Ring Current Investigations: The Quest for Space Weather Prediction

321 Pages·2020·28.38 MB·English

by  Vania K. Jordanova (editor), Raluca Ilie (editor), Margaret W. Chen (editor)

Ring Current
Investigations
The Quest for Space
Weather Prediction
Edited by
Vania K. Jordanova
Raluca Ilie
Margaret W. Chen
Elsevier
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Contributors
Margaret W. Chen
The Aerospace Corporation, Space Sciences Application Laboratory,
Los Angeles, CA, United States
Mei-Ching Fok
Geospace Physics Laboratory, NASA Goddard Space Flight Center, Greenbelt,
MD, United States
Raluca Ilie
University of Illinois at Urbana-Champaign, Champaign, IL, United States
Vania K. Jordanova
Los Alamos National Laboratory, Space Science and Applications, Los Alamos,
NM, United States
Lynn M. Kistler
University of New Hampshire, Space Science Center and Physics Department,
Durham, NH, United States; Nagoya University, Institute for Space Earth
Environmental Research, Nagoya, Aichi, Japan
Barry H. Mauk
The Johns Hopkins University Applied Physics Laboratory, Laurel, MD,
United States
James L. Roeder
The Aerospace Corporation, Los Angeles, CA, United States
Frank Toffoletto
Rice University, Physics and Astronomy Department, Houston, TX, United States
ix
Preface
The inner regions of the Earth’s space environment, or the inner magnetosphere,
are composed of several distinct plasma populations that could be differentiated
by their specific temperature or density (e.g., plasmasphere, ring current, radiation
belts, and plasma sheet). These inner magnetospheric plasma populations interact
with each other and with the outer magnetosphere and ionosphere through a variety
of physical processes leading to particle injections, acceleration, and loss. Abrupt
changes of several orders of magnitude can occur in the particle distributions, and
the most dramatic variations, related to the development of large geomagnetic
storms, are linked to harmful space weather effects. As society becomes more and
more dependent on sophisticated technologies operating both in space and on the
ground, the need to provide a timely and reliable forecast of the space environ-
ment increases. Despite years of ground-based, global imaging, and in situ satel-
lite observations, as well as numerical modeling studies, accurate “space weather”
forecasts remain a big challenge, due to the complexity of the highly dynamic
near-Earth region.
This book is motivated by the growing interest in space weather prediction.
It provides in-depth coverage of the dynamics of energetic particles forming
the ring current populations, the main signature of a geomagnetic storm, using
observations, theory, and numerical modeling. The development of the Earth’s
ring current depends strongly on the plasma sheet source population and the
magnitude of electromagnetic fields, which control particles’ injection, depth of
penetration, and trapping. Its decay is dictated by losses due to collisions with
neutral and charged particles, wave-particle interactions, flow out to the dayside
magnetopause, and particle precipitation into the atmosphere. With ring current
observations at other strongly magnetized planets of the solar system, such as
Jupiter, Saturn, Uranus, and Neptune, similarities and differences to the ring cur-
rent system at Earth have been discovered. This book provides a comprehensive
review of important advances in ring current research from recent publications
and stimulating discussions at the International Space Science Institute in Bern,
Switzerland, the American Geophysical Union Fall Meetings, and the National
Science Foundation/Geospace Environment Modeling Workshops. It contains
nine highly coordinated chapters that have been independently refereed, and an
Appendix with useful links to illustrative video clips, public data, and open-
source code downloads. The book material also reviews relevant concepts in
basic plasma physics theory, electromagnetism, and kinetic theory, in the con-
text of ring current development and decay. The book is intended to serve as
xi
xii Preface
a comprehensive reference to researchers, professors and students interested in
understanding the underlying physical mechanisms of geomagnetic storms and
in simulating their effects.
