Idealized Aquaplanet Simulations of Tropical Cyclone Activity: Significance of Temperature Gradients, Hadley Circulation, and Zonal Asymmetry
Idealized Aquaplanet Simulations of Tropical Cyclone Activity: Significance of Temperature Gradients, Hadley Circulation, and Zonal Asymmetry
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DOI：
10.1175/jas-d-20-0079.1
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发表时间：
2021-03
影响因子：
3.1
通讯作者：
Gan Zhang;Levi G. Silvers;Ming Zhao;T. Knutson
中科院分区：
文献类型：
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作者：
Gan Zhang;Levi G. Silvers;Ming Zhao;T. Knutson
早期的研究提出了许多气候与热带气旋活动之间的半经验关系。为了探索这些关系，本研究进行了理想化的aquaplanet实验，使用对称和不对称的海表温度（SST）强迫。对于在10°N处有最大值的纬向对称SST强迫，减小类地球参考状态附近的纬向SST梯度会导致热带辐合带减弱和向南位移。由于南半球温度梯度几乎是平的，特别是由于高纬度TC活动的增加，暖半球TC数量增加了近100倍。赤道SST梯度的降低有助于热带向极扩展，这与热带气旋形成或达到其一生最大强度的纬度向极迁移有关。然而，这些变化不能简单地归因于Hadley环流的向极扩展。引入纬向非对称SST强迫倾向于减少全球TC数量。区域SST变暖-规定或没有SST冷却在其他地区-影响当地的TC活动，但不一定增加TC的成因。虽然区域变暖通常抑制TC活动在偏远地区与相对寒冷的SST，一个实验表明，一个令人惊讶的大增加TC的成因。相对较冷的SST上TC生成的增加与局部对流层冷却有关，该冷却降低了15°N附近的静态稳定度和25°N附近的垂直风切变。模拟结果与尺度分析进行了讨论，并对“对流准平衡和弱温度梯度”框架的应用产生了影响。
Earlier studies have proposed many semiempirical relations between climate and tropical cyclone (TC) activity. To explore these relations, this study conducts idealized aquaplanet experiments using both symmetric and asymmetric sea surface temperature (SST) forcings. With zonally symmetric SST forcings that have a maximum at 10°N, reducing meridional SST gradients around an Earth-like reference state leads to a weakening and southward displacement of the intertropical convergence zone. With nearly flat meridional gradients, warm-hemisphere TC numbers increase by nearly 100 times due particularly to elevated high-latitude TC activity. Reduced meridional SST gradients contribute to a poleward expansion of the tropics, which is associated with a poleward migration of the latitudes where TCs form or reach their lifetime maximum intensity. However, these changes cannot be simply attributed to the poleward expansion of Hadley circulation. Introducing zonally asymmetric SST forcings tends to decrease the global TC number. Regional SST warming—prescribed with or without SST cooling at other longitudes—affects local TC activity but does not necessarily increase TC genesis. While regional warming generally suppresses TC activity in remote regions with relatively cold SSTs, one experiment shows a surprisingly large increase of TC genesis. This increase of TC genesis over relatively cold SSTs is related to local tropospheric cooling that reduces static stability near 15°N and vertical wind shear around 25°N. Modeling results are discussed with scaling analyses and have implications for the application of the “convective quasi-equilibrium and weak temperature gradient” framework.