Mechanism for the formation of equatorial superrotation in forced shallow-water turbulence with Newtonian cooling
Mechanism for the formation of equatorial superrotation in forced shallow-water turbulence with Newtonian cooling
复制标题
牛顿冷却强迫浅水湍流中赤道超自转的形成机制
DOI：
10.1175/jas-d-14-0235.1
复制
发表时间：
2015
影响因子：
3.1
通讯作者：
Izumi Saito and Keiichi Ishioka
中科院分区：
文献类型：
--
作者：
高山和雄;三村菜摘;萩原康子;立花雅史;櫻井文教;神田勝弘;川端健二;水口裕之;辻 かおる;Izumi Saito and Keiichi Ishioka
本文研究了牛顿冷却的旋转球体上的强迫浅水湍流，目的是阐明R.K.Scott和L.M.Polvani所报道的赤道超级旋转的强健形成的机制。结果表明，牛顿冷却项使霍夫模的结构发生了扭曲。这种变形表现为等位线随纬度绝对值的增大而向西或向东倾斜，Hough模的结构变化导致纬向平均气流的加速。基于弱非线性理论的统计分析预测，随机激发的Hough模会产生一个前进的赤道急流，其廓线与非线性时间演化中得到的集合平均纬向平均气流的廓线是定量一致的。预报的赤道进流流主要来源于Rossby模产生的加速度，其等相线被牛顿冷却项向西倾斜。阐明了Hough模等相线的这种倾斜，并将本文提出的加速机制与其他出现赤道超旋的数值研究中的加速机制进行了比较。
Forced shallow-water turbulence on a rotating sphere with Newtonian cooling is examined with the aim of elucidating the mechanism of the robust formation of equatorial superrotation reported by R. K. Scott and L. M. Polvani. It is shown that the Newtonian cooling term distorts the structure of the Hough modes. This distortion can be visualized as either the westward or eastward tilting of the equiphase line with increasing absolute value of latitude; the structural change of the Hough modes leads to the acceleration of the zonal-mean flow. A statistical analysis based on a weak-nonlinear theory predicts that stochastically excited Hough modes generate a prograde equatorial jet, the profile of which is quantitatively consistent with that of the ensemble-averaged zonal-mean flow obtained in nonlinear time evolutions. The predicted prograde equatorial jet originates mainly from the acceleration produced by Rossby modes, the equiphase line of which is tilted westward by the Newtonian cooling term. This tilt of the equiphase line of the Hough modes is clarified and a comparison between the acceleration mechanism presented in the present paper and that in other numerical studies in which equatorial superrotation emerges is made.