Ground-based Observations and Timing
of the Substorm Expansion Phase
University of [email protected]
GEM 2009 – Substorm Expansion Phase Onset: The First Ten Minutes
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
ULF Waves at Substorm Onset• Pi2s
– 40 – 150s– Large amplitude– Global impulsive waves
observed near onset
• Pi1s– 1 – 40s– Small amplitude– Isolated– Continuous and
broadband
2
~120 nT
~20 nT
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www.CARSIMA.caData available from www.cssdp.ca
AWESOME
• 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
Automated Wavelet Estimation of Substorm Onset and Magnetic Events
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AWESOME
Example• Estimate background noise level• Define onset when ULF power
rises continuously above the background
• Onset defined at 0540:48 UT 16s
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xj = j + σ(j)
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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
3rd June 2005ULF onset 05:40:48 UT 16s @
GILL (24 - 96s: Pi1/2) Optical onset 05:44:23 UT
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32 Second Contours
Murphy et al. [2009] JGR
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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
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17th July 2005• ULF onset
0706:20-0706:36 UT
• Global auroral intensification 0705:54–0714:15 UT20th July 2005
• ULF onset 0524:08-0524:40 UT
• Global auroralintensification 0526:42–0528:48 UTMurphy et al. [2009] JGR
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7th March 2007: Magnetic Onset
Magnetic waves occur in a localised region at SNKQ at the same time as auroral arc undulations
32 second contours
Rae et al. [2009] JGR
11 Developed by Andy Kale
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FUTURE - Ground and In-Situ
• 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
29th February
2008
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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– [email protected]
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
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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
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The Magnetometers
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The Complete Ground-based Arsenal
20+ all sky imagers
50+ magnetometers
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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
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
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)
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29th February 2008
• Azimuthally extended undulating arc
• Pi1/2 onset defines arc location
