Geomagnetically induced currents – physics and applications
Antti Pulkkinen
UMBC/GEST @ NASA/GSFC
June 25, 2010, GEM Workshop,
Snowmass, CO.
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Contents
• Motivation/background – why should we care?
• Some observational facts of interest about geomagnetically induced currents (GIC).
• Theory and modeling.
• Forecasting – the Solar Shield project.
• Future challenges.
• Summary.
June 25, 2010, GEM Workshop,
Snowmass, CO.
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June 25, 2010, GEM Workshop,
Snowmass, CO.
Geomagnetically induced current (GIC)
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Why do we care? (applications)
• GIC causes saturation of power transformers:
• Transformer damage
• Electric blackout
June 25, 2010, GEM Workshop,
Snowmass, CO.
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Why do we care? (physics)
June 25, 2010, GEM Workshop,
Snowmass, CO.
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What does GIC look like?
Typical amplitudes
Bursts
Sudden start
Complex waveform
June 25, 2010, GEM Workshop,
Snowmass, CO.
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57 ° geomag. lat.
What drives (large) GIC?
June 25, 2010, GEM Workshop,
Snowmass, CO.
Huttunen et al. (Space Weather, 2008)
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35 ° geomag. lat.
What drives (large) GIC?
(CME-driven)
Pulkkinen et al. (JASR, 2010)
Coronal mass ejections the most significant driver of large GIC at mid- and high-latitudes.
June 25, 2010, GEM Workshop,
Snowmass, CO.
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57 ° geomag. lat.
What drives (large) GIC?
storm-time substorms storm-time pulsations
June 25, 2010, GEM Workshop,
Snowmass, CO.
Viljanen et al. (Space Weather, 2006)
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Theory and modeling
• Modeling of GIC is done in two steps:
– Geophysical step – compute the geoelectric field using geomagnetic induction theory.
– Engineering step – compute the GIC using the known system parameters.
June 25, 2010, GEM Workshop,
Snowmass, CO.
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


Geomagnetic (quasi-static) induction
  E 
Theory and modeling medium

(1)   B  0

0
  E  

 t
B (3)

  B  
0 j  
0

0

 t
E j   E (5)

(2)
(4)
June 25, 2010, GEM Workshop,
Snowmass, CO.
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
Theory and modeling
Time derivative of the horizontal magnetic field
E y
 
1

0


 t
Source field needs to be known (proportional to t source currents) g x
 t ' dt '
Conductivity
History needs to be known
Conductivity structure needs to be known
June 25, 2010, GEM Workshop,
Snowmass, CO.
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Complex Image Method
Pirjola and Viljanen (Annales Geophysicae, 1998) j ( r ') j ( r ')



 e z
 ( z )

 i


0
4 

V
A r


0
4 
Snowmass, CO.
 j ( r ') r  r ' dV '
C  j ( C  r ') r  r '  2 p (  ,  ( z )) e z dV '
(1)

(2)

A i
, A r
C  j ( C  r ')
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Theory and modeling - GIC
• General solutions for discretely and continuously grounded systems by Lehtinen and Pirjola, Ann. Geophys. (1985) and
Pulkkinen et al., J. Appl. Geophys. (2001).
• In practice, GIC can be computed from:
GIC i
 a i
E x
( r i
)  b i
E y
( r i
)
System parameters can be solved empirically or theoretically Output of the geomagnetic
June 25, 2010, GEM Workshop,
Snowmass, CO.
 induction computations
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Forecasting – Solar Shield
• In Solar Shield, we developed a two-level experimental system to forecast space weather effects on the North American power grid; project funded by
NASA’s Applied Sciences Program.
• NASA/GSFC/CCMC and Electric Power Research
Institute (EPRI) the key players.
• Pulkkinen et al. (Natural Hazards, 2009).
June 25, 2010, GEM Workshop,
Snowmass, CO.
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June 25, 2010, GEM Workshop,
Snowmass, CO.
Level 1 forecasts
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Solar observations of eruptive events
Level 1 forecasts parameters. NASA/ESA providing probabilistic estimate for GIC at individual nodes of the power grid. GIC forecast file is generated.
Plasma “cone” introduced to the inner boundary of a heliospheric MHD model. Model propagates the disturbance to the Earth. Computations carried out at the
Community Coordinated Modeling Center.
April 3, 2008 17

June 25, 2010, GEM Workshop,
Snowmass, CO.
Level 2 forecasts
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Lagrange 1 observations used as boundary conditions for magnetospheric MHD. NASA’s ACE data used. induction and GIC code providing GIC at individual nodes of the power grid. GIC forecast file is generated.
Magnetospheric MHD model used to model the magnetospheric-ionospheric dynamics. Computations carried out at the Community Coordinated Modeling
Center.
April 3, 2008 19

Level 2 forecast example
June 25, 2010, GEM Workshop,
Snowmass, CO.
Oct 24, 2003
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Future challenges
• Need to account for the 3D structure of the Earth?
• Do we capture the substorm-related ionospheric current fluctuations in the global MHD-based modeling approach? Substorms important driver of large GIC.
• Need to expand the global MHD-based modeling approach to cover lower latitudes. This is of significant
US and possibly European interest.
June 25, 2010, GEM Workshop,
Snowmass, CO.
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Summary
• GIC global phenomenon that a) impacts long conductor systems and b) is at the end of chain of complex physical processes.
• CMEs the most significant driver of large GIC.
• Modeling of GIC carried out in two steps - geophysical and engineering steps.
• Emerging capability to forecast GIC based on the firstprinciples.
• Many interesting challenges ahead.
June 25, 2010, GEM Workshop,
Snowmass, CO.
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