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IR-based satellite and radar rainfall estimates of convective storms over northern Italy

Published online by Cambridge University Press:  01 March 2000

R Amorati
Affiliation:
Institute FISBAT-CNR, via Gobetti 101, I-40129 Bologna, Italy and Dept. of Physics, University of Bologna, viale Berti Pichat 6/2, I-40127 Bologna, Italy
P P Alberoni
Affiliation:
ARPA-Servizio Meteorologico Regionale, Bologna, viale Silvani 6, I-40122 Bologna, Italy and Institute FISBAT-CNR, via Gobetti 101, I-40129 Bologna, Italy
V Levizzani
Affiliation:
Institute FISBAT-CNR, via Gobetti 101, I-40129 Bologna, Italy EUMETSAT, Am Kavalleriesand 31, D-64295 Darmstadt, Germany
S Nanni
Affiliation:
ARPA-Servizio Meteorologico Regionale, Bologna, viale Silvani 6, I-40122 Bologna, Italy
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Abstract

Convective precipitation events in northern Italy during 1996 and 1997 are analysed using two infrared-based geosynchronous satellite rainfall estimation methods to verify the level of applicability of the techniques for operational applications in the area, their quantitative results, and relative performances. The Negri–Adler–Wetzel (NAW) and the convective stratiform technique (CST) are applied to METEOSAT's thermal infrared (IR) data. C-band radar reflectivity fields detail the vertical and horizontal structure of the cloud systems, and radar rainfall data are retrieved. Satellite rain areas are checked against simultaneous radar rainfall retrievals through a contingency analysis procedure. A semi-quantitative analysis is presented. Positive brightness temperature differences between water vapour and thermal IR channels are also examined and related to the storms' development stage and rainrate. Results show that NAW and CST perform reasonably in delimiting rain areas during active convection and care should be used in the initial and final development stage when statistical parameters lose most of their significance. NAW tends to overestimate rainfall while CST approaches more closely radar measurements. Most common errors arise from considering only portions of the storm, contamination from cold non-precipitating cloud, and merging of two or more cloud masses of independent origin. Operational applications, though not completely quantitative, are also possible, including positive values of the difference between water vapour and IR brightness temperature.

Type
Research Article
Copyright
© 2000 Meteorological Society

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