Equatorial Atlantic Rain Frequency: An Intercentennial Comparison

Abstract

Analyses of the frequency of rain occurrence over the equatorial Atlantic Ocean from two sources are compared: a nineteenth-century journal publication based on ship's logbook entries, and a 3-yr average, 1998?2000, of observations from the precipitation radar aboard the Tropical Rainfall Measuring Mission satellite observatory. The sources agree remarkably well on the position and shape of the equatorial maximum, with a correlation coefficient of 0.99. However, the magnitudes differ by about a factor of 2, with the modern estimate being lower. This disparity is likely to be attributable to characteristics of the observing systems. The radar sensitivity and scanning characteristics combine to underestimate rain occurrence. The precise nature of the nineteenth-century sources are not documented; however, they almost certainly have been incorporated into the Comprehensive Ocean?Atmosphere Data Set (COADS).