Comparison of TOGA COARE optical raingage data with radar reflectivity



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This thesis compares bin-by-bin radar reflectivity data with optical raingage data from TOGA COARE. Radar and raingage data were used from two ships, each carrying one radar and two raingages. This study analyzes six cases including a total of nine echoes. At simultaneous times, radar data from the opposite ship of the raingages, located at a distance of 100 to 135 km, were used to compare with the raingage data. Also, at a time prior to the echo passing over the ship, radar data from the same ship of the raingages were used to compare with the raingage data. The ray of radar data most likely to have passed over the ship was chosen. Its bin-by-bin reflectivity data were converted to rainfall rates using a Z-R relationship from GATE. These rates were compared with the rainfall rates from the raingages at the corresponding times by performing a timespace conversion using the echo speed. The data was then plotted using identical scales for direct comparisons. Graphs were also generated to compare cumulative percentages of area from the echo occupied by a rainfall rate with cumulative percentages of time from the raingages that the rainfall rate was occurring. The radar data from the same ship as the raingages showed excellent representations of the raingage data. The trends and maximum peaks were quite comparable between these two data sets. Most of the time rainfall rates recorded by the raingages exceeded rates recorded by the radars. These two sets of data differed by a factor of two or less. Due to beam widening and interference from intervening echoes, using the opposite radars at a distance of 100 to 135 km showed poor representations of the raingage data .



Precipitation (Meteorology) -- Observations, Radar meteorology -- Observations, Boundary layer (Meteorology) -- Observations