How Warm Can Snow Survive Its Fall Through the Melting Layer Before Fully Melting

Abstract:

The goal of this study is to quantify how far snow can fall into the melting layer before all snow has melted. The melting layer (ML) is an important feature of stratiform precipitation, for radar studies as well as hydrologic applications. A combination of in-situ observations-aircraft measurements using Lagrangian spiral descents from above through the melting layer, and descents and ascents into the ML, as well as an extensive data base of NOAA surface observer reports during the past 50 years, are used in this study. The airborne data contains information on the particle population-size distributions and shapes, as well as temperature, relative humidity, and vertical velocity. A wide range of temperatures and ambient relative humidities are used, both for the airborne and ground-based data. It is shown that an ice bulb temperature of 0⁰C, together with the air temperature, are good first order predictors of how warm a temperature that snowflakes can survive into the melting layer before completely melting. Particle size is also important-if the relative humidity is too low, the particles will sublimate completely as they fall into the melting layer. Snow as warm as +7⁰C is observed from the aircraft measurements. From the observations at the surface, snow is observed as warm as +7⁰C.