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程晶晶, 李青青, 陈锦鹏. 2023. 不同强度环境垂直风切变影响下热带气旋外核区冷池特征[J]. 大气科学, 47(5): 1510−1524. doi: 10.3878/j.issn.1006-9895.2203.21216
引用本文: 程晶晶, 李青青, 陈锦鹏. 2023. 不同强度环境垂直风切变影响下热带气旋外核区冷池特征[J]. 大气科学, 47(5): 1510−1524. doi: 10.3878/j.issn.1006-9895.2203.21216
CHENG Jingjing, LI Qingqing, CHEN Jinpeng. 2023. Characteristics of Cold Pools in the Outer Core of Tropical Cyclones under Different Vertical Wind Shear Magnitudes [J]. Chinese Journal of Atmospheric Sciences (in Chinese), 47(5): 1510−1524. doi: 10.3878/j.issn.1006-9895.2203.21216
Citation: CHENG Jingjing, LI Qingqing, CHEN Jinpeng. 2023. Characteristics of Cold Pools in the Outer Core of Tropical Cyclones under Different Vertical Wind Shear Magnitudes [J]. Chinese Journal of Atmospheric Sciences (in Chinese), 47(5): 1510−1524. doi: 10.3878/j.issn.1006-9895.2203.21216

不同强度环境垂直风切变影响下热带气旋外核区冷池特征

Characteristics of Cold Pools in the Outer Core of Tropical Cyclones under Different Vertical Wind Shear Magnitudes

  • 摘要: 本文基于高分辨率数值模式模拟结果分析了不同强度的环境垂直风切变影响下热带气旋外核区近地面冷池特征。结果表明:外核区对流性和非对流性冷池在不同切变环境中表现出相似的特征。两类冷池均伴随局地位温、相当位温和水汽混合比的降低和近地面高压扰动,冷池厚度通常低于400 m,平均强度4~6 m s−1,均远小于中尺度对流系统冷池,其中非对流性冷池的厚度和强度显著大于对流性冷池,表明外核区不同类型的冷池强度主要取决于冷池厚度。冷池内普遍存在下沉运动,对流性冷池中向下垂直质量输送约为非对流冷池的两倍。下沉运动导致冷池局地高压的主要原因为云下降水粒子的蒸发冷却和雨滴拖曳作用,对流云中的凝结潜热释放则不利于地面高压发展,其中对流性冷池中次云层蒸发冷却和降水拖曳作用较强,导致该类冷池地面增压也较大。不同强度的环境垂直风切变对不同类型冷池特征也有一定影响。弱切变环境中外核区冷池多表现为尺度较小且分布离散的对流性冷池,随切变增强,冷池总数目和对流性冷池数目减少,而尺度较大且多位于层云降水区域的非对流性冷池增多,同时厚度加深、强度增强。环境风切变增大还导致对流性和非对流性冷池造成的局地辐散出流均有所减弱但气旋式流速增强。

     

    Abstract: The characteristics of cold pools in the outer core of tropical cyclones under different magnitudes of vertical wind shear were investigated using high-resolution idealized numerical simulations. The results indicate that convective and nonconvective cold pools in the outer core exhibit similar characteristics under different vertical wind shear magnitudes. In addition, the pools exhibit similar potential temperatures, equivalent potential temperatures, water vapor mixing ratio deficits, and positive pressure perturbations. The depth of cold pools in the outer core is mostly<400 m with an average strength of approximately 4–6 m s−1, which is much lower than that observed in midlatitude mesoscale convective systems. Nonconvective cold pools are deeper than their convective counterparts and exhibit higher intensity, indicating that the intensity of different types of cold pools mainly depends on its depth. Cold pools are caused by widespread convective-scale downdrafts, and the downward vertical mass transport in convective cold pools caused by strong downdrafts is nearly twice that observed in nonconvective pools. Budgets of near-surface perturbation pressure reveal that subcloud evaporative cooling and water loading are conducive to high pressure near the surface in cold pools, while in-cloud warming arising from latent heat release leads to a decrease in pressure. Furthermore, more significant precipitation drag and subcloud evaporation in convective cold pools result in a higher pressure rise compared with nonconvective cold pools. The characteristics of both types of cold pools also vary with shear values: Weak shear primarily gives rise to small-scale and discrete convective cold pools. As the shear increases, the total number of outer-core cold pools and the frequency of convective cold pools decrease, while the number of nonconvective cold pools with large horizontal extent increases. Additionally, nonconvective cold pools tend to deepen and intensify. Increased environmental wind shear also leads to a local weakening of the divergent outflow but an enhancement of the cyclonic flow in convective and nonconvective cold pools.

     

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