WG3 “Ionospheric Storms” Summary Report The main overarching science question in WG3 was:

1. WG3 “Ionospheric Storms” Summary Report The main overarching science question in WG3 was: "How does the TEC respond to geomagnetic storms, and what are the physical mechanisms that control the response.” An initial series of sub-questions were assembled to focus the discussion: 1. What happens in the first 60 minutes of a storm? 2. Does the storm-enhanced density (SED) feature at mid latitude develop from the sub-auroral polarization stream (SAPS), or are there other processes involved? 3. How does the neutral wind impact the development of the storm, and what is the relative importance between penetration and dynamo electric fields in driving the response? 4. How is the plasma "bulge" created, or transported, to high mid-latitude (50 magnetic latitude). (It is this bulge of plasma that apparently is transported by the SAPS to produce a SED) 5. Are models able to follow the response and recovery of O/N2 over the duration of the storm, and how strong is its control of the ionospheric response. 6. What causes the strong longitude dependence in the TEC response, and how does the UT time sequence of the storm affect the different longitude sectors.

2. Participants and Data Providers

3. Focused Event List #15 Oct 19 1998 #25 Apr 6/7 2000 #27 July 16 2000 #37 Mar 31 2001 #50/51 April 17-20 2002 #68/69 Oct 30-31 2003 #70 Nov 20 2003

4. WG2/3 joint session science questions (Tuesday AM): 1. What is controlling the response of the penetration electric field to the expansion of the convective electric field and the degree of shielding. 2. When and where does the ring current produce SAPS and what is their relationship to SEDS and plumes. 3. How does the magnetospheric convection pattern expand. 4. Is there a "real" longitude dependence.

5. WG3 Philosophy….. • During early discussion of it soon became clear we all had our own mental picture or model of how things worked and that communicating ideas needed to be based on clear definitions, and the need to separate “physical processes” from an observed “phenomena”.

6. Millstone Hill Azimuth Scan April 12, 2001 UT Westward Ion Velocity Polarization Stream SED L=2 L=4 Bulge Plasmasphere Trough EnhancedEq Anomaly TEC Hole Illustration of some of the challenges in the Ionospheric Storms Working Group 3: SEDs, SAPS, “bulges”, etc. Foster et al.

7. Conclusions Reached: • 1. There was general agreement that a SED could be caused by transport on the equatorward edge of the SAPS picking up plasma from the “bulge” of dayside ionization. (See previous figure for distinction between the SED and “bulge”). Note that questions remain regarding the detailed structure of the feature. • 2. It is possible that sufficiently large and long-lived electric fields can transport plasma poleward from low latitudes, and that if accompanied by opposing equatorward directed winds can produce large TEC at high mid latitudes. The reality of the required drifts and winds are still to be determined. • 3. That the "historical" system response time of shielding to penetration electric fields (30-60 mins.) is not inconsistent with long duration (few hours) electric fields at low latitudes from this physical process, and depends on the time history of the magnetospheric driver. • 4. Penetration and dynamo electric fields can have comparable magnitudes at the equator on the nightside during storms.The fields can oppose or reinforce depending on the timing and complexity of the forcing. • 5. The latitude structure of penetration electric fields may be influenced by the ionospheric conductivity structure, and that ionosphere-magnetosphere feedback influences the evolution of the fields. • 6. Neutral composition changes can reach low latitudes and have a significant impact on plasma loss particularly during the recovery phase of a storm.

8. Outstanding Science Issues: • Encroachment of high latitude processes on the mid latitude ionosphere and their relationship to magnetospheric processes: SEDs, SAPS, plasmapause location, ring current, etc. • Encroachment of low latitude processes on the mid latitude ionosphere: “bulge” creation, penetration electric fields, shielding timescales, conductivity feedback, etc. • The longitude and/or local time dependence of the ionospheric response • Impact of neutral wind and composition • Large scale M-I coupling

9. Approach to Science Questions: SAPS and SED • How does the magnitude of the SAPS flow develop, evolve, and recover as ionospheric conductivity responds to the drift, and as the magnetospheric convection changes? -RCM (Stan S.), CTIPE (F-R), SAMI2 (Joe Huba), DMSP (Rod), ISR ( J. Foster) • What is the relationship between plasmasphere features from IMAGE and ionospheric structure? - observational perspective (ISR :John Foster and IMAGE Jerry Goldstein) - modeling perspective: (RCM Stan S.and CTIPe F-R) • What is the relationship between TEC features, such as “shoulders” and SEDs and topside electron density from DMSP? (Tony M., Rod H.) • Is a SED simply the transport of a plasma bulge? a) Impose bulge artificially in CTIPe with a realistic SAPS from RCM. (F-R) b) Trajectory analysis in AMIE. (Crowley) • Is there a seasonal effect in the SED formation - stagnation in sunlit or dark conditions? • Is the SAPS wall stable in the presence of density and temperature gradient instabilities? (Keskinen, Santi, joint with WG2) • Is there equatorward movement of plasma in subauroral regions in response to the expansion of the magnetospheric convection pattern? (Rod H., superDARN?)

10. Approach to Science Questions: Creating the “bulge” • What does it take to create a bulge of TEC at high mid latitudes? a) Increase penetration and/or dynamo fields artificially in models? (Joe H., F-R) b) Determine impact of poleward ion drift with opposing meridional wind? (Joe Huba, Rod H.) c) Are observed values of winds and drifts consistent with those required? (John E., Rod H., Huey Ching Y.) d) Can models produce the required magnitudes? (F-R, Stan S., Crowley) • Is the conventional shielding response time of penetration electric fields (30-60 minutes) consistent with the apparent long duration penetration events at Jicamarca. (Chaosong H., Stan S.) • If plasma is already depleted at low latitudes how does it affect the latitude structure of the penetration electric field? (Stan S., F-R) • Is a penetration electric field event necessary in order to develop a plasma bulge at high mid-latitudes? (anyone)

11. Approach to Science Questions: Longitude/LT confinement of “bulge” • Why is the bulge confined to a narrow longitude or local time sector? • Are large uplifts at the magnetic equator confined to longitudes for which local dusk coincides with rapid changes in Dst. (Sunanda B.) • Does the location of the bulge depend on the UT start time of the storm or is it always in the same longitude sector? • Can a long-lived zonal plasma drift at low latitudes on the dayside lead to stagnation and a build up of plasma in the late afternoon sector?

12. Approach to Science Questions:Winds and Composition • Is there a feedback between the O/N2 change depleting the ionosphere, reducing ion drag, and enhancing the winds? (F-R, Crowley, Rod H.) • Is the O/N2 modeled response and recovery consistent with GUVI observations? (Larry P., Geoff C., F-R) • Are the model winds consistent with the climatological storm circulation and direct observations? (Geoff C., F-R, John Emmert) • Is there a feedback of dynamo driven winds on the inner magnetosphere? Science Questions: Large scale M-I • Is their evidence for asymmetries in Region 1 and 2 currents for saturation conditions at solstice? • What is the percentage change of plasma in the plasmasphere after a storm. • What is the volume and mean density change of the plasmasphere? • Joint events with WG2: April 17-20, 2002 and March 31, 2001

13. Huba et al. 2005 Response of ionosphere to prolonged 120 m/s perpendicular/poleward ion drift and 0 - 250 m/s equatorward neutral wind.