An Initiation Process of Tropical Depression-type Disturbances under the Influence of Upper-level Troughs
An Initiation Process of Tropical Depression-type Disturbances under the Influence of Upper-level Troughs
复制标题
高层低压槽影响下热带低压型扰动的启动过程
DOI：
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发表时间：
2021
影响因子：
3.1
通讯作者：
Y. Takayabu
中科院分区：
文献类型：
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作者：
Yuya Hamaguchi;Y. Takayabu
在这项研究中，研究了北太平洋西部和中部热带对流层上层槽（TUTT）与夏季热带低压型扰动（TDD）的启动之间的统计关系。通过对 34 年的亮温记录应用时空滤波器并使用 JRA-55 再分析产品，可以检测到 TDD 事件启动并将其分类为波谷相关 (TR) 或非波谷相关 (non-TR)。传统的理解是 TDD 主要起源于对流层低层；我们的结果进一步完善了这一观点，揭示了 10°N-20°N 纬度范围内大约 30% 的 TDD 是在 TUTT 的影响下产生的。 TR-TDD 和非 TR-TDD 的超前-滞后综合分析表明，TR-TDD 发生在对流层低层相对干燥且收敛程度较低的大尺度条件下。这一结果表明TR-TDD可以在相对不利的低层环境中形成。波浪活动通量的三维结构揭示了对流层上层波浪能量向南和向下传播，并在TR-TDD发生区域周围的对流层中层汇聚，表明温带强迫的存在。此外，使用准地转欧米伽方程分析了与 TUTT 相关的动态强迫对 TR-TDD 启动的作用。结果表明，对流层中高层的增湿与TUTT东南侧的持续动力上升有关，这先于深对流加热的发生。由于 TUTT 的不稳定效应导致对流可用势能较高，对流层中上层的湿润也有助于准备有利于 TDD 启动的环境。
In this study, the statistical relationship between tropical upper-tropospheric troughs (TUTTs) and the initiation of summertime tropical-depression type disturbances (TDDs) over the western and central North Pacific is investigated. By applying a spatiotemporal filter to the 34-year record of brightness temperature and using JRA-55 reanalysis products, TDD-event initiations are detected and classified as trough-related (TR) or non-trough-related (non-TR). The conventional understanding is that TDDs originate primarily in the lower-troposphere; our results refine this view by revealing that approximately 30% of TDDs in the 10°N-20°N latitude ranges are generated under the influence of TUTTs. Lead-lag composite analysis of both TR- and non-TR-TDDs clarifies that TR-TDDs occur under relatively dry and less convergent large-scale conditions in the lower-troposphere. This result suggests that TR-TDDs can form in a relatively unfavorable low-level environment. The three-dimensional structure of the wave activity flux reveals southward and downward propagation of wave energy in the upper troposphere that converges at the mid-troposphere around the region where TR-TDDs occur, suggesting the existence of extratropical forcing. Further, the role of dynamic forcing associated with the TUTT on the TR-TDD-initiation is analyzed using the quasi-geostrophic omega equation. The result reveals that moistening in the mid-to-upper troposphere takes place in association with the sustained dynamical ascent at the southeast side of the TUTT, which precedes the occurrence of deep convective heating. Along with a higher convective available potential energy due to the destabilizing effect of TUTTs, the moistening in the mid-to-upper troposphere also helps to prepare the environment favorable to TDDs initiation.