An intercomparison of oceanic precipitation frequencies from 10 special sensor microwave/imager rain rate algorithms and shipboard present weather reports

Oceanic precipitation frequencies produced by 10 satellite microwave algorithms submitted to the first Precipitation Intercomparison Project are compared with frequencies derived from ship reports. It is found that most algorithms yield distributions in reasonable agreement with the ship-derived climatology at low latitudes, but the majority fail to register more than very infrequent (similar to 1%) precipitation at latitudes poleward of about 45 degrees, in contrast to the much larger (similar to 10%) frequencies indicated by surface reports. Only two algorithms, both of which were based on the brightness temperature transformations of Petty [1994a, b], appear to approximately reproduce ship-observed precipitation frequency patterns at both tropical and high latitudes. All 10 algorithms, however, appear to have difficulty producing realistic precipitation frequencies in the ''dry'' subtropical trade belts. This problem is tentatively attributed to the unique physical characteristics of precipitation in those regions.