Buoyancy of convective-scale updrafts in the outer cores of sheared tropical cyclones

通常认为局地浮力与对流活动息息相关。本文统计分析了不同强度垂直风切变影响下热带气旋外核区对流尺度上升运动的浮力特征。研究发现,弱至中等强度的垂直风切变环境下,顺切变象限的浮力大于逆切变象限的浮力,顺切变象限的总浮力随风切变的增大而减小。而在极端强度的风切变影响下,大部分总浮力为负值。热力浮力、动力浮力与上升运动垂直质量输送没有明显相关性,因此总浮力和垂直质量输送也无显著相关性。上述结果加深了我们对热带气旋外核区对流发生发展过程的物理认识。

In this paper,the authors present the statistical characteristics of the buoyancy of outer-core convective-scale updrafts in numerically simulated sheared tropical cyclones(TCs).The total buoyancy is predominantly positive in weak-to-strong ambient vertical shears,whereas much of the total buoyancy under an extreme shear environment becomes negative.Thermal buoyancy positively contributes to the total buoyancy value.For weakly and moderately sheared TCs,the updraft buoyancy is statistically significantly stronger downshear but smaller upshear.Such a downshear preference of strong buoyancy becomes less evident as the shear magnitude increases.The total buoyancy of updrafts shows a decreasing tendency with radius.Both thermal and dynamic buoyancy do not significantly correlate with vertically averaged vertical mass fluxes.This also leads to no significant correlation between the total buoyancy and vertical mass fluxes of outer-core updrafts.