Cooley Kylene M, Fewings Melanie R, Lerczak James A, O'Neill Larry W, Brown Kevin S
College of Earth, Ocean, and Atmospheric Sciences Oregon State University Corvallis OR USA.
Department of Chemical, Biological, and Environmental Engineering Oregon State University Corvallis OR USA.
J Geophys Res Oceans. 2022 Jul;127(7):e2021JC018338. doi: 10.1029/2021JC018338. Epub 2022 Jul 15.
We identified anomalously warm sea surface temperature (SST) events during 1980-2019 near the major upwelling center at Punta Lavapié in the central Chile-Peru Current System, using the European Centre for Medium-Range Weather Forecasts reanalysis and focusing on time scales of 10 days to 6 months. Extreme warm SST anomalies on these time scales mostly occurred in the austral summer, December through February, and had spatial scales of 1000s of km. By compositing over the 37 most extreme warm events, we estimated terms in a heat budget for the ocean surface mixed layer at the times of strongest warming preceding the events. The net surface heat flux anomaly is too small to explain the anomalous warming, even when allowing for uncertainty in mixed-layer depth. The composite mean anomaly of wind stress, from satellite ocean vector wind swath data, during the 37 anomalous warming periods has a spatial pattern similar to the resulting warm SST anomalies, analogous to previous studies in the California Current System. The weakened surface wind stress suggests reduced entrainment of cold water from below the mixed layer. Within 100-200 km of the coast, the typical upwelling-favorable wind stress curl decreases, suggesting reduced upwelling of cold water. In a 1000-km area of anomalous warming offshore, the typical downwelling-favorable wind stress curl also decreases, implying reduced downward Ekman pumping, which would allow mixed-layer shoaling and amplify the effect of the positive climatological summertime net surface heat flux.
我们利用欧洲中期天气预报中心的再分析数据，聚焦于10天至6个月的时间尺度，确定了1980 - 2019年期间智利-秘鲁海流系统中部蓬塔拉瓦皮耶主要上升流中心附近异常温暖的海表温度（SST）事件。这些时间尺度上的极端温暖SST异常大多发生在南半球夏季，即12月至2月，空间尺度达数千公里。通过对37次最极端的温暖事件进行合成分析，我们估算了事件发生前最强变暖时期海洋表面混合层热收支中的各项。即使考虑到混合层深度的不确定性，净表面热通量异常也太小，无法解释异常变暖现象。从卫星海洋矢量风条带数据得出的37个异常变暖时期的风应力合成平均异常，其空间模式与由此产生的温暖SST异常相似，这与之前在加利福尼亚海流系统中的研究类似。减弱的表面风应力表明从混合层下方夹带冷水的量减少。在海岸100 - 200公里范围内，典型的有利于上升流的风应力旋度减小，表明冷水上升流减少。在离岸1000公里的异常变暖区域，典型的有利于下沉流的风应力旋度也减小，这意味着埃克曼抽吸向下减弱，这将使混合层变浅，并放大正的气候学夏季净表面热通量的影响。
