STUDY OF THE POLAR CAP PLASMA FLOWS WITH THE CLYDE RIVER SUPERDARN RADAR
Date
2019-02-01
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Journal ISSN
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ORCID
Type
Thesis
Degree Level
Masters
Abstract
Plasma flows in the high latitude ionosphere reflect complex physical processes occurring when the Sun-originated solar wind blows around the Earth. One way of monitoring and quantifying these flows is to use Doppler velocity measurements with ground-based high-frequency (HF) radars such as the Super Dual Auroral Radar Network (SuperDARN) radars.
The research presented in this thesis includes two major topics. First, we investigate quality of SuperDARN HF velocity measurements for a relatively new radar in the network, the Clyde River (CLY) radar. This has never been done in the past while the radar is critical in the network as its field of view allows one to measure plasma flow velocity roughly along magnetic parallels at extremely high latitudes. Second, after successfully validating the Clyde River radar measurements, variations in the plasma flows at radar latitudes are investigated.
To accomplish the first task, measurements of the plasma velocity collected over the year 2016 at Clyde River are compared with nearly simultaneous velocity measurements from the Resolute Bay Incoherent Scatter Radar-Canada (RISR-C). Our results show that the CLY radar velocity measured in beams 4-6 is statistically comparable to the ExB component of the plasma drift along these beams (azimuthal plasma flows) measured by the RISR-C. The agreement between the two types of radars was found to be not ideal; the lines of linear fit had slopes in the range of 0.5-0.7. This is comparable with the slopes in other experiments, but slightly lower than usual. We showed that the correction of HF velocities for the index of refraction effect does not increase the slope of the line to 1 mostly because of lower HF velocities at large ExB drifts of > 700 m/s. This “underestimation” effect was found to be stronger at nighttime and its compensation by considering the index of refraction effect was less successful than at daytime. We carried out a similar comparison between Rankin Inlet (RKN) SuperDARN radar velocity measurements and that of RISR for the same period of 2016 and found reasonably good agreement as well. We showed that the strongest disagreements between HF and RISR-C velocity occurred for periods with very low CLY and RKN velocities, below 100-200 m/s in magnitude, indicating that some ionospheric echoes could be misidentified by the SuperDARN radar processing technique; this effect is more pronounced for the RKN radar. Finally, we investigated self-consistency of SuperDARN HF measurements by comparing velocities of the CLY radar and the SuperDARN radar at Inuvik (INV) in about the same direction. We found that the CLY-INV agreement is reasonable for ranges of >1000 km with pure F region echo detection by both radars. Evidence is presented that measurements at short ranges of <800 km, that are traditionally thought to be pure F region scatter as well, is sometimes contaminated with scatter from the E region with velocities below the ExB drift.
On the second task, we considered multi-year CLY data set to assess seasonal variation of the plasma flow velocity in the azimuthal direction, at magnetic latitudes of ~ 81 degrees and at southward orientation of solar-related interplanetary magnetic field (IMF) Bz < 0 . We noticed several changes from winter to summer and found them to depend on the polarity of the IMF azimuthal component By . For IMF By < 0 , we report that summer CLY velocities stay positive much longer over a day duration. For IMF By > 0, CLY velocities remain much longer negative. In general, we found that CLY velocity data in the azimuthal direction can be interpreted in terms of a more “round” overall pattern in summer.
Description
Keywords
Polar cap, SuperDARN
Citation
Degree
Master of Science (M.Sc.)
Department
Physics and Engineering Physics
Program
Physics