P2.5 Observations of Snow Particle Size Distribution with 2-d Video Disdrometer and Polarimetric Radar

1. INTRODUCTION Across much of the United States, and in many parts of the world, winter precipitation can come in many forms. It can range from all-liquid rain, to partially frozen particles, and completely frozen particles such as ice pellets or snow. The results of winter precipitation, then, are highly dependent on what type of precipitation falls. If rain falls into subfreezing environments, can down power lines and destroy trees, potentially paralyzing day-today life. Snow can block roadways and high accumulations can put large amounts of pressure on man-made structures (Stewart 1992). Winter storms are responsible for billions of dollars of damage, and can cause significant injury and death (Cortinas et al 2004, Cortinas 2000). Conceptually, rain and snow are relatively predictable compared to other forms of winter precipitation. A common situation occurs following the passage of a surface cold front (or ahead of a warm front), where a shallow layer of cold air at the surface sits below a melting layer. Freezing rain falls when particles that become liquid in the melting layer do not refreeze in the cold layer but do freeze upon reaching the surface. If the particles do refreeze before hitting the ground, ice pellets fall at the surface. This process can be very complex, and see varying degrees of melting (Zerr 1997). An event can have freezing rain or ice pellets exclusively, periods of each, and the two may even coexist (Stewart 1992). Winter precipitation can be observed using in situ measurements, such as rain and snow gauges, as well as disdrometers. They can also be observed with remote sensing instruments, such as satellites and radars (both airborne and ground-based). In general, rain events are studied more commonly than winter events (Henson 2007). While studies of frozen and liquid hydrometeors using polarimetric radar or ____________________