Abstract:Using the simulation of AVIM GOALS(Atmosphere Vegetation Interaction Model and GlobalOcean Atmosphere Land System) which is developed in the Institute of Atmospheric Physics, Chinese Academy of Sciences(IAP/CAS), the sensible and latent heat fluxes are analyzed and compared with the ERA-40 reanalysis data, the results showed that AVIMGOALS basically reproduce main features of the annual mean climatologic state and seasonal cycle of the surface fluxes. The zonal distribution of the sensible heat flux is bimodal, and the latent heat flux has an obvious change from January to July, shifting from a single peak type to the double peak type. The spatial distribution shows that a high value area of the surface fluxes is mainly distributed in the Southern Hemisphere and low latitude regions of the Northern Hemisphere in January, where a big increasing of the surface fluxes occurs in the high latitudes of the Northern Hemisphere, and the surface fluxes in the Southern Hemisphere still remain greater values, and the spatial correlation coefficients of AVIMGOALS and ERA-40 reanalysis data are all above 0.01 significance level according to the t test. The standard deviation distribution of the surface fluxes is small in low latitudes and large in high latitudes, and it agrees with ERA-40 reanalysis data, which shows the good simulation performance of AVIMGOALS. The correlation coefficient of the annual variation in the Northern Hemisphere is larger than that in the Southern Hemisphere, which are 0.97 and 0.89 for the sensible heat flux and latent heat flux, respectively. Further analysis on the surface fluxes from AVIMGOALS and reanalysis data for annual changes of the correlation coefficient in spatial distribution shows that the larger correlation coefficient is mainly distributed in high latitudes of the Northern and Southern hemispheres. The most areas north of 30°N, South America, South Australia, and the Antarctic region are above 0.01 significance level according to the t test, which shows the coupled model captures the obvious signal of the seasonal change in these regions. In addition to the analysis of the correlation coefficient between the surface flux and its global mean value, the result shows that the correlation coefficient in most areas of the Northern Hemisphere is larger than 0.6, similar to the reanalysis data. The areas to the north of 20°N in the Northern Hemisphere and Africa beside 20°S are above 005 significance level according to the t test, which indicates the regions significantly contribute to the seasonal change of the global mean surface fluxes.

Abstract:An extreme event, an unusual snowstorm happening in South China in January 2008, is studied with observational data analysis and numerical modeling experiments. It is found that diabatic heating was centered in the tropical oceans, Central Asia, the Tibetan Plateau, and the North Atlantic Ocean. The results from the numerical experiments demonstrate that global diabatic heating anomalies are responsible for this extreme event. A series of numerical experiments are further designed to identify the key areas where the diabatic heating anomalies occur. The results indicate that the diabatic heating anomalies in Central Asia and the Tibetan Plateau could account for the extreme heavy snow event. Such anomalies generate anomalous air mass rising as well as southerly winds over South China. These features facilitate the water vapor transportation and result in the heavy rain and snow. Meanwhile, an anomalous heating in the North Atlantic enhances the positive phase of the North Atlantic Oscillation, which could contribute to the occurrence of this unusual snow event. On the contrary, a La Nina event happening over the same period, strengthening the heat source in the western Pacific and the heat sink in the eastern and central Pacific, is more likely to counteract the ascent and suppress the rain and snow over South China.

Abstract:A frozen soil parameterization scheme is developed based on the NCAR CLM3.0(Community Land Model). Using the equilibrium thermodynamic relationship and the empirical equation considering the effect of ice on the matrix potential, the authors define the maximum liquid water content below the freezing point temperature and take account of the resistance of ice to hydraulic conductivity. Only when the liquid water exceeds the maximum, it freezes to ice. Both the original and modified scheme are tested using the observations of Gaize station on the Tibetan Plateau from April 2003 to December 2004. Results show that the original model can perform a good prediction of the radiation flux, but underestimates the liquid water content, and overestimates the ice content in winter, so soil temperature bias has thus occurred. The modified scheme obviously improves the estimation of soil liquid water and ice content, and the simulated soil temperature is closer to the observation. Thus it partly improves the simulation performance of CLM3.0 on frozen soil processes.

Abstract:The lateral boundary forcing effects in the buffer zones of a nesting modeling system by improving the calculation method of temperature forcing terms are simulated. This new method makes the regional climate model have the ability to describe the daily temperature evolution characteristics that are consistent with the change rules under different underlying surfaces. By using the regional climate model ASRegCM, a numerical experiment is conducted to test the effects of the lateral boundary emulation. Simulation results show that the anomalous intensity of the surface temperature and precipitation is improved with the improvement of temperature calculation in lateral boundary buffer zones, whereas there is no significant change in the distribution pattern of anomalous signs. It also shows that there is more evident improvement in the simulation of precipitation than that of surface temperature though the sensitive test is conducted on temperature only. The improvement in numerical simulation may be concluded into two aspects. One is the amplification effects on wave amplitudes of the surface temperature. The other is the effects of adding the zonal and longitudinal low frequency wave variability component with a 7~10day cycle into the process of lateral buffer emulation. The coeffects restrain the unstable convective precipitation process, and increase the continuous nonconvective precipitation process. And then the instability between cumulus convection and unconvective clouds in tropical and semi tropical zones are weakened during the model simulation.

