ring current
Definition: A westward current carried by energetic ions and electrons drifting around Earth, which weakens the surface magnetic field during storms.
Why it matters here: During a geomagnetic storm, energetic ions and electrons trapped in Earth’s inner magnetosphere are injected and energized (ultimately drawing energy from the solar wind via magnetic reconnection at the magnetopause and in the magnetotail), forming an enhanced "ring current" that circles Earth westward at a few Earth radii’ distance.
Relationship: Use this term alongside Dst index; the lecture's quantitative model is summarized below.
\[ \frac{Dst^*}{B_0} = -\frac{2}{3}\frac{E_{\rm ring}}{E_0}, \qquad E_0 = \frac{B_0^2 R_E^3}{6\mu_0}, \qquad E_{\rm ring} = -\frac{3}{2}\frac{Dst}{B_0}E_0 \]
Boundary or common confusion: Treating the Carrington Event’s Dst value as a directly measured historical quantity with the same certainty as the 2017 storm’s Dst. The 1859 event predates the standardized Dst index by nearly a century, so its "Dst" is a modern reconstruction from historical magnetometer traces, with two independent published estimates differing by more than a factor of two -- this course states both values and their factor-of-two-plus disagreement explicitly, rather than picking one number and presenting it as certain.
Dst index
Definition: An hourly, longitude-averaged low-latitude magnetic perturbation designed to track the symmetric storm-time ring current.
Why it matters here: The real, published minimum Dst index for the storm following this course’s 6 September 2017 case-study CME was -142 nT (a G4, "severe" storm) -- substantially smaller in magnitude than either published estimate for the Carrington Event of 1-2 September 1859 (Dst estimated between -800 and -1750 nT, live-verified this session), the most intense geomagnetic storm in the era of ground-based magnetometer records.
Relationship: Use this term alongside Dessler-Parker-Sckopke relation; the lecture's quantitative model is summarized below.
\[ \frac{Dst^*}{B_0} = -\frac{2}{3}\frac{E_{\rm ring}}{E_0}, \qquad E_0 = \frac{B_0^2 R_E^3}{6\mu_0}, \qquad E_{\rm ring} = -\frac{3}{2}\frac{Dst}{B_0}E_0 \]
Boundary or common confusion: Treating the Carrington Event’s Dst value as a directly measured historical quantity with the same certainty as the 2017 storm’s Dst. The 1859 event predates the standardized Dst index by nearly a century, so its "Dst" is a modern reconstruction from historical magnetometer traces, with two independent published estimates differing by more than a factor of two -- this course states both values and their factor-of-two-plus disagreement explicitly, rather than picking one number and presenting it as certain.
Dessler-Parker-Sckopke relation
Definition: An energy theorem relating the pressure-corrected Dst depression to the total kinetic energy of trapped magnetospheric particles.
Why it matters here: The Dessler-Parker-Sckopke (DPS) relation is a standard textbook result (Baumjohann & Treumann, Basic Space Plasma Physics) connecting the fractional depression of Earth’s equatorial magnetic field to the ring current’s total kinetic energy: Dst*/B0 = -(2/3)(E_ring/E0), where E0 = B0^2 R_E^3/(6 mu0) is a fixed reference energy (the dipole field’s own magnetic energy outside Earth’s surface, down to R_E), giving E_ring = -(3/2)(Dst/B0) E0.
Relationship: Use this term alongside geomagnetic storm; the lecture's quantitative model is summarized below.
\[ \frac{Dst^*}{B_0} = -\frac{2}{3}\frac{E_{\rm ring}}{E_0}, \qquad E_0 = \frac{B_0^2 R_E^3}{6\mu_0}, \qquad E_{\rm ring} = -\frac{3}{2}\frac{Dst}{B_0}E_0 \]
Boundary or common confusion: Treating the Carrington Event’s Dst value as a directly measured historical quantity with the same certainty as the 2017 storm’s Dst. The 1859 event predates the standardized Dst index by nearly a century, so its "Dst" is a modern reconstruction from historical magnetometer traces, with two independent published estimates differing by more than a factor of two -- this course states both values and their factor-of-two-plus disagreement explicitly, rather than picking one number and presenting it as certain.
geomagnetic storm
Definition: A prolonged global disturbance of Earth's magnetosphere driven by enhanced solar-wind energy and momentum input.
