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This paper presents a review on the impact of El Nino on the interannual variability of atmospheric circulations over East Asia and rainfall in China through the anomalous anticyclone over western North Pacific (WNPAC). It explains the formation mechanisms of the WNPAC and physical processes by which the WNPAC affects the rainfall in China. During the mature phase of El Nino, the convective cooling anomalies over western tropical Pacific caused by the weakened convections trigger up an atmospheric Rossby wave response, resulting in the generation of the WNPAC. The WNPAC can persist from the winter when the El Nino is in its peak to subsequent summer, which is maintained by multiple factors including the sustained presence of convective cooling anomalies and the local air-sea interaction over western tropical Pacific, and the persistence of sea surface temperature anomalies (SSTA) in tropical Indian and tropical North Atlantic. The WNPAC can influence the atmospheric circulations over East Asia and rainfall in China not only simultaneously, but also in the subsequent summer after an El Nino year, leading to more rainfall over southern China. The current paper also points out that significant anomalies of atmospheric circulations over East Asia and rainfall over southern China occur in El Nino winter but not in La Nina winter, suggesting that El Nino and La Nina have an asymmetric effect. Other issues, including the impact of El Nino diversity and its impact as well as the relations of the factors affecting the persistence of the WNPAC with summer rainfall anomalies in China, are also discussed. At the end of this paper some issues calling for further investigation are discussed.

Scientific issues relevant to interactions between aerosols and the Asian monsoon climate were discussed and evaluated at the 33rd “Forum of Science and Technology Frontiers” sponsored by the Department of Earth Sciences at the Chinese Academy of Sciences. Major results are summarized in this paper. The East Asian monsoon directly affects aerosol transport and provides a favorable background circulation for the occurrence and development of persistent fog-haze weather. Spatial features of aerosol transport and distribution are also influenced by the East Asian monsoon on seasonal, inter-annual, and decadal scales. High moisture levels in monsoon regions also affect aerosol optical and radiative properties. Observation analyses indicate that cloud physical properties and precipitation are significantly affected by aerosols in China with aerosols likely suppressing local light and moderate rainfall, and intensifying heavy rainfall in southeast coastal regions. However, the detailed mechanisms behind this pattern still need further exploration. The decadal variation in the East Asian monsoon strongly affects aerosol concentrations and their spatial patterns. The weakening monsoon circulation in recent decades has likely helped to increase regional aerosol concentrations. The substantial increase in Chinese air pollutants has likely decreased the temperature difference between land and sea, which favors intensification of the weakening monsoon circulation. Constructive suggestions regarding future studies on aerosols and monsoons were proposed in this forum and key uncertain issues were also discussed.

Using 32-yr National Centers for Environment Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis data, we investigated zonal propagation and circulation characteristics of the low-frequency circulation for the prevailing period over Eurasian mid-high latitude in boreal summer (May-August) in terms of empirical orthogonal function (EOF), linear regression, and phase analysis and so on. We found that the dominant periods of the low-frequency circulation are 10–30 days and it clearly shows meridional (southward) and zonal (westward) propagation features at the middle troposphere (500 hPa). The average zonal speed of the 10–30 days low-frequency oscillation (LFO) is about 9–10 longitudes per day. Further analysis shows that the southernmost part of the polar vortex in the northern hemisphere exhibits westward clockwise rotation in the eastern hemisphere in boreal summer. Also, the southernmost tips of 5400 and 5500 gpm contours, which indicate the site of the major trough in the eastern hemisphere, obviously move westwards. The southernmost tip of 5500 gpm contour line propagates westwards at the speed of about 9–10 longitudes per day, which is consistent with the mean zonal speed of the westward propagation of the low-frequency circulation. Moreover, the 10–30-day LFO-related cold air also shows west propagation feature with respect to LFO phases. The westward propagation of the LFO is the low-frequency-scale embodiment of the clockwise rotation of polar vortex. The cold air activities closely related to polar vortex or to ridge-trough system activities is the essential circulation of 10–30 days LFO circulation over the Eurasian mid-high latitude in boreal summer.

This study analyzes the inter-decadal variations of rainfall over southern China in spring (March–April–May) using the observed precipitation data for 1979–2004. The result shows that the variations of spring rainfall over southeastern China are opposite to those over and southwestern China in both inter-annual and inter-decadal time scales. The precipitation over southern China exhibits an apparent inter-decadal shift in the late 1980s. The accumulated spring rainfall has reduced 30% over southeastern China after the late 1980s, whereas it has increased twice as much over southwestern China. The atmospheric circulations related to this shift show that an abnormal high at lower and middle troposphere appears over Asian middle and high latitudes, accompanied by stronger-than-normal northerly wind over eastern China. Consequently, the wet air flows from tropical oceans are weakened over southern China, resulting in less rainfall over southeastern China and more rainfall over southwestern China. Furthermore, the anomalous atmospheric circulation over Asian middle and high latitudes is closely related to the inter-decadal downward shift of Eurasian spring snow in the late 1980s, indicating that the inter-decadal shift of Eurasian spring snow in the late 1980s is probably an important factor in the decadal shift of spring rainfall over southern China.

A vertical one-dimensional numerical model for heat transferring within the near-surface snow layer of the Antarctic Ice Sheet was developed based on simplified parameterizations of associated physical processes for the atmosphere, radiation, and snow/ice systems. Using the meteorological data of an automatic weather station (AWS) at Dome A (80°22′S, 70°22′E), we applied the model to simulate the seasonal temperature variation within a depth of 20 m. Comparison of modeled results with observed snow temperatures at 4 measurement depths (0.1, 1, 3, 10 m) shows good agreement and consistent seasonal variations. The model results reveal the vertical temperature structure within the near-surface snow layer and its seasonal variance with more details than those by limited measurements. Analyses on the model outputs of the surface energy fluxes show that: 1) the surface energy balance at Dome A is characterized by the compensation between negative net radiation and the positive sensible fluxes, and 2) the sensible heat is on average transported from the atmosphere to the snow, and has an evident increase in spring. The results are considered well representative for the highest interior Antarctic Plateau.

Fog and haze are two kinds of weather phenomena. Fog is referred to as water droplets suspended in the air near earths surface, which reduces the visibility to less than 1 km. A fog consisting of ice crystals is called ice fog. Haze is the particles suspended in the air that reduce visibility by scattering the light, and is usually a mixture of aerosol and photochemical smog. Fog and haze usually coexist. The occurrence and evolution of haze and fog are closely related with meteorological conditions.