Abstract
Abstract. Kelvin waves excited by tropospheric convection are considered to be one of the main drivers of the stratospheric quasi-biennial oscillation (QBO). In this paper we combine several measured data sets with the Gravity wave Regional Or Global RAy Tracer (GROGRAT) in order to study the forcing and vertical propagation of Kelvin waves. Launch distributions for the ray tracer at tropospheric altitudes are deduced from space-time spectra of European Centre for Medium-Range Weather Forecasts (ECMWF) operational analyses, as well as outgoing longwave radiation (OLR) and rainfall data measured by the Tropical Rainfall Measuring Mission (TRMM) satellite. The resulting stratospheric Kelvin wave spectra are compared to ECMWF operational analyses and temperature measurements of the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite instrument. Questions addressed are: the relative importance of source variability versus wind modulation, the relative importance of radiative and turbulent damping versus wave breaking, and the minimum altitude where freely propagating waves dominate the spectrum.
Highlights
Kelvin waves are the most prominent global scale equatorially trapped wave mode in atmospheric temperatures (e.g., Tindall et al, 2006a)
3.4.3 Compatibility of vertical wavelength ranges. Another cross-check was made, whether visibility filtering of the Gravity wave Regional Or Global RAy Tracer (GROGRAT) simulations is required to remove Kelvin waves with vertical wavelengths too short to be contained in the European Centre for Medium-Range Weather Forecasts (ECMWF) analyses, or too short to be visible by the SABER satellite instrument, since these two data sets will be used as a reference in Sects. 4 and 5
In our study we present a novel approach of combining space-time spectral analysis of measured data as well as ECMWF operational analyses with ray tracing techniques
Summary
Kelvin waves are the most prominent global scale equatorially trapped wave mode in atmospheric temperatures (e.g., Tindall et al, 2006a). While the wave signal observed in the troposphere is located at relatively slow phase speeds and mostly directly coupled to the convective systems, Kelvin waves observed in the stratosphere are dominated by “free” wave modes, which are excited by deep convection in the troposphere but not longer linked with the space-time patterns of the convective forcing (Randel and Wu, 2005; Ern et al, 2008; Kiladis et al, 2009) It has been demonstrated by Salby and Garcia (1987) how the atmospheric response in the near field (directly at the top of the heating source processes) is generated.
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