Particularly cool sea surface temperatures (SSTs) were observed in 2012 along the Northern Gulf of Guinea coast. This strong cooling event was seen from February to June and reached maxima in the coastal upwelling areas: SST anomalies of −1°C were observed in Sassandra Upwelling area in Côte d'Ivoire (SUC, situated east of Cape Palmas) and SST anomalies of −0.5°C were observed in Takoradi Upwelling area in Ghana (TUG, located east of Cape Three Points). In SUC and TUG regions, the 2012 decrease in SST was the coldest event recorded over the 1990–2018 period (29 years). From the analysis of regional simulations, we show that the mechanisms behind this SST decrease differ in the two regions. In the SUC region, we identify changes in both zonal advection (related to zonal SST gradient changes) and increased vertical mixing as the main drivers of the anomalous cooling. The anomalous vertical mixing is linked to increased vertical shear of the zonal current in response to the Guinea Current strengthening. In the TUG region, acceleration of the southward advection of the surface water, due to the intensification of the meridional Ekman current generated by the strengthening of the zonal wind stress, was identified as the major cause of the SST anomalous cooling.

中文翻译：

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2012年几内亚湾北部冷事件成因

2012 年在几内亚湾北部海岸观察到特别凉爽的海面温度 (SST)。这种强烈的降温事件发生在 2 月至 6 月，并在沿海上升流区达到最大值：在科特迪瓦的 Sassandra 上升流区（SUC，位于帕尔马斯角以东）观测到 -1°C 的海温异常，以及-0.5°C 在加纳的 Takoradi Upwelling 区域（TUG，位于 Cape Three Points 以东）观测到。在 SUC 和 TUG 地区，2012 年 SST 的下降是 1990-2018 年（29 年）期间记录的最冷事件。通过对区域模拟的分析，我们表明这两个区域海温下降背后的机制不同。在 SUC 地区，我们确定纬向平流的变化（与纬向 SST 梯度变化相关）和垂直混合的增加是异常冷却的主要驱动因素。异常垂直混合与响应几内亚洋流加强的纬向洋流垂直剪切增加有关。在TUG地区，由于纬向风应力增强而产生的经向埃克曼海流加剧，地表水向南平流加速，被认为是海温异常冷却的主要原因。