The dominant mode of atmospheric circulation over the North Atlantic region is the North Atlantic Oscillation (NAO). The boreal spring NAO may imprint its signal on contemporaneous sea surface temperature (SST), leading to a North Atlantic SST tripolar pattern (NAST). This pattern persists into the following summer and modulates the East Asian summer monsoon (EASM). Previous studies have shown that the summer NAST is caused mainly by the preceding spring NAO, whereas the contemporaneous summer NAO plays a secondary role. The results of this study illustrate that, even if the summer NAO plays a secondary role, it may also perturb summer SST anomalies caused by the spring NAO. There are two types of perturbation caused by the summer NAO. If the spring and summer NAO patterns have the same (opposite) polarities, the summer NAST tends to be enhanced (reduced) by the summer NAO, and the correlation between the spring NAO and EASM is usually stronger (weaker). In the former (latter) case, the spring-NAO-based prediction of the EASM tends to have better (limited) skill. These results indicate that it is important to consider the evolution of the NAO when forecasting the EASM, particular when there is a clear reversal in the polarity of the NAO, because it may impair the spring-NAO-based EASM prediction.

Based on International Satellite Cloud Climatology Project (ISCCP) Convection Tracking Database (CTD) data set, a new definition for the Tibetan Convective System (TCS) is introduced, in which the effects of cirrus and cirrostratus are excluded from the TCS over this region. 2032 TCSs are selected to study their seasonal variations in initiation, frequency, spatial distribution, life cycle, cloud physics, precipitation, and dynamic and thermodynamic characteristics. It is found that the number of TCSs varies seasonally, with the maximum in July and minimum in December. The 10%, 8%, 9%, and 73% TCSs are originated from Tibetan shear, vortex, low, and the rest, respectively. TCSs play an important role in the precipitation of the Tibetan Plateau and its adjacent regions. Even in winter, the rainfall of TCS contributes up to 70% of the total precipitation over the central-eastern Tibetan Plateau and 30%–70% over Sichuan basin and upper-middle segment of Yangtze River basin. The seasonal changes of TCSs' cloud properties from ISCCP indicate that the strongest TCSs happen in summer and the weakest in winter, which are consistent with the seasonal variation of TCSs' rainfall observed by TRMM. Besides, TCSs show an asymmetric dynamic and thermodynamic distribution, especially in summer.

Future climate projections suggest a poleward shift of the maximum intensity of tropical cyclones (TCs) over the western North Pacific. However, the global nature of the latitudinal change in TC genesis under global warming remains poorly understood. We show, using large‐ensemble high‐resolution atmospheric model simulations (d4PDF) with four warming scenarios, that the poleward shift is a robust change over the globe, attributable to the weakening of the Hadley circulation. The weakened ascent driven by the upper‐tropospheric warming suppresses the TC genesis within 5°–20° latitudes, whereas the weakened descent enhances the TC genesis in the poleward latitudes. We further estimate the poleward shift of TC genesis to emerge at the 2 K global warming over the Arabian Sea, South Atlantic and Pacific Oceans and at the 4 K warming over the North Pacific. The present results underscore the potential for increasing social and economic risks associated with TCs at higher latitudes.

In early January 2011, southern China experienced another severe wintertime storm as in the winter of 2008. The storm consisted of a narrow east‐west‐oriented freezing rain band over central Guizhou with an extensive area of snow to the north and a rain swath to the south. This study investigates this event using conventional surface and radiosonde data as well as final (FNL) analyses data from the US National Center for Atmospheric Research/National Centers for Environmental Prediction(NCAR/NCEP). The results show that forcing by geostrophic and diabatic heating built up a positive direct secondary circulation perpendicular to the quasi‐stationary front beneath 700 hPa to maintain the surface cold layer and warm layer aloft through surface cold advection and warm advection aloft. In addition, turbulence induced by strong wind shear in the middle and lower stratiform clouds with a low concentration of ice nuclei plays an important role in the growth of cloud drops and the enhancement of supercool raindrop precipitation over Guizhou. Copyright © 2011 Royal Meteorological Society