University of University of SaskatchewanSaskatchewan

PHYSICS AND ENGINEERING PHYSICS

Spectral widths of F-region PolarDARN echoes,

a statistical assessment

A.V. Koustov, S. Toderian and P.T. Jayachandran (UNB)

University of University of SaskatchewanSaskatchewan

Outline

1. Motivation

2. Narrow spectra

3. Spectral width vs flow angle

4. Spectral width vs ExB magnitude

5. Conclusions

University of University of SaskatchewanSaskatchewan

Motivation

1. Information on spectral width has been of limited use. In recent past, interest to the width has almost evaporated

2. New FITACF approach changed the typical values of the width (dramatically)

3. It has been suggested that F-region spectral widths should be considered in “Hz” rather than “m/s”

4. Limited data on the spectral width in the polar cap, on open magnetic flux lines. Nisitani et al. 2004 reported occurrence of “narrow” echoes in the polar cap

University of University of SaskatchewanSaskatchewan

FoVs of the Northern hemisphere SuperDARN radars as of January 2011

Polar cap echoes can be detected by all auroral zone radars as well as by Inuvik (INV) and Rankin Inlet (RKN).

University of University of SaskatchewanSaskatchewan

Auroral radars and RKN widths in m/s

RKN radar and the auroral zone radars show comparable widths in the polar cap (>80 MLAT).

RKN, Jan 2010Villain et al., 2002: Auroral radars

University of University of SaskatchewanSaskatchewan

RKN echo width, 1/s

There is MLT variation: echoes are broader during pre-noon hours

June 2010December 2010noonnoon

Gates 26-30Over Resolute

Gates 20-22

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Issue #1:

Nature of “narrow” PolarDARN echoes

University of University of SaskatchewanSaskatchewan

Typical RKN echo width in units of 1/s. Beams 4,5

As we consider larger ranges, narrow component becomes dominating. Data were combined over 0-24 MLT

Range: 945 km Range: 1215 km Range: 1755 km

University of University of SaskatchewanSaskatchewan

Typical RKN echo width in units of 1/s, beams 5,6, prenoon sector, 1 hour slot

Gates 10-11

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Typical RKN echo width in units of 1/s, beams 5,6, prenoon sector

Gates 14-15

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Typical RKN echo width in units of 1/s, beams 5,6, prenoon sector

Gates 18-19

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Typical RKN echo width in units of 1/s, beams 5,6, prenoon sector

Gates 22-23

University of University of SaskatchewanSaskatchewanGates 26-27, over Resolute

Typical RKN echo width in units of 1/s, beams 5,6, prenoon sector

University of University of SaskatchewanSaskatchewanGates 30-31

Typical RKN echo width in units of 1/s, beams 5,6, prenoon sector

University of University of SaskatchewanSaskatchewan

Typical RKN echo width in units of 1/s, beams 5,6, prenoon sector

Gates 34-35

University of University of SaskatchewanSaskatchewan

Typical RKN echo width in units of 1/s, beams 5,6, prenoon sector

Gates 38-39

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Typical RKN echo width in units of 1/s, beams 5,6, prenoon sector

Gates 42-42

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800 MLAT

ResBay

Typical RKN echo width in units of 1/s. Beams 4,5

Max widths are at ~ 1000-1200 km. Decrease towards the Pole.Summer echoes are more narrow, by ~10-15 (1/s).INV shows similar trends

Range=1125

University of University of SaskatchewanSaskatchewan

Nature of narrow spectra

Hypothesis 1: Narrow component is due to mixed scatter (GS contamination)

Hypothesis 2: Narrow component is due to a special type of irregularities that exist only in the polar cap. (One opinion is that they are associated with polar cap patches)

University of University of SaskatchewanSaskatchewan

John Gelleta tracings for RKN

Echoes at 1000-1500 km can be either ½ hop F region or 1&1/2 hop E region. E region GS is possible

Elev=10

Elev=20

midnightnoon

University of University of SaskatchewanSaskatchewan

RKN echo width, 1/sf<11.2 MHz

There are lots of narrow echoes in the midnight sector as well as in the noon sector. This is NOT what is expected from the GS contamination hypothesis as GS is more frequent at noon hours

Gates 21-22, midnight

Gates 21-22, all MLTs

Testing GS hypothesis #1, 1

Gates 21-22, noon

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Spectral width over RB in Dec 2010

