Radiative cooling profiles calculated from ECMWF analyses and ISCCP C1 data, and their application to determination of distributions of apparent convective heating in the equatorial Pacific
Abstract
A meteorologically important quantity whose magnitude has not been thoroughly examined is vertical distribution of heating in the tropics. The details of the vertical distribution of heating have a significant impact on a number of phenomena, including the 30-60 day oscillation, sometimes known as the Intra-Seasonal Oscillation (ISO). Prior attempts to establish the structure of the heating relied on limited field data or assimilated data, coupled with climatological radiative heating parameters. The availability of high-quality global-scale data sets has made it possible to make more accurate calculations than were possible a few years ago. The longwave heating distribution is found using the ECMWF/WCRP/TOGA Archive II and ISCCP C1 datasets. A method is developed that can be used to estimate the low cloud amounts, and the results are used with a wideband longwave parameterization (Harshvardhan et al., 1987) to produce longwave cooling rates over the tropical Pacific Ocean. The ECMWF data are used to calculate apparent heat source $\rm (Q\sb1)$ and the results are combined to produce profiles of convective heating. Also, the precipitation rates were found using methods similar to prior work (e.g., Vincent et al., 1991). Outgoing Longwave Radiation (OLR) and Clear-sky OLR were calculated and compared to ERBE results. The calculated values were generally higher than ERBE; this discrepancy was attributed to the longwave model lacking trace gases and insufficient upper tropospheric water vapor in the ECMWF archive. Spatially, the results agree quite well with available observations of longwave radiation. $\rm Q\sb1$ budget derived precipitation rates agree with rain gauge data only in a general way, but this is likely due to the problems inherent in island rain gauge data. The vertical structure of the convective heating was found to be similar to that found in most prior studies, with the level of maximum heating near 400 mb in areas with deep convection. Its shape is strongly affected by the radiative profile, confirming that longwave radiation is highly important in calculating these values.
Degree
Ph.D.
Advisors
Vincent, Purdue University.
Subject Area
Atmosphere
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.