Observed Microphysical Structure of Midlevel, Mixed-Phase Clouds

Abstract

This paper analyzes airborne measurements of six midlevel clouds observed over the Great Plains of the United States in late 1999 and early 2000 during the fifth of the Complex Layered-Cloud Experiments (CLEX-5). Data show that these innocuous-looking clouds display complicated microphysical and thermodynamic structures. Five of the six cases exhibit mixed-phase conditions in temperatures ranging from near 0° to ?31°C, at altitudes of 2400 to 7200 m MSL. Four of the cases consist of a single cloud layer, while the other two are multilayered systems. In the thin, mixed-phase, single-layered clouds that the authors observed, there is an increase of liquid water content with altitude, whereas the ice water content maximizes in the mid- to lower part of the clouds. This contrasts the two multilayered systems the authors observed, in which significant amounts of ice occur in the top as well as the bottom of the individual layers of each system. A lack of significant temperature inversions or wind shears in the observed clouds is a major difference from the thermodynamic structure of most stratocumulus systems. Virtual potential temperature jumps were less than or equal to 1°?2°C at the top and bottom of cloud layers. In the thin, single-layer clouds, particle size distributions show an increase in drop size with increasing altitude. A noteworthy contribution to this observational study was the use of the Cloud Particle Imager (CPI) instrument for the qualitative analysis of particle shapes and altitudes of occurrence through the cloud. Finally, the liquid water contents observed in this research are compared with those of previous observational studies of altocumulus and altostratus clouds.