Meridional movement of geopotential height anomalies in the subtropics and the relationship to the base‐state flow
Meridional movement of geopotential height anomalies in the subtropics and the relationship to the base‐state flow
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DOI：
10.1002/qj.3937
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发表时间：
2020-11
影响因子：
8.9
通讯作者：
Jennifer Gahtan;P. Roundy
中科院分区：
文献类型：
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作者：
Jennifer Gahtan;P. Roundy
本文利用小波分析方法，分析了副热带对流层上部位势高度异常纬向运动的性质。结果表明，功率，这代表了直接纬向运动的波的存在或振幅的增加，在相应的赤道风在对流层上部西风或弱东风的地区增加。在副热带急流出口附近，赤道向功率增强，而在急流入口附近，极向功率增强。对流层上层风、位势高度和向外长波辐射（OLR）对小波变换的回归表明，小波正在识别与热带有组织对流有关的热带-热带外相互作用的信号。评估功率与背景状态流特征（包括水平风和切变）的关系。经向风和经向风的经向切变（du/dy）与功率的关系似乎更清楚，而不是经向风和经向风的经向切变（dv/dx）。波浪的运动方向与纬向风相同，相反方向的波浪运动减少，则波浪的动力更有利。此外，功率在北方半球随着纬向风的纬向切变的增加而增加，在南半球随着纬向风的纬向切变的减少而增加。向赤道方向的功率比向极方向的功率强，受背景气流特征的影响更大。此外，功率较小的尺度和时间尺度的小波往往有一个更高的敏感性，背景水平流相比，较大的尺度和时间尺度。
Qualities of the meridional movements of geopotential height anomalies in the upper troposphere of the subtropics are analysed via wavelet analysis using a meridional–temporal partial Morlet wavelet. Results show that power, which represents increased presence or amplitude of waves with direct meridional movement, is increased in regions where the corresponding equatorial winds in the upper troposphere are westerly or weakly easterly. Furthermore, equatorward power is enhanced near subtropical jet exit regions whereas poleward power is enhanced in jet entrance regions. Regressions of upper‐tropospheric winds, geopotential height, and outgoing long‐wave radiation (OLR) against the wavelet transforms demonstrate that the wavelets are identifying signals with tropical–extratropical interactions that are connected to organized convection in the tropics. The relationship of power with background‐state flow characteristics, including the horizontal winds and shear, are evaluated. Instead of the zonal wind and meridional shear of the zonal wind (du/dy), both the meridional wind and the zonal shear of the meridional wind (dv/dx) appear to have a clearer relationship with the power. Power is favoured for waves whose movement is aligned in the same direction as the meridional wind, and reduced in the opposite direction. Additionally, power increases with increasing zonal shear of the meridional wind in the Northern Hemisphere and with decreasing zonal shear of the meridional wind in the Southern Hemisphere. Power in the equatorward direction is stronger than in the poleward direction and more heavily influenced by background flow characteristics. Furthermore, power for wavelets with smaller meridional and temporal scales tends to have a higher sensitivity to the background horizontal flow as compared to larger meridional and temporal scales.