凝结质量汇与热带风暴的增强
Condensation mass sink and intensification of tropical storms
AI总结：
本研究针对热带风暴增强机制的未解问题，通过观测分析与数值模拟证明凝结质量汇是调控热带风暴动力学的主导过程，其提供的正反馈可使风暴环流在增强时更紧凑，纠正了以往对质量汇作用的误读。
摘要：
以中心气压变化率衡量的热带风暴增强，代表了风暴核心区域空气流入与流出之间约为$10^{-3}$量级的细微不平衡。驱动这种不平衡的因素，尤其是在快速增强的案例中，目前仍不明确。本文通过分析北大西洋气旋的增强速率与降水情况，证明风暴平均加深速率与局地最大降水从大气柱中移除质量的速率相当。生命周期最大增强速率与最大同期降水（乘以重力加速度）的平均值分别为$23$和$17$ hPa day$^{-1}$。这种等效性并不局限于平均值：增强速率与降水对最大风速半径倒数的依赖关系完全一致。进一步通过数值模型证明，当关闭质量汇时，仅由感热和潜热驱动的风暴要么完全无法发展，要么发展速度显著减慢，达到的最大强度更低。本文讨论指出，以往研究认为质量汇相对不重要的结论，源于长期以来将质量不守恒评估误读为质量汇对风暴动力学实际影响的评估。凝结质量汇为地表气压与垂直速度之间提供了一种基本的正反馈机制，此前的研究已表明这种反馈在风暴增强的解析描述中发挥着关键作用。这种反馈使风暴环流在增强过程中变得更紧凑，这与模拟的热驱动风暴在增强时最大风速半径增大的特征形成对比。这些发现表明，凝结质量汇是调控热带风暴动力学的主导过程。
英文摘要：
Intensification of tropical storms measured as the central pressure tendency represents a subtle imbalance, of the order of $10^{-3}$, between the inflow and outflow of air in the storm core. Factors driving this imbalance, especially in cases of rapid intensification, remain elusive. Here, using an analysis of intensification rates and precipitation in North Atlantic cyclones, it is shown that the storms on average deepen at a rate with which maximum local precipitation removes mass from the atmospheric column. Means for lifetime maximum intensification rate and maximum concurrent precipitation (multiplied by the acceleration of gravity) are, respectively, $23$ and $17$ hPa day$^{-1}$. This equivalence is not limited to average values: both intensification rates and precipitation have the same dependence on the inverse radius of maximum wind. It is further shown using a numerical model that with the mass sink switched off, storms driven by sensible and latent heat alone either do not develop at all or develop significantly more slowly reaching lower maximum intensities. It is discussed that the conclusions of previous studies about the relative insignificance of the mass sink arose from a long-standing misinterpretation of mass nonconservation assessments for assesments of the actual impact of the mass sink on storm dynamics. Condensation mass sink provides for a fundamental positive feedback between surface pressure and vertical velocity that was earlier shown to be instrumental in analytical descriptions of storm intensification. This feedback allows the storm circulation to get more compact during intensification in contrast to modeled heat-driven storms that increase their radius of maximum wind as they intensify. These findings indicate that the condensation mass sink is a dominant process governing the dynamics of tropical storms.
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