This study investigates the contributions of incipient vortex circulation and midlevel moisture to tropical cyclone (TC) expansion within an idealized numerical modeling framework. We find that the incipient vortex circulation places the primary constraint on TC expansion. Increasing the midlevel moisture further promotes expansion but mostly expedites the intensification process. The expansion rate for initially large vortices exhibits a stronger response to increasing the midlevel moisture compared to initially small vortices. Previous studies have noted a proclivity for relatively small TCs to stay small and relatively large TCs to stay large; that is, TCs possess a sort of “memory” with respect to their incipient circulation. We reproduce this finding with an independent modeling framework and further demonstrate that an initially large vortex can expand more quickly than its relatively smaller counterpart; therefore, with all other factors contributing to expansion held constant, the contrast in size between the two vortices will increase with time. Varying the incipient vortex circulation is associated with subsequent variations in the amount and scale of outer‐core convection. As the incipient vortex circulation decreases, outer‐core convection is relatively scarce and characterized by small‐scale, isolated convective elements. On the contrary, as the incipient vortex circulation increases, outer‐core convection abounds and is characterized by relatively large rainbands and mesoscale convective systems. A combined increase in the amount and scale of outer‐core convection permits an initially large vortex to converge a substantially greater amount of absolute angular momentum compared to its relatively smaller counterpart, resulting in distinct expansion rates.

中文翻译：

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初始涡旋环流和环境湿度对热带气旋扩张的贡献

这项研究调查了理想的数值模拟框架内初始涡旋循环和中层水汽对热带气旋（TC）膨胀的贡献。我们发现，最初的涡旋环流是TC扩张的主要制约因素。增加中层水分进一步促进了膨胀，但主要是加快了强化过程。与最初的小旋涡相比，最初的大旋涡的膨胀率对增加中层水分表现出更强的响应。先前的研究表明，相对较小的TC保持较小，相对较大的TC保持较大的可能性。也就是说，TC在其初始发行方面具有某种“记忆”。我们用一个独立的建模框架重现了这一发现，并进一步证明，最初的大涡旋比其相对较小的涡旋可以更快地膨胀。因此，在所有其他有助于膨胀的因素保持不变的情况下，两个漩涡之间的大小对比将随着时间增加。初始涡旋循环的变化与外核对流的数量和规模的后续变化有关。随着初始涡旋环流的减少，外核对流相对稀少，并具有小规模，孤立的对流元素。相反，随着初期涡旋环流的增加，外核对流比比皆是，其特征是雨带和中尺度对流系统相对较大。外核对流的数量和规模的总和增加，使得初始大的涡流与其相对较小的对流相比，会聚出明显更多的绝对角动量，从而导致明显的膨胀率。