Microphysical Parameters Retrieval of Rainfall Using Ka Band Radar Profiler at Central Andes of Peru

Peru is a country vulnerable to natural hazards from hydrometeorological origin with great social and economic impact, such as the intense rainfall in the northern and central coast during the "Niño Costero 2017" phenomenon. The complex topography of the Andes, which covers much of the Peruvian territory, makes the precipitation obtained by satellite be underestimated. On the other hand, the atmospheric models are not able to adequately represent the rains, because the physical and microphysical processes of clouds and precipitation in the Andes are not well known. In order to obtain atmospheric data to study the physical processes associated with water and energy balance; in 2015 the Instituto Geofísico del Perú implemented the Atmospheric Microphysics And Radiation Laboratory (LAMAR), Huancayo Observatory, at 3300 m.a.s.l; being the Ka band cloud-profiling radar (MIRA- 35C) one of the main instrument.

In the present work, an algorithm to retrieve microphysical parameters of rainfall using the MIRA-35C is developed. Doppler spectra are used to calculate the drop size distribution (DSD), and the different microphysical parameters, such as rainfall intensity and liquid water content. Also, algorithms for correction of wet antenna attenuation and path-integrated attenuation are included. These algorithms are necessary for the correct estimation of precipitation.

Preliminary results, for four rainfall events, indicate that the attenuation caused by wet antenna can reach 9 dB generating errors of around 400%. With attenuation correction, the rainfall intensity near the surface is compared with in situ data (rain gauge and disdrometer). The analysis of the precipitation estimated by the radar versus rain gauge, for the cases of study, show in average an error of 2 mm and an absolute relative error of 29%. The wet antenna attenuation correction algorithm is still in development; it is expected that the results can be greatly improved with further studies.