Mesospheric winds measured by medium-frequency radar with full correlation analysis: error properties and impacts on studies of wind variance

摘要

The mesosphere is one of the most difficult parts of theatmosphere to sample; it is too high for balloon measurements and too low forin situ satellites. Consequently, there is a reliance on remote sensing(either from the ground or from space) to diagnose this region. Ground-basedradars have been used since the second half of the 20th century to probe thedynamics of the mesosphere; medium-frequency (MF) radars provide estimatesof the horizontal wind fields and are still used to analyse tidal structuresand planetary waves that modulate the meridional and zonal winds. Thevariance of the winds has traditionally been linked qualitatively to theoccurrence of gravity waves. In this paper, the method of wind retrieval(full correlation analysis) employed by MF radars is considered withreference to two systems in Antarctica at different latitude (Halley at76∘ S and Rothera at 67∘ S). It is shown that the widthof the velocity distribution and occurrence of “outliers” is related to themeasured levels of anisotropy in the received signal pattern. The magnitudeof the error distribution, as represented by the wind variance, varies withboth insolation levels and geomagnetic activity. Thus, it is demonstratedthat for these two radars the influence of gravity waves may not be theprimary mechanism that controls the overall variance.