Characteristics of atmospheric gravity wave activity in the polar regions revealed by GPS radio occultation data with CHAMP

Abstract

[1] Using GPS radio occultation data during 2001-2005, we studied the climatological behavior of atmospheric gravity waves in the polar stratosphere. We calculated temperature fluctuations with vertical wavelengths shorter than 7 km and then determined the wave potential energy, E p , every month in a longitude-latitude cell of 20°Â 10°b etween 12 km and 33 km. In the Arctic region (50-90°N), E p shows an annual variation with maximum in winter, consistent with the zonal mean horizontal wind, V, and the Eliassen-Palm (E-P) flux, F z . The large F z values indicate higher planetary wave activity, resulting in distortion of the polar vortex. The unbalanced flow can then excite gravity waves through geostrophic adjustment. In the Antarctic region (50-90°S), E p gradually increases during winter and reaches its maximum in spring before decreasing rapidly. The time derivative of V coincides with the E p peak and the horizontal distribution of E p has a similar structure to V, suggesting that the E p enhancement is closely related to the decay of the polar vortex. During major warming events over the Arctic, the divergence of E-P flux, DF, was enhanced, coinciding with large E p . In the Antarctic, DF strongly correlates with E p in spring. Gravity waves seem to be effectively generated through planetary wave transience and/or breaking. Orographic generation of gravity waves seems to be important in limited areas only, such as Scandinavia and the Antarctic Peninsula, showing that it is less important than the polar night jet in determining the climatological behavior of gravity waves.Citation: Hei, H., T. Tsuda, and T. Hirooka (2008), Characteristics of atmospheric gravity wave activity in the polar regions revealed by GPS radio occultation data with CHAMP,

Global distribution of vertical wavenumber spectra in the lower stratosphere observed using high-vertical-resolution temperature profiles from COSMIC GPS radio occultation

“…The ratio at 10 • S-10 • N latitude showed a steady enhancement, exceeding 1.0, regardless of season and longitude. The ratio at middle latitudes in the NH in region (a) was significantly enhanced in winter, being close to 1.0, suggesting the evident effects of topography in generating GWs by the Tibetan Plateau, located at around 30-50 • N ( Alexander et al, 2008a;Hei et al, 2008). At 50-80 • N the ratio was about 0.6-0.75 in winter, again indicating a relationship with topography (refer to Fig.…”

“…However, at 45-65 • S in region (a), the annual cycle seen at low latitudes became unclear, indicating a gap at around 45 • S. However, in region (b), the seasonal cycle was extended smoothly down to about 55 • S. Thus, effects of topography (Australian continent) seem to be important in the E T p variations in region (a). In the Antarctic region, E T p became maximum in spring, showing a good correlation with the polar vortex (Yoshiki et al, 2004;Baumgaertner and McDonald, 2007;Hei et al, 2008;Sato et al, 2012). The differences in the magnitudes of E T p between regions (a) and (b) could be attributed to the difference in topography.…”

“…Orographic generation of GWs has previously been observed with balloon soundings and satellite measurements over the Andes (Alexander et al, 2008a) and Antarctica (Baumgaertner and McDonald, 2007;Sato and Yoshiki, 2008). Effects of the polar night jet and sudden stratospheric warming events on GW excitation have also been studied (Yoshiki et al, 2004;Hei et al, 2008).…”

An intercomparison of stratospheric gravity wave potential energy densities from METOP GPS radio occultation measurements and ECMWF model data

“…However, global satellite observations are needed to determine dominant tropospheric source regions and processes as well as global propagation pathways and the resulting gravity wave drag imposed on the mean flow to constrain GW parameterizations for climate and weather prediction models (Alexander et al, 2010;Geller et al, 2013). Since the pioneering work by Fetzer and Gille (1994), Wu and Waters (1996), and Eckermann and Preusse (1999) there have been many attempts to characterize the global distribution of gravity wave activity using such different remote-sensing techniques as Limb (e.g., Ern et al, 2004Ern et al, , 2011Preusse et al, 2009;Zhang et al, 2012) and Nadir sounders (e.g., Hoffmann et al, 2016;Ern et al, 2017), as well as GPS-based radio occultation (RO) measurements (e.g., Tsuda et al, 2000;Hei et al, 2008;Schmidt et al, 2008Schmidt et al, , 2016Fröhlich et al, 2007;Hindley et al, 2015;Šácha et al, 2015;Khaykin et al, 2015;Khaykin, 2016). This paper focusses on the derivation of gravity wave potential energy densities (E P ) from GPS RO measurements on board the operational METOP-A and METOP-B satellites operated by EUMETSAT (European Organisation for the Exploitation of Meteorological Satellites) and the subsequent systematic comparison of E P fields with ECMWF (European Centre for Medium-Range Weather Forecasts) operational forecast and reanalysis data.…”

Spectral energy transfer of atmospheric gravity waves through sum and difference nonlinear interactions

“…Gravity wave activity has been statistically investigated based on various observations (Tsuda et al, 1990;Manson and Meek, 1993;Nekrasov et at., 1995;Vincent and Alexander, 2000;Zink and Vincent, 2001;Alexander and Teitelbaum, 2007;Yi, 2005, 2007;Hei et al, 2008;Zhang et al, 2010), and possible mechanisms of generation and dissipation of gravity waves have been extensively explored in the past decades (Walterscheid and Schubert, 1990;Fovell et al, 1992;Fritts and Luo, 1992;Alexander et al, 1995;Hecht, 2001;Lane et al, 2001;Kshevetskii and Gavrilov, 2005;Liu and Gardner, 2005;Liu, 2009;Vadas and Liu, 2009). Nonlinearity is an important aspect of gravity wave dynamics.…”