2011, 16(1):1-14. DOI: 10.3878/j.issn.1006-9585.2011.01.01
Abstract:Atmospheric processes associated with the South China Sea (SCS) monsoon trough which caused the heavy rainfall in pentad 3 of August 2007 in South China are analyzed using the reanalysis data of NCEP and satellite images. The results indicate that the Asian summer monsoon trough has independent space structure, convergence in the low layers and divergence in the high layers are in the south of the Asian summer monsoon trough. The climate analysis shows that both the Indian monsoon trough and the SCS monsoon trough reach their maximum in 〖JP2〗August. The SCS monsoon trough in pentad 3 of August 2007 was located in South China coastal areas and had strong intensity. The convergence in the low layers and divergence in the high layers were also stronger. The Indian monsoon trough was also stronger. The strengthened South Asian high locating over the Tibetan Plateau is the main cause for the strengthening of the Asian monsoon trough. The subtropical high in the western Pacific is located over Japan and is intensified, which is propitous to the northward 〖JP〗movement and the enhancing of the SCS monsoon and monsoon trough. The increased temperature over the Tibetan Plateau induces the stronger easterly in the upper levels, westerly in the low levels,and the enhancing convergence in the low layers and divergence in the high layers of the SCS monsoon trough. The longwave trough in the westerly belt is intensified and extends to Southwest China, which causes the SCS monsoon trough to become stronger. The SCS monsoon trough has an intraseasonal period. The intraseasonal oscillation has an important effect on the northward movement and enhancement of the SCS summer monsoon trough.
2011, 16(1):15-30. DOI: 10.3878/j.issn.1006-9585.2011.01.02
Abstract:A study of the interaction and mutual response between dynamical core and physical parameterizations by atmospheric general circulation models CAM3.1 and IAP AGCM4.0 is presented. Both the two models were integrated 60 d with ideal physics (Held-Suarez forcing) and with full physical package, respectively. The results show that the mutual responses between dynamical core and physical parameterizations are very different in the troposphere at low latitudes and high latitudes. In the tropical troposphere, the variability of temperature tendency due to dynamical core and that due to physical parameterizations are both large and have significant contributions to the variability of total temperature tendency, and they are in inverse correlation to compensate each other. In the polar middle and upper troposphere, the variability of total temperature tendency mainly relies on the tendency due to dynamical core, while the variation of temperature tendency due to physics is very slow, which can be seen as a stationary forcing. Unlike the tropical regions, there is a positive correlation between the temperature tendency due to dynamics and that due to physics in Polar regions. Moreover, the interactions and mutual responses between the individual physical parameterizations are also analyzed. The results show that the variation of temperature tendency due to moist process is the largest of all the physical parameterizations, and it contributes most to the total temperature tendency due to physics. The variation of temperature tendency due to long wave radiation is also large at high latitudes, while the variation of temperature tendency due to short wave radiation and that due to vertical diffusion are relatively small. There is a negative feedback between the cooling rate of long wave radiation and the heating rate of short wave radiation.
2011, 16(1):31-38. DOI: 10.3878/j.issn.1006-9585.2011.01.03
Abstract:“Three Fu” (TF) is a typical regional climate phenomenon in association with the hottest period in summer in part of China. The traditional concept of the TF has been described as an uncomfortably hottest period in summer, lasting for 30 or 40 days, without a quantified meteorological definition. In order to study this typical monthly-scale extreme climate event, the authors present a quantified definition of the TF characteristis in using the Temperature-Humidity Index (THI) based on the daily minimum/maximum temperatures (Tmin/Tmax) and the relative moisture observations during 1960-2004. Four divisions are categorized in China: TF, quasi-TF, potential-TF, and none-TF areas. The TF area covers most of southeastern China, where Asian summer monsoon prevails. To compare the TF characteristics in different 〖JP〗climatological zones, the TF area is further divided into three subregions: the North China Plain (NC), the YangtzeHuaihe River basins (YH), and the areas south of the Yangtze River (SY). The beginning dates of the TF are mainly between 4 and 25 July, but on average, around 16 July in NC (lasting for 26 days), 16 July in YH (lasting for 29 days), and 13 July in SY (lasting for 34 days). The intensity (in terms of THI) of the TF is the strongest in YH, slightly weaker in SY, and the weakest in NC. The new TF index based on Tmin exhibits an enhancing trend during 1960-2004, but that based on Tmax is of strong interdecadal variations.
