Numerical Simulation of a Life-Cycle of Atmospheric Blocking and the Analysis of Potential Vorticity
Numerical Simulation of a Life-Cycle of Atmospheric Blocking and the Analysis of Potential Vorticity
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大气阻塞生命周期的数值模拟及位涡分析
DOI：
10.2151/jmsj1965.76.6_983
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发表时间：
1998
影响因子：
3.1
通讯作者：
Hiroshi L. Tanaka
中科院分区：
文献类型：
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作者：
Hiroshi L. Tanaka
在这项研究中，我们进行了一系列数值实验来研究大气阻塞，使用一个简单的正压模型，该模型具有造波器来激发天气扰动。该模型的分辨率相当于 R20，仅包含五个物理过程：作为斜压不稳定性的造波器、地形强迫、双调和扩散、纬向表面应力和埃克曼泵浦。时间积分结果表明，模型中持续出现偶极子阻塞，显示出合理的生命周期。在模型大气中，天气扰动被造波器呈指数放大。指数增长很快就会因与罗斯贝波破碎相关的天气波到行星波的能量非线性散射而饱和。位涡（PV）分析表明阻塞的发生是由罗斯贝波破碎引起的。高低PV的翻转往往发生在地形静止的山脊处。一旦罗斯贝波破碎形成块体，后续的罗斯贝波就会被阻挡并经历经向拉伸。然后，拉伸的波分解，在阻塞系统的北部沉积新的低PV，在南部沉积高PV，以维持该阻塞。结果与所谓的涡流应变机制一致。结果表明，天气扰动的指数增长对于阻塞的发生和维持都是至关重要的。
In this study, we conducted a series of numerical experiments to investigate atmospheric blocking, using a simple barotropic model that featured a wavemaker to excite synoptic disturbances. The model has a resolution equivalent to R20 and consists of only five physical processes: a wavemaker as baroclinic instability, topographic forcing, biharmonic diffusion, zonal surface stress, and Ekman pumping. Results of time integrations show that persistent dipole blockings appear one after another in the model, showing a reasonable life-cycle. In the model atmosphere, the synoptic disturbances are amplified exponentially by the wavemaker. The exponential growth soon saturates with nonlinear scattering of energy from synoptic to planetary waves associated with a Rossby wave breaking. The analysis of potential vorticity (PV) indicates that the onset of blocking is brought on by the Rossby wave breaking. The overturning of high and low PVs tends to occur at the topographic stationary ridge. Once a block is formed by the Rossby wave breaking, subsequent Rossby waves are blocked and undergo meridional stretch. The stretched wave then breaks down, depositing fresh low PV at the north and high PV at the south of the blocking system to maintain the block. The result is consistent with the so-called eddy straining mechanism. The result suggests that the exponential growth of synoptic disturbances is essential both for the onset and the maintenance of blocking.