Variabilidade do balanço de calor na camada de mistura do Oceano Atlântico Equatorial utilizando dados in situ do ePIRATA

Abstract

In this study we analyze the variability of heat balance terms within the mixed layer using buoy data from ePIRATA, a project that consists of an enhanced daily data set developed to fill temporal gaps in PIRATA buoy data. The buoys used in this study are located in the Equatorial Atlantic Ocean, at 0N0E, 0N10W, 0N23W and 0N35W. This region is very dynamic, characterized by warming and cooling events and has been suffering anomalous warming in recent years. The Mixed Layer is shallower in the eastern part than in the western part of the basin with maximum values in the second half of the year for all buoys. The monthly climatology of all buoys shows that the heat balance at the ocean-atmosphere interface is positive, indicating that the ocean is gaining heat through the surface, with the 0N10W buoy receiving the most heat. The climatology of the heat term stored in the mixed layer indicates that in April, May and June there is cooling of the mixed layer for all buoys. In the case of buoy 0N10W, located within the equatorial upwelling region, we see that the maximum depth of the mixed layer is ~30m in October, the average heat storage is below -50W/m2 (this negative value is associated with refrigeration seasonal in the equatorial upwelling region) in June, the average Advection (transport of a property by currents) and the Residual term (the combination of errors from the other three terms, turbulent mixing processes as well as horizontal diffusion) are ~-50 and ~140W/m2, respectively, in June. For the analysis of atypical events, we focused our attention on the 0N10W buoy (in the center east) as this is a region where equatorial upwelling is more intense. Years with warm events (2019 and 2021 Niño) and cold events (2001 and 2005 Niña) in the equatorial Atlantic were analyzed. The results indicate that the cold events of 2001 and 2005 did not result from greater heat loss from the ocean to the atmosphere. Similarly, when we focus on the hot events of 2019 and 2021, we can see that the heat gain did not come from the atmosphere at buoy 0N10W. This suggests that other factors would be responsible for these anomalous heating and cooling events. Therefore, both the advective term and the residue proved to be important in the heat gains and losses in the mixed layer during the anomalous events at 0N10W.