Satellite-based rainfall estimation techniques over complex orography usually show unsatisfactory results at any frequency, also averaging over large basin and/or integrating over many hours intervals. At shorter wavelengths (visible-infrared) cloud top radiances are not sensitive to lower cloud layers forcing, resulting in a rainfall underestimation. On the other side, passive microwave algorithms are sensitive to the variability of the ground emissivity over complex terrain so that they cannot work using the emission signal of lower precipitating layers; in such a way it becomes difficult to take properly into account the orographic forcing as well. To overcome these difficulties, ancillary parameters are derived from satellite data (e.g. cloud motion winds) or independent datasets (e.g. digital elevation model) and the sensitivity of measured and estimated rainfall to orographic forcing is evaluated. The use of cloud resolving models outputs are used to test independently the sensitivity of the rainfall fields to the considered parameters and to drive their use inside the rainfall estimation techniques. The application to heavy-rainfall flood-causing rainfall event in the Mediterranean area is discussed and performances evaluated.
On the capabilities of VIS/IR satellite data to resolve orographic precipitation
PORCU', Federico;
2003
Abstract
Satellite-based rainfall estimation techniques over complex orography usually show unsatisfactory results at any frequency, also averaging over large basin and/or integrating over many hours intervals. At shorter wavelengths (visible-infrared) cloud top radiances are not sensitive to lower cloud layers forcing, resulting in a rainfall underestimation. On the other side, passive microwave algorithms are sensitive to the variability of the ground emissivity over complex terrain so that they cannot work using the emission signal of lower precipitating layers; in such a way it becomes difficult to take properly into account the orographic forcing as well. To overcome these difficulties, ancillary parameters are derived from satellite data (e.g. cloud motion winds) or independent datasets (e.g. digital elevation model) and the sensitivity of measured and estimated rainfall to orographic forcing is evaluated. The use of cloud resolving models outputs are used to test independently the sensitivity of the rainfall fields to the considered parameters and to drive their use inside the rainfall estimation techniques. The application to heavy-rainfall flood-causing rainfall event in the Mediterranean area is discussed and performances evaluated.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
