yvonne rinne, departement of physics, university of oslo mesoscale transient flow channels observed...
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![Page 1: Yvonne Rinne, Departement of Physics, University of Oslo Mesoscale transient flow channels observed in the cusp ionosphere by the EISCAT Svalbard Radar](https://reader035.vdocuments.site/reader035/viewer/2022081506/5697bfda1a28abf838cafdd1/html5/thumbnails/1.jpg)
Yvonne Rinne, Departement of Physics, University of Oslo
Mesoscale transient flow channels observed in the cusp ionosphere by the EISCAT Svalbard Radar
by
Y. Rinne J. MoenH. C. CarlsonK. Oksavik
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Yvonne Rinne, Departement of Physics, University of Oslo
Outline
• The Fast Scan Mode at the EISCAT Svalbard Radar (ESR)
• SP-NO Data base• Occurrence of Reversed Flow
Events (RFEs)• Discussion• Conclusion
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Yvonne Rinne, Departement of Physics, University of Oslo
The radar sweeps azimut sectors in a windshield wiper mode, centered at the location of the cusp
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Yvonne Rinne, Departement of Physics, University of Oslo
Large spatial coverage decreases the spatial resolution
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Yvonne Rinne, Departement of Physics, University of Oslo
SP-NO Fast Scan Data base
• We gathered data during january and december 2001
• The analyzed data set spans 11 days (36 hours) and consists of 767 scans
• Data was gathered beween 9-15MLT
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Yvonne Rinne, Departement of Physics, University of Oslo
Definition of Reversed Flow Events (RFEs)
• A Reversed Flow Event is an elongated segment of enhanced ion flow in the opposite direction of the background flow
• The RFE has to be evident in more than one radar beam direction/azimuth (this criterion should eliminate bad measurements).
• The line-of-sight ion velocity inside the RFE must be greater than |250| m/s for at least one scan.
• The RFE has to have a longitudinal extent of at least 400-600 km in the radar field– of-view.
• The RFE has to stay in clear contrast to the background, i.e. the background flow must exhibit uniform opposite velocities higher than |250| m/s in the area surrounding the RFE.
• The RFE has to be embedded within the background flow for at least one scan (this criterion avoids large-scale convection reversals being detected as RFE).
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Yvonne Rinne, Departement of Physics, University of Oslo
Occurrence of RFEs
• RFEs occured 16% of the time throughout the dataset
• Their average lifetime was 19 minutes • They exceeded the field of view in length (>
400-600km) and are around 100-200km wide• No preference was found for the IMF Bz polarity • It may seem as if flow channels are as well IMF
By independent RFEs appear to be a regular feature of the
active cusp
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Yvonne Rinne, Departement of Physics, University of Oslo
RFE occurrences versus MLT
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Yvonne Rinne, Departement of Physics, University of Oslo
86% of the RFEs were characterized by reversed ion flow with respect to the direction of the background flow, i.e. in opposite direction of magnetic tension
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Yvonne Rinne, Departement of Physics, University of Oslo
RFEs as a posible signature of Southwood FTEs?
• RFEs cannot be interpreted as the centre flux in the Southwood model due to the direction of the ion flow beeing opposite to the magnetic tension force
• If they should be interpreted as the return flow, two channels are expected to appear simultaneously
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Yvonne Rinne, Departement of Physics, University of Oslo
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Yvonne Rinne, Departement of Physics, University of Oslo
Summary
• RFEs seem be regular feature of the cusp ionosphere, occuring at least 16% of the time in the current data set
• Their average lifetime is 19 minutes• They occur near the cusp inflow region in the MLT range
from 11:45 to 12:45MLT in association with enhanced plasma flow, and seem to be L-shell aligned
• The occurrence of RFEs is independend of IMF Bz (and By)• 86% of the RFEs were characterized by ion flow opposite
to the magnetic tension force, meaning that they cannot be interpreted as FTE centre flux according to Southwood
• RFEs coexist but never appear simultaneously• RFEs cannot be attributed the same FTE as claimed by
Oksavik et al. (2004)