Why it matters here: The real, published minimum Dst index for the storm following this course’s 6 September 2017 case-study CME was -142 nT (a G4, "severe" storm) -- substantially smaller in magnitude than either published estimate for the Carrington Event of 1-2 September 1859 (Dst estimated between -800 and -1750 nT, live-verified this session), the most intense geomagnetic storm in the era of ground-based magnetometer records.
Relationship: Use this term alongside storm main phase; the lecture's quantitative model is summarized below.
\[ \frac{Dst^*}{B_0} = -\frac{2}{3}\frac{E_{\rm ring}}{E_0}, \qquad E_0 = \frac{B_0^2 R_E^3}{6\mu_0}, \qquad E_{\rm ring} = -\frac{3}{2}\frac{Dst}{B_0}E_0 \]
Boundary or common confusion: Treating the Carrington Event’s Dst value as a directly measured historical quantity with the same certainty as the 2017 storm’s Dst. The 1859 event predates the standardized Dst index by nearly a century, so its "Dst" is a modern reconstruction from historical magnetometer traces, with two independent published estimates differing by more than a factor of two -- this course states both values and their factor-of-two-plus disagreement explicitly, rather than picking one number and presenting it as certain.
storm main phase
Definition: The interval of rapid Dst decrease as sustained solar-wind driving injects and energizes ring-current particles.
Why it matters here: This ring current’s own magnetic field opposes (partially cancels) Earth’s main dipole field at the equator, producing the negative magnetic-field depression measured by a global network of low-latitude magnetometer stations and combined into the standard Dst (Disturbance storm time) index, continuously available since 1957 (and reconstructed further back using historical magnetometer records, as for the Carrington Event).
Relationship: Use this term alongside recovery phase; the lecture's quantitative model is summarized below.
\[ \frac{Dst^*}{B_0} = -\frac{2}{3}\frac{E_{\rm ring}}{E_0}, \qquad E_0 = \frac{B_0^2 R_E^3}{6\mu_0}, \qquad E_{\rm ring} = -\frac{3}{2}\frac{Dst}{B_0}E_0 \]
Boundary or common confusion: Treating the Carrington Event’s Dst value as a directly measured historical quantity with the same certainty as the 2017 storm’s Dst. The 1859 event predates the standardized Dst index by nearly a century, so its "Dst" is a modern reconstruction from historical magnetometer traces, with two independent published estimates differing by more than a factor of two -- this course states both values and their factor-of-two-plus disagreement explicitly, rather than picking one number and presenting it as certain.
recovery phase
Definition: The interval after peak storm intensity when ring-current losses return Dst toward its quiet-time baseline.
Why it matters here: The real, published minimum Dst index for the storm following this course’s 6 September 2017 case-study CME was -142 nT (a G4, "severe" storm) -- substantially smaller in magnitude than either published estimate for the Carrington Event of 1-2 September 1859 (Dst estimated between -800 and -1750 nT, live-verified this session), the most intense geomagnetic storm in the era of ground-based magnetometer records.
Relationship: Use this term alongside ring current; the lecture's quantitative model is summarized below.
\[ \frac{Dst^*}{B_0} = -\frac{2}{3}\frac{E_{\rm ring}}{E_0}, \qquad E_0 = \frac{B_0^2 R_E^3}{6\mu_0}, \qquad E_{\rm ring} = -\frac{3}{2}\frac{Dst}{B_0}E_0 \]
Boundary or common confusion: Treating the Carrington Event’s Dst value as a directly measured historical quantity with the same certainty as the 2017 storm’s Dst. The 1859 event predates the standardized Dst index by nearly a century, so its "Dst" is a modern reconstruction from historical magnetometer traces, with two independent published estimates differing by more than a factor of two -- this course states both values and their factor-of-two-plus disagreement explicitly, rather than picking one number and presenting it as certain.