Presentation given at COSPAR 2008. Looking at using meteor radar to study atmospheric gravity waves. Covers introduction to the method and then Arctic / Antarctic comparisons and seasonal behaviour

1. Seasonal variability of gravity waves and tidal/gravity-wave interactions in the Arctic and Antarctic MLT Charlie Beldon & Nick Mitchell Centre for Space, Atmospheric and Oceanic Science Department of Electronic and Electrical Engineering University of Bath [email_address] COSPAR 2008

3. Rothera, Antarctica (68ºS, 68ºW) Esrange, Sweden (68ºN, 21ºE) Location of Radars

9. Example of the data

10. Seasonal behaviour

12. Summer Profiles:

14. Summer Profiles:

15. What controls the summer wave activity? Rothera Esrange

19. Exclusion circles 20 km Zonal Phase Speed -50 0 50 50 0 -50 Meridional Phase Speed URAP zonal winds

20. Exclusion circles Zonal Phase Speed -50 0 50 50 0 -50 Meridional Phase Speed 30 km URAP zonal winds

21. Exclusion circles Zonal Phase Speed -50 0 50 50 0 -50 Meridional Phase Speed 40 km URAP zonal winds

22. Exclusion circles Zonal Phase Speed -50 0 50 50 0 -50 Meridional Phase Speed 50 km URAP zonal winds

23. Exclusion circles Zonal Phase Speed -50 0 50 50 0 -50 60 km Meridional Phase Speed URAP zonal winds

24. Exclusion circles Zonal Phase Speed -50 0 50 50 0 -50 Meridional Phase Speed 70 km URAP zonal winds

25. Exclusion circles Zonal Phase Speed -50 0 50 50 0 -50 Meridional Phase Speed 80 km URAP zonal winds

26. Exclusion circles Zonal Phase Speed -50 0 50 50 0 -50 Meridional Phase Speed 81.1 km Radar zonal and meridional winds

27. Exclusion circles Zonal Phase Speed -50 0 50 50 0 -50 Meridional Phase Speed 84.6 km Radar zonal and meridional winds

28. Exclusion circles Zonal Phase Speed -50 0 50 50 0 -50 Meridional Phase Speed 87.5 km Radar zonal and meridional winds

29. Exclusion circles Zonal Phase Speed -50 0 50 50 0 -50 Meridional Phase Speed 90.4 km Radar zonal and meridional winds

30. Exclusion circles Zonal Phase Speed -50 0 50 50 0 -50 Meridional Phase Speed 93.3 km Radar zonal and meridional winds

31. Exclusion circles Zonal Phase Speed -50 0 50 50 0 -50 Meridional Phase Speed 96.8 km Radar zonal and meridional winds

33. What controls the wave activity? (Temperature data from L ü bken et al, 2004, falling sphere climatology)

35. Equinoctial minima – filtering of low phase-speed waves Seasonal cycle

36. COMPOSITE YEAR VARIANCE, ESRANGE Note : Esrange data shifted by 6 months Arctic/Antarctic comparisons COMPOSITE YEAR VARIANCE, ROTHERA

40. Tidal/gravity-wave interactions

41. Modulations of gravity-wave activity AMPLITUDE (m 2 s -2 ) PERIOD (DAYS)

51. i.e., more gravity-wave activity in spring over Rothera than Esrange less gravity-wave activity in summer over Rothera at greater heights Inter-hemispheric Comparisons

53. Meridional Winds

54. Modulation of Gravity-wave Activity

55. Gravity wave scales sizes Meteor radars cannot easily resolve individual waves of short horizontal wavelength (< ~ 1,000 km) or high frequency (periods < ~ 2 hours)

56. Equinoctial minima – filtering of low phase-speed waves Seasonal Cycle - Filtering

57. NB, six routine height gates of 5, 3, 3, 3, 3, 5 km Meteor radar winds January 6, 2007 over Rothera (68 ˚S) Can not easily resolve individual waves of short horizontal wavelength (< ~ 1,000 km) or high frequency (periods < ~ 2 hours)

58. January 6, 2007 over Rothera (68 ˚S) Meteor radar winds NB, six routine height gates of 5, 3, 3, 3, 3, 5 km

62. Seasonal cycle and short-term variability Rothera (68˚S) Variance (m 2 s -2 ) Variance (m 2 s -2 )

63. 12-hours 24-hours Modulation of gravity-wave activity

64. Modulation of gravity-wave activity