Thermodynamic Characteristics of Downdrafts in Tropical Cyclones as Seen in Idealized Simulations of Different Intensities
Thermodynamic Characteristics of Downdrafts in Tropical Cyclones as Seen in Idealized Simulations of Different Intensities
复制标题
不同强度理想化模拟中热带气旋下沉气流的热力学特征
DOI：
10.1175/jas-d-21-0006.1
复制
发表时间：
2021
影响因子：
3.1
通讯作者：
Shay, Lynn K.
中科院分区：
文献类型：
--
作者：
Wadler, Joshua B.;Nolan, David S.;Zhang, Jun A.;Shay, Lynn K.
在 3 类和 5 类热带气旋 (TC)（Ideal3 和 Ideal5）的理想化模拟中探讨了下降气流对边界层和附近上升气流的热力学效应。在 Ideal5 中，由于 2 公里高度以下的眼墙混合，眼墙下方的下降气流不会造成负面热力学影响。此外，高度在 1 至 2 公里之间的较高 θe 层与低层外流相关，从眼壁区域向外延伸 40 公里，形成了一个“热力学屏障”，可防止下降气流的负面影响。在 Ideal3 中，来自眼壁正下方的下降气流的地块轨迹显示，低 θe 空气最初径向向内移动，允许眼内进行一些恢复，但仍然进入平均 θ 不足 5.2 K 的眼壁上升气流。源自低空下降气流的地块通常会在 400 m 以下停留一个多小时，并将其 θe 增加 10-14 K，这表明空气-海洋焓通量会产生足够的能量恢复。热力学上最不利的下降气流发生在上升气流径向向外约 5 公里处，并将低θ中对流层空气输送至流入层。这里，低θe空气在不到5分钟的时间内夹带进入上升气流，平均θ缺失为8.2 K。一般来说，θe恢复是最小地块高度的函数，因此具有最大负面影响的下降气流是那些夹带到流入层顶部的下降气流。由于模拟的热带气旋都暴露在环境垂直风切变下，这项研究强调在讨论热带气旋强度演化范式时必须考虑风暴结构和个体下沉气流特征。
The thermodynamic effect of downdrafts on the boundary layer and nearby updrafts are explored in idealized simulations of category-3 and category-5 tropical cyclones (TCs) (Ideal3 and Ideal5). In Ideal5, downdrafts underneath the eyewall pose no negative thermodynamic influence because of eye–eyewall mixing below 2-km altitude. Additionally, a layer of higherθebetween 1- and 2-km altitude associated with low-level outflow that extends 40 km outward from the eyewall region creates a “thermodynamic shield” that prevents negative effects from downdrafts. In Ideal3, parcel trajectories from downdrafts directly underneath the eyewall reveal that low-θeair initially moves radially inward allowing for some recovery in the eye, but still enters eyewall updrafts with a meanθedeficit of 5.2 K. Parcels originating in low-level downdrafts often stay below 400 m for over an hour and increase theirθeby 10–14 K, showing that air–sea enthalpy fluxes cause sufficient energetic recovery. The most thermodynamically unfavorable downdrafts occur ~5 km radially outward from an updraft and transport low-θemidtropospheric air toward the inflow layer. Here, the low-θeair entrains into the updraft in less than 5 min with a meanθedeficit of 8.2 K. In general,θerecovery is a function of minimum parcel altitude such that downdrafts with the most negative influence are those entrained into the top of the inflow layer. With both simulated TCs exposed to environmental vertical wind shear, this study underscores that storm structure and individual downdraft characteristics must be considered when discussing paradigms for TC intensity evolution.