Numerical study of horizontal shear instability waves along narrow cold frontal rainbands
Numerical study of horizontal shear instability waves along narrow cold frontal rainbands
复制标题
窄冷锋雨带水平剪切不稳定波的数值研究
DOI：
10.1175/2010jas3599.1
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
M
中科院分区：
文献类型：
--
作者：
Kawashima;M
通过一系列理想的云分辨模拟，研究了低层环境垂直切变和水平切变对传播到中性和稍微不稳定环境的窄冷锋雨带沿锋变率的影响。在初始条件为轻微不稳定探空和弱环境横锋垂直切变的情况下，nfrs沿线降水的核隙结构与波状扰动有关，这种扰动的动能主要来自平均的局部垂直切变和浮力。然而，在广泛的环境条件下，由于沿nfrs的水平剪切不稳定性（HSI）波的发展，降水的核隙结构会发生。随着环境横锋风垂直切变的减小，HSI波的增长速度和振幅显著减小。这些减少是由于紧接在前缘后面的低水平局部垂直切变增强的结果。强的局地垂直切变作用于切变带冷空气侧的涡度边波，通过两个涡度边波的相互作用抑制HSI波的生长。随着水平切变的增加，HSI波的初始波长明显增加。前缘附近的局部垂直切变对长HSI波的抑制作用强于短波，垂直切变幅度相对于水平切变幅度的减小可以解释波长对水平切变的依赖性。
The effects of variations in low-level ambient vertical shear and horizontal shear on the alongfront variability of narrow cold frontal rainbands (NCFRs) that propagate into neutral and slightly unstable environments are investigated through a series of idealized cloud-resolving simulations.In cases initialized with slightly unstable sounding and weak ambient cross-frontal vertical shears, core-gap structures of precipitation along NCFRs occur that are associated with wavelike disturbances that derive their kinetic energy mainly from the mean local vertical shear and buoyancy. However, over a wide range of environmental conditions, core-gap structures of precipitation occur because of the development of a horizontal shear instability (HSI) wave along the NCFRs.The growth rate and amplitude of the HSI wave decrease significantly as the vertical shear of the ambient cross-front wind is reduced. These decreases are a consequence of the enhancement of the low-level local vertical shear immediately behind the leading edge. The strong local vertical shear acts to damp the vorticity edge wave on the cold air side of the shear zone, thereby suppressing the growth of the HSI wave through the interaction of the two vorticity edge waves. It is also noted that the initial wavelength of the HSI wave increases markedly with increasing horizontal shear. The local vertical shear around the leading edge is shown to damp long HSI waves more strongly than short waves, and the horizontal shear dependency of the wavelength is explained by the decrease in the magnitude of the vertical shear relative to that of the horizontal shear.