Abstract
We revisit previously unpublished analysis of observations of the dynamics of the mesopause region over the Norwegian Island of Andøya (69°N, 16°E) made during a 1-week period in summer 1987 during the Middle Atmosphere Cooperation-Summer in Northern Europe (MAC-SINE) campaign using the mobile SOUSY VHF (53.5 MHz) Doppler radar operating in a six-beam mode. We do this in the light of: (1) more recent developments in the measurement of the components of the density-normalized Reynolds stress tensor using meteor radars, and with medium-frequency partial reflection radars using the hybrid Doppler interferometric technique, and (2) satellite measurements of the absolute upward flux of horizontal momentum. We consider of the density-normalized total upward flux of horizontal momentum left( {overline{{u^{prime}w^{prime}}} + overline{{v^{prime}w^{prime}}} } right) for the 83–90 km height interval. Values of the component of the density-normalized flux for the 6 min to 12.8 h period range, after the tidal components have been removed, and the effects of the aspect sensitivity on the radar beam look directions have been accounted for vary between 5 m2 s−2 below 86 km and 13 m2 s−2 above 86 km. The major contribution is from the 6 to 12.8 h period range. The results of the analysis have implications for meteor radar estimates of momentum flux and also for Doppler radar measurements of the same term in the presence of aspect-sensitive scattering.
Highlights
The challenge of the measurement of the upward flux of horizontal momentum in the mesosphere lower thermosphere (MLT) region has been explored since the work of Vincent and Reid (1983), hereinafter VR83, which presented a method for doing this using multi-beam Doppler radars, using only the assumption that the statistics of the wave field are horizontally isotropic
The contribution from the 6 to 12.8 h period range dominates the other period bands. These results are consistent with those of Placke et al (2015) who used the Saura MF radar, located close to the former position of the mobile sounding system (SOUSY) radar, and the VR83 approach, to measure momentum flux and who provide the mean for June 2011
The results agree somewhat over a restricted range in summer. These authors did not correct for aspect sensitivity, nor did they remove the tidal components from their data, so there is some uncertainty around their results
Summary
The challenge of the measurement of the upward flux of horizontal momentum in the mesosphere lower thermosphere (MLT) region has been explored since the work of Vincent and Reid (1983), hereinafter VR83, which presented a method for doing this using multi-beam Doppler radars, using only the assumption that the statistics of the wave field are horizontally isotropic. We applied the least-squares inversion to calculate the individual variances and covariances corresponding to the Reynolds stress tensor terms from our data (following the removal of tidal and longer period components as described below) and found the results to be physically unreasonable except for w′2 , and extremely sensitive to outliers in the radial velocity vector This is not unexpected given the governing equations described above and given that we have a direct measure of w′2. Mean winds and tides The tidal components during this observational period have previously been discussed by Lübken et al (1990), Manson et al (1992) and Rüster (1992, 1994) for the entire MAC/SINE campaign, and further details on the results of the analysis of the mean and tidal winds may be found therein These components need to be removed from the radial velocity time series, and so we describe the approach used to calculate and remove them and note a few details.
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