Based on the traditional theory of wave mean flow interaction, an improved quasi-geostrophic Eliassen-Palm flux with diabatic heating included is deduced. It is shown that there exists an intrinsic relation between the atmospheric energy cycle derived by Lorenz and the wave energy transfer derived by Eliassen and Palm. From this relation it becomes clear that the energy propagation process of large-scale stationary wave is indeed a part of Lorenz energy cycle, and the energy transform from mean flow to wave equals the global mass integral of the divergence of local wave energy flux or the global integral of local wave energy. The diagnostic results by using NCEP/NCAR reanalysis data suggest that the classical adiabatic Eliassen-Palm flux relation can present only the wintertime wave energy transformation. For other seasons, however, the diabatic effect must be taken into account.
Interdecadal and interannual timescales are dominant in the North China rainfall in rainy season (July and August). On the interdecadal timescale, the North China rainfall exhibited an abrupt decrease at the end of 1970s. In this study, we examined the effect of this abrupt rainfall decrease on the association between rainfall and circulation on the interannual timescale, and found that the interdecadal variation does not change the physical mechanism responsible for the interannual variation of North China rainfall. There is a linear relationship between the interdecadal and interannual variabilities of North China rainfall in rainy season.
LU Riyu Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100080, China
Based on the 1958-1999 monthly averaged reanalysis data of the National Center for Environmental Prediction(NCEP)/National Center for Atmospheric Research(NCAR)and the rainfall data of 160 Chinese surface stations,the relationship between rainfall and the atmospheric circulation anomaly over East Asia(EA)in July and the sensible heating(SH)over the Tibetan Plateau(TP)from April to June(AMJ)is investigated by using the rotational experimental orthogonal function(REOF)method.The results show that the TP is an isolated heating source in this period.The lagged correlation analysis between the first rotational principal component(RPC)of SH over the TP in May and rainfall of EA in July demonstrates that strong SH over the TP before July leads to a positive rainfall anomaly over the TP,the valley between the Yangtze River and Huaihe River,and the regions south and southeast of the TP,and the Sichuan Basin and Yunnan-Guizhou Plateau,but less rainfall anomaly over the regions north,northeast,and west of the TP.Such rainfall anomaly patterns are shown to be well coordinated with those of the circulation and vapor flux fields,and are explained by using the thermal adaptation theory and quasi-stationary large-scale vorticity equation.Therefore,the status of SH over the TP during AMJ can be used as a predictor for the rainfall anomaly over EA,especially in the valley between the Yangtze River and Huaihe River.
Based on the data from International Satellite Cloud Climatology Project (ISCCP) and Earth Radiation Budget Experiment (ERBE), the climatic cloud properties and cloud radiative forcing in the eastern China and the Indian monsoon region are compared. Although both of the Indian monsoon region and the eastern China are included in the Asian monsoon region and the seasonal cycles of rainfall are in phase, the properties of clouds and related cloud radiative forcing are significantly different. All of cloud components in the Indian region have similar phase structure of seasonal cycle. The maximum cloud fractions occur in the summer monsoon period and high clouds dominate the total cloud fraction. However, the seasonal features of clouds in the eastern China are complex. It is the mid-low clouds rather than high clouds dominating the total cloud fraction. The maximum total cloud fraction occurs in spring season. The total cloud and mid-low cloud fractions in winter season are larger than that in summer season. A unique global distinction of clouds in the eastern China is the largest cover of nimbostratus clouds. Reflecting to the cloud properties, the maximums of negative short wave, positive long wave and negative net cloud radiative forcing in the Indian monsoon region are in the summer season. In the eastern China, large negative short wave cloud radiative forcing occurs in early summer. The annual mean negative net cloud radiative forcing in the eastern China is obviously larger than that in the Indian region. Key words Cloud Radiative Forcing - Cloud Fraction Monsoon - Nimbostratus This work was jointly supported by the National Natural Science Foundation of China (Grant No.40023001) and Chinese Academy of Sciences under grant “ Hundred Talents” for “ Validation of Coupled Climate system models”.
