Numerical Simulation of the Relationship between the Anomaly of Subtropical High over East Asia and the Convective Activities in the Western Tropical Pacific

In this paper, a close relationship between the intraseasonal variation of subtropical high over East Asia and the convective activities around the South China Sea and the Philippines is analysed from OLR data.This relationship is studied by using the theory of wave propagating in a slowly varying medium and by using a quasi-geoslrophic, linear, spherical model and the IAP-GCM, respectively. The results show that when the SST is warming around the western tropical Pacific or the Philippines, the convective activities are intensified around the Philippines. As a consequence, the subtropical high will be intensified over East Asia. The computed results also show that when the anomaly of convective activities are caused around the Philippines, a teleconnection pattern of circulation anomalies will be caused over South Asia, East Asia and North America.

Global Response to Tropical Diabatic Heating Variability in Boreal Winter

Global teleconnections associated with tropical convective activities were investigated, based on monthly data of 29 Northern Hemisphere winters： December, January, February, and March （DJFM）. First, EOF analyses were performed on the outgoing longwave radiation （OLR） data to characterize the convective ac tivity variability in the tropical Indian Ocean and the western Pacific. The first EOF mode of the convective activity was highly correlated with the ENSO. The second EOF mode had an east–west dipole structure, and the third EOF mode had three convective activity centers. Two distinct teleconnection patterns were identified that were associated, respectively, with the second and third EOF modes. A global primitive equation model was used to investigate the physical mechanism that causes the global circulation anoma lies. The model responses to anomalous tropical thermal forcings that mimic the EOF patterns matched the general features of the observed circulation anomalies well, and they were mainly controlled by linear processes. The importance of convective activities in the tropical Indian Ocean and western Pacific to the extended and longrange forecasting capability in the extratropics is discussed.

THE RELATIONSHIP BETWEEN THE MOVEMENT OF THE MEIYU/BAIU RAIN BELT AND THE PERIODIC NORTHWESTWARD PROPAGATION OF THE CONVECTIVE ACTIVITY FROM TROPICAL WEST PACIFIC

In order to investigate the effect of the factors in tower latitudes on Meiyu/Baiu front,a diagnostic analysis for the two cases during June to July of 1985 and 1986 was examined.We found that (1)when the tropical convective activity moves westward to 10.5-15.5′N/140°E from east side of 10.5-15.5°N/160°E,the northward shifts of the Meiyu/Baiu rain belt occurs;(2)the main factor which results in the northward and southward shifts of Meiyu/Baiu rain belt is thought as the 8,18 and 30 day oscillations of the tropical convective activity around West Pacific. Meanwhile,the wave train propagating from Lake Baikal via Okhotsk Sea to the tropics could sometimes shift Baiu rain belt southward;(3)the onsets of Meiyu in China of both cases tend to take place just when the convective activity around lower latitudes moves westward through about 140°E with the 8,18 and 30 day oscillation periods firstly coming to June.

THE ROLE OF TROPICAL CONVECTION IN VARIATION OF INTRASEASONAL TELECONNECTIONS OF TROPICAL AND EXTRATROPICAL CIRCULATIONS

Based on ECMWF objective analysis data, the relationships between tropical convective activi- ties and extratropical circulation, as well as the low frequency kinetic energy, have been investigat- ed by making use of diagnostic analysis methods on the intraseasonal time scale in winters of 1983/ 1984 and 1986/1987. From this study, it is found that the different intensities of the tropical con- vective activities may bring about both the different intraseasonal teleconnection wave trains be- tween the tropics and the extratropics and the different dispersions of the low frequency wave ener- gy. Moreover, the tropical convection can be an important junction factor for the teleconnection ef- fect of the tropical and extratropical circulations on the intraseasonal time scale.