Gravity wave flux retrievals using meteor radars

Abstract

The ability of all‐sky interferometric meteor radars to measure mean wind and high‐frequency gravity wave wind perturbations from meteor radial velocities is assessed. A Monte‐Carlo technique that models line‐of‐sight meteor wind measurements with realistic errors in angle‐of‐arrival and range is used to investigate uncertainties in mean wind and gravity wave wind parameters as a function of meteor echo rate. It is shown that mean horizontal wind speeds are recovered with reasonable accuracy at meteor rates as low as 10 hr−1. Mean‐square horizontal wind perturbation can be derived with relatively little averaging, but momentum fluxes are recovered with much less accuracy, which means that considerable averaging is required to produce meaningful values. Results are illustrated using meteor wind radar observations taken over a 30‐day period in January–February 2006 in Northern Australia.

Momentum flux determination using the multi-beam Poker Flat Incoherent Scatter Radar

“…In this section, we extend the simulations to include a realistic wave field, mainly to investigate the effects of realistic horizontal variations in the perturbed radial velocity fields, similar to the approach taken by others (e.g., Fritts et al, 2010Fritts et al, , 2012Vincent et al, 2010). We simulate a case which is similar to Case 1 of Fritts et al (2010) and Fritts et al (2012), in which we have fixed mean, diurnal tide and semidiurnal tidal amplitudes for the background winds in addition to imposed gravity wave variations.…”

“…Kudeki and Franke, 1998;Thorsen et al, 2000;Vincent et al, 2010). For the case of this simulation, we have assumed that N 3 = 60 statistically independent points exist with which to compute the line-of-sight variances and corresponding wind variances and co-variances.…”

“…Similar approaches have been extended to MF broad beam interferometric radars (Thorsen et al, 1997), incoherent scatter radars (ISRs) operating at VHF and UHF Fritts et al, 2006;Janches et al, 2006), and Doppler lidar systems (Acott, 2009). More recently, Hocking (2005) has generalized the approach for application to meteor radars, a technique that has been employed in several studies of gravity waves (GWs) (e.g., Antonita et al, 2008;Clemesha et al, 2009;Placke et al, 2011b,a), validated by Fritts et al (2010) in applications of the SAAMER meteor radar in studies of mean winds, tides and GWs, and used by Vincent et al (2010) in an assessment of GW momentum flux measurements by meteor radars. In this paper, we outline a technique for multi-beam radars to estimate the vertical flux of Hocking (2005), this technique is more applicable to the case of fixed-look directions determined a priori, rather than to the case of line-of-sight wind measurements from random meteor trail locations.…”

Gravity-wave momentum fluxes in the mesosphere over Ascension Island (8° S, 14° W) and the anomalous zonal winds of the semi-annual oscillation in 2002

“…Although not originally designed to measure momentum fluxes, standard Skiymet systems nevertheless have a proven ability to do so (e.g. Hocking, 2005;Fritts et al, 2010Fritts et al, , 2012Vincent et al, 2010;Andrioli et al, 2013;de Wit et al, 2014;Placke et al, 2015), albeit with a lower resolution than advanced systems specifically designed for this task (Fritts et al, 2012). The ability to estimate gravity-wave momentum fluxes ultimately relies on being able to separate the contributions to the radial velocity of each individual meteor made by gravity waves from the contributions made by background winds, tides and planetary waves.…”

Improved analysis of all-sky meteor radar measurements of gravity wave variances and momentum fluxes

“…These include Antonita et al (2008) for Trivandrum in the tropics, Clemesha et al (2009) at three low-latitude locations in Brazil, Fritts et al (2010) for Tierra del Fuego at middle latitude, Placke et al (2011b) for Collm at middle latitude, and Placke et al (2011a) at three locations in Europe. While the main aim of Hocking's analysis is the study of GW momentum fluxes, Vincent et al (2010) showed that it is necessary to average for more than one month to get useful results for traditional meteor radars, basically because determination of the momentum fluxes requires the measurement of small vertical velocities. In this paper we present an improvement in the analysis of the traditional meteor radar data that allow us to infer at least a monthly mean of GW momentum fluxes using Hocking's analysis.…”