Rossby wave instability and apparent phase speeds in large Ocean basins
Rossby wave instability and apparent phase speeds in large Ocean basins
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大洋盆地罗斯贝波不稳定性和视相速度
DOI：
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
J. Pedlosky
中科院分区：
文献类型：
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作者：
P. Isachsen;J. LaCasce;J. Pedlosky
本文考察了大洋盆中斜压Rossby波的稳定性，推广了LaCasce和Pedlosky的准地转(QG)结果。首先，利用两层浅水系统，推导了大尺度波浪扰动的稳定性方程。这些方程与QG稳定性方程相似，不同之处在于它们保留了内部变形半径随纬度的变化。通过本征模计算和时间步长对不同初始条件下的方程进行了数值求解。增长最快的本征模在高纬度增强，而增长较慢的本征模在低纬增强。在本征模增强的纬度范围内，所有模式都具有与变形半径相当的子午线尺度和生长时间。如果人们把QG理论应用在纬度带上，这就是人们所期望的。然后利用区域海洋模式系统原始方程模式模拟了大尺度海浪的演变。结果与理论预测一致，变形尺度扰动的增长速率与局部变形半径成反比。波在中高纬度地区屈服于扰动，但在此之前能够在低纬度地区穿过盆地。此外，不稳定产生的正压波传播速度快于斜压长波速度，这可能解释了Cherton和Schlax注意到的速度差异。
The stability of baroclinic Rossby waves in large ocean basins is examined, and the quasigeostrophic (QG) results of LaCasce and Pedlosky are generalized. First, stability equations are derived for perturbations on large-scale waves, using the two-layer shallow-water system. These equations resemble the QG stability equations, except that they retain the variation of the internal deformation radius with latitude. The equations are solved numerically for different initial conditions through eigenmode calculations and time stepping. The fastest-growing eigenmodes are intensified at high latitudes, and the slower-growing modes are intensified at lower latitudes. All of the modes have meridional scales and growth times that are comparable to the deformation radius in the latitude range where the eigenmode is intensified. This is what one would expect if one had applied QG theory in latitude bands. The evolution of large-scale waves was then simulated using the Regional Ocean Modeling System primitive equation model. The results are consistent with the theoretical predictions, with deformation-scale perturbations growing at rates inversely proportional to the local deformation radius. The waves succumb to the perturbations at the mid- to high latitudes, but are able to cross the basin at low latitudes before doing so. Also, the barotropic waves produced by the instability propagate faster than the baroclinic long-wave speed, which may explain the discrepancy in speeds noted by Chelton and Schlax.