Spatial correlation of cloud occurrence and reflectivity from CloudSat

Launched in late April 2006, CloudSat uses a near nadir-pointing millimeter-wavelength (94 GHz) radar to probe the vertical structure of clouds and precipitation from space. The CloudSat radar does not scan, but generates a curtain or two-dimensional cross-section through the atmosphere as the satellite moves along its orbital trajectory. A primary objective of the CloudSat mission is to provide global observations of cloud and precipitation structure that can be used in the analysis of global climate models. To that end, CloudSat observations are being used to construct joint histograms of radar reflectivity with height (Marchand et al. 2009). CloudSat observations contain much more information on the structure of cloud fields then is captured in these simple histograms. The histograms are single-point statistics. One could arbitrarily reorder the radar profiles in any sequence (destroying all along-track or horizontal correlation) or shift the observed reflectivity at a given height an arbitrary distance relative to the layer above or below (destroying vertical correlation) and obtain the same reflectivity-height joint histogram. The two-dimensional transects observed by CloudSat can also be used to construct two (or higher) point statistics. In this presentation we will examine some simple two-points statistics, including vertical and horizontal covariances in hydrometeor (cloud and precipitation) occurrence and reflectivity. We will show how these statistics vary over the globe and how they relate to local-scale cloud structures.

Marchand, R., J. Haynes, G. G. Mace, T. Ackerman, and G. Stephens (2009), A comparison of simulated cloud radar output from the multiscale modeling framework global climate model with CloudSat cloud radar observations, J. Geophys. Res., 114, D00A20, doi:10.1029/2008JD009790.