physics and engineering physics
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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. Outline:. Introduction and objectives Seasonal variations, overall Seasonal variations, MLT curve - PowerPoint PPT PresentationTRANSCRIPT
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