6A.6

**Comparing TRMM and ground-based radar observations in Israel during intense precipitation events occurred in March 2003**

**Marco Gabella**, MeteoSwiss, Locarno, Switzerland; and E. Morin

Among many esteems of the first ever speceborne meteorological radar, one is certainly represented by its long-term, continuously monitored electronic stability. The calibration factor is assumed to have a remarkable accuracy: its uncertainty is smaller than 1 dB. Consequently, TPR provides the possibility of assessing the average bias of ground-based radars around the world. Quantitative assessments of this kind have been performed, e. g., in Florida, Colorado, Texas, Marshall Islands, Australia and Cyprus. In this last case, a novel comparison between the TPR and the ground-based radar (GR) was also suggested, based on the fact that the GR and the TPR provide a complementary view: the (GR) measures rain from a lateral direction, while the space-borne radar sees it from the top. On the one hand, the lateral GR measurements are used for quantitative precipitation estimation at distances between 10 km (or even less) and 100 km (or even more). Because of this large ratio of distances, the scattering volume changes by a factor of over 100, since the volume increases with the square of the distance. On the other hand, the scattering volume of TPR has a similar size in all the locations. Its size is not correlated to the distance between the echo and the GR. This advantage of TPR stimulated the idea of using TRMM radar to estimate the influence of sampling volume of the ground-based radar. Our analysis is based on the average, linear radar reflectivity, in circular rings around the GR site as a function of the range, D, from the GR site. The lateral GR measurements are acquired, in the present case, at distances between 10 and 120 km. For both radars, we compute the average Z in the same circular ring. We use 8 rings “centered” at 25, 50, 65, 75, 85, 95, 105, 115 km. Rings are 10 km wide, but the 1st and 2nd ones that are 30 and 20 km wide. Hence, the volumes used to determine the averages are large, even much larger than the rather coarse TPR pulse volume resolution. The large sampling volume reduces mismatches caused by different beam widths and by changes in the weather in space and time. One effect of the beam divergence is a 1/r^2 range-dependence that is already corrected by the radar equation. A second phenomenon is the influence of non-homogeneous beam filling in combination with the average decrease of the vertical reflectivity profile with height, which is the focus of this paper. As an example, at longer ranges of the GR, the lower part of the volume could be in rain, whereas the upper part of the same pulse could be filled with snow, or even be without an echo. This influence becomes more important at longer ranges, since the scattering volume increases in size. Let

Session 6A, Spaceborne Radar II

**Tuesday, 6 October 2009, 10:30 AM-12:00 PM**, Auditorium** Previous paper
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