convection measurements by incoherent scatter radars and superdarn:

Convection measurements by incoherent scatter radars and SuperDARN: Toward resolving occasional discrepancies

A. V. Koustov, U of Saskatchewan, Saskatoon, CANADA

D.W. Danskin, NRCan Geom Lab, Ottawa, CANADADespite the fact that both incoherent and coherent scatter radars monitor plasma convection

at the F region heights, all conducted so far comparisons show occasional significant

differences between measured velocities. It is generally believed that these discrepancies are

caused by different spatial and temporal resolutions of the instruments. In this presentation,

a review of previous comparisons is given and new more recent EISCAT/SuperDARN data

on plasma convection are presented to illustrate the need for more systematic and

comprehensive joint studies. This topic might be of interest to observations of the AMISR

radar (both at Poker Flat and Resolute Bay) and the existing SuperDARN radars

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HF velocities agree with Sondrestrom measurements. At large ExB, HF velocity is larger that ExB component.

Sondrestrom-Goose Bay HFRuohoniemi et al. (1987)

3EISCAT-Hankasalmi HF:Davies et al., 1999

Agreement is good. The slope of the linear fit line is ~0.7, HF velocities are smaller than ISR velocities

Sondrestrom-GooseBay (HF) –Stokkseyri (HF):Xu et al. (2001), line-of-sight comparison

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Range, km

Vel

ocit

y, m

/s

HF velocity is comparable with ExB l-o-s component

Sondrestrom-GooseBay (HF) –Stokkseyri (HF): Xu et al. (2001), projection comparison

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Agreement is reasonable with a few exceptions

Sondrestrom-2-D SuperDARN:

Xu et al.(2001), vector comparison

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Agreement is reasonable but data spread is significant. Tendency for HF vectors to be somewhat smaller at large ExBs.

EISCAT-CUTLASS:

Danskin (2003), projection comparison

Agreement is astonishingly good for Feb 12, 1999 event and not so for the previous day of Feb 11, 1999.

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8EISCAT-Pikkvibaer: Danskin (2003), large-range projection comparison

At larger ranges, data spread increases; still there are a lot of points of reasonable agreement.

Other comparisons (Danskin):

For scanning mode and patchy ionosphere, the agreement is not very good

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Convection derived by FIT technique with only one HF radar agrees reasonably with EISCAT measurements

Potential geometry of the PolarDARN-AMISR (Resolute) work

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Information on Ne(h, MLAT) and ExB (h, MLAT) is desired

For Rankin, scans roughly along geographic meridian are needed

For Inuvik, scans at -45 deg from geomagnetic meridian are needed – not feasible?

Summary and potential work

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1. Previous ISR-SuperDARN comparisons show that there is reasonable agreement between HF radar velocity and ExB as measured by incoherent scatter radars. However, there are periods when HF shows quite different velocities. Also, a tendency has been noticed that at large ExB, the HF velocities are somewhat smaller, statistically speaking.

2. Possible extension of previous work is joint observations of PolarDARN radars with Resolute AMISR. Some Resolute beam orientations seem to be suitable. The goals of the investigation could be:

a. Reasons for differences in velocity measurements between HF and ISRb. Validation work on performance of the SD map technique at very high latitudes c. Estimates of the heights of HF echoes by using information on Ne profilesd. Modes of HF signals. Are Pedersen rays fairly frequent?

Relevant publications: Danskin, D.W., Auroral HF backscatter from the F and E regions, PhD Thesis, U of Saskatchewan, Saskatoon, Canada, 2003. Davies, J.A., M. Lester, S. E. Milan, and T. K. Yeoman, A comparison of velocity measurements from the CUTLASS Finland radar and the EISCAT UHF system, Ann. Geophys., 17, 892-902, 1999. Davies, J.A., Yeoman, T.K., Lester, M. and Milan, S.E.: A comparison of F-region ion velocity observations from the EISCAT Svalbard and VHF radars with irregularity drift velocity measurements from the CUTLASS Finland HF radar, Ann. Geophys, 18, 589–594, 2000.

Milan, S.E., Davies, J.A., and Lester, M.: Coherent HF radar backscatter characteristics associated with auroral forms identified by incoherent radar techniques: A comparison of CUTLASS and EISCAT observations, J. Geophys. Res., 104, 22,591-22,604, 1999.

Ruohoniemi, J. M., R. A. Greenwald, K. B. Baker, J.-P. Villain, and M. A. McCready, Drift motions of small-scale irregularities in the high-latitude F region: An experimental comparison with plasma drift Geophys. Res., 92, N5, 4553-4564, 1987.

Villain, J.-P., Caudal, G., and Hanuise, C., A SAFARI-EISCAT comparison of F region small-scale irregularities and the ion drift, Ann. Geophysicae, 90, 8433–8443, 1985. Yeoman, T.K., Wright, D. M., Stocker, A. J., and Jones, T. B.: An evaluation of range accuracy in the SuperDARN over-the-horizon HF radar systems, Radio Sci., 36, 801-813, 2001.

Xu, L., A. V. Koustov, J. Thayer and M. McCready, SuperDARN convection and Sondrestrom plasma drift, Ann. Geophys., 19, 749-759, 2001.

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