Vania K. Jordanova
Los Alamos National Laboratory, Los Alamos, NM
Raluca Ilie
University of Illinois at Urbana-Champaign, Urbana, IL
Margaret W. Chen
The Aerospace Corporation, Los Angeles, CA
CHAPTER
1
Introduction and historical
background
Vania K. Jordanovaa, Raluca Ilieb, Margaret W. Chenc
aLos Alamos National Laboratory, Space Science and Applications, Los Alamos, NM, United States;
bUniversity of Illinois at Urbana-Champaign, Champaign, IL, United States; cThe Aerospace
Corporation, Space Sciences Application Laboratory, Los Angeles, CA, United States
1.1 Historical overview
The defining characteristic feature of a geomagnetic storm that is observed in the
magnetograms of near-equatorial ground-based stations is the decrease of the hori-
zontal component of the Earth’s magnetic field and its subsequent recovery. Hourly
values of the average global variation of this component, measured at low-latitude
observatories (Fig. 1.1A), are used to specify the intensity of the geomagnetic storm
and are referred to as the Dst index (Sugiura, 1964). This index has been compiled
by the World Data Center for Geomagnetism in Kyoto, Japan, since 1964. Usually,
the largest magnetic storms are preceded by a sudden impulse called storm sudden
commencement (SSC), signaling the arrival of an interplanetary shock structure. The
main phase of the geomagnetic storm is associated with the enhancement of the ring
current due to particle energization and trapping, while the recovery phase is associ-
ated with its decay due to various loss processes. Another index available since 1932
from the Institute of Geophysics in Gottingen, and later from the GFZ Helmholtz
Centre in Potsdam, Germany, and used to classify the geomagnetic activity on a
global scale is the Kp index, a number between 0 and 9 indicating the level of distur-
bance in a given 3-hour interval of the universal day. A detailed description of various
geomagnetic indices and their use is given by Mayaud (1980).
Time variations in the Earth’s magnetic field were reported for the first time around
1635, in a book entitled “A discourse mathematical on the variation of the mag-
neticall needle: Together with its admirable diminution lately discovered” by Henry
Gellibrand, professor of Astronomy at the Gresham College (Gellibrand, 1635).
However, it was not until 1847, when Carl Friedrich Gauss, together with Wilhelm
Weber, established the first magnetic observatory in Gottingen, Germany, and mea-
surements of the terrestrial magnetic field in various regions of the Earth were made
possible. Gauss’ method of measuring the horizontal component of the terrestrial
magnetic field has provided the mathematical foundation in assessing the geomag-
netic disturbances on the ground. Ground disturbances were reported to have various
periodicities: from diurnal, first discovered in London in 1722 by George Graham
1
Ring Current Investigations. http://dx.doi.org/10.1016/B978-0-12-815571-4.00001-9
Copyright © 2020 Elsevier Inc. All rights reserved.
2 CHAPTER 1 Introduction and historical background
FIGURE 1.1
(A) Hourly Dst values during the geomagnetic storm of July 9 1966 based on ground-
based data from Honolulu, Tucson, San Juan, Guam and Surlari magnetometers. (B)
Directional intensities of protons with energies between 31 and 49 keV as a function of
radial distance, during the July 9, 1966 geomagnetic storm.
Source: From Frank (1967).
(a clockmaker also interested in astronomy and geomagnetism), to secular; however,
some irregular disturbances were also reported and remained unexplained until 1912,
when Carl Stormer interpreted them as a consequence of the formation of a donut-
shape equatorial ring of electrons, moving on closed field lines in a region between
30,000 and 10,000,000 km (Stormer, 1912). This is the first time the existence of a
“ring current” is hypothesized.
It was not until 1967, when ring current particles were first detected by instru-
ments onboard the OGO 3 spacecraft (Frank, 1967); Fig. 1.1B shows the first mea-
surements of ring current proton fluxes during the geomagnetic storm of July 9, 1966.
Numerous studies followed, that focused on the detection and estimation of ring
current characteristic properties (Hoffman and Cahill, 1968; Konradi et al., 1973;
Longanecker and Hoffman, 1973; Cahill, 1973; Williams and Lyons, 1974; Berko
et al., 1975).
