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\begin{document}

\title{Characteristics of Convectively Generated Gravity Waves Resolved by ERA5
Reanalysis}



\author[1]{Hamid A. Pahlavan}%
\author[1]{John M Wallace}%
\author[1]{Qiang Fu}%
\affil[1]{University of Washington}%


\vspace{-1em}



  
  \date{May 27, 2024}


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\begin{abstract}
ERA5 reanalysis with hourly time steps and 30 km horizontal resolution
resolves a substantially larger fraction of the gravity wave spectrum
than its predecessors. Based on a novel representation of the two-sided
zonal wavenumber-frequency spectrum, we show evidence of gravity wave
signatures with phase speeds centered around \selectlanguage{ngerman}±35 m/s in a suite of
atmospheric fields. Cross-spectrum analysis reveals (i) a substantial
upward flux of geopotential for both eastward and westward propagating
waves, (ii) an upward flux of westerly momentum in eastward propagating
waves and easterly momentum in westward propagating waves, and (iii)
anticyclonic rotation of the wind vector with time---all characteristics
of vertically propagating gravity and inertio-gravity waves. That
two-sided meridional wavenumber-frequency spectra computed along
individual meridians and then zonally averaged exhibit characteristics
similar to the spectra computed on latitude circles indicates that these
waves propagate in all directions. The three-dimensional structure of
these waves is also documented in composites of the temperature field
relative to grid-resolved, wave-induced downwelling events at individual
reference grid points along the equator. It is shown that the waves
radiate outward and upward relative to the respective reference grid
points, and their amplitude decreases rapidly with time. Within the
broad continuum of gravity wave phase speeds there are preferred values
around ±49 m/s and ±23 m/s , the former associated with the first
baroclinic mode in which the vertical velocity perturbations are of the
same sign throughout the depth of the troposphere, and the latter with
the second mode in which they are of opposing polarity in the lower and
upper troposphere.%
\end{abstract}\selectlanguage{ngerman}%



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