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Comparison of equatorial wave activity in the tropical tropopause layer and stratosphere represented in reanalyses
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2019
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Source: Atmos. Chem. Phys., 19, 10027–10050
[PDF-16.60 MB]
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Journal Title:Atmospheric Chemistry and Physics
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NOAA Program & Office:
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Description:Equatorial Kelvin and mixed Rossby-gravity (MRG) waves in the tropical tropopause layer and stratosphere represented in recent reanalyses for the period of 1981–2010 are compared in terms of spectral characteristics, spatial structures, long-term variations and their forcing of the quasi-biennial oscillation. For both wave types, the spectral distributions are broadly similar among most of the reanalyses, while the peak amplitudes exhibit considerable spread. The longitudinal distributions and spatial patterns of wave perturbations show reasonable agreement between the reanalyses. A few exceptions to the similarity of the spectral shapes and spatial structures among them are also noted. While the interannual variations of wave activity appear to be coherent for both the Kelvin and MRG waves, there is substantial variability in long-term trends among the reanalyses. Most of the reanalyses which assimilate satellite data exhibit large increasing trends in wave variance (~ 15–50 % increase in the 30 years at 100–10 hPa), whereas one reanalysis (JRA-55C) produced without satellite data does not. Several discontinuities are found around 1998 in the time series of the Kelvin and MRG wave variances, which manifest in different ways depending on the reanalysis, and are indicative of impacts of the transition of satellite measurements during that year. The equatorial wave forcing of the quasi-biennial oscillation, estimated by the Eliassen–Palm flux divergence, occurs in similar phase-speed ranges among the reanalyses, while the forcing magnitudes show considerable spread. The forcing maxima of the Kelvin waves exhibit slightly different altitudes between the reanalyses (by ~ 3 km at around 15 hPa). In addition, at around 20 hPa, a wave signal which appears only in easterly mean winds with westward phase speeds is found and discussed.
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Source:Atmos. Chem. Phys., 19, 10027–10050
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Rights Information:CC BY
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Compliance:Submitted
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