What are Geomagnetic Storms Whitney Q Lohmeyer MIT

What are Geomagnetic Storms? Whitney Q. Lohmeyer MIT – Aero. Astro GEM 2013

Gonzalez et al. [1994] define geomagnetic storms as… “An interval of time when a sufficiently intense and long-lasting interplanetary convection electric field leads… to an intensified ring current strong enough to exceed some key threshold of the quantifying storm time Dst index”

Gonzalez et al. [1994] define geomagnetic storms as… “An interval of time when a sufficiently intense and long-lasting interplanetary convection electric field leads… to an intensified ring current strong enough to exceed some key threshold of the quantifying storm time Dst index”

Interplanetary Convection Electric Field Solar ejecta can cause traveling shock waves • Southward IMF at shock arrival magnetic reconnection – Solar wind and southward IMF cause electric field and drive magnetospheric convection Four primary mechanisms cause enhanced electric fields in interplanetary medium: • Primary phenomena: CMEs (solar max) and CIRs (declining) • HILDCAAs and Russell-Mc. Pherron effect

Gonzalez et al. [1994] define geomagnetic storms as… “An interval of time when a sufficiently intense and long-lasting interplanetary convection electric field leads… to an intensified ring current strong enough to exceed some key threshold of the quantifying storm time Dst index”

Intensified Ring Current • Ring current forms from drifts due to magnetic field gradient and curvature – Ions move from midnight to dusk – Electrons move from midnight towards dawn • Field decrease is linearly related to total energy of the ring current – Storm time ring current is largest consumer of energy in the magnetosphere Image Credit: Dmitriy Subbotin, 2010

Gonzalez et al. [1994] define geomagnetic storms as… “An interval of time when a sufficiently intense and long-lasting interplanetary convection electric field leads… to an intensified ring current strong enough to exceed some key threshold of the quantifying storm time Dst index”

Dst – Disturbance Storm Time Index • Dst: hourly average of global variation in horizontal component of earth’s magnetic field – Measured at four widely separated mid-latitude observatories – Range: approximately 100 to -600 n. T – Quiet/undisturbed conditions: 0 to -20 n. T Storm Classification Dst Threshold (n. T) Big <-200 Intense/Great -100 to -200 Moderate -50 to -100 Weak/Small -30 to -50

Kp: Another Geomagnetic Index • Kp: 3 -hour interval of observed fluctuation from ground-based magnetometers • Range: 0 -9 (9 is severe) • Kp has been more widely used than Dst – Available in final form in only a few weeks – Dst requires more analysis to produce, and has been delayed for up to years – Difficult to interpret physically b/c variations caused by many conditions (magnetopause currents, auroral electrojects, etc. )

Kamide et al. , 1998

Who cares about storms? • “The economic cost of a severe geomagnetic storm could reach US$1 -2 trillion during the first year alone with recovery times of 4 -10 years” – Space Studies Board of the U. S. National Academies, 2008 [NRC, 2008; Baker, 2009] • Satellite systems and continental-scale power generation/distribution systems – 1989 Hydro Quebec power system – Space systems: internal charging (Anik E 1/E 2) – Solar protons harm humans!

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