Surface Meteorology and Air–Sea Fluxes in the Southwestern Tropical Atlantic Ocean

Abstract

<p> Recent studies suggest that the Tropical Atlantic Warm Pool (PQAT) contributes to modulate the variability of the ZCIT in the Atlantic Ocean basin and, consequently, the precipitation regime in Brazilian northeastern. Hourly surface meteorology observations from the PIRATA buoy at 19°S, 34°W from August 2010 to November 2018 was used to characterize and estimate the exchanges of heat, freshwater, and momentum between the ocean and the atmosphere over the Tropical. We focus here on recent efforts to observe the surface meteorology and air-sea fluxes using those data to gain insights into how atmospheric variability may govern the structure and variability of the upper ocean there at diurnal and seasonal time scales. The surface fluxes are calculated using the COARE 3.0 algorithm, positive values are to the ocean. Using the observations collected from the mooring deployments, we developed a good understanding of the annual march of the surface forcing of the ocean by the atmosphere. During spring (March, April) mean SST and air temperature are the hottest of the year, 28<sup>o</sup>C and 26.7<sup>o</sup>C, respectively; SST is greater than air temperature all over the year, 1<sup>o</sup>C on average. Wind speed is minimum, the air is drier and there is a peak of precipitation in April. During the autumn (August, September), mean SST and air temperature are the coldest of the year, 24.5<sup>o</sup>C and 23.6<sup>o</sup>C. Wind speed increases form 4.4m/s in March to 5.9 m/s in December. The monthly averaged incoming shortwave radiation in July was the lowest of the whole year and maximum in December. Net longwave radiation shows an inverse variability, i.e., maximum in the winter, minimum in the summer. This occurs because the winter air is drier than in the summer. Sensible heat flux is maximum in August due to the increase of the wind speed and an increase of the air-sea temperature difference. Latent flux is higher between April and August due to an increase in wind speed and a drier atmosphere. In the summer the humidity increases and, consequently, the latent heat flux diminishes. Finally, the net heat flux, positive between January and March, is negative between April and August (maximum -36W/m<sup>2</sup> in July ) and, again, positive between September and December, maximum +116 W/m<sup>2</sup> in December.</p>