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

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.