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- Author or Editor: Asha Guruprasad x
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Abstract
A simple objective method for delineation of the ITCZ from daily 2.5 degree data on satellite measured outgoing longwave radiation and albedo is described. The method involves identification of grid points with a large fraction of deep convective clouds by imposition of a bispectral threshold and subsequent filtering to retain organized large-scale convection. The thresholds are derived so as to make the delineation by the objective method as close as possible to that from subjective scans by Sikka and Gadgil. The results of the objective method are similar to those obtained by McBride by subjective analysis of the winter monsoon region and Murakami's identification of convective regions based on pixel data.
Abstract
A simple objective method for delineation of the ITCZ from daily 2.5 degree data on satellite measured outgoing longwave radiation and albedo is described. The method involves identification of grid points with a large fraction of deep convective clouds by imposition of a bispectral threshold and subsequent filtering to retain organized large-scale convection. The thresholds are derived so as to make the delineation by the objective method as close as possible to that from subjective scans by Sikka and Gadgil. The results of the objective method are similar to those obtained by McBride by subjective analysis of the winter monsoon region and Murakami's identification of convective regions based on pixel data.
Abstract
The outgoing longwave radiation (OLR) fluxes derived from NOAA-SR (1974–78) are found to he consistently higher than those from NOAA-7 (1982 onward) over a large part of the tropical belt. Analysis of the variation of the mean July–August OLR and the rainfall over the Indian region suggests that the lower values of OLR in the latter period cannot be attributed to more intense convection. Thus, the consistently lower values of OLR in the latter period over a large part of the tropical belt (including the oceanic regions) may be a manifestation of a systematic bias arising from various factors such as changes in instruments, equatorial crossing time, etc. Obviously, if such a bias is present, it has to be removed before the dataset can be used for the study of interannual variations. If the bias is removed by a simple method based on the variation of convection over the entire tropical belt, the OLR variations over the Indian region become consistent with the rainfall variations.
Abstract
The outgoing longwave radiation (OLR) fluxes derived from NOAA-SR (1974–78) are found to he consistently higher than those from NOAA-7 (1982 onward) over a large part of the tropical belt. Analysis of the variation of the mean July–August OLR and the rainfall over the Indian region suggests that the lower values of OLR in the latter period cannot be attributed to more intense convection. Thus, the consistently lower values of OLR in the latter period over a large part of the tropical belt (including the oceanic regions) may be a manifestation of a systematic bias arising from various factors such as changes in instruments, equatorial crossing time, etc. Obviously, if such a bias is present, it has to be removed before the dataset can be used for the study of interannual variations. If the bias is removed by a simple method based on the variation of convection over the entire tropical belt, the OLR variations over the Indian region become consistent with the rainfall variations.
