S. Michaelides

Variation of weather radar sensitivity at ground level and from space : case studies and possible causes

Firstly, this paper summarizes the procedure for correcting the variation of sensitivity of radars at ground level, using a radar in space for reference, as already described in the literature. Around 10dB have to be added to the measured radar reflectivity Z (in mm 6 /m 3 ), when increasing the range from 10 km to 100 km. In other words, instead of an r -2 -dependence (where r is the range, i.e. the distance between the radar and the meteorological target), we find an apparent reduction proportional to r -3 . A similar procedure is used to analyze the dependence of the TRMM radar, using the adjusted data of the radar at ground level for reference. We have to add around 3dB to the measured reflectivity, when increasing the distance from close to Nadir (10 km) to the edge of the swath (100 km). In other words, instead of a constant sensitivity over the swath of the satellite, we find a reduction of sensitivity with the range, proportional to r -0.3 . Secondly, the paper illustrates possible causes of the systematic range dependence of both radars. The old, dominant cause - overshooting of precipitation - is already vastly discussed in literature. We describe the variability of the precipitation with three case studies. The variability of the precipitation is difficult to quantify. It is concluded to be responsible for the variable range dependence and for many disillusions with radar.

Climatological validation of TRMM precipitation radar monthly rain products over Cyprus during the first 5 years (December 1997 to November 2002)

A climatological network of rain gauges operating since 1917 in the island of Cyprus has been used to validate the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar product over the southeastern Mediterranean Sea. A gridded, monthly TRMM product has been used: the so-called 3A-25hr, version-5. All the rain gauges are covered by eight (3A-25hr) 0.5° x 0.5° pixels: between 32° (33.5°) and 34° (34.5°) East (North). The comparison during the first 5 years of the TRMM mission (December 1997-November 2002) shows that quantitative estimates of TRMM Precipitation Radar are remarkably reliable during three (out of four) wettest months: November, December and January. The gauge and TRMM 5-year average is respectively 284 and 279 mm/(3 months). With respect to the previous 81 years, the rain gauges show an increase of rainfall in the rainiest month, December (+19 mm/month), a decrease in January (-40 mm/month) and February (-24 mm/month) and an overall decrease (from 566 mm/year to 520 mm/year). The TRMM Ku-band radar confirms the paradoxical increase of rain in a single month in spite of decrease in total value per year.

Preliminary comparison of TRMM and ground‐based precipitation radars for a European test site

This paper describes the first comparison performed in Europe between the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) and a (C‐band) ground‐based radar. The scope of the research is within the research activities of VOLTAIRE, a European Commission project. Notwithstanding the time lag and differences in the frequency of operation, sample volume, geometrical viewing angles, attenuation and radar sensitivity, there is a reasonable agreement between the two sensors (∼1–2u2009dBZ). Ground‐based and space‐borne radar measurements provide a complementary view of such a complex phenomenon like the precipitation field.

Adjusting ground radar using space TRMM Precipitation Radar

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