On meridional circulation and heat budget of the troposphere over the Equatorial Central Pacific

Abstract

The existence of an equatorial dry zone in the Central Pacific enclosed between moister belts in both hemispheres is borne out by rainfall measurements and daily ESSA III and ESSA V cloud mosaics. The tropospheric wind regime is studied mainly on the basis of aerological soundings during the Line Islands Experiment (LIE) in spring 1967 and observations of earlier periods. During LIE, upper-tropospheric Westerlies extend continuously across the equator. In the lower layers, Easterlies dominate in the equatorial belt. The meridional wind component in the region of the Line Islands is from the South in the lower layers, and from the North in the upper troposphere.

From the vertical profiles of heat content and the distribution of diabatic heat sources and sinks during LIE, vertical profiles of divergence are derived, with the constraint that both the atmospheric heat and moisture budgets are satisfied. Lower-layer convergence and upper-tropospheric divergence result for the rain belt (Palmyra), with the opposite pattern prevailing in the equatorial dry zone (Christmas). Circulation in a mean meridional-vertical plane, derived from these profiles under certain assumptions is characterized by poleward flow in the lower layers, ascending motion in the rain belt, equatorward flow in the upper troposphere, and subsidence in the equatorial dry zone.

The ocean-troposphere system gains heat by radiation in both the rain belt and the equatorial dry zone. In the rain belt, export of potential energy and sensible heat exceeds the lower-layer import of latent heat; both troposphere and ocean in this region act as exporters of heat to other parts of the globe. In the equatorial dry zone, import of potential energy and sensible heat exceeds the export of latent heat, resulting in a net import of heat for the tropospheric column as a whole. Heat surplus from this region is disposed of only by the ocean.