Geomagnetic Activity: A Talk on “Current Events”!

1. Geomagnetic Activity: A Talk on “Current Events”! Christine Gabrielse, UCLA GEM Tutorial, June 17, 2012 Changes in currents above the ionosphere controlled by solar wind parameters  changes in the magnetic field at earth’s surface.

2. Dipole Axis Magnetic Field Lines Symmetric Ring Current Storms Sudden Commencement Dst Index: Direct measure of the hourly average of the northward (“H”) perturbation in the magnetic field at equatorial and mid-latitudes Measures symmetric ring current strength 50 Main Phase 0 Dst Recovery Phase -100 -150 134 136 Day 142 144

3. Substorms

4. Auroral Electrojet H Z Substorm Current Wedge

5. Substorm Indices Kp Index:Perhaps best to monitor substorm expansion phase during storms. 0-4 is below storm AU: Amplitude Upper AL: Amplitude Lower AE: Auroral Electrojet = AU - AL AO: (AU + AL) / 2

6. Substorm Signatures Runov et al., 2011

7. Sawtooth Events: Identity Crisis Substorms? Solar wind driven? Similar signatures Driving conditions are stronger than those during substorms and SMCs Similar conditions as CME: Storm time event? 3 hour periodicity > Magnetosphere cavity oscillations Not substorms? Signatures occur over wide range in MLT Periodic More intense at geostationary orbit Ion outflows may play a role deciding if we get SMC or sawtooth event [Brambles et al., 2011] Internally driven? Occur during stable IMF Similar conditions as steady magnetospheric convection

8. SteadyMagnetosphericConvection Kissinger et al. , 2011, 2012 • Timescale: >4-6 hours • Many are initiated by substorm • Balanced dayside/nightside reconnection • Auroral zone currents dominated by convection-driven current system, not substorm related currents • Midlatitude disturbances from partial ring current Substorm SMC -20 -20 Y GSM 0 0 20 20 0 -35 X GSM -35 X GSM 0

9. Relevant GEM Focus Groups • Modes of Magnetospheric Response • SMCs, drivers/effects of other convection modes: sawtooth events, non-linear coupling to the solar wind driver, polar cap saturation, ion outflow, ionospheric effects, and global simulation results • Monday: 10:30, 1:30, Salon D • Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures • Magnetic reconnection, FTEs, and Hot Flow Anomalies • Tuesday: 1:30, 3:30, Salon C • Substorm Expansion Onset: The First 10 Minutes • Signature propagation and timing from tail toward the inner magnetosphere and to the ground; signatures measured in the distant tail • Tuesday: 10:30, 1:30, 3:30, Salon D • Dayside FACs and Energy Deposition • Relation between enhanced dayside Poynting flux and field-aligned currents, sources of field-aligned currents in the solar wind and magnetosphere and their impacts in the ionosphere-thermosphere system • Thursday: 10:30, Salon C

10. References • Slide 1 • Image courtesy of USGS: http://geomag.usgs.gov/about.php • SOHO movie of CME courtesy of NASA/GSFC http://www.nasa.gov/multimedia/videogallery/index.html?media_id=135023881 • SDO movie of prominence erupting courtesy of NASA • http://www.nasa.gov/multimedia/videogallery/index.html?media_id=135023881 • Slide 2 • CME movie courtesy of the Center for Space Environment Modeling (CSEM), University of Michigan. http://www.windows2universe.org/sun/activity/csem_cme_model_zoom.html • Figures courtesy of R. McPherron’s UCLA class notes • Slide 3 • Substorm movie courtesy of NASA: http://www.nasa.gov/multimedia/videogallery/index.html?media_id=135023881 • Figure: Miyashita et al. (2009), J. Geophys. Res., doi:10.1029/2008JA013225 • Slide 4 • Substorm current wedge figure courtesy of R. McPherron class notes • IMAGE plots created by J. Reistad at UNIS Substorm class, 2010

11. References • Slide 5 • AE index courtesy of WDC Kyoto: wdc.kugi.kyoto-u.ac.jp/ae_provisional/ • Kp index: • http://www.swpc.noaa.gov/info/Kindex.html • Rostoker, Ann. Geophysicae 18, 1390-1398 (2000) • FAC image: Keiling et al., Substorm current wedge driven by plasma flow vortices: THEMIS observations, J. Geophys. Res., 114, A00C22, doi:10.1029/2009JA014114. • Slide 6 • Substorm signatures figure: Runov, A., V. Angelopoulos, X.‐Z. Zhou, X.‐J. Zhang, S. Li, F. Plaschke, and J. Bonnell (2011), A THEMIS multicase study of dipolarization fronts in the magnetotail plasma sheet, J. Geophys. Res., 116, A05216, doi:10.1029/2010JA016316. • Substorm injection figure courtesy of LANL: http://lwsde.gsfc.nasa.gov/LWS_Space_Weather/LANL_descrip.html • Substorm figure modified from Miyashita et al. (2009), J. Geophys. Res., doi:10.1029/2008JA013225. • Injection boundary figure: Mauk and Meng, JGR, VOL. 86, NO. A4, PAGES 3055-3071, APRIL 1, 1983

