The Relationship Between the Buoyancy of Near - Air and the Potential Temperature of the Tropopause.

It was hypothesized that the mixing that defines the upper limit of the troposphere is associated with severe storms. Further, that the air at, and just below, the tropopause is surface air of maximum thermodynamic energy content, drawn into the cores of severe convective cells and rising without dilution to its level of buoyant equilibrium. This thesis reports a quantitative investigation of the hypothesis. It was found that the potential temperature of tropopause air was indeed very similar to the effective potential temperature of air near the surface at the same location or somewhat upwind. The local relationship was found almost throughout the year (centered around the summer) at stations in the northern, western, tropical Pacific and during the summer in Florida and Puerto Rico. This relationship was not found at all at Hilo, Hawaii and over most of the stations on the United States Pacific Coast and over the continental United States. When a local relationship was not evident, an upwind source of near-surface air with an appropriate energy content could always be identified. Effective potential temperatures over the ocean were estimated by assuming that air at the surface was saturated at the average sea surface temperature. Isobaric streamlines for various averaging periods were used to estimate the transport of tropopause-level air. Analysis of sea surface temperatures and convective activity indicated that various southern hemisphere tropical areas were the likely source of relatively warm tropopause air observed over the northern, western, tropical Pacific and Florida/Puerto Rico during the northern hemisphere winter. Areas over the subtropical Pacific were found to be the most likely source of relatively warm tropopause air over the United States Pacific stations. The results presented here indicate that the character of lower tropospheric air plays a large role in determining the depth of the troposphere and that more research on this subject is justified. Suggestions for further research concern more in-depth studies of the surface-tropopause relationship to climate and atmospheric chemistry.