1. University of Saskatchewan PHYSICS AND ENGINEERING PHYSICS Spectral widths of F-region PolarDARN echoes, a statistical assessment A.V. Koustov, S. Toderian and P.T. Jayachandran (UNB)

2. University of Saskatchewan Outline 1. Motivation 2. Narrow spectra 3. Spectral width vs flow angle 4. Spectral width vs ExB magnitude 5. Conclusions

3. University of Saskatchewan Motivation 1. Information on spectral width has been of limited use. In recent past, interest to the width has almost evaporated 2. New FITACF approach changed the typical values of the width (dramatically) 3. It has been suggested that F-region spectral widths should be considered in “Hz” rather than “m/s” 4. Limited data on the spectral width in the polar cap, on open magnetic flux lines. Nisitani et al. 2004 reported occurrence of “narrow” echoes in the polar cap

4. University of Saskatchewan FoVs of the Northern hemisphere SuperDARN radars as of January 2011 Polar cap echoes can be detected by all auroral zone radars as well as by Inuvik (INV) and Rankin Inlet (RKN).

5. University of Saskatchewan Auroral radars and RKN widths in m/s RKN radar and the auroral zone radars show comparable widths in the polar cap (>80 MLAT). RKN, Jan 2010Villain et al., 2002: Auroral radars

6. University of Saskatchewan RKN echo width, 1/s There is MLT variation: echoes are broader during pre-noon hours June 2010December 2010 noon Gates 26-30 Over Resolute Gates 20-22 Midnight gap

7. University of Saskatchewan Issue #1: Nature of “narrow” PolarDARN echoes

8. University of Saskatchewan Typical RKN echo width in units of 1/s. Beams 4,5 As we consider larger ranges, narrow component becomes dominating. Data were combined over 0-24 MLT Range: 945 kmRange: 1215 kmRange: 1755 km

9. University of Saskatchewan Typical RKN echo width in units of 1/s, beams 5,6, prenoon sector, 1 hour slot Gates 10-11

10. University of Saskatchewan Typical RKN echo width in units of 1/s, beams 5,6, prenoon sector Gates 14-15

11. University of Saskatchewan Typical RKN echo width in units of 1/s, beams 5,6, prenoon sector Gates 18-19

12. University of Saskatchewan Typical RKN echo width in units of 1/s, beams 5,6, prenoon sector Gates 22-23

13. University of Saskatchewan Gates 26-27, over Resolute Typical RKN echo width in units of 1/s, beams 5,6, prenoon sector

14. University of Saskatchewan Gates 30-31 Typical RKN echo width in units of 1/s, beams 5,6, prenoon sector

15. University of Saskatchewan Typical RKN echo width in units of 1/s, beams 5,6, prenoon sector Gates 34-35

16. University of Saskatchewan Typical RKN echo width in units of 1/s, beams 5,6, prenoon sector Gates 38-39

17. University of Saskatchewan Typical RKN echo width in units of 1/s, beams 5,6, prenoon sector Gates 42-42

18. University of Saskatchewan 80 0 MLAT ResBay Typical RKN echo width in units of 1/s. Beams 4,5 Max widths are at ~ 1000-1200 km. Decrease towards the Pole. Summer echoes are more narrow, by ~10-15 (1/s). INV shows similar trends Range=1125

19. University of Saskatchewan Nature of narrow spectra Hypothesis 1: Narrow component is due to mixed scatter (GS contamination) Hypothesis 2: Narrow component is due to a special type of irregularities that exist only in the polar cap. (One opinion is that they are associated with polar cap patches)

20. University of Saskatchewan John Gelleta tracings for RKN Echoes at 1000-1500 km can be either ½ hop F region or 1&1/2 hop E region. E region GS is possible Elev=10 Elev=20 midnight noon

21. University of Saskatchewan RKN echo width, 1/s f<11.2 MHz There are lots of narrow echoes in the midnight sector as well as in the noon sector. This is NOT what is expected from the GS contamination hypothesis as GS is more frequent at noon hours Gates 21-22, midnight Gates 21-22, all MLTs Testing GS hypothesis #1, 1 Gates 21-22, noon

