Nonsystematic errors of monthly oceanic rainfall derived from SSM/1

About 10 yr (July 1987-December 1997 with December 1987 missing) of oceanic monthly rainfall based on data taken by the Special Sensor Microwave/Image r (SSM/I) on board the Defense Meteorological Satellite Program satellites have been computed. The technique, based on the work of Wilheit ct al., inc ludes improved parameterization of the beam-filling correction, a refined I and mask and sea ice filter. Monthly means are calculated for both 5 degrees and 2.5 degrees latitude-lo ngitude boxes. Monthly means over the latitude band of 50 degrees N-50 degr ees S and error statistics are presented. The time-averaged rain rate is 3. 09 mm day(-1) (std dev of 0.15 mm day(-1)) with an error of 38.0% (std dev of 3.0%) fur the 5 degrees monthly means over the 10-yr period. These stati stics compare favorably with 3.00 mm day(-1) (std dev of 0.19 mm day(-1)) a nd 46.7% (std dev of 3.4%) computed from the 2.5 degrees monthly means for the period January 1992-December 1994. Examination of the different rain ra te categories shows no distinct discontinuity, except for months with a lar ge number of missing SSM/I data. An independent estimate of the error using observations from two satellite, shows an error of 31% (std dev of 2.7%), consistent with the 38% estimated using (A.M.. and P.M.) data from one satellite alone. Error estimates (31% ) based on the 5 degrees means by averaging four neighboring 2.5 degrees bo xes are larger than those (23%) estimated by assuming the means for these n eighboring boxes are independent, thus suggesting spatial dependence of the 2.5 degrees means. Multiple regression analyses show that the error varies inversely as the sq uare root of the number of samples but exhibits a somewhat weaker dependenc e on the mean rain rate. Regression analyses show a power law dependence of -0.255 to -0.265 on the rain rate for the 2.5 degrees monthly means using data from a single satellite and a dependence of -0.366 for the 5 degrees m onthly means and -0.337 for the 2.5 degrees monthly means based on two sate llite measurements. The latter estimate is consistent with that obtained by Bell et al, using a different rainfall retrieval technique.