Abstract
Abstract. Gravity waves are one of the main drivers of atmospheric dynamics. The spatial resolution of most global atmospheric models, however, is too coarse to properly resolve the small scales of gravity waves, which range from tens to a few thousand kilometers horizontally, and from below 1 km to tens of kilometers vertically. Gravity wave source processes involve even smaller scales. Therefore, general circulation models (GCMs) and chemistry climate models (CCMs) usually parametrize the effect of gravity waves on the global circulation. These parametrizations are very simplified. For this reason, comparisons with global observations of gravity waves are needed for an improvement of parametrizations and an alleviation of model biases. We present a gravity wave climatology based on atmospheric infrared limb emissions observed by satellite (GRACILE). GRACILE is a global data set of gravity wave distributions observed in the stratosphere and the mesosphere by the infrared limb sounding satellite instruments High Resolution Dynamics Limb Sounder (HIRDLS) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). Typical distributions (zonal averages and global maps) of gravity wave vertical wavelengths and along-track horizontal wavenumbers are provided, as well as gravity wave temperature variances, potential energies and absolute momentum fluxes. This global data set captures the typical seasonal variations of these parameters, as well as their spatial variations. The GRACILE data set is suitable for scientific studies, and it can serve for comparison with other instruments (ground-based, airborne, or other satellite instruments) and for comparison with gravity wave distributions, both resolved and parametrized, in GCMs and CCMs. The GRACILE data set is available as supplementary data at https://doi.org/10.1594/PANGAEA.879658.
Highlights
Our work is focused mainly on the stratosphere and mesosphere, i.e., on the middle atmosphere in the approximate altitude range from 20 to 90 km
Some comparisons are based on gravity wave variances or amplitudes (e.g., Choi et al, 2009, 2012; Stephan and Alexander, 2015), while others use momentum fluxes (e.g., Ern et al, 2006; Fröhlich et al, 2007; Orr et al, 2010; Trinh et al, 2016; Kalisch et al, 2016). Because these first comparisons have already led to promising results, the aim of our work is to provide a climatological data set, GRACILE (GRAvity wave Climatology based on Infrared Limb Emissions observed by satellite), of gravity wave temperature variances, squared temperature amplitudes, potential energies, horizontal wavenumbers, vertical wavelengths, and momentum fluxes based on 3 years (March 2005 until February 2008) of High Resolution Dynamics Limb Sounder (HIRDLS) observations, and on 13 years (February 2002 until January 2015) of Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) observations
We describe how the data were gridded from observed altitude profiles into global maps and zonal-average cross sections, and which data sets are available in the GRACILE gravity wave climatology
Summary
Our work is focused mainly on the stratosphere and mesosphere, i.e., on the middle atmosphere in the approximate altitude range from 20 to 90 km. One of the major challenges of methods for removing the atmospheric background state from observed temperature altitude profiles is to effectively separate the fluctuations due to planetary waves (which are usually much larger in amplitude) from those of gravity waves. This separation is done via a separation of scales, either vertically or horizontally. Scale separation in vertical direction works well in the wintertime polar lower stratosphere where vertical wavelengths of planetary waves are quite long, while those of gravity waves are usually much shorter This approach has its shortcomings in the tropics where planetaryscale equatorial wave modes and gravity waves generally have similar vertical wavelengths (e.g., Ern et al, 2008; Ern et al, 2014). Another general problem is that, by introducing a strong low-pass for vertical wavelengths, the remaining spectral range of gravity waves is considerably narrowed down
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