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

University of Saskatchewan Outline: 1.Introduction and objectives 2.Seasonal variations, overall 3.Seasonal variations, MLT curve 4.Story on a noon “deep” 5.Story on SAS outperforming RKN 6.Discussion

University of Saskatchewan 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> Introduction Objectives Observations Discussion Conclusions

University of Saskatchewan Objectives: 1.Assess echo occurrence rates for RKN, INV and SAS radars with a focus on F region polar cap echoes 2.Infer seasonal, MLAT, and MLT tendencies 3.Highlight possible reasons for differences or similarities Introduction Objectives Observations Discussion Conclusions

University of Saskatchewan INV and RKN seems to perform comparably at MLAT > SAS is comparable at noon. Occurrence rates for winter conditions Introduction Objectives Observations Discussion Conclusions

University of Saskatchewan MLAT profiles for INV and RKN in the noon and midnight sectors - INV detects echoes at ~ 2 0 lower latitudes than RKN, this is consistent with its ~ 2 0 MLAT lower location. - However, at high latitudes echo detection rates are often comparable, especially at noon. January 2010 Introduction Objectives Observations Discussion Conclusions

University of Saskatchewan MLAT profiles for SAS and RKN in the noon and midnight sectors - SAS detects echoes at the same high latitudes at noon - SAS detects echoes at much lower latitudes at midnight January 2010 Introduction Objectives Observations Discussion Conclusions

University of Saskatchewan Seasonal variation at MLAT= Average over ALL MLT sectors

University of Saskatchewan

Saskatchewan Seasonal variation at MLAT= Dawn, Noon, Dusk, Midnight

University of Saskatchewan Seasonal Variation of F-region Echoes in 2009 Introduction Objectives Observations Discussion Conclusions

University of Saskatchewan Seasonal changes in the MLT variation at individual latitudes: MLAT=83 o, 84 o and 85 o

University of Saskatchewan RKN Changes in a Shape of the MLT Dependence in 2009 Introduction Objectives Observations Discussion Conclusions

University of Saskatchewan 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

University of Saskatchewan A story about a “deep” in PolarDARN (and SAS) echo detection near winter noon

University of Saskatchewan MLAT= 82°- 83° Occurrence at different MLATs vs. MLT: Jan 2009 Deep within the near noon maximum MLAT= 82°- 83° INUVIKRKN Introduction Objectives Observations Discussion Conclusions

University of Saskatchewan Density gradients smoothed as the FoV becomes sunlit Increase in D region absorption Noon deep at far ranges for winter observations 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 7

University of Saskatchewan SAS occurrence in January 2009 Rankin Inlet

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

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

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

University of Saskatchewan 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

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

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

University of Saskatchewan Summary #3 -Since echoes at MLATS= 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

University of Saskatchewan Reasons for some identified features in occurrence of polar cap echoes

Factors important for HF coherent echo detection Irregularity generation HF propagation conditions - Gradient-Drift instability: E field, density gradient, diffusion - Damping effect of E region conductance - F layer Ne: Proper amount of refraction to meet orthogonality - F layer Ne: Threshold for detection ~ 2x10 5 cm- 3 - D layer Ne: Radio wave absorption in the D region Introduction Objectives Observations Discussion Conclusions

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

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

Equinox Ne at 270 km Svalbard, MLAT~75 0 Dusk maxima should be more pronounced due to better Ne FoV at Equinox Threshold Ne Introduction Objectives Observations Discussion Conclusions 3) Equinox: maxima at dusk/midnight and dawn. Production: Propagation: Not so much Sun light as at summer time (+) Densities are strong and stay strong up to dawn/dusk (+) Stronger midnight E fields (?)

University of Saskatchewan 1)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) Summary+plans Introduction Objectives Observations Discussion Conclusions

University of Saskatchewan Thank you for attention