Chapter 6 - Nimbostratus and the Separation of Convective and Stratiform Precipitation

Abstract

Abstract Nimbostratus clouds occur in connection with organized storms, mostly fronts, tropical cyclones, and mesoscale convective systems. They are produced by nearly stable air motions and are deep enough to allow precipitation particles to grow to the sizes of raindrops and snowflakes. Their depth and robust precipitation production distinguish them from the shallow stratus and stratocumulus clouds considered in Chapter 5 , which do not have sufficient vertical extent to produce much precipitation. The precipitation from nimbostratus is usually referred to as stratiform precipitation, and it is produced by widespread lifting in fronts and tropical cyclones. However, it also occurs in large quantities in mesoscale convective systems. This chapter discusses the structure of stratiform precipitation as seen by radar. It features a horizontal bright band at the melting layer that distinguishes it from vertical convective precipitation cells. This chapter details how stratiform precipitation appears and develops in both frontal and deep convective situations. In the latter, the stratiform precipitation develops from active convective cells, by dissipation and/or shearing of the active cells. When stratiform precipitation occurs in connection with convective precipitation, it is important to separate the two. This chapter discusses techniques for separation of convective and stratiform precipitation.