Sensible and latent heat exchange in low latitude synoptic scale systems

Abstract

The transfer equations are applied to a set of forty-six days of data collected from an oceanographic research vessel on a station in the low latitude western Atlantic. In this region the lapse rate and shear in the boundary layer of the atmosphere is such that the transfer equations may be applied with a reasonable degree of confidence. In particular, the most accurate results are likely when large transfers occur, the least accurate when small transfers occur. Under these conditions a linear dependence of the eddy exchange coefficient with wind speed and stability were used to compute latent and sensible heat transfer from time averages over one hour of specific humidity, temperature and wind speed at 6 m and at the sea surface. Sea surface temperatures were measured at 10 cm and compared with infrared radiometer measurements.

Individual synoptic scale systems that moved over or close to the point of observation were examined. Over limited regions of these disturbances latent and sensible heat transfers were found to increase by an order of magnitude. Integrated over the whole disturbance the energy flux is found to be double the undisturbed values. By using both streamline analysis and a rainfall amount and occurrence technique, the frequency and size of synoptic systems are determined. This makes possible the construction of summer, winter and annual maps of latent and sensible heat transfer for the tropical Atlantic. Significant differences are found when they are compared with results of earlier workers. The role of synoptic scale disturbances in the atmospheric energy balance is emphasized by these results.