Effects of Rotation Rate and Seasonal Forcing on the ITCZ Extent in Planetary Atmospheres
Effects of Rotation Rate and Seasonal Forcing on the ITCZ Extent in Planetary Atmospheres
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DOI：
10.1175/jas-d-16-0014.1
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发表时间：
2017-02
影响因子：
3.1
通讯作者：
S. Faulk;Jonathan L. Mitchell;S. Bordoni
中科院分区：
文献类型：
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作者：
S. Faulk;Jonathan L. Mitchell;S. Bordoni
作者用一个理想化的湿环流模式研究了大范围的大气环流，以评估热带辐合带迁移的控制机制。他们采用了一个固定深度的纬向对称的水行星板状海洋，并迫使大气层顶部的日射保持固定在极点，以进行“永恒的冬至”模拟，并在一系列旋转速率下随季节变化，保持所有其他参数与地球相似。当自转速率为Ω_E/8或更慢时，纬向平均降水的瞬时最大值出现在夏季极点;然而，与Hadley环流上升分支相关的ITCZ位于约60°处。作者评估了ITCZ位置的广泛使用的预测因子在这个广泛的参数空间中的表现。标准预测的基础上不同的估计哈德利细胞的极向程度相关，但高估了离赤道ITCZ的位置。有趣的是，在地球自转速率的冬至情况下，ITCZ仍然在亚热带纬度，即使低层潮湿的静态能量在夏季极点最大化。虽然表面上与对流准平衡论点不一致，但这可能发生，因为在地球的自转速率下，对流区域的热分层只能在热带地区内传播，那里的温度梯度被限制为弱。因此，作者开发的ITCZ的位置的基础上的顶部的大气层能量和边界层动量预算的理解，并认为摩擦力和压力梯度的力量决定了最大收敛的区域，提供了一个修改后的动力学观点的季风一样的季节性天气模式的类地行星。
The authors study a wide range of atmospheric circulations with an idealized moist general circulation model to evaluate the mechanisms controlling intertropical convergence zone (ITCZ) migrations. They employ a zonally symmetric aquaplanet slab ocean of fixed depth and force top-of-atmosphere insolation to remain fixed at the pole for an “eternal solstice” simulation and also vary seasonally for a range of rotation rates, keeping all other parameters Earth-like. For rotation rates Ω_E/8 and slower, a transient maximum in zonal-mean precipitation appears at the summer pole; however, the ITCZ associated with the ascending branch of the Hadley circulation lies at ~60°. The authors assess how widely used predictors of the ITCZ position perform in this wide parameter space. Standard predictors based on different estimates of the Hadley cell’s poleward extent are correlated with but overestimate off-equatorial ITCZ locations. Interestingly, in the eternal-solstice case for Earth’s rotation rate, the ITCZ remains at subtropical latitudes even though the lower-level moist static energy maximizes at the summer pole. While seemingly at odds with convective quasi-equilibrium arguments, this can happen because at Earth’s rotation rates, the thermal stratification set in convective regions can only be communicated within the tropics, where temperature gradients are constrained to be weak. The authors therefore develop an understanding of the ITCZ’s position based on top-of-atmosphere energetics and the boundary layer momentum budget and argue that friction and pressure gradient forces determine the region of maximum convergence, offering a modified dynamical perspective on the monsoon-like seasonal weather patterns of terrestrial planets.