How many waves are in the gravity wave spectrum?

Abstract

Abstract. Parametric modelling of density perturbation measurements obtained with the University of Western Ontario's Purple Crow Lidar on 5 nights are used to infer that the typical vertical wavenumber spectrum in the upper stratosphere is dominated by a few quasi-monochromatic waves. In general only 2 of these waves, with growth or decay rates on the order of 1/(14 km) or less, carry most of the spectral energy. These waves are present about half the time on the nights studied. When analyzed using classical spectral techniques these waves appear to form a continuous spectrum. These results may help explain why general circulation models obtain reasonable climatologies when gravity wave parameterization schemes based on a small number of propagating gravity waves are employed. The ProblemStatistical estimation techniques for the vertical wavenumber spectrum of gravity waves, such as the periodogram or, its equivalent, the correlogram, exhibit a rn 'p power law in the "tail" of the m-spectrum, wherep is typically between 2 and 3 (m is the vertical wavenumber and the tail of the spectrum is defined to be the region of the spectrum between approximately 1/(2500 m) and 1/(100 m)). However, this concept of a smooth spectral form in the tail is now being questioned, especially at high temporal and/or spatial resolution. The analysis of high resolution radiosonde measurements by Vincent et al. [1997] has suggested that the gravity wave field in the lower stratosphere may actually be composed of a mixture of quasi-monochromatic gravity waves and a broad spectrum. Sica and Russell [ 1999] have also shown that intermittent features with narrow bandwidths often tend to dominate the upper straWspheric m spectrum, although a smooth rn'3-type power law exists if sufficient averaging (e.g. hours) is performed.The presence of only a few "dominant" quasi-monochromatic gravity waves in stratospheric m spectra has also been observed in computer simulations. Alexander et al. [1995] have shown that forcing by deep convective processes in squall lines can generate high frequency, narrow bandwidth gravity waves which then propagate into the middle atmosphere with little dispersion. Prusa et al. [1996] have shown tropospheric forcing by Gaussian sources such as topographic features or deep convection can also produce quasi-monochromatic waves in the upper stratosphere and mesosphere through dispersive processes.Characterization of the stratospheric rn spectrum has important implications for constraining gravity wave parameterization schemes used in many global circulation models (GCMs), in part because these parametrizations range from those using a small Prony's method allows individual waves in the spectrum to be estimated from a given data series. In this study the data series are height profries of density perturbations measured by the Purple Crow Lidar's Rayleigh-scatter system [Sica et al. 1995]. A Prony analysis of these density perturbation measurements will then allow us to determine whether or not the spectrum is compris...

Advection, Phase Distortion, and the Frequency Spectrum of Finescale Fields in the Sea

“…This effort complements a recent thrust in atmospheric research, in which both dynamic (Hines 1991;Chunchuzov 1996Chunchuzov , 2002 and kinematic (Eckermann 1999;Sica and Russell 1999;Klaassen and Sonmor 2006) efforts to model the vertical wavenumber spectrum of horizontal velocity have been developed. Here, the frequency spectrum associated with any given wavenumber spectrum is modeled using a purely statistical approach.…”

A review of Mesosphere–Stratosphere–Troposphere (MST) radar developments and studies, circa 1997–2008

“…The question also arises as to whether the universal spectrum is really only a long-term average, or something more robust. For example, Sica and Russell (1999) have proposed that above any one site, there are really only a few waves present at any one time, and the universal spectrum only results when using long-term averages. Studies of this spectrum have been less frequent since the mid-1990s than before.…”

Seasonal and nightly variations of gravity-wave energy density in the middle atmosphere measured by the Purple Crow Lidar

“…This procedure acknowledges the fact that the wave spectrum over London is typically dominated by 1 or 2 long vertical wavelength (e.g. 10 km) waves (Sica and Russell, 1999). It also avoids using temperature measurements to determine fluctuations.…”

“…Brasseur and Solomon, 1984). Since a typical gravity wave spectrum over London contains only a few waves carrying most of the energy, it is reasonable to assume the KED determinations are due to only a few dominant monochromatic waves (Sica and Russell, 1999). This physical picture will guide us in looking at individual nights, as well as the seasonal averages.…”