Vertical Velocity Profiles in Convectively Coupled Equatorial Waves and MJO: New Diagnoses of Vertical Velocity Profiles in the Wavenumber-Frequency Domain
Vertical Velocity Profiles in Convectively Coupled Equatorial Waves and MJO: New Diagnoses of Vertical Velocity Profiles in the Wavenumber-Frequency Domain
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DOI：
10.1175/jas-d-19-0209.1
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发表时间：
2020-06-01
影响因子：
3.1
通讯作者：
Yasunaga, Kazuaki
中科院分区：
文献类型：
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作者：
Inoue, Kuniaki;Adames, Angel F.;Yasunaga, Kazuaki
开发了一种新的诊断框架，并将其应用于ERA-TERTER，以定量评估波数-频率域中的垂直速度(Omega)剖面。热带海洋欧米伽剖面的前两个EOF-PC对定义了两个量：顶重比和倾斜率。顶重比和倾斜率分别定义为PC1和PC2的同谱和正交谱除以PC1的功率谱。它们代表了对流最大时欧米伽剖面的顶重程度，以及欧米伽剖面在波的时空演化中包含的倾斜度。顶部-重量比显示，随着时间尺度(空间尺度)变长(更大)，omega剖面变得更加顶部-重量。MJO具有最重的顶部剖面，而向东的惯性重力波(EIG)和向西的惯性重力波(WIG)具有最多的底部重剖面。倾斜比表明，属于对流耦合重力波的Kelvin波、WIG波、EIG波和混合Rossby重力波(MRG波)在omega剖面上有明显的倾斜，而属于慢运动水汽模式的赤道Rossby(ER)波和MJO波的倾斜较小。还计算了每波的总湿稳定度(GMS)、云辐射反馈和有效GMS。顶重欧米伽分布最大的MJO表现出较高的GMS，但由于强的云辐射反馈，具有负的有效GMS。同样，ER波也表现出负的有效GMS，具有顶部重的omega分布。这些结果可能表明，顶重欧米伽廓线通过强的云辐射反馈建立了更多的湿静态能量，因此，更有利于水汽模式的不稳定。
A new diagnostic framework is developed and applied to ERA-Interim to quantitatively assess vertical velocity (omega) profiles in the wavenumber-frequency domain. Two quantities are defined with the first two EOF-PC pairs of omega profiles in the tropical ocean: a top-heaviness ratio and a tilt ratio. The top-heaviness and tilt ratios are defined, respectively, as the cospectrum and quadrature spectrum of PC1 and PC2 divided by the power spectrum of PC1. They represent how top-heavy an omega profile is at the convective maximum, and how much tilt omega profiles contain in the spatiotemporal evolution of a wave. The top-heaviness ratio reveals that omega profiles become more top-heavy as the time scale (spatial scale) becomes longer (larger). The MJO has the most top-heavy profile while the eastward inertio-gravity (EIG) and westward inertiogravity (WIG) waves have the most bottom-heavy profiles. The tilt ratio reveals that the Kelvin, WIG, EIG, and mixed Rossby-gravity (MRG) waves, categorized as convectively coupled gravity waves, have significant tilt in the omega profiles, while the equatorial Rossby (ER) wave and MJO, categorized as slow-moving moisture modes, have less tilt. The gross moist stability (GMS), cloud-radiation feedback, and effective GMS were also computed for each wave. The MJO with the most top-heavy omega profile exhibits high GMS, but has negative effective GMS due to strong cloud-radiation feedbacks. Similarly, the ER wave also exhibits negative effective GMS with a top-heavy omega profile. These results may indicate that top-heavy omega profiles build up more moist static energy via strong cloud-radiation feedbacks, and as a result, are more preferable for the moisture mode instability.