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. In a convective system, convective clouds can detrain to form other high clouds. In the APSM regions, large areas of high-thin and high-thick clouds cause different CRF at the TOA. These two types of CRF relate to precipitation, atmospheric vertical motion, and cloud life cycles etc. and should be separated from the APSM time evolution. We divided the APSM precipitation into two categories. As in the heavy-precipitation stage, clouds with large optical depth shield solar radiation and cause local and instantaneous surface cooling. The outgoing longwave radiation (OLR) is generally lower than 210 (Wm -2 ). The net CRF at the TOA is large negatively.
Highlights
This is a critical problem when dealing with cloud effects especially in the Indian summer monsoon (ISM) and western North Pacific summer monsoon (WNPSM) regions, which are generally dominated by high clouds (Kau et al 2003) associated with convective systems
We analyze the role of cloud radiative forcing (CRF) in the Asian-Pacific summer monsoon (APSM)
We define two stages based on strength of area-mean precipitation to connect different clouds and their CRF in time evolution
Summary
Jakob (2003) pointed out that one of the major model errors in most convective active regions on Earth is caused by errors in times (frequently observed) when deep convection is suppressed This is a critical problem when dealing with cloud effects especially in the ISM and WNPSM regions, which are generally dominated by high clouds (Kau et al 2003) associated with convective systems. The mean cloud top pressure of high clouds (the major cloud types in this study) in ISCCP is lower than 440 mb and includes three types: cirrus (CI), cirrostratus (CS), and deep convection (DC) These cloud types form by clouds which interconnect with each other and feedback into the climate individually or through their communities. We define these regions as the APSM regions in this study
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