Characterization of Stratiform Rainfall by Cloud Profiling Radar in the Peruvian Andes

Previous studies based on TRMM observations in the central Peruvian Andes showed that stratiform rainfall occurs more frequently than convective rainfall, which in turn provide a major water contribution to the hydrological system. Here, we analyzed the different microphysics processes and mechanisms of stratiform rainfall, such as coalescence, break-up, evaporation, and kinematic using a cloud profiling radar (MIRA-35C) installed in the Atmospheric Microphysics And Radiation Laboratory (LAMAR) at the Huancayo Observatory. Three events with distinct stratiform rain were selected for this study: January 29, February 10 and March 01, 2016.

Stratiform rainfall is characterized by the presence of a well-defined melting layer. Preliminary results from the vertical profile of equivalent reflectivity Ze showed that the melting layer peak varies from 4300 m.a.s.l. to 5100 m.a.s.l. Below the melting layer, Ze values decrease slowly due to break-up of larger raindrops and evaporation of smaller raindrops. Also, strong Doppler velocity gradient is observed in the melting layer region, which indicates a change in the raindrop size distribution (DSD) due to the phase transition from solid to liquid, where the diameter of hydrometeors grow exponentially because the coalesce process. Below the melting layer, hydrometeor terminal velocity transitions from low velocities in the solid phase to higher velocities in the liquid phase. Finally, DSD was estimated from the Doppler spectra of the three events. Findings show higher concentration of cloud particles with a diameter of 0,025 mm and higher concentration of raindrop with a diameter of 2 mm., and the power spectra of the cloud particles present narrower width than raindrops.