Abstract Observational studies and cloud resolving numerical simulations have shown that developing tropical cyclones often have markedly asymmetric distributions of moist convection. The present study uses a shallow-water model on the f-plane to gain further insight into the variety of vortex intensification pathways that may exist under such conditions. The diabatic forcing associated with asymmetric convection is represented by a localized mass sink displaced from the initial center of rotation. The pathway of vortex intensification is found to depend on whether the velocity-convergence generated by the mass sink exceeds a critical value s c , and thereby prevents the escape of fluid that flows into the mass sink. The critical value is approximately given by s c = 2 V l / ρ s , in which ρ s is the radial size of the mass sink, and V l is the magnitude of the local vector-difference between the broader cyclonic velocity field and the drift velocity of the mass sink. If the convergence is supercritical so as to exceed s c , the core of the vortex reforms in the vicinity of the mass sink and rapidly intensifies. Two other modes of intensification are found in subcritical systems. One common mode occurs at a moderate pace and entails a gradual drift of the vortex center toward the mass sink, coinciding with significant contraction of the radius of maximum azimuthal velocity. A slower mode can occur when a subcritical mass sink has substantial azimuthal drift. The slower mode resembles that expected for a symmetric system in which the mass sink is uniformly spread over its orbital annulus, whose radius from the vortex center is roughly constant over time. If the mass sink pulsates so as to periodically generate modestly supercritical values of convergence, a transition may occur from a subcritical mode of intensification to a supercritical mode as the pulsation period increases beyond a certain threshold. In a distinct set of simulations where the mass sink drifts radially outward from the initial vortex center with velocity r ˙ s , supercritical convergence determined with V l = r ˙ s in the formula for s c is generally necessary for major vortex intensification.

中文翻译：

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受非对称“非绝热”强迫作用的浅水涡旋的不同强化途径

摘要 观测研究和云解析数值模拟表明，发展中的热带气旋通常具有明显的湿对流分布不对称。本研究使用 f 平面上的浅水模型来进一步了解在这种条件下可能存在的各种涡流增强途径。与不对称对流相关的非绝热强迫由从初始旋转中心位移的局部质量汇表示。发现涡流增强的路径取决于质量汇产生的速度收敛是否超过临界值 sc ，从而防止流入质量汇的流体逸出。临界值近似由 sc = 2 V l / ρ s 给出，其中 ρ s 是质量汇的径向尺寸，V l 是较宽的气旋速度场与质量汇的漂移速度之间的局部矢量差的大小。如果收敛是超临界的以超过 sc ，涡旋的核心在质量汇附近重新形成并迅速增强。在亚临界系统中发现了另外两种强化模式。一种共模以适中的速度发生，并且需要涡中心向质量汇逐渐漂移，同时与最大方位角速度半径的显着收缩相吻合。当亚临界质量汇有明显的方位角漂移时，可能会出现较慢的模式。较慢的模式类似于对称系统的预期模式，其中质量汇均匀分布在其轨道环上，其距涡旋中心的半径随时间大致恒定。如果质量汇脉动从而周期性地产生适度的超临界收敛值，则随着脉动周期增加超过某个阈值，可能会发生从亚临界强化模式到超临界模式的转变。在一组不同的模拟中，质量汇从初始涡中心以速度 r ˙ s 径向向外漂移，在 sc 的公式中用 V l = r ˙ s 确定的超临界收敛通常是主要涡增强所必需的。