Seasonal and regional variability of upper ocean diapycnal heat flux in the Atlantic cold tongue
Seasonal and regional variability of upper ocean diapycnal heat flux in the Atlantic cold tongue
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大西洋冷舌上层海洋二重热通量的季节和区域变化
DOI：
10.1016/j.pocean.2012.11.001
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发表时间：
2013
影响因子：
4.1
通讯作者：
B. Bourlés
中科院分区：
文献类型：
--
作者：
Hummels;M. Dengler;B. Bourlés
大西洋冷舌（ACT）区域内的SST变率与周围大陆的气候相关。微结构观测的多航次数据集用于推断ACT地区上层海洋混合和底辟热通量的区域和季节变化。混合强度的变异性与航行期间另外观察到的大尺度背景条件的变异性有关。观测结果表明，在剪切和分层的混合层（ML）的西部和东部赤道ACT地区造成临界弗劳德数（Fr）更频繁地观察到在西赤道ACT的背景条件的根本差异。临界Fr出现在ML以下的分布反映了混合强度的区域性和季节性变化。赤道（2°N-2°S）上温跃层的湍流耗散率（ε）比赤道外的位置大大增加。此外，在赤道ACT西部，从5月到11月，相对于东部而言，赤道ACT的温度升高，而北半球夏季则是整个赤道ACT地区混合强度最高的季节，与ACT的发展相吻合。从ε和层结推断，西赤道ACT地区ML底部的经向热通量范围从北方夏季的90 Wm − 2到9月的55 Wm − 2和11月的40 Wm − 2。在东赤道ACT地区，最大值约为25 Wm − 2，在北半球夏季估计，到年底时降至约5 Wm − 2。在赤道区域以外，推断的经向热通量很低，很少超过10 Wm −2。在赤道10°W处的ML热收支中积分所获得的热通量估计值，强调了在北半球夏季和初秋期间，横辐热通量是最大的ML冷却项。在西赤道ACT升高的纬向速度切变在上层温跃层有助于加强在这一地区在北方的夏季和秋季的diapycnal热通量。升高的纬向速度切变似乎与季节内波活动有关。
SST variability within the Atlantic cold tongue (ACT) region is of climatic relevance for the surrounding continents. A multi cruise data set of microstructure observations is used to infer regional as well as seasonal variability of upper ocean mixing and diapycnal heat flux within the ACT region. The variability in mixing intensity is related to the variability in large scale background conditions, which were additionally observed during the cruises. The observations indicate fundamental differences in background conditions in terms of shear and stratification below the mixed layer (ML) for the western and eastern equatorial ACT region causing critical Froude numbers (Fr) to be more frequently observed in the western equatorial ACT. The distribution of critical Fr occurrence below the ML reflects the regional and seasonal variability of mixing intensity. Turbulent dissipation rates (ɛ) at the equator (2°N–2°S) are strongly increased in the upper thermocline compared to off-equatorial locations. In addition, ɛ is elevated in the western equatorial ACT compared to the east from May to November, whereas boreal summer appears as the season of highest mixing intensities throughout the equatorial ACT region, coinciding with ACT development. Diapycnal heat fluxes at the base of the ML in the western equatorial ACT region inferred from ε and stratification range from a maximum of 90Wm−2in boreal summer to 55Wm−2in September and 40Wm−2in November. In the eastern equatorial ACT region maximum values of about 25Wm−2were estimated during boreal summer reducing to about 5Wm−2towards the end of the year. Outside the equatorial region, inferred diapycnal heat fluxes are comparably low and rarely exceeding 10Wm−2. Integrating the obtained heat flux estimates in the ML heat budget at 10°W on the equator accentuates the diapycnal heat flux as the largest ML cooling term during boreal summer and early autumn. In the western equatorial ACT elevated meridional velocity shear in the upper thermocline contributes to the enhanced diapycnal heat flux within this region during boreal summer and autumn. The elevated meridional velocity shear appears to be associated with intra-seasonal wave activity.
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