Abstract

In this study, the intensity change of tropical cyclone (TC) Noru (1705) is investigated by using numerical simulations. TC Noru experienced a weakening stage during the binary interaction with TC Kulap (1706). In the presence of Kulap, the model captures well the observed intensity change. On the contrary, once Kulap is removed, it fails to reproduce the weakening stage of Noru. Possible mechanisms are proposed as follows: During the mutual interaction, the competition of moisture supplies will lead to a dry air layer wrapped around Noru. Meanwhile, due to the circulation of nearby Kulap, the vertical shear is relatively larger in the adjacent of Noru. As proposed by previous studies, the negative impacts by dry air layer will be enhanced through two possible pathways. The first is that the dry air directly impacts the TC inner core convection under vertical wind shears. The second is through the downward entropy flux into boundary layer, by which reducing the boundary layer entropy and thus convection. Dynamically, along with the approach of Kulap, it will induce barotropic instability at the outer region, by which greatly enhances the inner-core asymmetry. The asymmetric component will grow at the expense of the mean flow, and thus TC intensity weakens.

中文翻译：

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二元热带气旋相互作用过程中NORU（2017）的强度变化

摘要

在这项研究中，通过使用数值模拟研究了热带气旋（TC）Noru（1705）的强度变化。在与TC Kulap（1706）进行二元互动时，TC Noru经历了一个衰弱阶段。在存在Kulap的情况下，该模型可以很好地捕获观察到的强度变化。相反，一旦除去Kulap，就无法重现Noru的弱化阶段。建议的可能机制如下：在相互影响期间，水分供应的竞争将导致围绕Noru的干燥空气层。同时，由于附近库拉普的环流，诺鲁附近的垂直切变相对较大。如先前的研究所提出的，干燥空气层的负面影响将通过两种可能的途径得到增强。首先是在垂直风切变作用下，干燥空气直接影响TC内芯对流。第二种是通过向下的熵通量进入边界层，从而降低边界层的熵从而减小对流。在动力学上，随着Kulap的接近，它将在外部区域引起正压不稳定性，从而大大增强了内核的不对称性。非对称分量将以平均流量为代价增长，因此TC强度会减弱。