PHYSICS AND ENGINEERING PHYSICS

1. PHYSICS AND ENGINEERING PHYSICS F-region echo occurrence in the polar cap: A comparison of PolarDARN and Saskatoon data Mohsen Ghezelbash, H. Liu, A.V. Koustov and D. André

2. Outline: • Introduction and objectives • Seasonal variations, overall • Seasonal variations, MLT curve • Story on a noon “deep” • Story on SAS outperforming RKN • Discussion

3. Introduction ObjectivesObservationsDiscussionConclusions Questions for studies: Why do we have so many PolarDARN echoes? How much are we better in monitoring polar cap with PolarDARN than with the auroral zone radars? We are interested in echoes at MLAT>780-800

4. Introduction ObjectivesObservationsDiscussionConclusions Objectives: • Assess echo occurrence rates for RKN, INV and SAS radars with a focus on F region polar cap echoes • Infer seasonal, MLAT, and MLT tendencies • Highlight possible reasons for differences or similarities

5. IntroductionObjectives Observations DiscussionConclusions Occurrence rates for winter conditions INV and RKN seems to perform comparably at MLAT > 800. SAS is comparable at noon.

6. IntroductionObjectives Observations DiscussionConclusions MLAT profiles for INV and RKN in the noon and midnight sectors January 2010 • - INV detects echoes at ~ 20 lower latitudes than RKN, • this is consistent with its ~ 20 MLAT lower location. • However, at high latitudes echo detection rates are often • comparable, especially at noon.

7. IntroductionObjectives Observations DiscussionConclusions MLAT profiles for SAS and RKN in the noon and midnight sectors January 2010 • - SAS detects echoes at the same high latitudes at noon • SAS detects echoes at much lower latitudes at midnight

8. Seasonal variation at MLAT= 800 - 900 Average over ALL MLT sectors

10. Seasonal variation at MLAT=800 - 900 Dawn, Noon, Dusk, Midnight

11. IntroductionObjectives Observations DiscussionConclusions Seasonal Variation of F-region Echoes in 2009

12. Seasonal changes in the MLT variation at individual latitudes: MLAT=83o, 84o and 85o

13. IntroductionObjectives Observations DiscussionConclusions RKN Changes in a Shape of the MLT Dependence in 2009

14. Summary #1 • - Average echo occurrences are about the same for INV and RKN • SAS sees ~3 times fewer echoes, overall, but comparable near noon • Occurrence decreases toward summer • by ~ 2 times • - Equinoctial maxima at dusk and dawn; dusk maxima are more pronounced

15. A story about a “deep” in PolarDARN (and SAS) echo detection near winter noon

16. IntroductionObjectives Observations DiscussionConclusions Occurrence at different MLATs vs. MLT: Jan 2009 INUVIK RKN MLAT= 82°- 83° MLAT= 82°- 83° Deep within the near noon maximum

17. Outline Introduction Objectives PolarDARN Echo Occurrence CADI Observations Summary Noon deep at far ranges for winter observations Density gradients smoothed as the FoV becomes sunlit Increase in D region absorption PolarDARN HF Echo Occurrence Near Winter Magnetic Noon ● M. Ghezelbash, A. V. Koustov, D. Mori, D. André 7

18. SAS occurrence in January 2009 Rankin Inlet

19. OutlineIntroduction Objectives PolarDARN Echo Occurrence CADI Observations Summary Ground Scatter Echoes Near Noon Ground Scatter LAT= 82°- 86° Magnetic Noon F-region Echo Occurrence in the Polar Cap: A Comparison of PolarDARN and Saskatoon Data ● M. Ghezelbash, A. V. Koustov, et al. 1

20. Ray racings for RKN, Ne(IRI)*1.3 midnight noon Elev=20 Elev=10 Echoes at 1000-1500 km can be either ½ hop F region or 1&1/2 hop E region. E/F region GS is possible

21. OutlineIntroduction Objectives PolarDARN Echo Occurrence CADI Observations Summary RKN Ionosphere and Ground Scatter Occurrence (December 2010) F-region Echo Occurrence in the Polar Cap: A Comparison of PolarDARN and Saskatoon Data ● M. Ghezelbash, A. V. Koustov, et al. 1

22. Summary #2 • - INV and RKN show near noon deep in echo occurrence during winter • - SAS also shows deep but at lower latitudes • Deep is seen, to much extent, due to GS blocking detection of ionospheric signals • There is a good chance that many near noon winter ionospheric echoes are mixed with GS

23. A story on SAS being better than RKN in detection of polar cap near noon echoes

24. OutlineIntroduction Objectives PolarDARN Echo Occurrence CADI Observations Summary Outperformance of SAS Over RKN at High-Latitudes! (December 2009) F-region Echo Occurrence in the Polar Cap: A Comparison of PolarDARN and Saskatoon Data ● M. Ghezelbash, A. V. Koustov, et al. 1

25. Summary #3 • Since echoes at MLATS=800-850 for SAS are 1&1/2 hop signals, they are still seen near noon (December) while RKN detects GS • So, an auroral zone radar can be actually better for detection polar cap echoes

26. Reasons for some identified features in occurrence of polar cap echoes

27. IntroductionObjectives Observations Discussion Conclusions Factors important for HF coherent echo detection Irregularity generation • Gradient-Drift instability: • E field, density gradient, diffusion • Damping effect of E region • conductance HF propagation conditions - F layer Ne: Proper amount of refraction to meet orthogonality - F layer Ne: Threshold for detection ~ 2x105 cm-3 - D layer Ne: Radio wave absorption in the D region

28. IntroductionObjectives Observations Discussion Conclusions Features identified 1) Summer: not much echoes, only near noon. Sunlight smoothes gradients (-) Production: E fields stronger near cusp/cleft (+)? Enhanced absorption (-) Propagation: Refraction and threshold are OK (+) Electron density at 270 km Svalbard, MLAT~ 75 deg. FoV of Our Radars in Summer E fields in cusp/cleft are enhanced Threshold Ne

29. IntroductionObjectives Observations Discussion Conclusions 2) Winter: Lots of echoes, mostly near noon. Not much Sunlight, good for GD instability (+) Production: E fields stronger near cusp/cleft (+) ? Not much absorption (+) Propagation: Ne is sufficient near noon (+) It is low at other MLTs (-) Electron density at 270 km Svalbard, MLAT~ 75 deg. FoV in Winter E fields in cusp/cleft are enhanced Threshold Ne

30. IntroductionObjectives Observations Discussion Conclusions Ne at 270 km Svalbard, MLAT~750 Equinox 3) Equinox: maxima at dusk/midnight and dawn. Not so much Sun light as at summer time (+) Production: Stronger midnight E fields (?) Densities are strong and stay strong up to dawn/dusk (+) Propagation: Threshold Ne Dusk maxima should be more pronounced due to better Ne FoV at Equinox

31. IntroductionObjectives ObservationsDiscussion Conclusions Summary+plans • PolarDARN radars detect currently ~ 3 times more echoes than the auroral zone radars except of near noon where occurrence rates are often comparable. • 2) A combination of irregularity production and wave propagation factors affect the rate of echo occurrence. We would like to learn specific role played by each of the factors. • 3) Our nearest task is to assess the typical values of the E field during echo detection and in their absence (from CADIs)

32. Thank you for attention