What Drives the North Atlantic Oscillation’s Temperature Anomaly Pattern? Part II: A Decomposition of the Surface Downward Longwave Radiation Anomalies
What Drives the North Atlantic Oscillation’s Temperature Anomaly Pattern? Part II: A Decomposition of the Surface Downward Longwave Radiation Anomalies
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DOI：
10.1175/jas-d-19-0028.1
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发表时间：
2019-12
影响因子：
3.1
通讯作者：
J. P. Clark;S. Feldstein
中科院分区：
文献类型：
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作者：
J. P. Clark;S. Feldstein
通过辐射传输计算，确定了温度和水汽异常对NAO地面晴空下行长波辐射(DLR)异常的贡献。这些计算的动机是发现，NAO的皮肤温度异常主要是由地表DLR的变化驱动的。晴空辐射传输计算的结果表明，晴空DLR异常可以解释大部分NAO的全天DLR异常。辐射传输计算的结果促使分析热力学能量和总柱水(TCW)收支方程，因为水汽和温度异常是NAO地面DLR异常的同等重要的驱动因素。对热力学能量方程的综合分析表明，北大西洋涛动的温度异常是由风驱动的：除对流层上部-平流层下部以气候风平流为主导外，气候风平流对北大西洋涛动各层温度异常均有驱动作用。对TCW预算的类似分析表明，TCW的变化是由水通量汇聚驱动的。除了确定温度和TCW异常的驱动因素外，热力学能量和水收支分析还表明，温度异常的衰减主要通过垂直混合发生，而水异常的衰减主要通过蒸发减去降水来实现。
Radiative transfer calculations are conducted to determine the contribution of temperature and water vapor anomalies toward the surface clear-sky downward longwave radiation (DLR) anomalies of the NAO. These calculations are motivated by the finding that the NAO’s skin temperature anomalies are driven primarily by changes in surface DLR. The clear-sky radiative transfer calculations follow the result that the clear-sky surface DLR anomalies can account for most of the all-sky surface DLR anomalies of the NAO. The results of the radiative transfer calculations prompt an analysis of the thermodynamic energy and total column water (TCW) budget equations, as water vapor and temperature anomalies are found to be equally important drivers of the surface DLR anomalies of the NAO. Composite analysis of the thermodynamic energy equation reveals that the temperature anomalies of the NAO are wind driven: the advection of climatological temperature by the anomalous wind drives the NAO’s temperature anomalies at all levels except for those in the upper troposphere–lower stratosphere where the advection of anomalous temperature by the climatological wind becomes dominant. A similar analysis of the TCW budget reveals that changes in TCW are driven by water flux convergence. In addition to determining the drivers of the temperature and TCW anomalies, the thermodynamic energy and water budget analyses reveal that the decay of the temperature anomalies occurs primarily through vertical mixing, and that of the water anomalies mostly by evaporation minus precipitation.