Large-Scale Conditions for Reintensification after the Extratropical Transition of Tropical Cyclones in the Western North Pacific Ocean
Large-Scale Conditions for Reintensification after the Extratropical Transition of Tropical Cyclones in the Western North Pacific Ocean
复制标题
北太平洋西部热带气旋温带转变后大范围再强化条件
DOI：
10.1175/jcli-d-20-0013.1
复制
发表时间：
2020
影响因子：
4.9
通讯作者：
Takamura Nao
中科院分区：
文献类型：
--
作者：
Yanase Wataru;Shimada Udai;Takamura Nao
对北太平洋西部完成温带转变（ETTC）的热带气旋进行统计分析，以阐明其重新强化的大范围条件。根据日本气象厅 1979 年至 2018 年期间记录的最佳轨迹数据，ETTC 数据集分为增强型、耗散型和中性型。增强型 ETTC 在 9 月至 10 月最常见，而消散型 ETTC 在晚季（10 月至 11 月）最常见。增强型 ETTC 发生在比耗散型 ETTC 更高的纬度，其上层的特征是高位涡 (PV) 和陡峭的 PV 水平梯度。综合分析表明，增强的ETTC与其西北部的深高层槽、东北部强烈的脊建设以及与涡度平流和暖空气平流相关的北部强烈上升气流有关。这些结果在统计上支持了先前研究的结果。此外，使用时间过滤器的分析证明了行星尺度环境与上层天气尺度动态之间的关系。 ETTC西北部的高PV不仅归因于东移的低压槽，还归因于环境PV。 ETTC 东北部的低光伏发电是由于与山脊建设相关的负光伏发电造成的，这几乎抵消了环境光伏发电。因此，相对高纬度的环境光伏增强了ETTC西北部的正光伏强度，并提高了东北部建脊幅度的上限。
Tropical cyclones that complete extratropical transition (ETTCs) in the western North Pacific are statistically analyzed to clarify the large-scale conditions for their reintensification. A dataset of ETTCs is grouped into intensifying, dissipating, and neutral classes based on the best track data documented by the Japan Meteorological Agency during the period 1979–2018. Intensifying ETTCs are most frequent in September–October, whereas dissipating ETTCs are most frequent in the later season, October–November. Intensifying ETTCs occur at higher latitudes than dissipating ETTCs, where the upper levels are characterized by high potential vorticity (PV) and a steep horizontal gradient of PV. The composite analysis demonstrates that intensifying ETTCs are associated with deep upper-level troughs to their northwest, intense ridge building to their northeast, and strong updrafts to their north associated with vorticity advection and warm-air advection. These results statistically support the findings of previous studies. Furthermore, an analysis using a time filter demonstrates the relationship between planetary-scale environments and synoptic-scale dynamics in the upper levels. The high PV to the northwest of ETTCs is attributed not only to eastward-moving troughs, but also to the environmental PV. The low PV to the northeast of ETTCs results from the negative PV formation associated with ridge building, which almost cancels the environmental PV. Thus, the environmental PV at relatively high latitudes enhances the intensity of positive PV to the northwest of ETTCs, and increases the upper limit of the magnitude of ridge building to the northeast.