Based on the 1958-1999 monthly averaged NCEP/NCAR reanalysis data,the REOF analysis is applied to obtain the main spatial modes of normalized atmospheric heating source over the Tibetan Plateau (TP) in July.Results show that the four leading modes are located over the northeast TP,southwest TP.Kashmir and southeast TP respectively,and the cumulative variances are no more than one third of the total.It indicates that the heating source distribution is very complicated over the TP in July.In other words.it is difficult to depict the heating spatial distribution with a few modes.By using wavelet analysis,a 2--4-year variation period is identified in these modes.Moreover,correlation coefficients between each RPC and zonal wind U, meridional wind V.zonal moisture flux Q,meridional moisture flux Q,and precipitation rate over East Asia are calculated to construct correlation fields,Results show that different heating modes over the TP correspond to different circulation,moisture flux as well as precipitation patterns,Precipitation over North China (or Kashmir) is negatively (or positively) correlated with REOF1.Similarly.notable negative (or positive) correlation can be found between the rainfall over south part of Southwest China.South China,and the Philippines (or Japan) and the REOF3. Due to high localization of diabatic heating over the TP.it is not enough to study the influence of TP thermal forcing on the climate with an area averaged heating index.
The studies in China on the formation of the summertime subtropical anticyclone on the climate timescale are reviewed. New insights in resent studies are introduced. It is stressed that either in the free atmosphere or in the planetary boundary, the descending arm of the Hadley cell cannot be considered as a mechanism for the formation of the subtropical anticyclone. Then the theories of thermal adaptation of the atmosphere to external thermal forcing and the potential vorticity forcing are developed to understand the formation of the subtropical anticyclone in the three-dimensional domain. Numerical experiments are designed to verify these theories. Results show that in the boreal summer, the formation of the strong South Asian High in the upper troposphere and the subtropical anticyclone over the western Pacific in the middle and lower troposphere is, to a great extent, due to the convective latent heating associated with the Asian monsoon, but affected by orography and the surface sensible heating over the continents. On the other hand, the formation of the subtropical anticyclone at the surface over the northern Pacific and in the upper troposphere over North America is mainly due to the strong surface sensible heating over North America, but affected by radiation cooling over the eastern North Pacific. Moreover, in the real atmosphere such individual thermal forcing is well organized. By considering the different diabatic heating in synthesis, a quadruple heating pattern is found over each subtropical continent and its adjacent oceans in summer. A distinct circulation pattern accompanies this heating pattern. The global summer subtropical heating and circulation may be viewed as 'mosaics' of such quadruplet heating and circulation patterns respectively. At last, some important issues for further research in understanding and predicting the variations of the subtropical anticyclone are raised.
Researches on nonlinear atmospheric dynamics in China (1999-2002) are briefly surveyed. This review includes the major achievements in the following branches of nonlinear dynamics: nonlinear stability theory, nonlinear blocking dynamics, 3D spiral structure in the atmosphere, traveling wave solution of the nonlinear evolution equation, numerical predictability in a chaotic system, and global analysis of climate dynamics. Some applications of nonlinear methods such as hierarchy structure of climate and scaling invariance, the spatial-temporal series predictive method, the nonlinear inverse problem, and a new difference scheme with multi-time Ievels are also introduced.
Coupled ocean-atmospheric general circulation models are the only tools to quantitatively simulate the climate system. Since the end of the 1980s, a group of scientists in the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS), have been working to develop a global OGCM and a global coupled ocean-atmosphere general circulation modei (CGCM). Prom the original flux anomaly-coupling modei developed in the beginning of the 1990s to the latest directly-coupling modei, LASG scientists have developed four global coupled GCMs. This study summarizes the development history of these models and describes the third and fourth coupled GCMs and selected applications. Strengths and weaknesses of these models are highlighted.