2011, 16(1):39-46. DOI: 10.3878/j.issn.1006-9585.2011.01.04
Abstract:Based on the data sets of Ozone Monitoring Instrument (OMI) O3 profiles over the Tibetan Plateau and the NCEP/NCAR reanalysis data in July 2006, the relationships between low O3 over the Tibetan Plateau and the longitudinal oscillation of the South Asia high are analyzed. The results show that the longitudinal oscillation of the South Asia high has an obvious correlation with the low O3 over the Tibetan Plateau. When the South Asia high exhibits the east (west) phase, the low O3 centers of the total column O3, the tropospheric column O3, and the stratospheric column O3 are located in the east (west) of the Tibetan Plateau. During the west phase of the South Asia high, the low O3 air is difficult to transport to the top of the Tibetan Plateau and the low O3 is weak over the Tibetan Plateau. While during the east phase of the South Asia high, the low O3 air from the Bay of Bengal is transported northward to the middle troposphere over the Tibetan Plateau by southeast currents and piles over the Tibetan Plateau， forming the low O3. So the longitudinal oscillation of the South Asia high is one of the most important factors contributing to the variation of the low O3 over the Tibetan Plateau, and the study is good for understanding the mechanism of the longitudinal oscillation of the South Asia high and improving the quality of climate forecast in China.
2011, 16(1):47-59. DOI: 10.3878/j.issn.1006-9585.2011.01.05
Abstract:Based on the MODIS observations, the performance of Interactive Canopy Model(ICM), a dynamic vegetation model including the carbon and nitrogen cycles of the terrestrial ecosystem, has been assessed. The Leaf Area Index (LAI), a key parameter with seasonal variation in vegetation dynamics, is simulated by ICM and compared with the MODIS data. The results show that ICM can simulate the main characteristics of the seasonal LAI fluctuations. Compared to the observation, LAI is overestimated in high and low latitudes, but underestimated in middle latitudes by the model. The underestimation of the LAI in middle latitudes is followed by the vegetation sprout for the reason that the modeled growth is always slower than the observed one. The bimodal distributions for the tropical evergreen broadleaf trees and crops have not been well captured. In addition, the simulated results for the grassland are more reasonable than other Plant Function Types (PFTs). The results will provide important clues for the parameterization improvement and parameters optimization of the ICM.
2011, 16(1):60-70. DOI: 10.3878/j.issn.1006-9585.2011.01.06
Abstract:Based on the statistical analyses, the vortices arising in summer (JJA) from 1991 to 2004 are divided into two categories，that is, the moving and stagnant ones. Based on the comparison of composite circulation in these two kinds of vortex cases, the three-dimensional structure of the background general circulation and the influence of the moisture condition on the development and movement of the southwest vortex are studied. The results show that in the moving vortex cases, the atmosphere in the middle and upper troposphere around middle latitudes over the eastern part of the Tibetan Plateau is much colder than that in the stagnant vortex cases caused by the cold air invading. The colder air leads to the lower geopotential height, on the south side of which, the stronger westerly winds prevail from the tropopause to 850 hPa, with the maximum on 200 hPa. The great gradient of the west wind velocity difference at the upper levels enhances the divergence and upflows over the eastern part of the Sichuan Basin. And the stronger westerly winds at the lower levels result in the stronger moisture transport in the southwestern part of the Sichuan Basin. It benefits the eastward movement of the southwest vortex.
2011, 16(1):71-84. DOI: 10.3878/j.issn.1006-9585.2011.01.07
Abstract:The main purpose is to analysis a regional fog episode occurring in most of middle and eastern China from 17 December to 19 December 2004 based on the observation and the fifth generation Pann State/NCAR Mesoscale Model modeling. The characteristics and evolution process of the regional fog event are investigated. The results show that it is a typical radiation fog event with a large spatial scale and the horizontal distribution is not uniform. The fog appeared at the surface firstly and then expended to the high level. The burst development features of the fog are not found. The temperature inversion and abundant water vapor are the beneficial factors to the fog formation and maintenance as well as breeze condition. The influences of the shortwave radiation warming and longwave radiation cooling are examined.
