Wind Estimates from Cloud Motions: Results from Phases I, II and II of an In Situ Aircraft Verification Experiment

Abstract

An experiment is in progress to verify geostationary satellite derived cloud motion wind estimates by in situ aircraft wind velocity measurements. One or more low-level aircraft equipped with Inertial Navigation Systems (INS) were used to define the vertical extent and horizontal motion of a cloud and to measure the ambient wind field. A high-level aircraft, also equipped with an INS, took photographs to describe the horizontal extent of the cloud field and to measure cloud motion. The aerial photographs were also used to make a positive identification in the satellite picture of the cloud observed by the low-level aircraft. To date the experiment has been conducted over the tropical oceans in the vicinity of Florida, Puerto Rico, Panama and in the western Gulf of Mexico. A total of 60 h have been spent tracking some 40 tropical cumulus and five cirrus clouds. Results for tropical cumulus clouds indicate excellent agreement between the cloud motion and the wind at cloud base. The magnitude of the vector difference between the cloud motion and the cloud base wind is less than 1.3 m s?1 for 67% of the cases with track lengths of I. h or longer. Similarly, the vector differences between the cloud motion and the wind at sub-cloud (150 m), mid-cloud and cloud-top levels are 1.5, 3.6 and 7.0 m s?1, respectively. The cirrus cloud motions agreed best with the mean wind in the cloud layer with a vector difference of about 1.6 m s?1.