Non-systematic errors of monthly oceanic rainfall derived from passive microwave radiometry

We compute the non-systematic errors of monthly oceanic rainfall over 5(0) latitude by 5(0) longitude boxes derived from data taken by the Special Sen sor Microwave Imager (SSM/I) on board the Defense Meteorological Satellite Program (DMSP) satellites and TRMM Microwave Imager (TMI). The mean rain ra tes between 1998 and 1999 are calculated to be 3.0, 2.85, 2.89 mm day(-1) a nd the non-systematic errors 22.2%, 22.4% and 19.7% for SSM/I onboard the D MSP F13, F14 and TMI respectively. The non-systematic error for the TMT is smaller than that for one SSM/I at the low rain rates but is comparable at rain rates higher than about 5mm day(-1). The TRMM objective of 1mm day(-1) for non-systematic error is met by TMI for rain rates up to 5-6mm day(-1). Improved space-borne sampling strategy, such as that proposed for the Glob al Precipitation Mission (GPM), is needed to achieve errors better than 10% at the higher rain rates.