12. References • Slide 7 • Sawtooth injection figure: Kubyshkina, M., T. I. Pulkkinen, N. Yu. Ganushkina, and N. Partamies (2008), Magnetospheric currents during sawtooth events: Event-oriented magnetic field model analysis, J. Geophys. Res., 113, A08211, doi:10.1029/2007JA012983 • Sawtooth info • Cai, X., J.‐C. Zhang, C. R. Clauer, and M. W. Liemohn (2011), Relationship between sawtooth events and magnetic storms, J. Geophys. Res., 116, A07208, doi:10.1029/2010JA016310. • Henderson, M. G. (2004), The May 2–3, 1986 CDAW-9C interval: A sawtooth event, Geophys. Res. Lett., 31, L11804, doi:10.1029/2004GL019941. • Huang, C.-S., A. D. DeJong, and X. Cai (2009), Magnetic flux in the magnetotail and polar cap during sawteeth, isolated substorms, and steady magnetospheric convection events, J. Geophys. Res., 114, A07202, doi:10.1029/2009JA014232. • Brambles et al., Science 332, 1183 (2011); DOI: 10.1126/science.1202869 • Slide 8 • SMC figures: • Kissinger, J., R. L. McPherron, T.-S. Hsu, and V. Angelopoulos (2011), Steady magnetospheric convection and stream interfaces: Relationship over a solar cycle, J. Geophys. Res., 116, A00I19, doi:10.1029/2010JA015763. • Kissinger, J., R. L. McPherron, T.-S. Hsu, and V. Angelopoulos (2012), Diversion of plasma due to high pressure in the inner magnetosphere during steady magnetospheric convection, J. Geophys. Res., 117, A05206, doi:10.1029/2012JA017579.

13. Extra

14. Schematic Illustration of Effects of Ring Current in H Component Projection of a uniform axial field onto Earth’s surface The coordinate system used in magnetic measurements of a magnetic storm

15. Sawtooth Events • Series of particle injection events [Belian et al., 1995] • Occur over a wider local time extent (than SS) • Injection boundary can include the entire nightside extending past the terminators • Quasiperiodic oscillations: 179.6 min with large standard deviation of 54.0 min [Cai and Clauer, 2009] • Triggered by solar wind discontinuities (e.g., pressure jumps [Lee et al., 2004] and/or interplanetary magnetic field (IMF) changes [Henderson et al., 2006a] • Related to an intrinsic period of the Earth’s magnetosphere and is independent of external solar wind drivers [Huang et al., 2003a; Henderson et al., 2006a] • Periodic substorms, or something altogether different? • Similar, except the particle injection boundary and the near‐Earth reconnection site are closer to the Earth than that during typical substorms [Henderson, 2004] • Special phenomena associated with unique solar wind conditions • Alfvénic Mach number is low • Particle injection is globally dispersionless, even around the local noon [Borovsky et al., 2009] • Solar wind driving conditions during sawtooth events are stronger than those during typical substorms and SMCs [DeJong et al., 2008]) • The statistical characteristics of the solar wind agree with those during an interplanetary coronal mass ejection (ICME) • Since ICMEs are capable of driving magnetic storms [e.g., Gonzalez et al., 1999], there is a hypothesis that sawtooth events are storm time phenomena • Occur during storms when ring current is enhanced • Driven by moderate (Bz~10 nT) and steadily southward IMF conditions • driven by extremely strong solar wind and continuously southward IMF during magnetic storms, and the magnetospheric-ionospheric disturbances during sawtooth events are generally much larger than those during quiet time isolated substorms

16. (1) are sawtooth events storm time phenomena, • (2) is there a sawtooth interval during each storm regardless of storm strength, • (3) does the sawtooth occurrence rate depend on the strength of the ring current, and • (4) is there a preferred storm phase for sawtooth occurrence?

17. Sawtooth Events The Debate: Quasi-periodic (~3 hour) substorms, or something altogether different? Are solar wind fluctuations the driver, or is an internal (magneospheric) source? Similar signatures: injections, dipolarizations, AE indices, auroral precipitation But periodic and widespread (affecting large range of MLT). Similar, except the particle injection boundary and the near‐Earth reconnection site are closer to the Earth than that during typical substorms [Henderson, 2004] Special phenomena associated with unique solar wind conditions Particle injection is globally dispersionless, even around the local noon [Borovsky et al., 2009] Dynamic pressure increases at all MLTs Solar wind driving conditions during sawtooth events are stronger than those during typical substorms and SMCs The statistical characteristics of the solar wind agree with those during an interplanetary coronal mass ejection (ICME) Since ICMEs are capable of driving magnetic storms, there is a hypothesis that sawtooth events are storm time phenomena Occur during storms when ring current is enhanced Driven by moderate (Bz~10 nT) and steadily southward IMF conditions driven by extremely strong solar wind and continuously southward IMF during magnetic storms, and the magnetospheric-ionospheric disturbances during sawtooth events are generally much larger than those during quiet time isolated substorms