First experimental verification of summertime mesospheric momentum balance based on radar wind measurements at 69° N

Abstract

Abstract. Gravity waves (GWs) greatly influence the background state of the middle atmosphere by imposing their momentum on the mean flow upon breaking and by thus driving, e.g., the upper mesospheric summer zonal wind reversal. In this situation momentum is conserved by a balance between the vertical divergence of GW momentum flux (the so-called GW drag) and the Coriolis acceleration of the mean meridional wind. In this study, we present first quantitative mean annual cycles of these two balancing quantities from the medium frequency Doppler radar at the polar site Saura (SMF radar, 69 • N, 16 • E). Three-year means for 2009 through 2011 clearly show that the observed zonal momentum balance between 70 and 100 km with contributions from GWs only is fulfilled during summer when GW activity is strongest and more stable than in winter. During winter, the balance between GW drag and Coriolis acceleration of the mean meridional wind is not existent, which is likely due to the additional contribution from planetary waves, which are not considered by the present investigation. The differences in the momentum balance between summer and winter conditions are additionally clarified by 3-month mean vertical profiles for summer

Mesospheric gravity wave momentum flux estimation using hybrid Doppler interferometry

“…They obtained good agreement between the gravity-wave-driven body forces and Coriolis torques in the zonal and meridional directions at Christchurch but inconsistent results at Buckland Park. In a more recent study employing DBS on the Saura MF radar, Placke et al (2015) note good agreement between body forces and Coriolis torques during summer in the MLT/I, but not during winter (as done here, attributing the winter result to planetary wave contributions to the momentum flux).…”

“…In an attempt to verify the validity of these experimental results, we (following the approaches of, e.g., Placke et al, 2015 andReid and have computed the body forces arising from the vertical divergence of the densityweighted wind field covariance, and have compared them to the Coriolis torque due to the perpendicular mean wind. These quantities should be equal when zonally averaged.…”

“…Antonita et al, 2008;Clemesha and Batista, 2008;Mitchell, 2009, 2010;Clemesha et al, 2009;Fritts et al, 2010aFritts et al, , b, 2012aVincent et al, 2010;Placke et al, 2011aPlacke et al, , b, 2014Placke et al, , 2015Andrioli et al, 2013aAndrioli et al, , b, 2015Liu et al, 2013;de Wit et al, 2014bde Wit et al, , a, 2016Matsumoto et al, 2016;Riggin et al, 2016). This has largely arisen from a need to obtain improved spatial coverage in the parameterization of GWs and their associated momentum transport in climate models of the whole atmosphere (e.g.…”

“…Fritts and Vincent, 1987;Reid and Vincent, 1987;Murphy andVincent, 1993, 1998) and to other high-frequency (HF) and very high-frequency (VHF) radars at various sites (e.g. Fukao et al, 1988;Reid et al, 1988;Fritts and Yuan, 1989;Fritts et al, 1990Fritts et al, , 1992Sato, 1990Sato, , 1993Sato, , 1994Tsuda et al, 1990;Fritts, 1990, 1991;Hitchman et al, 1992;Nakamura et al, 1993;Murayama et al, 1994;Placke et al, 2014Placke et al, , 2015Riggin et al, 2016). It was obvious in some of these studies, especially those involving radars with relatively broad ( 3 • ) transmit and receive beams, that the aspect sensitivity (or Bragg anisotropy; Muschinski et al, 2005) of the partially reflecting scatterers illuminated by the transmit beam needed to be measured and/or accounted for, or else the apparent receive beam zenith angles would overestimate the true values (see, e.g., Reid and Vincent (1987); Murphy and Vincent (1993) for two such approaches).…”

Frequency spectra and vertical profiles of wind fluctuations in the summer Antarctic mesosphere revealed by MST radar observations

“…While PMSE themselves are unique and interesting phenomena in the mesosphere, various information around the mesopause height can be deduced from PMSE observations, e.g., gravity wave characteristics Stober et al, 2013], electron density [Swarnalingam et al, 2009;Varney et al, 2011], altitude dependence of turbulence [Smirnova et al, 2012], and dust particles by HF heating experiments [Chilson et al, 2000;Rapp and Lübken, 2000;Havnes, 2004;Kassa et al, 2005]. Atmospheric wave properties are an essential factor for understanding the residual mean circulation in the mesosphere, which is determined approximately by the balance between the Coriolis force and momentum deposition by gravity waves [e.g., Holton, 1983;Watanabe et al, 2008;Becker, 2012;Placke et al, 2015]. Becker and Schmitz [2003] and subsequent studies suggest a possible interhemispheric coupling via modulation of propagation and breaking levels of planetary waves and gravity waves [Becker, 2012].…”