On the Sensitivity of Zonal-Index Persistence to Friction
On the Sensitivity of Zonal-Index Persistence to Friction
复制标题
论带状指数持久性对摩擦的敏感性
DOI：
10.1175/jas-d-14-0067.1
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发表时间：
2014
影响因子：
3.1
通讯作者：
P. Zurita‐Gotor
中科院分区：
文献类型：
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作者：
P. Zurita‐Gotor
摩擦力是大气建模中的一个重要参数，可能以多种方式影响内部变化。它直接抑制环形模式的可变性，但它也有助于通过斜压反馈来维持环形模式的可变性。此外，通过确定中纬度急流的平均强度和位置，摩擦力会影响驱动这种变化的内部动力学。这项工作使用理想化的准地转两层模型研究了所有这些因素与环带变化的持续性对纬向平均摩擦力变化的敏感性的相关性。该模型产生真实的可变性，但它非常简单，可以清楚地区分不同的效果。研究发现，持久性对摩擦的敏感性主要由直接阻尼效应决定，而涡动量强迫和平均射流的变化并不那么重要。与在更复杂的模型中一样，该模型中射流异常的持续性随着摩擦力的增加而完全滞后，但这些异常的长期去相关衰减率对摩擦力非常不敏感。虽然这意味着涡流反馈必须随着摩擦力的增加而增加，以维持异常抵抗增强的阻尼，但事实证明这不是由于斜压效应所致。假设涡流强迫不随摩擦力变化的模型可以很好地再现数值结果。决定模型对摩擦敏感度的关键因素是涡动量强迫的谱结构。
Frictionis an important parameterin atmospheric modelingthat may affect internal variability in a number of ways. It directly damps the annular-mode variability, but it also helps to maintain it through baroclinic feedbacks. Also, by determining the mean strength and position of the midlatitude jet, friction affects the internal dynamics that drive this variability. This work investigates the relevance of all of these factors for the sensitivity of the persistence of annular variability to changes in the zonal-mean friction using an idealized quasigeostrophic two-layer model. This model produces realistic variability, yet it is so simple that one can cleanly separate the different effects. It is found that the sensitivity of persistence to friction is dominated by the direct damping effect, while changes in the eddy momentum forcing and in the mean jet are not as important. As in more complex models, the persistence of the jet anomalies in this model decreases at all lags with increasing friction, but the long-time decorrelation decay rate of these anomalies is remarkably insensitive to friction. Although this implies that the eddy feedback must increase with friction to maintain the anomalies against the enhanced damping, it is shown that this is not due to baroclinic effects. A model that assumes that the eddy forcing does not change with friction can reproduce reasonably well the numerical results. The crucial factor that determines the model’s sensitivity to friction is the spectral structure of the eddy momentum forcing.