Baroclinic Frontal Arrest: A Sequel to Unstable Frontogenesis
Baroclinic Frontal Arrest: A Sequel to Unstable Frontogenesis
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DOI：
10.1175/2010jpo4493.1
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发表时间：
2011-03
影响因子：
3.5
通讯作者：
J. McWilliams;M. Molemaker
中科院分区：
文献类型：
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作者：
J. McWilliams;M. Molemaker
摘要在大尺度形变气流中，近地表边界附近的斜压锋生作用使侧向和垂直浮力梯度变陡。在锋生过程中产生一个“热直接”的非地转次级环流单元，以维持前锋气流的地转、流体静力(热风)动量平衡。锋生过程中，锋面切变流的斜压不稳定将锋面势能转化为涨落能，从而导致三维不稳定涨落的发展。在有限的振幅下，涨落提供了沿锋面平均的涡动量和浮力通量，即使在形变流动持续的情况下也阻止了锋面的锐化。锋面非地转次级环流逆转，成为锋面中心的“热间接”环流。这使得锋面浮力梯度方差(即锋面强度)平衡方程中的非地转平流和涡通量散度之间存在近似的对立，暗示了锋面方程的存在。
Abstract In a large-scale deformation flow, lateral and vertical buoyancy gradients sharpen through baroclinic frontogenesis near the surface boundary. A “thermally direct” ageostrophic secondary circulation cell arises during frontogenesis to maintain geostrophic, hydrostatic (thermal wind) momentum balance for the alongfront flow. Unstable three-dimensional fluctuations can grow during frontogenesis by baroclinic instability of the alongfront shear flow that converts frontal potential energy to fluctuation energy. At finite amplitude, the fluctuations provide alongfront-averaged eddy momentum and buoyancy fluxes that arrest the frontal sharpening even while the deformation flow persists. The frontal ageostrophic secondary circulation reverses to become a “thermally indirect” cell in the center of the front. This allows an approximate opposition between ageostrophic advection and eddy-flux divergence in the frontal buoyancy gradient variance (i.e., frontal strength) balance equation, implying frontal equ...