Understanding what controls vertical motion profile shape is fundamental to understanding tropical precipitation patterns. Two controls have been previously studied: the thermodynamic profiles of the environment and the dynamics imposed by sea surface temperature (SST) patterns. To fit these two perspectives together, we focus on two regions with distinctly top and bottom-heavy vertical motion: The Western Pacific and the Central Eastern Pacific. These regions have roughly the same column-integrated water, precipitation, and column-integrated horizontal moisture advection, however the shape in the West is top heavy while the East is bottom heavy. The top-heaviness angle is introduced to describe this difference. To study thermodynamic controls on vertical motion profile shape, we use weak temperature gradient simulations. We are able to simulate the shape differences between our two regions from the thermodynamics. We then show that the dry static stability and the underlying SST are the most important for the vertical motion shape differences between our two regions. We show that the qualitative shape differences can be explained using a simple entraining plume model. The entraining plume model accepts the temperature and moisture profiles as inputs and outputs the plume's buoyancy, which is directly related to the vertical motion profile shape. We find that increasing the dry static stability leads to bottom-heaviness. We hypothesize that the SST gradients lead to a cooler equilibrium lower tropospheric temperature compared with no gradient, and this leads to a more conducive thermodynamic environment to bottom-heaviness. Hence the dynamics control top-heaviness through influencing the thermodynamic profiles.

中文翻译：

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综合热力学和动力学观点通过弱温度梯度模拟控制太平洋 ITCZ 对流头重

了解控制垂直运动剖面形状的因素是了解热带降水模式的基础。之前已经研究了两种控制：环境的热力学概况和海面温度（SST）模式所施加的动力学。为了将这两种观点结合起来，我们重点关注两个具有明显顶部和底部严重垂直运动的区域：西太平洋和中东太平洋。这些地区的柱积分水、降水和柱积分水平水汽平流大致相同，但形状是西部上重，东部下重。引入头重角来描述这种差异。为了研究垂直运动轮廓形状的热力学控制，我们使用弱温度梯度模拟。我们能够从热力学角度模拟两个区域之间的形状差异。然后我们表明，干静态稳定性和底层海温对于我们两个区域之间的垂直运动形状差异是最重要的。我们表明，可以使用简单的夹带羽流模型来解释定性形状差异。夹带羽流模型接受温度和湿度剖面作为输入，并输出羽流的浮力，该浮力与垂直运动剖面形状直接相关。我们发现增加干静态稳定性会导致底部沉重。我们假设，与没有梯度相比，海温梯度会导致对流层温度更低的平衡，这会导致更有利于底部重的热力学环境。因此，动力学通过影响热力学曲线来控制头重。