Abstract:Based on the precipitation, cloud cover, and fog observational dataset from five meteorological stations in Tianjin region, the facts of climate change in Tianjin during the last 50 years are analyzed. The results indicate that the urbanization effect on the local climate change in Tianjin is increasing significantly, and the changes of cloud cover, precipitation, and fog have been influenced by aerosol pollution by human activities. It shows that the low cloud cover is increasing, the decrease in the drizzle days is slowing down, and the foggy days in winter have increased dramatically since the 1980s, especially in the areas of obvious urbanization. Whereas the change of the precipitation over the past 50 years in Tianjin region also includes the influence of the largescale background condition changes.

Abstract:To explore the association between Aerosol Optical Depth(AOD) with air pollutants and meteorological factors, and to provide evidence for the prediction of AOD, time series analysis was used. The data of AOD, air pollutants, and meteorological factors were from January 2002 to December 2004 in Hangzhou. The data of the first 35 months was collected to establish ARIMA（Autoregressive Integrated Moving Average）model, and the data of the last month was used for evaluation. After a time difference, ARIMA(0,0,2)(0,0,0) model was established, the Ljung-Box Q test and the residual plots showed the model fit well. The true values were all above 95% confidence level. From the model, the AOD was not only affected by the air pollutants and meteorological factors on the same day, but also by those in several days before.

Abstract:Strong convective clouds existed in Beijing and its surrounding areas during the opening ceremony of the 2008 Olympic Games. Clouds developed vigorously especially in the directions of southwest and northeast. They moved towards Beijing city zone and an encirclement trend was formed. Such impending clouds and precipitation posed a significant threat to the ongoing ceremony activities at the National Stadium. According to the actual weather condition, weather modification organizations implemented cloud seeding operations by firing lots of special rockets to mitigate or suppress precipitation. Using the rainfall data of automatic weather stations, radar detection of clouds and precipitation, and two cloud parameters retrieved from satellite data, the authors analyzed the main characteristics of cloudprecipitation together with some physical evidence from weather modification activities during the period of the opening ceremony. The results displayed that strong convection developed in the southwest and northeast outskirts of Beijing in the evening and night on 8 Aug 2008. From 1900 LST to 2300 LST, precipitation was concentrated in Fangshan district and Huairou, Miyun county of Beijing. Strong convective clouds and the followed rainfall distribution in the north and northeast mainly moved slowly towards northeast. There also occurred a bit extending to the west and south. In the southwest, convective clouds stepped slowly after they entered into Fangshan district. The rainfall distribution moved toward northeast and posed a serious threat to the city zone and the National Stadium. Then the main body of it moved slowly toward southeast and finally away from Beijing. Combining with the sites distribution of groundbased rocket launchers and the operation time of cloud seeding, some changes of the macromicro characteristics of cloud and precipitation derived from automatic weather stations rainfall, radar detection, and satellite data retrieval showed that the intense large scale firing rockets and seeding clouds with AgI had played a certain role in inhibiting the formation and development of cloud and precipitation in the target area.

Abstract:The main study results on the heavy rain in Xinjiang are summarized from 1960 to 2009, which include largescale circulation, synoptic scale systems, mesoscale systems, and water vapor characteristics. Because heavy rain in Xinjiang were less focused and studied, the gaps of heavy rain researches between the reasearches on precipitation in eastern China and Xinjiang are becoming larger and larger in recent years, which bring about severe lacks of capabilities coping with disaster prevention and reduction. Some problems remaining to be resolved are pointed out as follows: The structure and physical formation mechanisms of the middleAsia vortex and easterly lowlevel jet stream and their impacts on rainfall; the structure features and physical mechanisms of the occurrence and development of mesoscale systems; the sourcesink structure and relayed transportation mechanisms of water vapor which induce heavy rain; the relationship between typical rainstorm processes and the highmiddlelow largescale water vapor transportation anomaly, etc. To solve the abovementioned problems, it is very important for improving the weather forecast accuracy of heavy rain and enhancing the capabilities of disaster prevention and reduction.

