Aircraft Measurements of Convective Draft Cores in MONEX

Abstract

Refinements have been made to a standard procedure for calculating vertical air velocities from parameters measured routinely during flights by the Electra aircraft of the National Center for Atmospheric Research. Accuracies generally near one or two meters per second have been attained. Using this procedure with the Electra aircraft, together with data from one of the WP-3D aircraft of the National Oceanic and Atmospheric Administration, a survey has been made of 99 different updraft cores and 43 downdraft cores encountered during the Winter and Summer Monsoon Experiments, in which vertical air speed exceeded 2 m s?1 for 1 s. Ignoring peripheral drafts of speed less than the threshold 1 m s?1, MONEX updraft cores were of median width 1.4 km, median peak updraft 3.2 m s?1, mean updraft 2.3 m s?1 and log10(mass transport, in kg s?1 m?1 normal to the flight track) equal to 3.4. Downdraft cores were of median width 1.3 km, peak downdraft 2.6 m s?1, mean downdraft 1.9 m s?1 and log(mass transport) equal to 3.2. The greatest 1 s updrafts reached 17 m s?1. For draft cores other than in vigorous cumulonimbus, an equation was found relating mean draft speed, air density and width. Generally the mean draft speed approximately equals 2.5 m s?1. Characteristics of draft cores were found to be similar to those found over the tropical Atlantic by LeMone and Zipser.