Thursday, 9 August 2007
Halls C & D (Cairns Convention Center)
To mosaic a radar image using an individual reflectivity from each radar of weather radar network is very important to synoptic or mesoscale forecast. The representative methods to mosaic a radar reflectivity image are Mosaic by Maximum Value (MMV), Averaged Value (MAV), Nearest Value (MNV) and Distance Weighted Value (MDW). A new method, Mosaic by Height-Weighted Value (MHW) method, was developed to mosaic reflectivity over the overlapped coverage of two radars in the present study. The MHW method adjusts the differences of reflectivity on overlapped coverage of neighboring two radars and then mosaic the radar reflectivity with weights. The weights are inversely proportion to the difference between the height of an interpolated reflectivity and the level of CAPPI. The MHW method was applied to the reflectivity fields of two events observed by Jindo and Gudeoksan S-band radars operated by Korean Meteorological Administration (KMA). The two events were the Typhoon 'Sansan' on 17 September 2006 and the mid-latitude cyclone on 22 October 2006, respectively. The reflectivities of Gudeoksan radar for the two events were adjusted to these of Jindo radar because Jindo radar was used as the reference radar for two events. The reference radar was determined by the comparison of rainfall intensities calculated from two radar using Marshall-Palmer relationship and these measured from rain gauges. To evaluate the composite of radar reflectivity by the MHW method, the continuity of reflectivity at the boundaries in overlapped coverage of two radars was analyzed using a correlation coefficient, RMSE and bias. The analyzed reflectivity continuity by the MHW method was compared with the one obtained by four different methods: MMV, MAV, MNV and MDW. After the application of MHW method, the correlation coefficient between the rainfall intensity obtained by Gudeoksan radar using Marshall-Palmer relationship and the one from rain gauges for two cases were 0.98 and 0.92 and RMSEs were 3.0 and 2.4, respectively. Also, the continuity of reflectivity was better than any other methods. Thus the present study suggests that MHW method is very useful to reduce the discontinuity of reflectivity in overlapped coverage by two radars and to enhance the accuracy of quantitative precipitation estimation using weather radar.
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