1. VT SuperDARN Group http://vt.superdarn.org Joseph Baker (jo.baker@vt.edu) Ground-Based Observations of the Plasmapause Boundary Layer (PBL) Region with The Super Dual Auroral Radar Network (SuperDARN) Joseph B. H. Baker and the Virginia Tech SuperDARN Group The Center for Space Science and Engineering Research (Space@VT) Virginia Tech

2. Joseph Baker (jo.baker@vt.edu) http://vt.superdarn.org VT SuperDARN Group The SuperDARN Radars The Super Dual Auroral Radar Network (SuperDARN) is an international network of high-frequency (HF) radars for researching the Earth’s upper atmosphere, ionosphere, and connection into geospace.

3. Joseph Baker (jo.baker@vt.edu) http://vt.superdarn.org VT SuperDARN Group SAPS: April 9 th 2011 Mid-latitude radars are able to capture the longitudinal structure of SAPS features and monitor its dynamics continuously. This is a SAPS event on April 9 th 2011. Clausen et al., JGR, 2012

4. Joseph Baker (jo.baker@vt.edu) http://vt.superdarn.org VT SuperDARN Group SAPS: April 9 th 2011 Color-coded electron flux measurements from a POES spacecraft verify that the most intense flows measured by the SuperDARN radars are sub-auroral. Estimates of Total Electron Content (TEC) from GPS Receivers suggest that the high velocity flows are located inside the mid-latitude low conductance trough. Clausen et al., JGR, 2012

5. Joseph Baker (jo.baker@vt.edu) http://vt.superdarn.org VT SuperDARN Group Irregularity Distribution Magnetic latitude All Measurements Low Velocity High Velocity Ribeiro et al., Radio Sci., 2011 Figure shows the latitude distribution of irregularities seen by the Blackstone mid-latitude radar color-coded by Kp index for all (top), low (middle) and high (bottom) velocity measurements. Main observation is the latitude of the low velocity measurements is insensitive to Kp. The location of the irregularities seen by the radars is therefore determined by HF propagation conditions We can therefore conclude that the low velocity ionospheric irregularities are ubiquitous in the subauroral ionosphere.

6. Joseph Baker (jo.baker@vt.edu) http://vt.superdarn.org VT SuperDARN Group Penetration Electric Fields Mid-latitude SuperDARN radars see considerable dynamics in convection velocities against a weak background, suggestive of penetration electric fields. This figure shows a Latitude versus UT time-series of vectors color-coded by the subauroral ionospheric convection velocity on May 6 th 2010. Some of the subauroral convection is correlated with auroral activity (AE index) and some of it is more directly related to interplanetary conditions. This sort of activity is ubiquitous in quiet time mid-latitude SuperDARN measurements. IMF AE Kp Latitude UT

7. Joseph Baker (jo.baker@vt.edu) http://vt.superdarn.org VT SuperDARN Group Penetration Electric Fields

8. Joseph Baker (jo.baker@vt.edu) http://vt.superdarn.org VT SuperDARN Group Plasmasphere Subcorotation The fact that mid-latitude SuperDARN radars see a substantial amount of subauroral plasma drifts, even during quiet periods, suggests that the plasmasphere is not corotating with the Earth. This figure shows an MLT profile of the median “Corotation Factor” calculated from subauroral plasma drifts seen by mid-latitude SuperDARN radars. The mid-latitude ionosphere is sub- corotational across the nightside and becomes corotational after 4MLT. The median corotation factor is 93%. This value is consistent with observations of plasmasphere subcorotation obtained by tracking features in IMAGE EUV images [Sandel et al., 2003; Galvan et al., 2010]. Corotation Factor Corotation = 1 MLT

9. Joseph Baker (jo.baker@vt.edu) http://vt.superdarn.org VT SuperDARN Group SED/TOI: Sept 26 th 2011 Tongue of ionization (TOI) seen entering dayside polar cap as channel of enhanced total electron content (TEC) during a strong geomagnetic storm on Sep. 26 th 2011. Strong anti-sunward flows measured by SuperDARN radars within the region of enhanced TEC at both middle and polar latitudes. Sep. 26 th, 2011 19:00 UT

10. Joseph Baker (jo.baker@vt.edu) http://vt.superdarn.org VT SuperDARN Group Later during the event, convection electric fields no longer extend into middle latitudes to actively draw plasma from the dense source region at lower latitudes. Plume of high TEC is no longer capable of forming a TOI, but co-rotates with the Earth at a near-constant latitude as a “fossil plume” persisting for several hours. Fossil Plume Sep. 26 th, 2011 23:00 UT

11. Joseph Baker (jo.baker@vt.edu) http://vt.superdarn.org VT SuperDARN Group BBF Generated Pi2: Feb 22, 2008 Blackstone Beam 7 Range Gate 21 BlackstoneBeam 7 Remus GMAG 316˚ THEMIS D ESA Ion Vx GSM AACGM ˚Lat. m/s nT km/s m/s BKS Beam 7 2330 MLT 0130 MLT 2130 MLT UT Frissell et al., 2011 Blackstone radar measured Pi2 pulsations in response to a BBF seen byTHEMIS. Dispersed response as a function of latitude is suggestive of a plasmapause compression

12. Joseph Baker (jo.baker@vt.edu) http://vt.superdarn.org VT SuperDARN Group ULF Pulsations It is also very easy to find ULF pulsations in mid-latitude SuperDARN data!

13. Joseph Baker (jo.baker@vt.edu) http://vt.superdarn.org VT SuperDARN Group Summary The recent expansion of SuperDARN into middle latitudes has opened up several avenues of new research at the ionospheric projection of the Plasmapause Boundary Layer region: Subauroral Polarization Streams during geomagnetic storms Subcorotation of the nightside subauroral ionosphere (and plasmasphere) Penetration electric fields during storms and non-storm periods Transport of subauroral plasma (cf. plasmaspheric plumes) Subauroral plasma irregularities (cf. plasmasphere instabilities) Pi2 and ULF pulsations If you are looking at PMI event periods that have occurred since 2009 then please consider including mid-latitude SuperDARN data in your analysis.

14. Joseph Baker (jo.baker@vt.edu) http://vt.superdarn.org VT SuperDARN Group

15. Joseph Baker (jo.baker@vt.edu) http://vt.superdarn.org VT SuperDARN Group Source for Irregularities? Greenwald et al., GRL 2006 Coordinated experiment between Wallops radar and Millstone Hill ISR. Millstone Hill: electron temperature gradient at the equatorward wall of the trough reverses direction and steepens at approximately 0120 UT. Wallops: backscatter intensifies over Millstone Hill at 0120 UT. INTERPRETATION: Temperature Gradient Instability (TGI) [Hudson and Kelley, 1976] was a dominant source for mid-latitude ionospheric irregularities during this particular period. February 22-23, 2006

16. Joseph Baker (jo.baker@vt.edu) http://vt.superdarn.org VT SuperDARN Group Penetration Electric Fields