Lidar observations of gravity wave activity in the middle atmosphere over Davis (69°S, 78°E), Antarctica

Abstract

A 16 month series of lidar measurements in the stratosphere and mesosphere-lower thermosphere (MLT) region over Davis Station (69 ∘ S, 78 ∘ E) in Antarctica is used to study gravity waves. The unprecedentedly large number of observations totaling 2310 h allows us to investigate seasonal variations in gravity wave activity in great detail. In the stratosphere the gravity wave potential energy density (GWPED) is shown to have a large seasonal variation with a double peak in winter and minimum in summer. We find conservative wave propagation to occur between 29 and 41 km altitude in winter as well as in summer, whereas smaller energy growth rates were observed in spring and autumn. These results are consistent with selective critical-level filtering of gravity waves in the lower stratosphere. In the MLT region the GWPED is found to have a semiannual oscillation with maxima in winter and summer. The structure of the winter peak is identical to that in the stratosphere, suggesting that the gravity wave flux reaching the MLT region is controlled by the wind field near the tropopause level. IntroductionAtmospheric gravity waves are important for vertical coupling in the atmosphere. They transport energy and momentum vertically and horizontally over large distances. At high latitudes, dissipation of these waves in the mesosphere-lower thermosphere region (hereafter MLT region) transfers momentum into the background flow, driving a global meridional circulation from the summer pole to the winter pole [Lindzen, 1981;Holton, 1983]. Associated with this circulation is the upwelling of air at the summer pole causing the strong adiabatic cooling of the summer MLT region [Andrews et al., 1987;Becker, 2012]. This gravity wave-induced cooling gives rise to observed temperatures as low as 130 K which are far from radiative equilibrium [Lübken, 1999;Lübken et al., 2014]. For this reason, phenomena like noctilucent clouds and polar mesospheric summer echoes are limited to the summer polar region [Olivero and Thomas, 1986]. Without gravity wave-induced cooling, temperatures in the summer MLT remain above the frost point [Rapp and Thomas, 2006]. The occurrence of noctilucent clouds is thus a result of gravity waves propagating from the troposphere/lower stratosphere into the MLT region.Gravity waves have been extensively studied in models [e.g., Zhang, 2004] as well as through employing observational techniques such as lidars [e.g., Rauthe et al., 2008;Yamashita et al., 2009], radars [e.g., Nicolls et al., 2010 Lue et al., 2013], radiosondes [e.g., Allen andVincent, 1995;Moffat-Griffin et al., 2011], satellite-based radiometers [e.g., Alexander et al., 2008;Wright and Gille, 2013], and Global Positioning System radio occultation [e.g., Wang and Alexander, 2010]. Among all observational techniques, lidars provide the highest temporal and vertical resolutions over a wide altitude range and observation periods up to several days.

Evaluation of methods for gravity wave extraction from middle-atmospheric lidar temperature measurements

“…By transporting energy and momentum from the lower atmosphere into the middle atmosphere, they are responsible for the formation of the cold polar summer mesopause (e.g., Lindzen, 1981). Although some processes related to gravity waves are believed to be well understood, there are still open questions.…”

“…The sliding polynomial fit has been applied in several studies (e.g., Duck et al, 2001;Alexander et al, 2011;Kaifler et al, 2015b). Different authors use temperature data with different altitude resolutions and slightly different parameter setups for L f , L w and γ .…”

“…Lidar technology has been used to study gravity waves in the middle atmosphere for the last 3 decades (e.g., Chanin and Hauchecorne, 1981;Gardner et al, 1989;Wilson et al, 1991;Whiteway and Carswell, 1995;Duck et al, 2001;Rauthe et al, 2008;Yamashita et al, 2009;Alexander et al, 2011;Kaifler et al, 2015b). Hence, lidar studies can potentially be used to infer long-term trends in gravity wave activity.…”

On the Interpretation of Gravity Wave Measurements by Ground-Based Lidars

“…However, the magnitudes and directions of horizontal propagation differ as a function of U, as expected from Equation (18) (Figure 7). Figure 8 depicts the vertical time series of the four cases: the phase lines for U = c Px (Figure 8a) are compressed compared to the case U = 0 (Figure 8b).…”

“…There are specific case studies, e.g., [1][2][3][4][5][6][7]; there are climatologies to determine the seasonal dependence of gravity wave activity or their relation to the atmospheric background conditions [8][9][10][11][12][13][14][15][16][17][18][19]; and there are studies developing the methodology to retrieve gravity wave signatures, e.g., [20]. Recently, the output of the high-resolution analyses of the Integrated Forecast System of the ECMWF was compared with lidar measurements in the middle atmosphere, e.g., [21].…”