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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 20 Feb 2019

Research article | 20 Feb 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Comparison of equatorial wave activity in the tropical tropopause layer and stratosphere represented in reanalyses

Young-Ha Kim1, George N. Kiladis2, John R. Albers2,3, Juliana Dias2,3, Masatomo Fujiwara4, James A. Anstey5, In-Sun Song6, Corwin J. Wright7, Yoshio Kawatani8, François Lott9, and Changhyun Yoo10 Young-Ha Kim et al.
  • 1Severe Storm Research Center, Ewha Womans University, Seoul, South Korea
  • 2Physical Sciences Division, NOAA/Earth System Research Laboratory, Boulder, Colorado, USA
  • 3Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, USA
  • 4Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Japan
  • 5Canadian Centre for Climate Modelling and Analysis, Environment and Climate Change Canada, Victoria, British Columbia, Canada
  • 6Korea Polar Research Institute, Incheon, South Korea
  • 7Centre for Space, Atmospheric and Oceanic Science, University of Bath, Bath, UK
  • 8Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan
  • 9Laboratoire de Météorologie Dynamique, Ecole Normale Supérieure, Paris, France
  • 10Department of Climate and Energy Systems Engineering, Ewha Womans University, Seoul, South Korea

Abstract. 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.

Young-Ha Kim et al.
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Young-Ha Kim et al.
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Publications Copernicus
Short summary
Reanalyses are widely used products of various meteorological variables, generated using observational data and assimilation systems. In this study, we compare six modern reanalyses, with focus on their representation of equatorial waves which are known to be important in stratospheric variability and stratosphere-troposphere exchange. Spreads among the reanalyses in the spectral properties, spatial distributions, and long-term variations of the waves are examined.
Reanalyses are widely used products of various meteorological variables, generated using...