Dynamics of the Antarctic and Arctic mesosphere and lower thermosphere – Part 1: Mean winds

Abstract

Abstract. Zonal and meridional winds have been measured in the upper mesosphere and lower thermosphere at polar latitudes using two ground-based meteor radars. One radar is located at Rothera (68 • S, 68 • W) in the Antarctic and has been operational since February 2005. The second radar is located at Esrange (68 • N, 21 • E) in the Arctic and has been operational since October 1999. Both radars have produced relatively continuous measurements. Here we consider measurements made up to the end of 2009. Both radars are of similar design and at conjugate geographical latitudes, making the results directly comparable and thus allowing investigation of the differences in the mean winds of the Antarctic and Arctic regions. The data from each radar have been used to construct climatologies of monthly-mean zonal and meridional winds at heights between 80 and 100 km. Both Antarctic and Arctic data sets reveal seasonally varying zonal and meridional winds in which the broad pattern repeats from year to year. In particular, the zonal winds display a strong shear in summer associated with the upper part of the westward summertime zonal jet. The winds generally reverse to eastward flow at heights of ∼90 km. The zonal winds are eastward throughout the rest of the year. The meridional winds are generally equatorward over both sites, although brief episodes of poleward flow are often evident near the equinoxes and during winter. The strongest equatorward flows occur at heights of ∼90 km during summer.There are significant differences between the mean winds observed in the Antarctic and Arctic. In particular, the westward winds in summer are stronger and occur earlier in the season in the Antarctic compared with the Arctic. The eastward winds evident above the summertime zonal wind reversal are significantly stronger in the Arctic. The summertime equatorward flow in the Antarctic is slightly weaker, but occurs over a greater depth than is the case in the Arctic.Correspondence to: D. J. Sandford (d.j.sandford@bath.ac.uk) Comparisons of these observations with those of the URAP and HWM-07 empirical models reveal a number of significant differences. In particular, the zonal winds observed in the Antarctic during wintertime are significantly weaker than those of URAP. However, the URAP zonal winds are a good match to the observations of the Arctic. Significant differences are evident between the observations and HWM-07. In particular, the strong wintertime zonal winds of the Arctic in HWM-07 are not evident in the observations and the summertime zonal winds in HWM-07 are systematically stronger than observed. The agreement with meridional winds is generally poor.There is a significant amount of inter-annual variability in the observed zonal and meridional winds. Particularly high variability is observed in the Arctic zonal winds in spring and is probably associated with stratospheric warmings.

Winds and tides in the mid-latitude Southern Hemisphere upper mesosphere recorded with the Falkland Islands SuperDARN radar

“…Although the data represent only one year, and previous studies have revealed significant natural interannual variability in the MLT region (e.g. Fraser et al, 1989;Portnyagin et al, 2006;Baumgaertner et al, 2006;Hibbins et al, 2007a;Sandford et al, 2010) we aim to highlight and interpret some of the observed similarities and differences. Fritts et al (2010) used a meteor radar located at Rio Grande on Tierra del Fuego (54 • S, 68 • W) to study the large scale winds and tides at meteor ablation altitudes during the period May 2008 to September 2009.…”

“…Pancheva, 2006;Buriti et al, 2008;Andrioli et al, 2009;Guo and Lehmacher, 2009;Lima et al, 2005Lima et al, , 2006Malinga and Poole, 2002;Kovalam and Vincent, 2003) and high latitude Antarctic stations (e.g. Portnyagin et al, 1998;Baumgaertner et al, 2005;Murphy et al, 2006;Hibbins et al, 2006;Merzlyakov et al, 2009;Sandford et al, 2010) In this paper we report on the first year of observations from the SuperDARN Falkland Islands radar (FIR) on the dynamics of the upper mesosphere above the South Atlantic. We use meteor trail drift velocities to determine hourly mean horizontal winds around 90 km altitude and use these to characterize the background winds, the quasi two-day wave and the diurnal, semidiurnal and terdiurnal tidal motions.…”

Simulation study for measurement of horizontal wind profiles in the polar stratosphere and mesosphere using ground-based observations of ozone and carbon monoxide lines in the 230–250 GHz region

“…Between altitudes of 40 to 60 km the standard deviation of the mean difference in zonal winds exceeds 20 m s −1 with the largest differences in winter when variability associated with large-scale planetary waves dominates. High-latitude mesospheric horizontal winds in HWM-07 (Drob et al, 2008) have standard deviations greater than 25 m s −1 and significant differences with observed zonal and meridional winds above 80 km (Sandford et al, 2010). With ECMWF producing specifications based on temperature soundings up to 75 km and fully assimilative high-top global circulation models being extended into the thermosphere, there is considerable urgency to verify the mean horizontal winds in models and meteorological (re)analyses.…”

Mean winds, temperatures and the 16- and 5-day planetary waves in the mesosphere and lower thermosphere over Bear Lake Observatory (42° N, 111° W)

“…Large meridional winds have been reported in the summertime MLT at polar-latitudes (e.g., Hocking, 2001;Sandford et al, 2010), mid-latitudes (e.g., Manson and Meek, 1987;Hall et al, 2008;Roper and Berkey, 2011) and equatoriallatitudes (e.g., Rajaram and Gurubaran, 1998;Kishore et al, 2000;Sharma et al, 2010).…”