Interpretation of the spectrum of eastward‐moving tropical convective anomalies
Interpretation of the spectrum of eastward‐moving tropical convective anomalies
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DOI：
10.1002/qj.3709
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发表时间：
2019-12
影响因子：
8.9
通讯作者：
P. Roundy
中科院分区：
文献类型：
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作者：
P. Roundy
波数-频率功率谱分析已被用作主要工具，以检测所观察到的对流耦合赤道波活跃的波数和频率范围。以前的工作表明，在这些波集群之间的活动大约12和60米的等效深度，因为光谱峰归一化除以平滑的光谱背景遵循这些范围。通过波数频率功率谱分析、滤波和线性回归的组合，这项工作表明，传统方法会产生混乱，因为它将来自世界各地的不同（有时是冲突的）信号合并在一起，这些信号对频谱的相同部分有贡献。结果还表明，传统的方法导致我们忽略了大量的权力与结构上与观察到的开尔文波一致的变化，但发生在较低的频率。在这些频率下的波信号比与归一化谱中的开尔文峰重合的开尔文波信号更强但类似于开尔文波信号。结果表明，波信号本身具有红色属性，可能是因为更强的对流耦合波传播得更慢。标准波段之外的更慢、更强的波浪信号会影响有形的天气信号，在操作中不应忽视。相反，结果支持这样的观点，即标记为开尔文波的扰动与Madden-Julian振荡（MJO）形成一个连续体，并建议从广泛认可的开尔文波段到MJO的整个光谱区域应一起考虑。
Wave‐number‐frequency power spectrum analysis has been used as a primary tool to detect the ranges of wave numbers and frequencies about which observed convectively coupled equatorial waves are active. Previous works have suggested that activity in these waves clusters between roughly 12 and 60 m equivalent depths because spectral peaks normalized by dividing by a smoothed spectral background follow those ranges. Through a combination of wave‐number‐frequency power spectrum analysis, filtering and linear regression, this work shows that the traditional approach generates confusion because it conflates different, sometimes conflicting, signals from around the world that contribute to the same parts of the spectrum. Results also suggest that the traditional method leads us to ignore substantial power associated with variability structurally consistent with observed Kelvin waves but that occurs at lower frequencies. Wave signals at these frequencies are stronger than but similar to Kelvin wave signals coincident with the Kelvin peak in the normalized spectrum. Results suggest that the wave signal itself has red properties, possibly because more strongly convectively coupled waves propagate more slowly. The slower, more intense wave signals outside of the standard band would impact tangible weather signals and should not be ignored in operations. Instead, results support the view that disturbances labelled as Kelvin waves form a continuum with the Madden–Julian Oscillation (MJO) and suggest that the whole region of the spectrum from the broadly recognized Kelvin band to the MJO should be considered together.