In 1951, observations of precipitating energetic neutral hydrogen into the upper
atmosphere during auroral substorms were linked to the existence of energetic neu-
tral atoms (ENAs) by Meinel (1951), and were discovered to contribute to the ring
current decay (Fite et al., 1958; Dessler and Parker, 1959; Stuart, 1959) by means of
charge exchange between protons and neutral atmospheric hydrogen atoms. These
discoveries led to the first global image of the ring current, based on measurements
of actual energetic neutral atom fluxes (Roelof, 1987) from the ISEE-1 spacecraft.
Besides the ring current, which is of major interest to this book, other magne-
tospheric current systems are the tail, field-aligned, and magnetopause currents
1.2 Relation to solar wind drivers 3
FIGURE 1.2
Schematic illustration of Earth’s magnetosphere, showing the major distinct regions and
electric current systems.
Source: From Pollock et al. (2003).
(Fig. 1.2). The relative contribution of each of these currents to Dst is not well estab-
lished and was estimated by different authors as being minor (Burton et al., 1975;
O’Brien and McPherron, 2000; Turner et al., 2000), major (Alexeev et al., 1996), or
storm-dependent (e.g., Ganushkina et al., 2004).
1.2 Relation to solar wind drivers
Satellite observations have shown that our planet Earth is immersed into the con-
tinuous flow of plasma from the Sun called the solar wind, traveling on average at
about 400 km/s, with a particle density of ∼10 cm–3, and carrying a magnetic field of
about 5 nT. The bulk of this flow is diverted around the planet by the strong intrinsic
magnetic field of the Earth, forming a tear-drop shaped magnetic cavity known as
the magnetosphere (Fig. 1.2). This cavity is populated by thermal plasma and ener-
getic charged particles whose motion is governed by the surrounding electric and
magnetic fields. At near-Earth distances, low-energy (electronvolt, eV) plasma coro-
tates with the Earth and forms the plasmasphere (Carpenter and Anderson, 1992),
populated by outflow from the ionosphere. Particles at relativistic (MeV) energies
4 CHAPTER 1 Introduction and historical background
FIGURE 1.3
Adiabatic flow pattern (solid arrows) of magnetospheric protons (E ∼10 − 200 keV) in the
equatorial plane. Dashed curves represent boundaries of plasma sheet and plasmasphere.
Source: From Schulz and Lanzerotti (1974).
get trapped on closed geomagnetic field lines thereby forming the radiation belts,
whose source is still the subject of intensive research (Mauk et al., 2013). The inter-
mediate-energy (keV) charged particles that are injected from the plasma sheet,
and for which the electric and magnetic drifts are of comparable importance, form
the ring current (Fig. 1.3). The strength of the ring current is commonly used as a
measure of geomagnetic storm intensity through the Dst index. The ring current is
centered at the magnetic equatorial plane, with an outer boundary located where the
magnetic field is no longer able to maintain closed particle orbits around the Earth
(stable trapping), and an inner boundary determined by the dense atmosphere. For
typical ring current energies from ∼1 keV to 300 keV, the inner magnetosphere
region under consideration thus extends between ∼2 and 8 Earth radii (R ) (Schulz
E
and Lanzerotti, 1974).
Gonzalez et al. (1994) suggested a definition of a geomagnetic storm as “an
interval of time when a sufficiently intense and long-lasting interplanetary convec-
tion electric field leads, through a substantial energization in the magnetosphere-
ionosphere system, to an intensified ring current strong enough to exceed some key
threshold of the quantifying storm time Dst index”. Furthermore, from all observed
Dst values during 1976–1986, approximately 1% were more negative than −100 nT
and were classified as great (intense) storms, approximately 7% were between −50
nT and −100 nT and were classified as moderate storms, and Dst values between
−30 nT and −50 nT, which occurred less than 20% of the time, were classified as