Abstract
Abstract. The impact of boreal spring intraseasonal wind bursts on sea surface temperature variability in the eastern tropical Atlantic Ocean in 2005 and 2006 is investigated using numerical simulation and observations. We especially focus on the coastal region east of 5° E and between the Equator and 7° S that has not been studied in detail so far. For both years, the southerly wind anomalies induced cooling episodes through (i) upwelling processes, (ii) vertical mixing due to the vertical shear of the current, and for some particular events (iii) a decrease in incoming surface shortwave radiation. The strength of the cooling episodes was modulated by subsurface conditions affected by the arrival of Kelvin waves from the west influencing the depth of the thermocline. Once impinging the eastern boundary, the Kelvin waves excited westward-propagating Rossby waves, which combined with the effect of enhanced westward surface currents contributed to the westward extension of the cold water. A particularly strong wind event occurred in mid-May 2005 and caused an anomalous strong cooling off Cape Lopez and in the whole eastern tropical Atlantic Ocean. From the analysis of oceanic and atmospheric conditions during this particular event, it appears that anomalously strong boreal spring wind strengthening associated with anomalously strong Hadley cell activity prematurely triggered the onset of coastal rainfall in the northern Gulf of Guinea, making it the earliest over the 1998–2008 period. No similar atmospheric conditions were observed in May over the 1998–2008 period. It is also found that the anomalous oceanic and atmospheric conditions associated with the event exerted a strong influence on rainfall off northeast Brazil. This study highlights the different processes through which the wind power from the South Atlantic is brought to the ocean in the Gulf of Guinea and emphasizes the need to further document and monitor the South Atlantic region.
Highlights
The eastern equatorial Atlantic Ocean shows a pronounced seasonal cycle in sea surface temperature (SST) (Wauthy, 1983; Mitchell and Wallace, 1992)
We first focus our study in the Cape Lopez region (CLR), east of 5◦ E and between the Equator and 7◦ S, where the seasonal and interannual SST variability is poorly documented
The boreal spring season is characterized by maximum winds amplitudes, the influence of which is made more effective by a shallow thermocline depth, itself strongly influenced by remote forcing
Summary
The eastern equatorial Atlantic Ocean shows a pronounced seasonal cycle in sea surface temperature (SST) (Wauthy, 1983; Mitchell and Wallace, 1992). We first focus our analysis on offshore Cape Lopez (defined as 0◦ N–7◦ S, 5◦ E–14◦ E and hereafter called the CLR for “Cape Lopez region”; see Fig. 2) and aim to improve understanding of its seasonal SST variability and the impact of intraseasonal winds on SST variability during boreal spring and summer. To this end, we use regional high-resolution model results as well as satellite SST data and sea surface height observations.
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