Characteristics of Tropical Convective Gravity Waves Resolved by ERA5 Reanalysis
Characteristics of Tropical Convective Gravity Waves Resolved by ERA5 Reanalysis
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DOI：
10.1175/jas-d-22-0057.1
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发表时间：
2022-11
影响因子：
3.1
通讯作者：
H. Pahlavan;J. Wallace;Q. Fu
中科院分区：
文献类型：
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作者：
H. Pahlavan;J. Wallace;Q. Fu
ERA5再分析的每小时时间步长和约30公里的水平分辨率比它的前人解析出的重力波谱要大得多。基于双边纬向波数-频谱的表示，我们展示了一组大气场中重力波特征的证据。交叉谱分析表明：(1)东向和西向传播波的位势向上通量都很大，(2)东向传播波的西风动量和西向传播波的东风动量都是向上的，(3)风矢量随时间的反气旋旋转--所有这些都是垂直传播重力波和惯性重力波的特征。沿单个子午线计算的双侧子午线波数频谱与在纬度圆上计算的子午线波数频谱特征相似，表明这些波在各个方向上传播。这些波的三维结构也被记录在赤道沿线各个参考网格点的与网格分辨的、由波引起的下流事件相关的温度场的合成中。结果表明，波相对于各参考网格点向外向上辐射，其幅度随时间迅速减小。在重力波相速度的宽广连续谱内，在±49m S−1和±23m S−1附近有较好的值，前者与第一斜压模有关，在对流层深处垂直速度扰动具有相同符号，后者与第二模有关，在对流层下部和上层具有相反的极性。
ERA5 reanalysis with hourly time steps and ~30 km horizontal resolution resolves a substantially larger fraction of the gravity wave spectrum than its predecessors. Based on a representation of the two-sided zonal wavenumber-frequency spectrum, we show evidence of gravity wave signatures in a suite of atmospheric fields. Cross-spectrum analysis reveals (i) a substantial upward flux of geopotential for both eastward and westward propagating waves, (ii) an upward flux of westerly momentum in eastward propagating waves and easterly momentum in westward propagating waves, and (iii) anticyclonic rotation of the wind vector with time— all characteristics of vertically propagating gravity and inertio-gravity waves. Two-sided meridional wavenumber-frequency spectra, which are computed along individual meridians and then zonally averaged, exhibit characteristics similar to the spectra computed on latitude circles, indicating that these waves propagate in all directions. The three-dimensional structure of these waves is also documented in composites of the temperature field relative to grid-resolved, wave-induced downwelling events at individual reference grid points along the equator. It is shown that the waves radiate outward and upward relative to the respective reference grid points, and their amplitude decreases rapidly with time. Within the broad continuum of gravity wave phase speeds there are preferred values around ±49 m s−1 and ±23 m s−1, the former associated with the first baroclinic mode in which the vertical velocity perturbations are of the same sign throughout the depth of the troposphere, and the latter with the second mode in which they are of opposing polarity in the lower and upper troposphere.