Surface and advective heat fluxes in the western margin of the Gulf of Tehuantepec.

Abstract

We present the annual cycles of the monthly surface and advective heat fluxes from La Boquilla and Tangolunda, two points in the western margin of the Gulf of Tehuantepec. Computations are function of averaged (2011–2013) daily seawater temperature at 5 m depth, interpolated daily SST satellite and daily meteorological data except cloud cover, estimated from ICOADS. The advective heat flux is a result of the imbalance between the net surface heat flux and the heat content rate of change in a 25 m depth water column. Most of the meteorological variables and heat fluxes, show intra-seasonal variability related to the cloud cover that accompanies the Intertropical Convergence Zone position relative to the study area. The latent heat flux, calculated using two distinct exchange coefficients, according to Bunker and to Liu, and the long wave heat flux, are about the same magnitude in each site. In all the computations, the net surface heat flux is positive throughout the year (into the ocean) and correspondingly there is an exportation of advective heat flux along the year from the water column. Large advective heat losses, in February and October, occur when measured southeastward currents are strong. Small losses occur, in May and January, when currents are weak and towards different directions. Currents arriving to the area from the west, seem correspond to mixed water from the tropical Pacific off central México in February. In October, however, similar currents seem to be part of the Costa Rica Coastal Current after leaving the Tehuantepec Bowl. The largest net surface heat flux difference between the two sites (<10 Wm-2), arises from the differences in the meteorological time series recorded at each site rather than from distinct SST and seawater temperature values, or from the two distinct exchange coefficients. In comparison to these results, the magnitude of the net surface heat flux from NCEP is smaller and negative in November, due to a smaller short wave gain but larger latent and sensible heat losses. These heat fluxes estimations are the first of their kind at the western margin of the Gulf of Tehuantepec and the southern coast of the Mexican Pacific.