A model study of the role of Convection in Westerly Wind Burst Dynamics
A model study of the role of Convection in Westerly Wind Burst Dynamics
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DOI：
10.1175/jcli-d-20-0723.1
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发表时间：
2021-06
影响因子：
4.9
通讯作者：
M. Fu;E. Tziperman
中科院分区：
文献类型：
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作者：
M. Fu;E. Tziperman
西风暴发(WWB)是一种在ENSO动力学中起重要作用的异常地面风暴。以前的研究已经确定了几种可能参与WWB动态的机制。特别是，许多人研究了大气深对流对WWB的重要性，包括热带气旋、赤道波和马登-朱利安涛动引起的对流。尽管如此，WWB的机制还没有完全被理解。在这项研究中，我们研究了导致WWB的大气对流的位置以及与地表蒸发有关的正反馈的作用。我们发现，在WWB达到峰值前几天禁用地表通量反馈并不会削弱这一事件，并反对局部地表通量反馈在个别事件上充当WWB增长机制。另一方面，通过抑制潜热释放或消除地表蒸发来直接抑制对流会迅速削弱WWB。通过选择性地抑制赤道附近或远离赤道的对流，我们发现与赤道外气旋涡旋相关的对流对赤道WWB风最重要，而赤道上对流不重要。尽管WWB的风型与赤道加热对赤道加热的响应非常相似，但我们的发现表明，赤道对流对WWB的发展并不是必需的。我们的结论与热带气旋的观点是一致的，热带气旋通常发生在距离赤道5°以上的地方，可能是造成WWB的主要原因。
Westerly wind bursts (WWBs) are anomalous surface wind gusts that play an important role in ENSO dynamics. Previous studies have identified several mechanisms that may be involved in the dynamics of WWBs. In particular, many have examined the importance of atmospheric deep convection to WWBs, including convection due to tropical cyclones, equatorial waves, and the Madden Julian Oscillation. Still, the WWB mechanism is not yet fully understood. In this study, we investigate the location of atmospheric convection which leads to WWBs and the role of positive feedbacks involving surface evaporation. We find that disabling surface flux feedbacks a few days before a WWB peaks does not weaken the event, arguing against local surface flux feedbacks serving as a WWB growth mechanism on individual events. On the other hand, directly suppressing convection by inhibiting latent heat release or eliminating surface evaporation rapidly weakens a WWB. By selectively suppressing convection near or further away from the equator, we find that convection related to off-equatorial cyclonic vortices is most important to equatorial WWB winds, while on-equator convection is unimportant. Despite strong resemblance of WWB wind patterns to the Gill response to equatorial heating, our findings indicate that equatorial convection is not necessary for WWBs to develop. Our conclusions are consistent with the idea that tropical cyclones, generally occurring more than 5° away from the equator, may be responsible for the majority of WWBs.