Lab 07: Capstone: Geomagnetically Induced Currents and the Full Flare-to-Grid Chain

Apparatus and Setup

This capstone lab estimates a representative geomagnetically induced current (GIC)-driving geoelectric field from a specified rate of magnetic-field change (Lecture 14), and synthesizes this course's full flare-to-grid physical chain using the real 6 September 2017 event and the Carrington Event as bracketing case studies.

Materials and Data

2024 Beggan et al. reanalysis (live-verified this session): Carrington-era field-change rate >700 nT/minute, exceeding the modern 1-in-100-year extreme value of 350-400 nT/minute at the same latitude. A simplified geoelectric-field estimate uses a uniform-half-space approximation, E ∝ sqrt(dB/dt) for a given ground conductivity (a standard, simplified space-weather-engineering approximation; level 3 for this course's specific numeric ground-conductivity choice, disclosed in ../reference-log.md).

Procedure

1. Compute the ratio of the Carrington-era field-change rate (using the reported >700 nT/min value) to the modern 1-in-100-year extreme value, and state this ratio as a measure of how anomalous the 1859 event's rate of change was, independent of its Dst magnitude.
2. Using the simplified E ∝ sqrt(dB/dt) scaling, compute the factor by which the induced geoelectric field (and hence GIC magnitude, which scales linearly with the geoelectric field in a simple resistive-line model) would increase for the Carrington-era rate of change relative to the modern extreme-value benchmark.
3. Tabulate this course's full seven-unit case-study chain for the real 6 September 2017 event: one specific real numeric quantity from each unit (structure/atmosphere, magnetism/sunspots, flares, CME/solar wind, missions, magnetosphere/Dst, and technological impact).
4. Identify, from your own tabulated chain, which single quantity is level 1 (live-verified this session), which are level 2 (standard published, not re-verified), and which (if any) are level 3 (order-of-magnitude/illustrative), and confirm this matches ../reference-log.md's disclosure.

Analysis and Uncertainty

Discuss why GIC risk assessment cannot rely on Dst magnitude alone (Lecture 14's central point) and why the Beggan et al. (2024) dB/dt reanalysis is a genuinely distinct, additional piece of evidence for Carrington-level risk, not merely a restatement of the already-known large Dst estimate.

Deliverables

• The dB/dt ratio and the implied geoelectric-field/GIC scaling factor.
• The complete seven-unit case-study chain table with provenance levels for each entry.

Assessment Criteria

• Correct dB/dt ratio arithmetic.
• Correct sqrt-scaling arithmetic for the implied GIC factor.
• Complete, accurate seven-unit chain table with correctly assigned provenance levels for every entry.

References and Provenance

• OpenStax Astronomy 2e (local extracted reference copy: references/openstax-astronomy-2e-extracted.txt) covers the Sun in Chapter 15 ("The Sun: A Garden-Variety Star"): 15.1 The Structure and Composition of the Sun, 15.2 The Solar Cycle, and 15.3 Solar Activity above the Photosphere. Chapter 15’s section numbering was cross-checked directly against its own embedded figure numbering this session (Figures 15.1 through 15.24 all appear under their matching section headers with no offset), so this citation is verified against the local extracted text rather than extrapolated by analogy from a prior course. OpenStax’s treatment throughout Chapter 15 is descriptive and qualitative; nearly every quantitative derivation in this course (the hydrostatic solar-atmosphere/scale-height argument, the sunspot magnetic-pressure balance, the Parker solar-wind critical-point argument and its numerical transonic solution, flare free-energy budgets, the Chapman-Ferraro magnetopause standoff distance, and the Dessler-Parker-Sckopke ring-current/Dst relation) goes well beyond OpenStax Astronomy 2e’s introductory level; each lecture states explicitly where this course extends beyond the assigned reading.
• 2024 Beggan et al. reanalysis: live-verified this session (via the Carrington Event Wikipedia article, citing Beggan, Clarke, Lawrence, Eaton et al. 2024, Space Weather 22, e2023SW003807); see materials/ASTR370/reference-log.md.
• Generated by materials/ASTR370/src/generate_astr370_content.py.