标题： 顶部和底部厚重的垂直速度结构：分层大气模型的物理模态 显示英文标题

标题： Top- and bottom-heavy vertical velocity structures: physical modes of layered atmospheric models

摘要： 热带东太平洋和西太平洋在垂直速度（或omega）剖面方面表现出差异。 东太平洋的剖面特征是底部较重，而西太平洋的剖面特征是顶部较重。 尽管已知水平海表温度梯度的跨盆地差异很重要，但这些omega结构变体存在的物理原因尚未完全理解。 这个问题通过一个稳态、线性模型在$f$平面上，具有$n$个大气层来解决。 对流和辐射被参数化为热力学扰动的线性响应，对流非线性近似为对流开/关状态。 该模型的自由（或本征）模态产生类似于观测到的热带大气的斜压模态的垂直结构，每个模态与一个特征水平尺度（本征值）相关联。 在标准参数条件下，第一斜压模态具有较大的空间尺度（$\sim$ 1500 km），而第二斜压模态具有较小的空间尺度（$\sim$ 250 km）。 当模型以强梯度和弱梯度地表温度（$T_s$）模式进行强迫时，所产生的omega剖面分别呈现出底部较重和顶部较重的结构——模拟了东太平洋和西太平洋之间的观测差异。 还观察到了对科里奥利力大小的额外依赖。 斜压模态的垂直结构与水平尺度之间的联系解释了为什么强梯度$T_s$ 剖面强烈投影到第二斜压模态，导致东太平洋出现底部较重的omega剖面，而弱梯度$T_s$ 剖面强烈投影到第一斜压模态，导致西太平洋出现顶部较重的omega剖面。 显示英文摘要

摘要： Tropical East and West Pacific Oceans display differences in their vertical velocity (or omega) profiles. The East Pacific is characterized by bottom-heavy profiles, while the West Pacific is characterized by top-heavy profiles. Although inter-basin differences in the horizontal SST gradient are known to be important, physical reasons for why these omega structure variants exist are not fully understood. This question is addressed using a steady, linear model on an $f$-plane with $n$ atmospheric layers. Convection and radiation are parameterized as linear responses to thermodynamic perturbations with convective nonlinearity approximated by convection on/off regimes. The free (or eigen) modes of the model yield vertical structures resembling the observed baroclinic modes of the tropical atmosphere, with each mode associated with a characteristic horizontal scale (the eigenvalue). In the standard parameter regime, the first-baroclinic mode has a large spatial scale ($\sim$ 1500 km) while the second-baroclinic mode has a smaller spatial scale ($\sim$ 250 km). When the model is forced with a strong- and weak-gradient surface temperature ($T_s$) patterns, the resulting omega profiles assume bottom- and top-heavy structures respectively -- mimicking the observed differences between East and West Pacific Oceans. Additional dependence on the magnitude of the Coriolis force is also observed. The connection between the vertical structure and the horizontal scale of the baroclinic modes explains why a strong-gradient $T_s$ profile projects strongly onto the second-baroclinic mode yielding bottom-heavy omega profiles in the eastern Pacific, while a weak-gradient $T_s$ profile projects strongly onto the first-baroclinic mode, yielding top-heavy omega profiles typical of the Western Pacific.