A Mechanism of Tropical Convection Inferred from Observed Variability in the Moist Static Energy Budget
A Mechanism of Tropical Convection Inferred from Observed Variability in the Moist Static Energy Budget
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DOI：
10.1175/jas-d-14-0015.1
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发表时间：
2014-03
影响因子：
3.1
通讯作者：
H. Masunaga;T. L’Ecuyer
中科院分区：
文献类型：
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作者：
H. Masunaga;T. L’Ecuyer
利用热带降雨测量任务(TRMM)和A-Train平台等不同卫星的测量结果，研究了湿静态能量(MSE)收支的时间变异性。通过观测得到了湿对流发展前后的合成时间序列，描述了MSE和水汽辐合的演变，以及在它们的组合中的总湿稳定度(GMS)。通过将垂直模分解为第一斜压模、第二斜压模和背景浅模，应用一种新的算法从能量收支约束中估计大尺度垂直运动。这些发现表明了热带对流的一种可能机制。正的第二斜压模式(拥挤模式)固有的MSE辐合逐渐抵消了背景状态中弱的MSE辐散，从而带来了逐渐的失稳。随着第一斜压模式开始加强，GMS被驱动到接近零的位置，加速了猛烈的大尺度上升气流和深对流的增长。当对流爆发达到峰值时，正的第二模切换到负的模(层状模)，并引入MSE散度的突然增加，这可能阻碍深对流的进一步维持。第一个模式迅速消散，均方根值从零开始增加，当定义包括辐射加热率以抵消均方误差收敛时，eventuallyreturningtothebackgroundshallow-modestate.AnotablecaveattothisscenarioisthatGMSserves是一个更可靠的度量。
Temporal variability in the moist static energy (MSE) budget is studied with measurements from a combination of different satellites including the Tropical Rainfall Measuring Mission (TRMM) and A-Train platforms. A composite time series before and after the development of moist convection is obtained from the observations to delineate the evolution of MSE and moisture convergences and, in their combination, gross moist stability (GMS). A new algorithm is then applied to estimate large-scale vertical motion from energy budget constraints through vertical-mode decomposition into first and second baroclinic modes and a background shallow mode. The findings are indicative of a possible mechanism of tropical convection. A gradual destabilization is brought about by the MSE convergence intrinsic to the positive second baroclinic mode (congestus mode) thatincreasingly counteracts a weak MSE divergence inthe backgroundstate.GMS isdriven to nearly zero as the first baroclinic mode begins to intensify, accelerating the growth of vigorous large-scale updrafts and deep convection. As the convective burst peaks, the positive second modeswitches tothe negative mode (stratiform mode) and introduces an abrupt rise in MSE divergence that likely discourages further maintenance of deep convection. The first mode quickly dissipates and GMS increases away from zero, eventuallyreturningtothebackgroundshallow-modestate.AnotablecaveattothisscenarioisthatGMSserves as a more reliable metric when defined with a radiative heating rate included to offset MSE convergence.