In Situ Observations of the Microphysical Properties of Wave, Cirrus, and Anvil Clouds. Part I: Wave Clouds

Abstract

The microphysical properties of wave clouds based on data collected during 17 missions flown by a Learjet research aircraft are presented and discussed. This extensive dataset expands upon previous aircraft studies of wave clouds and introduces some new findings. While most aspects of the observations are consistent with basic cloud physics, some aspects remain difficult to interpret. Most notable among these are ice nucleation and aspects of the dynamical structure of wave clouds. A new hypothesis to explain the ice nucleation behavior is presented. The average and standard deviation of bulk microphysical parameters are presented for various locations within the wave clouds. Using digital imagery from a cloud particle imager (CPI), the shapes of ice particles are studied and crystal habits are classified. For certain categories—rosette shapes, columns, and irregular shapes—power-law parameterizations of particle area from particle length are presented. Polycrystals with rosette shapes dominate the ice mass while small spheroidal and irregularly shaped crystals dominate the ice number concentration. The concept and difficulties of using wave clouds as natural cloud physics laboratories are discussed and evaluated. A study of the riming threshold size of columns is in good agreement with the results of previous studies, showing that column width is the predominate factor in determining riming threshold. The first reported studies of the riming threshold size of rosette shapes and the threshold size for side-plane growth are presented.