The time-space exchangeability of satellite retrieved relations between cloud top temperature and particle effective radius

• Main Authors: I. M. Lensky, D. Rosenfeld
• Format: Article
• Language: English
• Published: Copernicus Publications 2006-01-01
• Series: Atmospheric Chemistry and Physics
• Online Access: http://www.atmos-chem-phys.net/6/2887/2006/acp-6-2887-2006.pdf

A 3-minute 3-km rapid scan of the METEOSAT Second Generation geostationary satellite over southern Africa was applied to tracking the evolution of cloud top temperature (<i>T</i>) and particle effective radius (<i>r_e</i>) of convective elements. The evolution of <i>T-r_e</i> relations showed little dependence on time, leaving <i>r_e</i> to depend almost exclusively on <i>T</i>. Furthermore, cloud elements that fully grew to large cumulonimbus stature had the same <i>T-r_e</i> relations as other clouds in the same area with limited development that decayed without ever becoming a cumulonimbus. Therefore, a snap shot of <i>T-r_e</i> relations over a cloud field provides the same relations as composed from tracking the time evolution of <i>T</i> and <i>r_e</i> of individual clouds, and then compositing them. This is the essence of exchangeability of time and space scales, i.e., ergodicity, of the <i>T-r_e</i> relations for convective clouds. This property has allowed inference of the microphysical evolution of convective clouds with a snap shot from a polar orbiter. The fundamental causes for the ergodicity are suggested to be the observed stability of <i>r_e</i> for a given height above cloud base in a convective cloud, and the constant renewal of growing cloud tops with cloud bubbles that replace the cloud tops with fresh cloud matter from below.