2011, 16(1):85-93. DOI: 10.3878/j.issn.1006-9585.2011.01.08
Abstract:A regional atmospheric and oceanic coupled model named Aviation Shortterm Regional Climate Model (ASRegCM) is developed and nested into the shortterm climate prediction model CGCM_1.1 from the National Meteorological Center，China Meteorological Administration, which forms an operational prediction system ASRCPOS for aviation climate prediction. 20-year experiments from 1983 to 2002 were conducted using ASRCPOS. Numerical results show that ASRCPOS can improve prediction accuracy as compared with global scale prediction system of CGCM_1.1, and with earlier results by statistic approach. ASRCPOS makes great progress in anomalous sign prediction accuracy particularly for the spatial continuous variables such as surface temperature. It also raises the prediction accuracy of the anomalous magnitude of spatial discontinuous variables such as precipitation. The present numerical experiments show there are still lots of works to be done to improve the prediction accuracy of ASRCPOS, particularly for the climate durations of the abnormal temperature, and for the forecasts with time scale below one month.
2011, 16(1):94-104. DOI: 10.3878/j.issn.1006-9585.2011.01.09
Abstract:Based on the long time series of mean Sea Surface Temperature (SST) and high-resolution wind field reanalysis data such as HadISST and ERA-40 reanalysis data, the variations of the SST in the offshore area of China and their relationship with the East Asian Monsoon (EAM) in winter (December to the next February) and summer (June to August) are analyzed using the Empirical Orthogonal Function (EOF) and linear regression analysis methods. The results show that: 1) The SST in the offshore area of China in winter or summer exhibited significant interannual and interdecadal variations, and experienced a climate shift in the mid-1980s. The areas with the strongest increase in SST are located in the East China Sea (ECS) in winter and in the Yellow Sea in summer. The SST increased by 1.96°C in winter for the period of 1955-2005 and 1.10 °C in summer for the period of 1971-2006. 2）The EAM has displayed distinct interannual and interdecadal variations with a weakening trend since the end of the 1980s in winter, and since the end of the 1970s in summer. In addition, the linear regression analysis indicates the relationship of the SST to EAM in winter on interdecadal timescale is closer than that on interannual timescale. The interdecadal weakening trend of EAM in winter contributes to the rise in SST in the offshore areas of China, particularly significant in the ECS. Moreover, the related areas of winter or summer mean SST on the interannual timescale in the offshore area of China to the EAM are located in the South China Sea (SCS), and the relationship in winter is much more obvious than that in summer. It is found that the interannual variation of SST in the SCS has obvious relation to the anomalies of the meridional southward and northward winds over the SCS and zonal migration of the subtropical anticyclone over the western Pacific.
2011, 16(1):105-112. DOI: 10.3878/j.issn.1006-9585.2011.01.10
Abstract:The backward trajectories of 239 precipitation processes from 1999 to 2007 at North China regional atmospheric background station were classified. Typical north-west, south-west and south-east backward trajectory precipitation samples were selected to research the characters of the precipitation pH, electrical conductivity, chemical composition, and the main sources affect the background area. Results showed that the south-west backward trajectory coming from the east-central inland area of China, passing through Taiyuan, Shijiazhuang, and Beijing, the north-west trajectory coming from Mongolia, passing through inner Mongolia area, and the south-east trajectory coming from oceanic area, passing through east coastal cities were the main backward trajectories affecting the precipitation at Shangdianzi station. The precipitation frequency in the south-west trajectory was the highest. The pH peaked in the south-west transportation direction and reached a minimum in the south-east. The electrical conductivities reached a maximum in the south-west transportation direction and a minimum in the north-west. SO2-4, NO-3, NH+4, and Ca2+ were the major ions of precipitation at Shangdianzi. The concentrations of the major ions of the south-west trajectory samples were much higher than that of the other directions. Soil dust, farm emission related to fertilization, pollutants from traffic and coal combustion emission were the main four sources identified affecting the background area. The natural source was the primary source affecting the background area in the north-west clean transportation direction, while the anthropogenic sources were more notable in the south-west transportation direction, such as traffic and coal combustion emission. Compare to 1999-2004,the averaged pH decreased from 2005 to 2007, which attributes to the decreasing of the concentrations of alkaline ions in precipitation. The results show that rainfall is significant for the conductivity, acid rain frequency, and the components of the precipitation. The values of conductivity and components concentration decrease and the acid rain frequency increase as the rainfall increase gradually.