station were analyzed by using the sonding data on May 23 to 24, 2004. Meanwhile, The relative storm helicity were calculated according the sonding data. The 3θ profile and its variation were analyzed during the dust storm process. The results show that the atmosphere stratification is in the ultra adiabatic condition near the surface layer and the mixed-layer is very deep before the dust storm occurring. The temperature, specific humidity and wind speed profiles are beneficial to occur dust storm at that time. In the dust storm period, the boundary layer is becoming thinner, the atmospheric boundary layer becomes stable at the end of dust storm. The values of relative storm helicity is smaller than the values of thunder storm, but there are good correlations between relative storm helicity and the sand storm intensity during the dust storm process.

• Characteristics of PM₁₀ Pollution at Four Provincial Cities in Yangtze River Delta District
• SHI Chun-e;ZHAI Wu-quan;YANG Jun;WANG Shui;YAO Ke-ya
• 2008 Vol. 27 (2): 408-414. 
• Abstract ( ) PDF (1669KB) ( )
• Statistic analyses were done based on the daily concentration/index data at four provincial capital cities in Yangtze River delta of East China from January 2001 to December 2005. Trajectory model(HYSPLIT4) was used to analysis the back-trajectories on medium and heavy air pollution days. The air quality turned better in all the four cities from 2002 to 2005. The seasons with the highest air pollution event were in spring and winter. The months with the highest air pollution event were in March and November. The PM₁₀ concentration was highly correlated with those of SO₂ and NO₂ in Shanghai. The correlations between PM₁₀ and SO₂, NO₂ in Hefei were not as good as those in Shanghai. The partial correlation between PM₁₀ and NO₂ was higher than that between PM₁₀ and SO₂ in both Shanghai and Hefei. The PM₁₀ concentration variations in four cities were highly consistent, especially in March and April. The back-trajectory analysis indicated that the air masses leading to medium to heavy polluted events were mainly from north-west China.

• Winter Blocking Episodes and Impact on Climate over East Asia
• JI Ming-xia;HUANG Jian-ping;WANG Shao-wu;WANG Xin;ZHENG Zhi-hai;GE Jin-ming
• 2008 Vol. 27 (2): 415-421. 
• Abstract ( ) PDF (1940KB) ( )
• Using the NCEP/NCAR daily 500 hPa reanalysis data from 1958 to 1996, the synoptic blocking activity over East Asia is analyzed based on the synoptic definition of blocking. The results show that the winter blocking activity has obvious interannual variability, but such variation is different in various regions. The highest of blocking day occur in Okhotsk region and the least, in Baikal. In this paper, the climatology index of blocking is proposed according to synoptic index. The statistical relationship between climatology index and surface temperature, and precipitation are also studied.

• The Seasonal Changes of Micro-Climate in Haibei Alpine Wetland in the Qilian Mountains
• LI Ying-nian;ZHAO Xin-quan;XU Shi-xiao;ZHAO Liang;ZHANG Fa-wei;GU Song
• 2008 Vol. 27 (2): 422-429. 
• Abstract ( ) PDF (1799KB) ( )
• The data of micro-meteorology were analyzed in Haibei alpine wetland of Qinghai in 2004, the results show that the surface-atmospheric long-wave/short-wave radiation, earth's surface reflectivity(A), the components of energy flux, moment flux(τ), air temperature, soil temperature, wind speed, friction velocity, CO₂ exchange, have obvious seasonal changes. Because of the special features of soil surface and plant vegetation in alpine wetland ecosystem, A was higher in January and February than other months, while lower from July to October, which was characterized by "U" sharp and bigger in winter while smaller in summer. The seasonal changes of surface long-wave effective radiation were not obvious. Meanwhile, the results suggested that it was an obvious heat source from spring to autumn, and a "cold island" in winter in Haibei alpine wetland. As to the seasonal variations of daily CO₂ exchange, it was evident, which there were two climaxes of CO₂ emission in April and October while strong CO₂ absorption in July and August.

• 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(ΔI_AO) 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 ΔI_AO, ΔR and ΔT. The significance of correlations between ΔR and ΔI_AO 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 ΔI_AO 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 ΔI_AO is higher than the significance of correlations between ΔT and ΔI_AO 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 ΔI_AO 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 ΔI_AO 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.

• A Diagnostic Analyses on Peculiar Persistent Cold Airflow Snowstorm Process in Shandong Peninsula
• YANG Cheng-fang;LI Ze-chun;LI Jing;CHE Jun-hui
• 2008 Vol. 27 (2): 442-451. 
• Abstract ( ) PDF (2036KB) ( )
• Using the NCEP/NCAR day-to-day 6 h reanalysis data and observational data, the peculiar persistent cold airflow snowstorm occurring off northern coast of Shandong Peninsula from 3 to 22 December 2005 is diagonally studied. The results show that the snowstorm occurred when northwest airflow prevailed and the snow distributing is of typical cold airflow snowstorm character. Frequently strong cold air causea great sea-air difference, which is the main reason to induce long term severe snowstorm. Sea-air temperature difference more than 22K is the essential condition and remarkable cold front is found in 850 hPa when cold airflow snow occurring. Snowstorm occurred in the high energy belt, updraft area with convergence in low troposphere and divergence in middle troposphere. Vapour from Bohai converges under the level of 925 hPa. Updraft layer is much more lower than summer heavy rain. The act of forming couples among vertical velocity, divergence and vorticity field in low and medial troposphere is helpful to the form of snowstorm. The force lift of special hill topography is the trigger of cold airflow snow and increase the snowstorm.

• 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.