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Ground-based Observations and Timing of the Substorm Expansion Phase

Ground-based Observations and Timing of the Substorm Expansion Phase. K.R. Murphy , I.J. Rae, I.R. Mann, D.K. Milling, C.E.J. Watt, V. Angelopoulos, H.U. Frey, A. Kale, L. Ozeke , K.-H. Glassmeier , H.-U. Auster , H. Singer. University of Alberta kmurphy@phys.ualberta.ca.

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Ground-based Observations and Timing of the Substorm Expansion Phase

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  1. Ground-based Observations and Timing of the Substorm Expansion Phase K.R. Murphy, I.J. Rae, I.R. Mann, D.K. Milling, C.E.J. Watt, V. Angelopoulos, H.U. Frey, A. Kale, L. Ozeke, K.-H. Glassmeier, H.-U. Auster, H. Singer University of Alberta kmurphy@phys.ualberta.ca GEM 2009 – Substorm Expansion Phase Onset: The First Ten Minutes

  2. ULF Waves at Substorm Onset ~120 nT ~20 nT • Pi2s • 40 – 150s • Large amplitude • Global impulsive waves observed near onset • Pi1s • 1 – 40s • Small amplitude • Isolated • Continuous and broadband

  3. www.CARSIMA.ca Data available from www.cssdp.ca

  4. AWESOME Automated Wavelet Estimation of Substorm Onset and Magnetic Events Estimate the onset of ULF waves during substorm expansion phase onset Wavelets are ideal; localised in time and frequency Meyer excellent for studying Pi2s @ substorm – Nose et al., 1998

  5. AWESOMEExample • Estimate background noise level • Define onset when ULF power rises continuously above the background • Onset defined at 0540:48 UT  16s xj = j + σ(j)

  6. 3rd June 2005 • Frey Substorm database • ~4000 substorms identified by IMAGE-FUV • Validate ULF onset by comparing to Optical onset • All Frey substorms identified in the southern hemisphere • Mapped to northern hemisphere as conjugate latitude and using Tsyganenko 96 (T96) • ULF onset 05:40:48 UT  16s @ GILL – Red line • Optical onset 05:44:23 UT – Purple line

  7. 3rd June 2005 ULF onset 05:40:48 UT  16s @ GILL (24 - 96s: Pi1/2) Optical onset 05:44:23 UT 32 Second Contours Murphy et al. [2009] JGR

  8. ULF onset at 05:40:48 UT  16s. Waves subsequently expand coherently away from an epicentre at the GILL magnetometer station Global auroral intensification observed between 0542:18-0544:23. ULF waves continue to expand across the Canadian sector

  9. 17th July 2005 • ULF onset • 0706:20-0706:36 UT • Global auroral intensification • 0705:54–0714:15 UT • 20th July 2005 • ULF onset • 0524:08-0524:40 UT • Global auroral • intensification • 0526:42–0528:48 UT Murphy et al. [2009] JGR

  10. 7th March 2007: Magnetic Onset 32 second contours Magnetic waves occur in a localised region at SNKQ at the same time as auroral arc undulations Rae et al. [2009] JGR

  11. Developed by Andy Kale

  12. FUTURE - Ground and In-Situ 29th February 2008 • 24-96s ULF space-based perpendicular wave amplitude with ground B • Intensification of ULF activity at GOES-11 coincident with KIAN dB and onset of small-scale undulations • Work required to closely time the in-situ ULF onset signature at TH-D, -E and -A

  13. AWESOME • The technique has been successfully validated by comparing the ULF onset to the optical onset defined by Frey et al. • Ability to track the expansion of ULF power on continent-wide scales • Provides necessary timing (~30s) • Long-period Pi1/short-period Pi2 pulsations arrive first in the ionosphere • Coincident in space with large-scale auroral onset • Coincident in time and space with formation of arc beading • First waves are typically in the 12-48s or 24-96s ULF wave bands, encompassing both the Pi1 and Pi2 • Collaborations • kmurphy@phys.ualberta.ca

  14. Acknowledgements • Funding to attend the GEM workshop was provided in part by the Profiling Alberta’s Graduate Students Travel Award. • MCMAC data provided courtesy Peter Chi • IMAGE data provided courtesy Harald Frey and Stephen Mende

  15. Collaborations Contact: kmurphy@phys.ualberta.ca Developed by Andy Kale

  16. ASI and Differenced Images False color real and 3s differenced images ~30s apart Beads prior to auroral break-up seen previously (e.g., Donovan et al., 2005; Liang et al., 2008) Magnetic onset occurs first at SNKQ – 0551:48 UT  16s Auroral beads occur first near SNKQ – 0552:15 UT

  17. The Magnetometers

  18. The Complete Ground-based Arsenal 20+ all sky imagers 50+ magnetometers

  19. Wavelet TimingNov 1st 2006 • Wavelet power spectra for magnetometers along the L~6.6 CARISMA line • One band that is observed first (12-48s; J=6) • 12-48s Pi1 ULF waves observed first at RABB, then FSMI, then FSIM • Characterise this ULF wave onset over entire Canadian sector Milling et al., 2008, GRL

  20. Pi1/2 Onset Arrival Times • ULF Onset starts at RABB (12 – 48s: Pi1/2) • Onset expands in coherent pattern outwards from epicenter • Why wavelets? How do we define onset? And do we observe this routinely? Milling et al., 2008, GRL

  21. Frey – IMAGE Optical SubstormDatabase • Frey et al. 2004, and Frey and Mende 2006 • ~4000 substorms identified by IMAGE-FUV • Validate ULF onset by comparing to Optical onset • Select isolated substorm onsets after April 1st 2005 at ~06:00 UT • Dense arrays of magnetometers • High temporal resolution • All Frey substorms identified in the southern hemisphere • Mapped to northern hemisphere as conjugate latitude and using Tsyganenko 96 (T96)

  22. 29th February 2008 • Azimuthally extended undulating arc • Pi1/2 onset defines arc location

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