Some Results on the Monsoon Studies

1. Interaction between ENSO and the Winter Monsoon in East Asia

a). Based on data and theoretic analyses,indicated at first in the world that the anomalous strong winter monsoon in East Asia can excite El Nino event. (Science in China_B, 976-985, 1989; Frontiers in Atmos. Sci., 156-165, 1989).

b). Further studies still indicated that the strong winter monsoon in East Asia exciting El Nino event has two major processes: Reducing trade wind in the equatorial centre-western Pacific, then exciting anomalous oceanic Kelvin waves; Enhancing cumulus convection over the equatorial western Pacific, then exciting strong tropical intraseasonal oscillation. (Advances in Atmos. Sci., 36-46, 1990).

c). ENSO also affect winter monsoon in East Asia,during El Nino (La Nina) winter, the winter monsoon is weaker (stroger) in general. (Chinese Science Bulletin, 1801-1805, 1989).

2. Intraseasonal Oscillation (ISO) and the Relationship with ENSO

a). The analyses of kinetic energy for the ISO showed that there is also stronger ISO in the equatorial eastern Pacific region, particularly in the upper troposphere; Tropical ISO has very clear interannual variation and it is related with El Nino. (Acta Meteorol. Sinica, 525-535, 1990; Advances in Atmos. Sci., 399-406, 1991).

b). Dynamics mechanism of tropcal ISO:

• To introduce the wave-CISK into dynamic study of tropical ISO and indicated that the moving CISK mode is an important mechanism to drive the 30-60 day oscillation of the summer monsoon in South Asia. (Science in China_B, 1197-1207, 1985).

• The theoretic analyses showed that cumulus heating feedback can not only excite CISK-Kelvin waves,but also CISK-Rossby waves,which propagate eastwards or westwards and can form the wave-train pattern. Therefore,both the CISK-Kelvin wave and the CISK-Rossby wave are the exciting mechanism to the tropical ISO,and it is mainly the CISK-Kelvin wave in the equator region but the CISK-Rossby wave in the area outside the equatoor (Chinese J. Atmos. Sci., 101-112, 1990; Acta Meteorol. Sinica, 41-53, 1993).

• Dynamic study showed that alone evaporation-wind feedback can not excite tropical ISO,but it can lead the CISK-Kelvin waves to be unstable when there are convection heating and evaporation-wind feedback. (J. Tropical Meteorol., 11-17, 1997).

c). The ISO in the mid-high latitudes is different from that in the tropics,such as propagation,zonal scale,vertical structure and dynamic mechanism;The low-frequency responses of atmosphere to the external forcing,instability of basic flow and nonlieane interaction are the fundamental mechanisms of the ISO in the mid-high latitudes. (Climate, Environment and Geophysical Fluid Dynamics, 99-110, 1993; Science in China_B, 1135-1145, 1995 ).

d). The interaction between El Nino and tropical ISO is indicated: The tropical ISO (particularly in the equatorial western Pacific region) is very strong prior to the occurrence of El Nino event, but the ISO is weaker during El Nino period; The El Nino will lead the structure of tropical ISO to be barotropic. (Chinese J. Geophysics, 213-224, 1994; Acta Meteorol. Sinica, 1-12, 1995).

e). The activity of ISO in the equatorial Western Pacific/South China sea area is related to the summer rainfall in the Huaihe- Changjiang river region. (Advances in Atmos. Sci., 246-254, 1997).