Can Shipboard Measurements Reveal Secular Changes in Tropical Air–Sea Heat Flux?

Abstract

A new Comprehensive Ocean-Atmosphere Data Set for the period 1854–1979 will soon become available for studies of secular climate changes in ocean surface heat flux. Of the observed variables from which heat flux is calculated, wind speed and sea surface temperature have undergone indeterminate spurious changes due to modifications in estimating and measuring. Analysis of a summertime ocean data set for the Philippine Sea revealed unacceptably large increases in air temperature and dew point readings resulting from daytime heating of the ship. Differences between ocean skin temperatures and subsurface temperatures lead to positive heat flux errors with light winds. Computing heat fluxes for individual ship reports and then averaging them improves matters. These errors, as well as those arising from spatial and temporal inhomogeneities of individual monthly averages, require that studies of ocean climate change first be confined to the most heavily traveled ship routes. Criteria of consistency, pattern persistence and physical reasonableness would need to be satisfied before one could accept evidence of secular changes in surface heat flux.