Typical width is ~ 27 1/s, red vertical line

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Spectral width over RB in Dec 2010

Typical width is ~ 22 1/s

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Spectral width over RB in Dec 2010

Typical width is ~ 45 1/s

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Spectral width over RB in Dec 2010

Typical width is ~ 42 1/s

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Spectral width over RB in Dec 2010

Typical width is ~ 35 1/s

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Spectral width over RB in Dec 2010

Typical width is ~ 30 1/s

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Spectral width over RB in Dec 2010

Typical width is ~ 15 1/s, very narrow echoes

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Spectral width over RB in Dec 2010

Typical width is ~ 32 1/s

University of University of SaskatchewanSaskatchewan

Spectral width over RB in Dec 2010

Typical width is ~ 30 1/s

University of University of SaskatchewanSaskatchewan

Spectral width over RB in Dec 2010

Typical width is ~ 30 1/s

University of University of SaskatchewanSaskatchewan

Spectral width over RB in Dec 2010

Typical width is ~ 30 1/s

University of University of SaskatchewanSaskatchewan

Spectral width over RB in Dec 2010

Typical width is ~ 25 1/s

University of University of SaskatchewanSaskatchewan

It seems to me that narrow echoes are a significant portion of all echoes when RKN looks along the flow (noon and late evening sectors)

Testing GS hypothesis #1, 1

There are lots of narrow echoes in the midnight sector as well as in the noon sector. This is NOT what is expected from the GS contamination hypothesis as GS is more frequent at noon hours

University of University of SaskatchewanSaskatchewan

Typical RKN echo width in units of 1/s

Echoes in central beams are, statistically speaking, more narrow.

GS is more frequent in central beams. Signals are expected to be stronger affected by GS in central beams.

Range: 1350 km

Testing GS hypothesis, feature 2

University of University of SaskatchewanSaskatchewan

RKN velocity and CADI l-o-s velocityfor narrow and broad echoes

The velocity of narrow echoes often disagrees with the CADI ExB component (up to 500 m/s) along RKN beam 5.

All echoes Noon, <50m/s

Testing GS hypothesis, feature 3

N=22139Bad 18%Good 55.0%

Midnight, <50m/s

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RKN LOS-Velocity Significantly Decreases at Noon

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 13 13

noon

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Joint KODIAK-Inuvik observations in “common” echo regions but from different ranges:

INV: F region, KOD: F region

Wkod<Winv,

by 10 Hz

Testing GS hypothesis, 4

University of University of SaskatchewanSaskatchewan

For the time being:

We cannot make for sure a statement on the nature of “narrow” echoes regularly detected by the PolarDARN radars, but it seems as many of these are GS contaminated ionospheric signals

University of University of SaskatchewanSaskatchewan

Issue #2:

Does spectral width of PolarDARN echoes depend on the flow angle of observations?

- CADI at Res Baymeasures ExBmagnitude and direction

- Consider only points for which CADI and RKN velocities are consistent

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Spectral widths for simultaneous INV and RKN echoes detected over RB

All flow angles are represented. Widths are comparable, overall. Winter: Both narrow and broad components at RKN have smaller widths

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RKN spectral width varies with the ExB azimuth. Tendencies are difficult to infer

Lowest ExB

Largest ExB

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Issue #3:

Does spectral width (in Hz) of RKN (INV) echoes depend on ExB magnitude?

3 data sets were compiled:

1) Joint RKN-RB CADI2) Joint INV-RB CADI3) Joint RKN-INV-RB CADI

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Spectral width (in Hz) vs CADI ExB magnitude

Range: 1350 kmS: Slope=0.14 (1/s)/(mV/m)r: Corr. Coeff.=0.14

RKN

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Spectral width (in Hz) vs CADI ExB magnitude

Range: ~1500 kmS: Slope=0.19 (1/s)/(mV/m)r: Corr. Coeff.=0.08

INV

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Conclusions for Spectral Width

6-dB threshold

1) Significant portion of PolarDARN F region echoes has very low spectral widths (<10 Hz)

2) Systematic decrease of the width with range (going towards the Pole)

3) No flow angle dependence

4) Weak (statistical) increase with ExB magnitude, but correlation coefficient of the tendency is low

5) Exact single reason for occurrence of “narrow” echoes is still unknown

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Thank you for attention