Northwest Indian Ocean’s Spring Cooling

Kern E Kenyon

doi:10.4236/ns.2014.610076

Abstract

A major cooling down of the northwestern Indian Ocean’s surface, including the Arabian Sea, starts in May, according to a well-known world atlas of SSTs. This is before the southwest monsoon which usually begins in June. Also within one year, there are two surface temperature maxima and two minima, which is not typical for the northern hemisphere. A surface current, cooler than the surrounding water, crosses the equator in April and May heading north and east on the western side of the ocean. That proposal is consistent with the given SST information. The warmer surrounding water is then moved to east and south as a consequence. Since wind driving is not available for initiation, the relatively cool northeastward current is thought to be caused by a thermohaline force related to the unstable northward temperature gradient in the west, which is of constant sign right across the equator beginning in May: cool in the south monotonically increasing to warm in the north.

Highlights

A classical atlas of sea surface temperatures of the world [1] contains an amazing piece of information about the Indian Ocean: maximum surface temperatures of the year, in the western and northern open ocean waters, occur in April and May! How can that be? How can the sea surface begin cooling off in the northern hemisphere spring? April and May are before the southwest monsoon which usually begins in June [2] [3], which is known to carry some heat away from the sea
In the thirty year average of the sea surface temperatures of the North Pacific the highest values occur in August and September over large areas of the middle of the ocean above 20 N, and there is even
The significant time delay of August and September from June 21 has been explained by the seasonal variation, mainly in position, of a very wide warm and sluggish surface current permanently flowing northeast off California [5]

Summary

Introduction

April and May are before the southwest monsoon which usually begins in June [2] [3], which is known to carry some heat away from the sea These maximum temperatures occur before June 21, when the greatest amount of excess solar radiation, per horizontal area and per unit time, is being absorbed in the top 100 m of the northern equatorial waters, i.e. when the sun is farthest north. May and June pages from the well-known world SST atlas (Figure 3 and Figure 4) are used to interpret the cooling in terms of a newly proposed northeast surface current in the west that crosses the equator beginning in May. Since the southwest monsoon cannot be the initial cause of the northeast current, because it starts too late (in June), a thermal driving force within the surface layer, related to the positive northward surface temperature gradient, is conjectured to be responsible

Temperature Features

Interpretation

Conclusion