Energy Budget in the Asian Monsoon Region
The energy distribution is an important facet of the monsoons. Using a radiative transfer model with temperature, humidity, and cloud amount data from synoptic observations and the Cloud-Radiation-Consistency-Method (CRCM), we derive the radiative flux convergences in the atmosphere (ATM) and at the surface (SFC) for winter, spring, and summer. In the CRCM, uncertainties in cloud parameters are constrained by the satellite observed OLR and albedo. The SFC (ATM) computed using the CRCM is quite reliable as uncertainties in cloud levels, cloud optical depth, cloud overlap, cirrus amount, and surface albedo cause small errors. The radiative heating profile in the atmosphere, SFC, and ATM derived from the new technique (CRCM) are believed to be the best currently available. By restricting the cloud particle radius to certain values, computations can be fast. Based on the SFC and ATM and using precipitation data, estimates of sensible heating over ocean and evaporation, other energy terms such as sensible heating over land, oceanic heat storage and transport, heat source, and moisture source are also derived. Many signals in the monsoon region are strong and cannot be masked by the large uncertainties in the estimates of precipitation over ocean and evaporation. The spatial and temporal distributions of these energy terms help to elucidate the significance of various monsoon processes. The energy budget, radiation and temperature fields indicate that the winter and summer monsoons are very different in nature. The winter monsoon is baroclinic which results from the rapid latitudinal decrease of the SFC due to the strong meridional gradients of solar insolation and albedo and the land-sea distribution in Asia. Strong baroclinicity causes development of baroclinic disturbances. The winter monsoon circulation is probably driven by the meridional sensible heating gradient and is much enhanced by the strong baroclinicity. The winter monsoon region is a moisture source and a heat sink. In contrast, the summer monsoon is quite barotropic which results from the rather uniform distributions of solar insolation and the SFC. The summer monsoon circulation is probably driven by sensible heating and latent heating of precipitation gradients. Moist processes are very important; latent heating of precipitation is often much larger than sensible heating and atmospheric cooling. The greatest difference in the energy budget between a strong and a weak summer monsoon is in the latent heat flux of precipitation. The summer monsoon region is a strong moisture sink and a strong heat source. The transition from winter to summer monsoon flow is related to diabatic heating and Rossby adjustment processes, which change the temperature field and consequently the wind field.
- Pub Date:
- RADIATIVE FLUX;
- Physics: Atmospheric Science