ANALYSIS AIDS FOR THE AMERICAN TROPICS

Abstract

Analysis of upper-level charts for the American Tropics, which is a largely oceanic area, is difficult because data are inadequate and are likely to remain so in the foreseeable future. Despite this handicap and the unsatisfactory character of the map, the 500-mb. analyses are routinely used for many different tropical forecasting procedures. Some aids are suggested for improving the analyses that are made to meet this continuing requirement. Since the lower troposphere is somewhat barotropic, pressure-height changes at 700 mb. and 500 mb. are largely a function of sea level pressure change so that a careful surface analysis along with a good differential analysis can yield great improvement in upper-air analysis compared to a straightforward analysis of upper-air data. Maps of normal thicknesses, 1000?700 mb., 700?500 mb., and 1000?500 mb., based on all constant pressure data from the American Tropics are presented for the hurricane season. Statistics relative to these fields of thickness such as 24-hour changes, correlation between the upper and lower strata, and typical anomaly patterns, are included and discussed. In addition, several indicators of anomaly which are useful in higher latitudes were investigated and found to be of limited value in this area. Finally it is concluded that tropical maps must be re-analyzed as late data become available and that analyses must be made under the control of thermal and time-continuity restraints discussed here.