Response of sea-surface temperature to atmospheric forcing processes

Abstract

The present investigation is devoted entirely to an analysis of the response of the sea -surface temperature to atmospheric forcing processes over various time and space scales. After an introductory chapter where the author has endeavoured to outline what he considers to be some of the more physical concepts involved, the simple but effective technique of 'superposed epochs' is used in an attempt to study the short -period variation of sea -surface temperature at Ocean Weather Stations 'M' and 'I' as a function of various meteorological parameters. Periods of enhanced turbulence associated with windy conditions are observed to produce a significant lowering of the sea -surface temperature when subsurface thermal stratification prevails (summer season), at both stations. Sudden increases or decreases of the sea- surface temperature at station 'I' are observed to accompany changes in the wind direction, more especially during the winter season. Failure of the sea -surface temperature at Ocean Weather Station 'I' to respond to periods of greatly increased evaporative and sensible heat cooling is attributed to a near -compensating effect of warmer water advection.A simple algebraic method is developed in chapter 3 with the intention of relating both the magnitude and direction of induced drift currents to the corresponding geostrophic wind vector, during periods of assumed predominantly advective sea -surface temperature change; the poor quality of the sea -surface temperature data used is invoked as being largely responsible for the relative lack of success of the method in the periods studied.Finally, following formulation in chapter 4, and description of acquiring model input data in the first part of chapter 5, an amended depth- integrated enthalpy continuity equation is used with input data from three case studies of dissimilar meteorological forcing, to provide values for the month -tomonth change of mean monthly anomalous sea -surface temperature, evaluation of the model being effected through comparison of predicted anomaly changes with those observed. The individual contributions of anomalous surface cooling and anomalous advection to sea temperature anomaly change give agreement of varying closeness but on all occasions the best results are achieved from a comination of these two processes; inclusion of a horizontal eddy conductivity term produces deteriorations over 'heat and advection'- predicted values in all case studies. In regions of significant anomalous wind stress curl, neither sea temperature anomaly changes produced in part by advection due to alternative meridional Sverdrup -type flow, nor changes otherwise consequent to vertical motion (and associated effects, as mentioned in the introduction), necessarily induced as a baroclinic compensation in the absence of Sverdrup type transport, are observed to be consistent with actual changes.