1 / 12

SuperDARN and reversed flow events in the cusp

SD2011. SuperDARN and reversed flow events in the cusp. K. Oksavik 1 , J. Moen 1,2 , E. H. Rekaa 2 , H. C. Carlson 3 , and M. Lester 4 1) UNIS, Longyearbyen, Norway 2) Department of Physics, Univ. Oslo, Oslo, Norway 3) CASS, Utah State University, USA

hateya
Download Presentation

SuperDARN and reversed flow events in the cusp

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. SD2011 SuperDARN and reversed flow events in the cusp K. Oksavik1, J. Moen1,2 , E. H. Rekaa2, H. C. Carlson3, and M. Lester4 1) UNIS, Longyearbyen, Norway 2) Department of Physics, Univ. Oslo, Oslo, Norway 3) CASS, Utah State University, USA 4) Department of Physics & Astronomy, Univ. Leicester, UK

  2. Background on RFE Reversed flow events (RFEs): • First seen with the EISCAT Svalbard radar • Longitudinally elongated, segments of transiently enhanced ion flow, in the direction opposite to the background flow • For both RFE and background flow: |Vlos| > 250 m/s (but in opposite directions) • Size: >400 km in longitude • Form one by one (not in pairs) Rinne et al. [2007]

  3. Three events will be studied • Solar wind is stable: • By positive • Bz negative • SD coverage: • 700-800 data points • VPC = 50-60 kV

  4. RFE seen by SuperDARN • The RFE flow channel (red color) is located in an area of sunward flow (blue color) in the postnoon sector • This is the first report of RFE in SD data!

  5. RFEs seem to occur in areas of high backscatter power and wide Doppler spectra The backscatter power / spectral width is often highest along one edge of RFEs, and low along the other edge Several examples of RFEs

  6. Events 1 and 2 were part of an interval of prolonged activity A transition took place at 09:05 UT The poleward edge of event 3 coincided with wide Doppler spectra and growing backscatter power Are RFE important for the formation of irregularities? 1 2 3 Time development of RFEs

  7. Formation of plasma irregularities via flow shears • The KH growth rate is [Keskinen et al., 1988]: • Most ∆VLOS are small, but some reach 800 m/s (i.e. growth time of 300 s) • A 42˚ angle between the radar beam and the large-scale flow decreases the net growth time to 200 s • Rinne et al. [2007] found examples of L = 12 km (i.e. growth time of 60 s) • KH may be efficient at producing irregularities! ∆VLOS Neighboring range gates

  8. Offset between SD and optics There appears to be an offset in latitude between RFE and the aurora

  9. Flow vorticity and FACs [Sofko et al., 1995]

  10. Determination of ground range • The clockwise flow reversal (i.e. upward FAC) aligns with the aurora, if we shift the Hankasalmi radar echoes equatorward by 140 km • Consistent with other studies [Yeoman et al., 1997]

  11. Conclusions • We have documented several examples of RFE channels seen by SuperDARN • The location of RFE flow shears relative to auroral arcs shows that the SD ground range was overestimated by 140 km • RFEs may be important for the formation of plasma irregularities via flow shear instabilities (Kelvin Helmholtz) • The large SuperDARN dataset offers new opportunities to learn more about RFEs

  12. From June 01, 2011 New address: Department of Physics and Technology, University of Bergen, P.B. 7803, NO-5020 Bergen, NORWAY. E-mail: kjellmar.oksavik@uib.no

More Related