Transcript Ground-based Observations & Timing of the Substorm Expansion

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
[email protected]
GEM 2009 – Substorm Expansion
Phase Onset: The First Ten Minutes
ULF Waves at Substorm Onset
• Pi2s
~120 nT
– 40 – 150s
– Large amplitude
– Global impulsive waves observed
near onset
• Pi1s
–
–
–
–
2
1 – 40s
Small amplitude
Isolated
Continuous and broadband
~20 nT
www.CARSIMA.ca
Data available from www.cssdp.ca
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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
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AWESOME
Example
• Estimate background noise level
• Define onset when ULF power rises
continuously above the background
xj = j + σ( j)
•
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Onset defined at 0540:48 UT  16s
rd
3 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
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rd
3 June 2005
ULF onset 05:40:48 UT  16s @ GILL (24 - 96s: Pi1/2)
Optical onset 05:44:23 UT
32 Second Contours
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Murphy et al. [2009] JGR
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 UT
20th July 2005
• ULF onset
0524:08-0524:40 UT
• Global auroral
intensification
0526:42–0528:48 UT
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Murphy et al. [2009] JGR
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
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Rae et al. [2009] JGR
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Developed by Andy Kale
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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
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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 continentwide 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
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• 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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Collaborations
Contact: [email protected]
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Developed by Andy Kale
ASI and Differenced Images
False color real and 3s
differenced images ~30s
apart
Beads prior to auroral breakup 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
50+ magnetometers
20+ all sky imagers
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Wavelet Timing
Nov 1st 2006
• Wavelet power spectra for
magnetometers along the L~6.6
CARISMA line
• One band that is observed first (1248s; 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 Substorm
Database
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•
•
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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