Transcript .ppt

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:
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
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Saskatchewan
Introduction
Objectives
Observations
Discussion
Conclusions
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?
University of
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Saskatchewan
We are interested in echoes at MLAT>78 -80
Introduction
Objectives
Observations
Discussion
Conclusions
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
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Saskatchewan
Introduction
Objectives
Observations
Discussion
Conclusions
Occurrence rates for winter conditions
INV and RKN seems to perform comparably
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at MLAT > 800. SAS is comparableSaskatchewan
at noon.
Introduction
Objectives
Observations
Discussion
Conclusions
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
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comparable, especially at noon.
Saskatchewan
Introduction
Objectives
Observations
Discussion
Conclusions
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
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Saskatchewan
Seasonal variation
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at MLAT= 80 - 90
Average over ALL
MLT sectors
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Saskatchewan
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Seasonal variation
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at MLAT=80 - 90
Dawn, Noon, Dusk,
Midnight
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Saskatchewan
Introduction
Objectives
Observations
Discussion
Conclusions
Seasonal Variation of F-region Echoes in 2009
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Saskatchewan
Seasonal changes in
the MLT variation at
individual latitudes:
o
o
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MLAT=83 , 84 and 85
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Introduction
Objectives
Observations
Discussion
Conclusions
RKN Changes in a Shape of the MLT Dependence in 2009
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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
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Equinoctial maxima at dusk and dawn;
dusk maxima are more pronounced
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Saskatchewan
A story about a “deep”
in PolarDARN (and SAS)
echo detection near winter
noon
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Saskatchewan
Introduction
Objectives
Observations
Discussion
Conclusions
Occurrence at different MLATs vs. MLT: Jan 2009
INUVIK
MLAT= 82°- 83°
RKN
MLAT= 82°- 83°
Deep within the near noon maximum
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Saskatchewan
Outline
Introduction
Objectives
PolarDARN Echo Occurrence
CADI Observations
Noon deep at far ranges for winter
observations
Density gradients smoothed as the FoV becomes sunlit
Increase in D region absorption
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Saskatchewan
PolarDARN HF Echo Occurrence Near Winter Magnetic Noon ● M. Ghezelbash, A. V. Koustov, D. Mori, D. André
Summary
SAS occurrence in January 2009
Rankin Inlet
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Saskatchewan
Outline
Introduction
Objectives
PolarDARN Echo Occurrence
CADI Observations
Summary
Ground Scatter Echoes Near Noon
Ground Scatter
LAT= 82°- 86°
Magnetic Noon
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Saskatchewan
F-region Echo Occurrence in the Polar Cap: A Comparison of PolarDARN and Saskatoon Data ● M. Ghezelbash, A. V. Koustov, et al.
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Ray racings for RKN, Ne(IRI)*1.3
noon
midnight
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
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possible
Saskatchewan
Outline
Introduction
Objectives
PolarDARN Echo Occurrence
CADI Observations
Summary
RKN Ionosphere and Ground Scatter Occurrence
(December 2010)
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Saskatchewan
F-region Echo Occurrence in the Polar Cap: A Comparison of PolarDARN and Saskatoon Data ● M. Ghezelbash, A. V. Koustov, et al.
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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
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Saskatchewan
A story on SAS being better
than RKN in detection of
polar cap near noon echoes
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Saskatchewan
Outline
Introduction
Objectives
PolarDARN Echo Occurrence
CADI Observations
Summary
Outperformance of SAS Over RKN at High-Latitudes!
(December 2009)
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Saskatchewan
F-region Echo Occurrence in the Polar Cap: A Comparison of PolarDARN and Saskatoon Data ● M. Ghezelbash, A. V. Koustov, et al.
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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
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Reasons for some
identified features
in occurrence of
polar cap echoes
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Introduction
Objectives
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
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Introduction
Objectives
Observations
Discussion
Conclusions
Features identified
1) Summer: not much echoes, only near noon.
Production:
Propagation:
Sunlight smoothes gradients (-)
E fields stronger near cusp/cleft (+)?
Enhanced absorption (-)
Refraction and threshold are OK (+)
Electron density at 270 km
Svalbard, MLAT~ 75 deg.
Threshold Ne
FoV of Our Radars
in Summer
E fields in cusp/cleft
are enhanced
Introduction
Objectives
Observations
Discussion
Conclusions
2) Winter: Lots of echoes, mostly near noon.
Production:
Not much Sunlight,
good for GD instability (+)
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.
Threshold Ne
FoV in Winter
E fields in cusp/cleft
are enhanced
Introduction
Objectives
Observations
Discussion
Conclusions
3) Equinox: maxima at dusk/midnight and dawn.
Production:
Not so much Sun light as at summer time (+)
Stronger midnight E fields (?)
Propagation:
Densities are strong and
stay strong up to dawn/dusk (+)
Ne at 270 km
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Svalbard,
MLAT~75
Equinox
Threshold Ne
Dusk maxima should be more
pronounced due to better Ne
FoV at Equinox
Introduction
Objectives
Observations
Discussion
Conclusions
Summary+plans
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
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in their absence (from CADIs)
Saskatchewan
Thank you for attention
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Saskatchewan