Aliasing effect due to convective rain in Doppler spectrum observed by micro rain radar at a tropical location

Abstract

The spectral reflectivity in terms of Doppler velocity obtained by micro rain radar (MRR) at a tropical location can reveal the splitting of Doppler spectrum of falling rain drops caused by strong downdraft. The phenomenon, known as aliasing, occurs in Doppler spectrum of MRR during intense convective events. In this case, the rain drop velocity exceeds the unambiguous Doppler velocity range that can be sensed by MRR. The downdraft affecting the raindrop velocity significantly causes an ambiguity in the Doppler spectrum of the radar signal scattered from raindrops. The aliasing effect is most prominent near the boundary layer height (0.8–2 km) for convective rain. Also at this altitude range, the resultant height gradient obtained from ECMWF vertical velocity of air mass data and drop terminal velocity, is maximum. The importance of the present study lies in the fact that the split in Doppler spectrum can be utilized to estimate downdraft velocity during rain. The de-aliasing technique has been applied to the raw Doppler spectrum of MRR to retrieve the rain drop size distribution conforming to ground based measurements.