Magnetosphere-Ionosphere Coupling as a Source of Large Geomagnetic Variations�

Chigo Ngwira

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Catholic University of America and NASA Goddard Space Flight Center

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Acknowledgement: Antti Pulkkinen, James W. Weygand, Toshi Nishimura, & David Sibeck

Content

• Introduction
• Geomagnetically Induced Currents
• Magnetosphere-Ionosphere coupling
• GIC Distribution and Drivers
• Summary

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Travel funded via NSF Grant Award 2117932/2300579

Space Weather

• Space weather is primarily controlled by solar activity.
• Which include, solar flares, SEPs and CMEs etc.
• Solar wind-magnetosphere coupling leads to geomagnetic storms.
• There is a growing concern of potential space weather impact on man-made technologies and national security.

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Time scales of different solar phenomenon

Credit: Blendspace.com

Geomagnetically Induced Currents (GICs)

Electric field is the major quantity that determines the level of GIC flowing in power systems.

• Faraday’s law:

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• We use a two-step approach to compute GIC flowing through specific power network node:

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• Geophysical step: Modeling geoelectric field based on magnetosphere-ionosphere currents and ground conductivity structure.

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• Engineering step: Modeling GIC flowing in the power system in response to the determined geoelectric field.

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Sample Time Series: October 29-31, 2003

[Ngwira et al., SW, 2009]

Transformer damage in South Africa

Why GICs Are Important – Impact on Technology

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The GIC Chain: Sun to Mug – [Juusola et al., 2023]

Near-Earth Space Current Systems

• Schematic illustration of Earth’s magnetosphere, illustrating major distinct regions and electric current systems. 

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• To accurately model ground magnetic perturbations, you need to capture the physics of near-space electric currents systems.

Magnetosphere-Ionosphere Coupling

• Jim Dungey suggested, in 1961, that neutral points should be formed where magnetic fields from the Sun and the Earth interconnect.
• Since then, the magnetosphere community has gradually accepted Dungey’s magnetic reconnection idea as the main driver of space storms around the Earth.
• The question of whether reconnection triggers substorms or is a secondary effect was resolved in 2008 via the NASA THEMIS mission, which showed conclusively that reconnection is in fact the trigger mechanism [Angelopoulos et al., 2008].
• M-I coupling is a major unresolved space physics problem that continues to challenge our understanding.
• One of the top priority challenges in the Decadal Survey.

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Magnetic Reconnection

Hones, [J. Phys., 1985]

Credit: NASA's Scientific Visualization Studio

Solar wind Coupling to the MI System

• Many solar wind coupling functions exit:
• Akasofu
• Borovsky
• Newell
• Then you have geomagnetic indices:
• Kp
• Dst/SYM-H
• AE/SML
• But for GICs, it is the electric field that must be defined
• However, dB/dt is a good proxy?

It is obvious that GIC forecasting cannot be

based on solar wind data only, but conditions

in the magnetosphere and ionosphere are

important too (Viljanen, 2006).

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Substorms and Auroral Zone

[Ritter and L ̈uhr, 2008]

Auroral region is the most dynamic environment

in terms of GIC occurrence

Auroral Boundary Dynamics

[Weygand et al, 2023]

How deep can the auroral boundaries extend

into lower geomagnetic latitudes during

magnetic storms?

• As the Bz component becomes more negative:
• VBz increases
• Sym-H index increases
• Magnetic midnight equatorial boundary shifts

equatorward during periods

Global Distribution of GICs

[Pulkkinen et al., 2012]

High latitudes

Largest GICs

Equatorial zone

[Pirjola et al., 2005]

What processes create the small-scale features associated with large peak dB/dt during geomagnetic storms?

Snapshot of extreme delta-B variations from Halloween 2003 storm

*This is a potential area that will be addressed by upcoming missions like GDC, EZIE, SNIPE, and TRACERS

“How do mesoscale phenomena contribute to

the global response of the system?”

[Gabrielse et al., 2023]

[Ohtani and Gjerloev 2021]

Spatiotemporal Characteristics: Localized Geomagnetic Response

• Example study of geomagnetic storm on March 9, 2012.
• Geomagnetic field from ground-based magnetometer stations in Alaska.
• Enhanced dB/dt seen between 08:40 UT (22:40 LT) and 09:10 UT (23:10 LT).

[Ngwira et al., 2018]

Drivers of the Extreme dB/dt Localization

• Comparison between the dB/dt and THEMIS All-Sky Imager (ASI) auroral keograms.
• Intense dB/dt confined to the poleward edge of the poleward-expanding aurora.
• This corresponds to the region of most powerful aurora during a substorm [Weygand et al., 2000].

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[Ngwira et al., 2018]

Magnetotail Reconnection Powering Large dB/dt

[Angelopoulos et al., 2020]

[Ngwira et al., In preparation, 2023]

Substorm onset key

to the localization

Extended Study of Extreme Events

[Ngwira et al., SW, 2013]

Amplification by the equatorial electrojet current during Sudden Commencement

[Carter et al., 2015]

What about the Mid-latitudes

First evidence of mid-latitude positive bay driving large GICs

Geomagnetic Pulsations Driving GICs

[Heyns et al., 2021]

Summary

• Space Weather is an important part of todays technology dependent society.
• A solid understanding of the magnetosphere-ionosphere physical processes is required to fully appreciate the GIC phenomena.
• From the space weather standpoint, GICs are driven by many different factors that depend on the M-I coupling process.
• Basic science research is the core to understanding GICs drivers and developing mitigation procedures.

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Up Coming Events in Lusaka, Zambia

• International Space Weather Initiative (ISWI) School
• September 26^th to 30^th 2023
• Open to graduate students at African institutions
• African Geophysical Society Conference
• October 2^nd to 4^th 2023
• Open to all Earth and Space science students and scientists
• Travel support available - Apply

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https://afgps.org/conference

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