Cyclogenesis in a conditionally unstable moist baroclinic atmosphere
Cyclogenesis in a conditionally unstable moist baroclinic atmosphere
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条件不稳定的湿润斜压大气中的气旋发生
DOI：
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发表时间：
1994
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通讯作者：
M. Mak
中科院分区：
文献类型：
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作者：
M. Mak
本文给出了一般加热廓线条件不稳定湿斜压基流不稳定问题的解析解和均匀加热廓线特殊情况下的定量结果。在这个通用的模式设置中，由于位涡异常的存在，在4个离散的垂直高度层上只存在4个离散的本征模。弱到中等加热有一个不稳定模式。在此范围内，最不稳定的湿Eady模的增长率和波长对加热强度有很强的非线性依赖关系。当加热强度增加到一个中等值时，发现这种模式的生长速率和波长的减少显着增强。这些不稳定性随加热强度的变化趋势是相反的，更强的加热，由于在四个层次的PV异常之间的相互作用的强烈干扰。该模式的相速度受冷凝加热的影响相对较小。对于中等到强加热，有两个新的分支较短的不稳定模式。其中一个分支的模态具有较大的相速度，并且主要局限于模式对流层顶和加热层顶部之间。它们主要来自这两个水平上PV异常的相互作用。另一个分支的模式主要局限于模型表面和加热层底部之间，具有由类似动力学起源产生的小相速度。自感加热和基本斜压切变共同决定了这些模态的存在。这两种模式可以共存。不稳定模式的能量与这样的动力学解释是一致的。DOI：10.1034/j.1600-0870.1994.00003.x
This paper reports the analytic solution of the instability problem of a conditionally unstable moist baroclinic basic flow for a general heating profile and the quantitative results for the special case of a uniform heating profile. There are 4 discrete eigenmodes arising from the existence of potential vorticity (PV) anomalies at only 4 discrete vertical levels in this generic model setting. There is one unstable mode for a weak to moderate heating. The growth rate and wavelength of the most unstable moist Eady mode have a strongly nonlinear dependence on the heating intensity in this range. Significant enhancement in the growth rate and reduction in the wavelength of this mode are found when the heating intensity is increased to a moderate value. The trends of variation of these instability properties with the heating intensity are reversed for stronger heating due to a strong interference of the interactions among the PV anomalies at the four levels. The phase velocity of this mode is affected relatively little by the condensational heating. For a moderate to strong heating, there are two new branches of shorter unstable modes. The modes of one branch have a large phase velocity and are largely confined between the model tropopause and the top of the heating layer. They primarily arise from the interaction of the PV anomalies at those 2 levels. The modes of the other branch are largely confined between the model surface and the bottom of the heating layer with a small phase velocity arising from a similar dynamical origin. The self-induced heating and the basic baroclinic shear are jointly responsible for the existence of these modes. These 2 branches of mode may coexist. The energetic of the unstable modes is consistent with such a dynamical interpretation. DOI: 10.1034/j.1600-0870.1994.00003.x