Abstract:Using observational daily maximum temperature of Chinese 181 stations for the period of 1957~2004, the spatiotemporal features of the climatology and decadal variability of the extreme hot event (EHE) frequency, intensity, onset date (EHEOD), and termination date (EHE_TD) are investigated. The climatological analysis indicates that southeastern China and Xinjiang are the two major domains for the EHE, and eastern China is a region with a strong interannual variability. The EHE experienced strong decadal variability in the last 48 years. The variabilities of the frequency and intensity are consistent, and the variabilities of the EHE_OD and EHE_TD are similar. Based on the EHE spatiotemporal feature, the whole China can be divided into four subregions: Southern China, central China, eastern northern China, and Northwest China. The EHE frequency is high in the 1960s and the 1980s for southern China,in the 1960s and the 1990s for central China, and in the 1990s for northern China. Further, the atmospheric circulations which are responsible for the interannual and decadal variability of the EHE in the above four sub-regions are explored. It suggests that the circulations impacting on the interannual and decadal variability are consistent. For northern China, the major circulation is the overlying geopotential height anomaly at middletoupper levels. For southern and central China, the major circulations are the overlying geopotential height anomaly at middletoupper levels and temperature advection by the meridional wind at lower levels.

Abstract:The main weather processes and their related circulations in summer 2009, including the South China Sea monsoon and the precipitation features over South China, the YangtzeHuaihe River basin, and northeast China, are discussed. There were not widearea floods, but serious heat wave and drought were reported over southern China. The South China Sea monsoon began at the fourth pentad of May. The Indian Monsoon was extremely abnormal than usual which may influenced the variation of rainband in China. The typical circulation and the related strong precipitation during the Meiyu period over the Yangtze River basin did not appeared, however, the westerlies troughs and landing typhoons brought several rainfall processes to the YangtzeHuaihe River basin. The total precipitation over North China was below normal. The vortices over northeastern China were very active in the summer of 2009, which resulted in the more precipitation and low temperature in that area. In addition, the heat wave and drought occurred in southern China during 8 to 24 July and 15 August to 14 September, and both of the periods were associated with the western Pacific subtropical high.

Abstract:An economical approach to implement the variational data assimilation (4Dvar) using the technique of Historical Sample Projection (HSP) is proposed, it is based on dimension reduction using an ensemble of historical samples to define a subspace, directly obtains an optimal solution in the reduced space and does not require implementation of the adjoint of tangent linear approximation. But the ensemble is composed of far fewer members than both the number of observational data and the degrees of freedom of the model variables, which would lead to many spurious correlations between observation locations and model grids. More practical and easier way to deal with this problem is through localization technique. Three groups of experiments have been done, the results show that the localization can effectively ameliorate the spurious long range of correlations. And the Schur product tends to reduce and smooth the analysis increments. In addition, the rootmeansquare errors of the 6h and 12h forecast are smaller after the localization.

Abstract:Relationship between the East Asia Westerly Jet (EAWJ) and the Huaihe River Valley (HRV) summer rainfall was investigated month by month, using the NCEP/NCAR reanalysis data and the monthly rainfall data at 160 stations in China from 1979 to 2008. It was found that the HRV summer rainfall is closely related to the monthly variation of the EAWJ. In the years with more rainfall over the HRV, the EAWJ is located northward than normal and the circulation pattern exhibits two ridges and one trough in midhigh latitudes of Asia in June. The cold air activities are weak and the HRV is controlled by anomalous southerlies, which favors more precipitation there. The situation is almost opposite in the years with less rainfall. In the years with more rainfall over the HRV, the EAWJ moves southward to its climatic location, the South Asia high is located eastward than normal, and the western Pacific subtropical high is stronger and is located westward than normal, resulting in more precipitation in the HRV during July and August, and vice versa. The analyses indicate that in June, the change in the intensity and location of the EAWJ is more influenced by the midhigh latitude circulations of Asia. However, in July and August, the intensity and location of the EAWJ is more affected by the variation of the tropical and subtropical circulations.

Abstract:The time series of drought and flood indices in the Three Gorges area are constructed according to Zindex system and the multiple time scales variation characteristics of the index series are analyzed by using Morlet wavelet transform method. The atmospheric circulation characteristics in the typical summer drought/flood years are investigated. It is found that the drought/flood variation is characterized by obvious interannual and interdecadal changes in the Three Gorges area. The drought index and the flood index time series have almost antiphase variations on the annual and seasonal time scales. The Morlet wavelet analyses show that the drought and flood indices in the Three Gorges Reservoir area have remarkable periodic oscillation and obvious local features in different time and frequency distributions. There are quasi5-year, quasi9-year， and quasi15-year interdecadal periodical oscillations. The periodical oscillations of the drought and flood features have significant seasonal differences. In flood years, the atmospheric circulation background in the Three Gorges Reservoir area shows that the anomaly of 500hPa geopotential height field is positive in the Ural Mountains, Siberia, and Lake Balkash, and negative in the Loop area and North China Plain as far as the Sea of Japan. The atmospheric circulation anomaly is opposite in drought years.