Multi-instrument gravity-wave measurements over Tierra del Fuego and the Drake Passage – Part 1: Potential energies and vertical wavelengths from AIRS, COSMIC, HIRDLS, MLS-Aura, SAAMER, SABER and radiosondes

Abstract

Abstract. Gravity waves in the terrestrial atmosphere are a vital geophysical process, acting to transport energy and momentum on a wide range of scales and to couple the various atmospheric layers. Despite the importance of these waves, the many studies to date have often exhibited very dissimilar results, and it remains unclear whether these differences are primarily instrumental or methodological. Here, we address this problem by comparing observations made by a diverse range of the most widely-used gravity wave resolving instruments in a common geographic region around the southern Andes and Drake Passage, an area known to exhibit strong wave activity. Specifically, we use data from three limb-sounding radiometers (MLS-Aura, HIRDLS and SABER), the COSMIC GPS-RO constellation, a ground-based meteor radar, the AIRS infrared nadir sounder and radiosondes to examine the gravity wave potential energy (GWPE) and vertical wavelengths (λz) of individual gravity wave packets from the lower troposphere to the edge of the lower thermosphere. Our results show important similarities and differences. Limb sounder measurements show high intercorrelation, typically > 0.80 between any instrument pair. Meteor-radar observations agree in form with the limb sounders, despite vast technical differences. AIRS and radiosonde observations tend to be uncorrelated or anticorrelated with the other datasets, suggesting very different behaviour of the wave field in the different spectral regimes accessed by each instrument. Except in spring, we see little dissipation of GWPE throughout the stratosphere and lower mesosphere. Observed GWPE for individual wave packets exhibits a log-normal distribution, with short-timescale intermittency dominating over a well-repeated monthly-median seasonal cycle. GWPE and λz exhibit strong correlations with the stratospheric winds, but not with local surface winds. Our results provide guidance for interpretation and intercomparison of such datasets in their full context, and reinforce the vital point that no one dataset can represent the whole spectrum of gravity waves in the terrestrial atmosphere.

Combining AIRS and MLS observations for three‐dimensional gravity wave measurement

“…Combined AIRS/MLS data can, in principle, resolve GWs with a vertical wavelength greater than ∼12 km, subject to the precise weighting function of the AIRS channel used [see, e.g., Wright et al, 2015a, Figure 1]. In the horizontal, the resolution is a function of the angle Δ between the wave vector and the MLS scan track, with a minimum resolvable horizontal wavelength h,r = h ∕cos(Δ ) > ∼200 km.…”

“…where h is Planck's constant, c the speed of light, k B Boltzmann's constant, k r the radiance channel's wave number, and R the radiance. Channel 75 is vertically centered at 2.5 hPa (∼42 km) and has a deep weighting function with a full width at half maximum (FWHM) of ∼14 km [illustrated in Figure 1 of Wright et al, 2015a]. Our analysis is generalizable to other AIRS channels.…”

“…We now illustrate our method further by considering fluxes from all waves observed over the southern Andes during August 2008. This region is extremely important wave dynamically [e.g., Eckermann and Preusse, 1999;Jiang et al, 2002;Yan et al, 2010;Sato et al, 2012;Hoffmann et al, 2013;Hindley et al, 2015], and GW activity as observed by AIRS and MLS during this month was not atypical for the season [Wright et al, 2015a].…”

The Role of Vertically and Obliquely Propagating Gravity Waves in Influencing the Polar Summer Mesosphere

“…Wright et al (2016) determined observational filters for a multi‐instrument data set based upon the physical properties of each instrument, the radiative transfer (Preusse et al, 2002), and weighting function considerations. The authors noted that for vertical wavelengths between 4 and 20 km SABER is sensitive to GWs with horizontal wavelengths longer than ~500 km.…”

Does the Madden‐Julian Oscillation modulate stratospheric gravity waves?

“…Thus, we interpolate all COSMIC profiles to 2 km resolution prior to analysis and as a result will only observe gravity waves with vertical wavelengths greater than 4 km. In addition, limb sounding instruments, such as COSMIC, are most sensitive to mid-and low-frequency gravity waves (i.e., inertia-gravity waves) that have short vertical and long horizontal wavelengths [e.g., Wright et al, 2015]. Hence, our results are only representative of this part of the wave spectrum.…”