Shipboard Radar Rainfall Patterns within the TOGA COARE IFA

Abstract

Radar rainfall measurements over the equatorial western Pacific warm pool were collected by two shipboard Doppler radars as part of the Tropical Oceans Global Atmosphere Coupled Ocean?Atmosphere Response Experiment during the intensive observing period (November 1992?February 1993). A comprehensive dataset of gridded rainfall fields, convective/stratiform identification maps, and vertical structure products has been produced, covering an area approximately 400 km (E?W) by 300 km (N?S) within the Intensive Flux Array (IFA), centered near 2°S, 156°E. The radar rainfall product, which was used as validation for the Third Algorithm Intercomparison Project of the Global Precipitation Climatology Project, indicates an overall average of 4.8 mm day?1; however, correction for range dependence increases the total to 5.4 mm day?1. Rainfall patterns varied considerably during the experiment with isolated convection dominating periods of light winds, while squall lines and organized mesoscale systems were abundant during two westerly wind bursts. An area-average rainfall of 9.9 mm day?1 was observed during the active 2-week period at the end of December, while 0.4 mm day?1 was observed during the quiescent week of 2?8 February. The eastern portion of the IFA received the most rainfall with localized maxima exceeding 16 mm day?1 for the most active 3-week period. Comparison of daily radar rainfall totals with those observed by an optical rain gauge (ORG) on the 2°S, 156°E buoy shows ORG totals to be systematically higher, by a factor of 2.5. The discrepancy results from a higher average rainfall rate, when raining, as reported by the buoy ORG. However, rainfall rate statistics from the ORGs on the research vessel Xiang Yang Hong #5 and from its radar are in excellent agreement under the following conditions: 1) the ship is drifting, and 2) the radar data are in the near vicinity of the ship (3?7 km).