A statistical comparison of Indian MST radar and Rawinsonde wind measurements

Abstract

Comparisons are made between horizontal wind measurements carried out using Indian mesosphere-stratosphere-troposphere (MST) radar at Gadanki (13.47 deg N, 79.18 deg E) and rawinsonde launched from the SHAR center, Sriharikota (13.7 deg N, 80.2 deg E). The spatial separation of MST radar and rawinsonde is about 90 km. The MST radar horizontal wind velocities are derived from Doppler wind measurements at a zenith angle of 20 deg in two orthogonal planes. For the first time, using Indian MST radar in the tropics, extensive intercomparison results are presented up to an altitude of 18 km. Measurements over a period of four months (June-September 1993) are considered, but the major part of the study involves a statistical analysis of data. The intercomparison was carried out using two methods. First, the comparison was made using the entire data obtained from both instruments. Second, the comparison was repeated with data excluded whenever the instruments have large disagreements in excess of +/- 15 m/s. Comparison of hourly-averaged radar and rawinsonde wind measurements shows fairly good agreement between them. However, radar-derived horizontal winds are underestimated when compared with rawinsonde values over the height range 3.6-18 km. The aspect sensitivity of radar echoes may cause an underestimation of horizontal wind. Comparison of horizontal wind measurements from the MST radar and the rawinsonde differs with a standard deviation of 2-2.5 m/s. The present comparisons successfully demonstrate that both radar and rawinsonde give consistent wind measurements.