An objective Analysis of the Boundary-Layer Thermodynamic Structure During GATE. Part II: Analysis

Abstract

Profiles of potential temperature, specific humidity and moist static energy are analyzed using the objective classification method described in Part I (Jalickee and Ropelewski, 1979). These profiles, extending from the surface to 890 mb, were derived from structure sonde data taken by the Fay and the Meteor during Phase III (30 August?18 September 1974) of GATE. The technique permits an objective separation of the data into groups and subgroups based on profile shapes. The initial classification, based on the shapes of the potential temperature profiles, yields two broad categories, i.e., those corresponding to undisturbed and disturbed boundary layers. While the potential temperature profiles in these groups are relatively homogeneous, that is, they resemble each other, the specific humidity and moist static energy profiles show large shape variations in each category. To form more homogeneous groups, the data within each of the broad classes are further subclassified using moist static energy as a discriminator in the objective analysis. This analysis yields two, clearly defined, moist static energy profile types. The first, a subclass of the undisturbed group, comprises 25% of the soundings and contains profiles which exhibit clearly defined mixed, transition and cloud layers. The mean mixed-layer top for these profiles was close to 960 mb with a mean transition-layer thickness of near 35 mb. The second type, while a subclass of the disturbed group, contains profiles that are not associated with organized convective precipitation at the time of the sounding. In these profiles 27% of the total, moist static energy decreased rapidly with height in the lowest 20?30 mb, i.e., to ?980 mb, and then became constant for the remainder of the profile. Profiles in this subclass may result from mass and energy transfers usually associated with organized deep convection.