New insights on geomagnetic storms from observations and modeling Page: 2 of 7
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New Insights on Geomagnetic Storms from Observations
Vania K. Jordanova
Los Alamos National Laboratory, Los Alamos, NM 87545, USA
Abstract. Understanding the response at Earth of the Sun's varying energy output and forecasting geomagnetic activity
is of central interest to space science, since intense geomagnetic stonns may cause severe damages on technological
systems and affect communications. Episodes of southward (B,<0) interplanetary magnetic field (IMF) which lead to
disturbed geomagnetic conditions are associated either with coronal mass ejections (CMEs) and possess long and
continuous negative IMF B, excursions, or with high speed solar wind streams (HSS) whose geoeffectiveness is due to
IMF B, profiles fluctuating about zero with various amplitudes and duration. We show examples of ring current
simulations during two geomagnetic storms representative of each interplanetary condition with our kinetic ring current-
atmosphere interactions model (RAM), and investigate the mechanisms responsible for trapping particles and for causing
their loss. We find that periods of increased magnetospheric convection coinciding with enhancements of plasma sheet
density are needed for strong ring current buildup. During the HSS-driven storm the convection potential is highly
variable and causes small sporadic injections into the ring current. The long period of enhanced convection during the
CME-driven storm causes a continuous ring current injection penetrating to lower L shells and stronger ring current
Keywords: ring current, electric fields, plasma motion, inner magnetosphere, magnetic storms
PACS: 94.05.Sd, 94.30.cb, 94.30.cs, 94.30.Lr, 94.30.Kq, 94.30.Xy
Geomagnetic storms are some of the most important space weather phenomena. They occur when an increase in
the population of energetic ring current particles drifting around the Earth leads to an observable depression of the
horizontal component of the terrestrial magnetic field, characterized by the Dst index. The immediate cause of
magnetic storms at Earth is related to periods of southward (BZ<0) interplanetary magnetic field (IMF) reconnecting
with the terrestrial magnetic field at the low-latitude dayside magnetopause [I] and allowing transfer of solar wind
energy into the magnetosphere. A large fraction of this energy is stored in the storm time ring current as it builds up
during the main phase of the storm. This energy is subsequently released during the recovery phase of the storm
causing plasmaspheric electron and ion heating, energetic neutral and ion precipitation, and stable auroral red arcs
Geomagnetic storms have their origin in the structure and dynamics of the solar atmosphere. Two categories of
magnetic storms have been identified based upon their solar origin; recurrent, that repeat with the solar rotation
period of 27 days, or transient, that occur only once. The recurrent storms are associated with corotating interaction
regions (CIRs)  that are formed between the high-speed streams (HSS) from coronal holes and the upstream dense
slow-speed solar wind plasma . The single non-recurrent events are usually associated with huge eruptions from
the Sun of plasma and magnetic flux called coronal mass ejections (CMEs) and often give rise to the largest
geomagnetic storms at Earth . Currents induced in the ionosphere and Earth's surface during large geomagnetic
storms disturb and even damage telecommunication and navigation satellites, telecommunication cables, and power
grids. The aims of space weather research are thus to enhance our knowledge about the Sun and the solar wind, the
magnetosphere and atmosphere, and to be able to predict adverse conditions in the space environment.
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Jordanova, Vania K. New insights on geomagnetic storms from observations and modeling, article, January 1, 2009; [New Mexico]. (digital.library.unt.edu/ark:/67531/metadc933491/m1/2/: accessed September 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.