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 University of SaskatchewanSaskatchewan

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 University of SaskatchewanSaskatchewan

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

Introduction Objectives Observations Discussion Conclusions

University of University of SaskatchewanSaskatchewan

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 University of SaskatchewanSaskatchewan

INV and RKN seems to perform comparablyat MLAT > 800. SAS is comparable at noon.

Occurrence rates for winter conditions

Introduction Objectives Observations Discussion Conclusions

University of University of SaskatchewanSaskatchewan

MLAT profiles for INV and RKN in the noon and midnight sectors

- 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.

January 2010

Introduction Objectives Observations Discussion Conclusions

University of University of SaskatchewanSaskatchewan

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 University of SaskatchewanSaskatchewan

Seasonal variationat MLAT= 800 - 900 Average over ALL MLT sectors

University of University of SaskatchewanSaskatchewan

University of University of SaskatchewanSaskatchewan

Seasonal variationat MLAT=800 - 900

Dawn, Noon, Dusk, Midnight

University of University of SaskatchewanSaskatchewan

Seasonal Variation of F-region Echoes in 2009

Introduction Objectives Observations Discussion Conclusions

University of University of SaskatchewanSaskatchewan

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

University of University of SaskatchewanSaskatchewan

RKN Changes in a Shape of the MLT Dependence in 2009

Introduction Objectives Observations Discussion Conclusions

University of University of SaskatchewanSaskatchewan

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 University of SaskatchewanSaskatchewan

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

University of University of SaskatchewanSaskatchewan

MLAT= 82°- 83°

Occurrence at different MLATs vs. MLT: Jan 2009

Deep within the near noon maximum

MLAT= 82°- 83°

INUVIK RKN

Introduction Objectives Observations Discussion Conclusions

University of University of SaskatchewanSaskatchewan

Density gradients smoothed as the FoV becomes sunlit

Increase in D region absorption

Noon deep at far ranges for winter observations

Outline Introduction Objectives PolarDARN Echo Occurrence PolarDARN Echo Occurrence CADI Observations Summary

PolarDARN HF Echo Occurrence Near Winter Magnetic Noon ● M. Ghezelbash, A. V. Koustov, D. Mori, D. André PolarDARN HF Echo Occurrence Near Winter Magnetic Noon ● M. Ghezelbash, A. V. Koustov, D. Mori, D. André 7 7

University of University of SaskatchewanSaskatchewan

SAS occurrence in January 2009

Rankin Inlet

University of University of SaskatchewanSaskatchewan

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 University of SaskatchewanSaskatchewan

Ray racings for RKN, Ne(IRI)*1.3

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

Elev=10

Elev=20

midnightnoon

University of University of SaskatchewanSaskatchewan

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 University of SaskatchewanSaskatchewan

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 University of SaskatchewanSaskatchewan

A story on SAS being better than RKN in detection of

polar cap near noon echoes

University of University of SaskatchewanSaskatchewan

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 University of SaskatchewanSaskatchewan

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

University of University of SaskatchewanSaskatchewan

Reasons for some identified features in occurrence of polar cap echoes

Factors important for HF coherent echo detection

Irregularity generation

HF propagation conditions

2

20

0

nP n

n

- 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 ~ 2x105 cm-3

- D layer Ne: Radio wave absorption in the D region

Introduction Objectives Observations Discussion Conclusions

Electron density at 270 kmSvalbard, MLAT~ 75 deg.

FoV of Our Radars in Summer

E fields in cusp/cleftare enhancedThreshold 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/cleftare enhanced

Electron density at 270 kmSvalbard, 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 kmSvalbard, MLAT~750

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 University of SaskatchewanSaskatchewan

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+plansIntroduction Objectives Observations Discussion Conclusions

University of University of SaskatchewanSaskatchewan

Thank you for attention