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 a lgorithms 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 t o 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 a lgorithms, both of which were based on the brightness temperature tran sformations of Petty [1994a, b], appear to approximately reproduce shi p-observed precipitation frequency patterns at both tropical and high latitudes. All 10 algorithms, however, appear to have difficulty produ cing realistic precipitation frequencies in the ''dry'' subtropical tr ade belts. This problem is tentatively attributed to the unique physic al characteristics of precipitation in those regions.