Snow Virga above the Swiss Plateau Observed by a Micro Rain Radar

Ruben Beynon,Klemens Hocke

doi:10.3390/rs14040890

Abstract

Studies of snow virga precipitation are rare. In this study, we investigated data from a vertically pointing Doppler Micro Rain Radar (MRR) in Bern, Switzerland, from 2008 to 2013 for snow virga precipitation events. The MRR data were reprocessed using the radar data processing algorithm of Garcia-Benardi et al., which allows the reliable determination of the snow virga precipitation rate. We focus on a long-lasting snow virga event from 17 March 2013, supported by atmospheric reanalysis data and atmospheric back trajectories. The snow virga was associated with a wind shear carrying moist air and snow precipitation in the upper air layers and dry air in the lower air layers. The lowest altitudes reached by the precipitation varied between 300 m and 1500 m above the ground over the course of the event. The duration of the snow virga was 22 h. In disagreement with the MRR observations, ERA5 reanalysis indicated drizzle at the ground over a time segment of 4 h during the snow virga event.

Highlights

IntroductionIce or snow falling within the troposphere and evaporating or sublimating at a level well above the ground
Virga above the Swiss PlateauVirga is rain, ice or snow falling within the troposphere and evaporating or sublimating at a level well above the ground
Several virga or virga-like events were found in the Micro Rain Radar (MRR) data between 2008 and 2013, of which two selected events of snow virga are presented in more detail in the thesis of Beynon [26]

Summary

Introduction

Ice or snow falling within the troposphere and evaporating or sublimating at a level well above the ground. Meteorological Society gives a more narrow definition of virga as “wisps or streaks of water or ice particles falling out of a cloud but vaporizing before reaching the Earth’s surface as precipitation” [1]. Radar and ceilometer measurements show that virga is continued by precipitation inside the cloud layer (e.g., Figure 1 in [2]). For atmospheric research and aviation, it might be desirable to include the precipitation inside the cloud layer into the virga research topic. Precipitation inside a cloud layer without virga precipitation below the cloud base has our interest. Virga is often seen in deserts and semi-arid continental regions where the cloud bases may be as much as 4 km above the ground. Rosenfeld and Mintz [3]

Results

Discussion

Conclusion