Surface Fluxes Modulate the Seasonality of Zonal-Mean Storm Tracks
Surface Fluxes Modulate the Seasonality of Zonal-Mean Storm Tracks
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DOI：
10.1175/jas-d-19-0139.1
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发表时间：
2020-02-01
影响因子：
3.1
通讯作者：
Shaw, Tiffany A.
中科院分区：
文献类型：
--
作者：
Barpanda, Pragallva;Shaw, Tiffany A.
观测到的纬向平均温带风暴路径表现出明显的半球季节性。此前，湿静态能量 (MSE) 框架用于诊断性地表明短波吸收（日照）主导季节性，但地表热通量会抑制南半球 (SH) 的季节性，并在北半球 (NH) 放大季节性。在这里，我们通过改变带状对称 1）海洋能量传输为零的板片海洋水行星模拟和 2）能量平衡模型（EBM）模拟中的混合层深度 d 来确定表面通量（海洋能量储存）的因果作用。使用尺度分析，我们定义了临界混合层深度 d(c) 并假设 1) 大混合层深度 (d > d(c)) 产生与短波吸收异相的表面热通量，导致较小的风暴路径季节性；2) 小混合层深度 (d < d(c)) 产生与短波吸收同相的表面热通量，从而导致较大的风暴路径季节性。水行星模拟证实了大混合层深度假设，并产生了 SH 风暴路径的有用理想化结果。然而，小混合层深度假说未能解释费雷尔环流和大气储存的巨大贡献。小混合层限制不会产生有用的北半球风暴路径理想化，因为费雷尔环流贡献的季节性与北半球中的静止涡流贡献相反。改变 EBM 中的混合层深度定性地支持了 aquaplanet 结果。
The observed zonal-mean extratropical storm tracks exhibit distinct hemispheric seasonality. Previously, the moist static energy (MSE) framework was used diagnostically to show that shortwave absorption (insolation) dominates seasonality but surface heat fluxes damp seasonality in the Southern Hemisphere (SH) and amplify it in the Northern Hemisphere (NH). Here we establish the causal role of surface fluxes (ocean energy storage) by varying the mixed layer depth d in zonally symmetric 1) slab-ocean aquaplanet simulations with zero ocean energy transport and 2) energy balance model (EBM) simulations. Using a scaling analysis we define a critical mixed layer depth d(c) and hypothesize 1) large mixed layer depths (d > d(c)) produce surface heat fluxes that are out of phase with shortwave absorption resulting in small storm track seasonality and 2) small mixed layer depths (d < d(c)) produce surface heat fluxes that are in phase with shortwave absorption resulting in large storm track seasonality. The aquaplanet simulations confirm the large mixed layer depth hypothesis and yield a useful idealization of the SH storm track. However, the small mixed layer depth hypothesis fails to account for the large contribution of the Ferrel cell and atmospheric storage. The small mixed layer limit does not yield a useful idealization of the NH storm track because the seasonality of the Ferrel cell contribution is opposite to the stationary eddy contribution in the NH. Varying the mixed layer depth in an EBM qualitatively supports the aquaplanet results.