The Role of Cloud Radiative Forcing in the Asian-Pacific Summer Monsoon

Abstract

Convective-cloud clusters with strong precipitation occur frequently in most of the Asian-Pacific summer monsoon (APSM) regions such as the Bay of Bengal (BOB), South China Sea (SCS), and Tropical Western North Pacific (TWNP). Cloud radiative forcing (CRF) is important in these regions. The net CRF at the top of the atmosphere (TOA) has shown large cooling over these APSM regions. This is on account of the presence of large amounts of high clouds with large optical depth. Through data analysis, the summer convective precipitation in TWNP is as strong as that in the BOB. However, the average net CRF at the TOA in the BOB (~ -36 Wm-2) is twice as big as in the TWNP (~ -17 Wm-2). The spectral analysis of cloud optical depth shows that in the BOB, the highest power is in the intra-seasonal timescale, while in the TWNP, the leading spectral peaks are less than 10 days. The radiative cooling from net CRF at the TOA could be associated with lowfrequency oscillation. The difference between the APSM regions is related to their sub-stages separating from CRF in time evolution.

Keywords

• Asian-Pacific Summer Monsoon
• Cloud Radiative Forcing
• GCMs