Johns Hopkins Applied Physics Laboratory, Laurel MD, USA EGU 2016 Solar and Interplanetary Causes of Extremely Intense Substorms During Superstorms Bruce T. Tsurutani Jet Propulsion Laboratory, California Institute of Technology, Pasadena, USA Rajkumar Hajra Laboratoire de Physique et Chimie de l’Environnement et de l’Espace (LPC2E), CNRS, Orléans, France Ezequiel Echer Instituto Nacional de Pesquisas Espaciais, Sao Jose dos Campos, SP, Brazil Jesper Gjerloev Johns Hopkins Applied Physics Laboratory, Laurel MD, USA

Supersubstorm/SSS events Extremely intense substorms with SML peak intensity < -2500 nT Identified by the negative bay development in the westward electrojet index – SML SML is SuperMAG AL index SuperMAG consists of > 300 ground-based magnetometers including not only the standard AL sites but also higher and lower latitude stations

Why Study Extremely Intense Substorms? It is found that supersubstorms (SSSs) are different than regular substorms during magnetic storms. SSSs can be externally triggered. Supersubstorms may cause power outages during storm intervals.

Supersubstorm onsets Two shocks 24 November 2001 What is this? Is this a ICME Loop? Tsurutani et al., AnGeo Comm., 33, 519-524, 2015

The Magnetic Perturbations at the Ground During the Two Supersubstorms Tsurutani et al., AnGeo Comm., 33, 519-524, 2015

SSS seasonal dependence Prominent annual variation Not a single year with two seasonal peaks “Semiannual” variation – artifact resulting from superposition of years with a dominant annual variation with opposite equinoctial maxima

Solar cycle phase Years # SSSs SSS/year Ascending 1987-1988, 1998-1999, 2011-2012 9 1.5 Maximum 1981, 1989-1991, 2000-2002 22 3.1 Descending 1982-1984, 1992-1994, 2003-2005 34 3.8 Minimum 1985-1986, 1995-1997, 2006-2010 0.9 Total 1981-2012 74 2.3

SSS event Relationship to Magnetic Storms Geomagnetic condition # SSSs % of SSS Magnetic storm main phase 64 86.5 Magnetic storm recovery phase 7 9.5 Quiet time 3 4 SSSs do not coincide with geomagnetic storm peaks

No strong correlation of SSSs with geomagnetic storm intensity

Superposed Epoch Analyses Enhanced solar wind density and ram pressure leading to SSS SSS peak

Precursor IMF Bsouth Enhanced dayside reconnection rate SSS peak

Interplanetary “precursor” for SSS events Peak VswBs at 1 h prior to SML peak is the most pertinent interplanetary precursor of the SSS strength

Average solar wind/interplanetary conditions during SSS events

Average (median) energy budget during 1 h prior to the peak SSS intensity – 24 events during SC 23 (1996-2008) Total energy (1016 J) Magnetosphere Eɛ 4.0±2.9 (3.2) Joule heating EJ 2.2±1.5 (1.3) Ring current (ER) 0.09±0.07 (0.08) Energy dissipation rate (%) Joule heating EJ/Eɛ 46.4±24.2 (46.1) Ring current ER/Eɛ 3.6±2.3 (3.8) Joule heating is the dominating energy dissipation mechanism during SSS events

Main results We identified 74 SSS events occurring from 1981 through 2012 using measurements from the SuperMAG network of ground-based magnetometers. The SSS events may occur during all phases of the solar cycle, with the highest occurrence rate in the descending phase. The number of SSS events showed an annual variation, with maximum altering between spring equinox in SC 22 and fall equinox in SC 23. Possible ionospheric control on the substorm triggering was suggested. Overwhelm majority (86.5%) occurred in the main phase of geomagnetic storms. About 9.5% occurred in the storm recovery phase and 4% in geomagnetically quiet. On average, ~46.4% of the magnetospheric input energy goes into Joule heating and only ~3.6% into ring current for the SSS events. The precursor IMF southward fields were provided by the magnetic clouds in 46% of the times and sheath fields in 54% of the times.

Thanks Form more details, contact: Bruce T. Tsurutani, JPL, NASA (bruce.t.tsurutani@jpl.nasa.gov) Rajkumar Hajra, LPC2E, CNRS, France (rajkumarhajra@yahoo.co.in)