A climatology of tides in the Antarctic mesosphere and lower thermosphere

Abstract

[1] A function that approximates atmospheric tidal behavior in the polar regions is described. This function is fitted to multistation radar measurements of wind in the mesosphere and lower thermosphere with the aim of obtaining a latitude-longitude-height description of the variation of tides over the whole Antarctic continent. Archival wind data sets are combined with present-day ones to fill the spatial distribution of the observations and to reduce the potential effects of spatial aliasing. Multiple years are combined through the compilation of monthly station composite days, yielding results for each month of the year. Despite potential problems associated with year-to-year variations in the tidal phase, a useful climatology of Antarctic zonal and meridional tidal wind components is compiled. The results of the fits reproduce the major features of the high-latitude tidal wind field: the dominance of the semidiurnal migrating mode in the winter months and the presence of a semidiurnal zonal wave number one component in the summer months. It is also found that the summer semidiurnal tide contains a zonal wave number zero component.

MF radar observations of the diurnal tide over Syowa, Antarctica (69° S, 40° E)

“…3.1 are mostly consistent with previous studies (Avery et al, 1989;Baumgaertner et al, 2005;Murphy et al, 2006;Hibbins et al, 2007) concerning the MLT diurnal tide over Antarctica as described in Sect. 1.…”

“…The westward-propagating semidiurnal tide with a zonal wavenumber 1 was observed at the South Pole throughout the year (Hernandez et al, 1993;Forbes et al, 1995;Portnyagin et al, 1998). Murphy et al (2006) divided semidiurnal components of zonal and meridional winds into migrating and nonmigrating tides with zonal wavenumbers 0-3 using data from several Antarctic stations. However, the nonmigrating diurnal tide with significant amplitude in the polar region has never been reported, so that the diurnal tide observed in the Antarctic MLT region is regarded as migrating.…”

Arctic tidal characteristics at Eureka (80° N, 86° W) and Svalbard (78° N, 16° E) for 2006/07: seasonal and longitudinal variations, migrating and non-migrating tides

“…Again, as noted earlier, Murphy et al (2006) also discussed the diurnal tide obtained from fitting spatial tidal harmonics to data from 5 "outer rim" radars. Hence, there is no technical or physical reason why the radars operating in Antarctica would not have detected tidal signals consistent with diurnal NMT if they existed.…”

“…12 that the Antarctic-winter SPW, which are relatively small, are responsible for significant NMT activity in the Arctic summer. Indeed, given the strong NMT activity in the Arctic-winter and spring that we are now reporting, when the local SPW are large, it is very likely that the prominent and observed NMT activity of the Antarctic-summer (Murphy et al, 2006;Baumgaertner et al, 2006;12-h NMT s=+1 as discussed in Sect. 1) is associated with the global presence of these NMT.…”

“…Enthusiasm to share the riches of the continent has provided up to five contemporaneous radars over the last 2 decades, more evenly spaced than in the NH, but still with a 120 • longitudinal gap. Murphy et al (2006) used these five radars plus early data from two others (plus assumptions of year to year stationarity) to identify a dominant semidiurnal NMT of s=+1 (and a lesser s=0) during summer-equinox months (October-March). The regional average latitude was 69 • S. They were did not demonstrate the presence of NMT for the diurnal tide away from the pole, as their monthly mean profiles (amplitude and phase) for the "outer rim" (67-78 • S) of MF radars were significant for the MT (s=+1) only.…”