GRAND CHALLENGE SCIENCE FOCUS: Explore the state of the sun-Earth system during extreme space weather. "Return to the Auroral Oval for the 50th Anniversary of the International Geophysical Year"
WHAT'S NEW?
The IMAGE spacecraft observed the development of a large-scale auroral spiral on the dawnside of the auroral oval and a long-duration finger-like structure on the duskside during intense substorms in the main phase of severe magnetic storms on 15 May and 24 August 2005. Consecutive images of the auroral emissions for each event give indication at times of vortical motion in the spiral. The unusual features,reported here, are absent during substorms occurring at other phases of the storms. In fact, "more typical" substorms outside of the storm main phase do not show any dramatic activity in the dawn to noon sector.
TIMED observations supplied information on the corresponding auroral spiral in the northern hemisphere on 15 May 2005. The northern hemisphere auroral spiral was on the duskside at the same time a southern hemisphere dawnside spiral was being observed by IMAGE in keeping with the expected changes in ionospheric potentials for large IMF By.
To our knowledge, neither of these structures has been previously reported as a feature of auroral substorms.
Similar structures have now been found in 4 other superstorms in 2003-2004 (29-30 Oct 2003, 20 Nov 2003, 07-08 Nov 2004 and 09-10 Nov 2004) and in the 17-22 Jan 2005 magnetic storm event in which the solar driver contained intervals of exceptional dynamic pressure and solar wind speed.
IMPLICATIONS:
Since large-scale auroral emissions generally mirror the structure and movement of source regions in geospace, these unusual auroral structures may imply new features during extreme space weather conditions in:
- Tthe geospace configuration
- Solar wind-magnetosphere coupling
- Stormtime energy dissipation mechanisms
- Storm-substorm coupling
They raise question about the aspects of the solar sources and heliospheric propagation capable of driving such extreme conditions, in particular aspects introduced by the interaction between active regions and coronal holes. They also motivate a search for associated features throughout geospace and in the ionosphere-atmosphere from pole to equator.
Some suggested science questions follow the descriptions of the events below. We invite additions to this list.
SOME BASIC INFORMATION ON THE EVENTS
(Based on a CAWSES Space Weather Workshop hosted at Stanford University in December 2005)
24 August 2005
Short Summary: Eruptions of AR10798 were accompanied by M2.6 and M5.6 x-ray flares at ~01 UT and ~17 UT, respectively on 22 August. Even though the AR was near the southwest limb of the Sun at the time, these eruptions produced Earthward-directed CMEs. Of particular interest, AR10798 was an "anemone" active region [Asai et al., 2006] and thus had the unusual property of being almost completely surrounded by a coronal hole. A shock, presumably from the first eruption, reached SOHO at 05:33 UTC on 24 August. The IMF Bz turned southward between ~09:00 UT and 11:00 UT reaching values as low as ~-60 nT but only for a short time. Minimum Dst reached -216 nT. Because of high dynamic pressure, it is expected that Dst* will drop below -250 nT, crossing the threshold to superstorm status. An intense substorm was triggered during the main phase. The quick look AL index from the WDC in Kyoto reached values as low as -4000 nT and hemispheric power from NOAA peaked near 1286 GW. During this exceptional substorm, auroral vortices developed on the dawnside and a finger-like extension persisted on the duskside in the southern hemisphere. The solar wind disruption from the second event reached Earth just after 21:00 UT that same day but Bz was near zero so no significant signature was seen in Dst. However, it triggered a substorm with more typical features and a minimum quick look AL~-1500 nT. Prior to the main phase of the superstorm, another substorm was triggered also with more typical features and a minimum quick look value of ~-1000 nT.
15 May 2005
Short Summary:An eruption of AR 10759 produced a fast halo CME and was associated with a long-duration M8 xray flare with peak emission at 16:57 UT reported by GOES on 13 May 2005. The CME mean plane-of-sky speed was 1640-45 km/s [c.f., LASCO CME list]. A strong EIT wave developed symmetric about the AR and a dimming appeared to the SW and NE of the AR. A new transient coronal hole may have developed from this dimming region lasting more than a day. The disturbance arrived at Earth ~3 UT on 15 May giving a transit time of ~33.5 hours. Minimum southward IMF Bz reached ~-45 nT driving a superstorm with minimum Dst =-263 nT. An intense substorm was triggered just as IMF Bz reached its lowest negative values. The minimum quick look AL reached -1700 nT and hemispheric power peaked at 1225 GW. During this substorm IMAGE observed an auroral vortex on the dawnside and a persistent finger-like structure on the duskside in the auroral oval. A substorm with comparable values of AL occurred just before 03:00 UT prior to the superstorm main phase. Another substorm occurs in the early recovery phase of the superstorm just prior to 09:00 UT. This second substorm has more typical features. A comparison among these events should give interesting insights into the conditions necessary for a "super" substorm.
CONFERENCE EVENTS
- Focus Events: 15 May 2005, 24 August 2005
- Supporting Superstorm Events: 6-7 April 2000, 15-16 July 2000, 31 March - 1 April 2001, 11-12 April 2001, 6-7 Nov 2001, 29-31 Oct 2003, 20-21 Nov 2003, 7-10 Nov 2004
- Other Interesting Events: 17-22 Jan 2005, and other occurrences of auroral vortices not in the main phase of superstorms (i.e. smaller substorms, steady convection events, etc.)
AN INCOMPLETE LIST OF BASIC QUESTIONS:
(Based in part on a CAWSES Space Weather Workshop hosted at Stanford University in December 2005)
- What effect does close proximity to a coronal hole have on the release and subsequent propagation of CMEs during these extreme events?
- How does background solar wind density affect processes from particle acceleration at shocks to preconditioning of the magnetosphere?
- How were the short-lived but intense spikes in IMF Bz produced? How important were propagation affects and the background solar wind state? Do these IMF Bz spikes affect how energy is apportioned throughout geospace? (ie. does a short-lived spike in -Bz fail to enhance the ring current but put a disproportionate amount of energy in the auroral oval?)
- Are vortical plasma flows associated with the auroral spirals? Do these spiral structures map into the magnetosphere? If so, do they have implications for mass and energy transport from the solar wind into the magnetosphere or for mixing plasma from the boundary layers into the plasma sheet? Do these features indicate a new form of storm-substorm coupling or reflect a new type of energy dissipation?
- How do the auroral spirals (vortices?) and the associated geospace configuration affect the state of the ionosphere-atmosphere?
- Are they associated with regions of enhanced joule heating, enhanced fluxes of upflowing ionospheric ions or other feedbacks to the magnetosphere.
- Are there corresponding vortices in dawnside and duskside neutral winds?
- How does this configuration impact equatorial electric fields, storm time ionospheric dynamics and the transport of heat and composition changes to low-latitudes?
- Are they a source of ionospheric irregularities?
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