22. University of Saskatchewan Spectral width over RB in Dec 2010 Typical width is ~ 27 1/s, red vertical line

23. University of Saskatchewan Spectral width over RB in Dec 2010 Typical width is ~ 22 1/s

24. University of Saskatchewan Spectral width over RB in Dec 2010 Typical width is ~ 45 1/s

25. University of Saskatchewan Spectral width over RB in Dec 2010 Typical width is ~ 42 1/s

26. University of Saskatchewan Spectral width over RB in Dec 2010 Typical width is ~ 35 1/s

27. University of Saskatchewan Spectral width over RB in Dec 2010 Typical width is ~ 30 1/s

28. University of Saskatchewan Spectral width over RB in Dec 2010 Typical width is ~ 15 1/s, very narrow echoes

29. University of Saskatchewan Spectral width over RB in Dec 2010 Typical width is ~ 32 1/s

30. University of Saskatchewan Spectral width over RB in Dec 2010 Typical width is ~ 30 1/s

31. University of Saskatchewan Spectral width over RB in Dec 2010 Typical width is ~ 30 1/s

32. University of Saskatchewan Spectral width over RB in Dec 2010 Typical width is ~ 30 1/s

33. University of Saskatchewan Spectral width over RB in Dec 2010 Typical width is ~ 25 1/s

34. University of Saskatchewan It seems to me that narrow echoes are a significant portion of all echoes when RKN looks along the flow (noon and late evening sectors) Testing GS hypothesis #1, 1 There are lots of narrow echoes in the midnight sector as well as in the noon sector. This is NOT what is expected from the GS contamination hypothesis as GS is more frequent at noon hours

35. University of Saskatchewan Typical RKN echo width in units of 1/s Echoes in central beams are, statistically speaking, more narrow. GS is more frequent in central beams. Signals are expected to be stronger affected by GS in central beams. Range: 1350 km Testing GS hypothesis, feature 2

36. University of Saskatchewan RKN velocity and CADI l-o-s velocity for narrow and broad echoes The velocity of narrow echoes often disagrees with the CADI ExB component (up to 500 m/s) along RKN beam 5. All echoes Noon, <50m/s Testing GS hypothesis, feature 3 N=22139 Bad 18% Good 55.0% Midnight, <50m/s

37. University of Saskatchewan RKN LOS-Velocity Significantly Decreases at Noon PolarDARN Echo Occurrence Outline Introduction Objectives PolarDARN Echo Occurrence CADI Observations Summary PolarDARN HF Echo Occurrence Near Winter Magnetic Noon ● M. Ghezelbash, A. V. Koustov, D. Mori, D. André 13 noon

38. University of Saskatchewan Joint KODIAK-Inuvik observations in “common” echo regions but from different ranges: INV: F region, KOD: F region W kod <W inv, by 10 Hz Testing GS hypothesis, 4

39. University of Saskatchewan For the time being: We cannot make for sure a statement on the nature of “narrow” echoes regularly detected by the PolarDARN radars, but it seems as many of these are GS contaminated ionospheric signals

40. University of Saskatchewan Issue #2: Does spectral width of PolarDARN echoes depend on the flow angle of observations? - CADI at Res Bay measures ExB magnitude and direction - Consider only points for which CADI and RKN velocities are consistent

41. University of Saskatchewan Spectral widths for simultaneous INV and RKN echoes detected over RB All flow angles are represented. Widths are comparable, overall. Winter: Both narrow and broad components at RKN have smaller widths

42. University of Saskatchewan RKN spectral width varies with the ExB azimuth. Tendencies are difficult to infer Lowest ExBLargest ExB

43. University of Saskatchewan Issue #3: Does spectral width (in Hz) of RKN (INV) echoes depend on ExB magnitude? 3 data sets were compiled: 1)Joint RKN-RB CADI 2)Joint INV-RB CADI 3)Joint RKN-INV-RB CADI

44. University of Saskatchewan Spectral width (in Hz) vs CADI ExB magnitude Range: 1350 km S: Slope=0.14 (1/s)/(mV/m) r: Corr. Coeff.=0.14 RKN

45. University of Saskatchewan Spectral width (in Hz) vs CADI ExB magnitude Range: ~1500 km S: Slope=0.19 (1/s)/(mV/m) r: Corr. Coeff.=0.08 INV

46. University of Saskatchewan Conclusions for Spectral Width 6-dB threshold 1)Significant portion of PolarDARN F region echoes has very low spectral widths (<10 Hz) 2)Systematic decrease of the width with range (going towards the Pole) 3)No flow angle dependence 4)Weak (statistical) increase with ExB magnitude, but correlation coefficient of the tendency is low 5)Exact single reason for occurrence of “narrow” echoes is still unknown

47. University of Saskatchewan Thank you for attention