Transcript Ionospheric Morphology An Introduction

Magnetospheric Morphology
Prepared by Prajwal Kulkarni and Naoshin Haque
Stanford University, Stanford, CA
IHY Workshop on
Advancing VLF through the Global AWESOME
Network
What is the Magnetosphere?
• Magnetosphere is region of
space controlled by the
Earth’s magnetic field.
• Within 5 - 6 Earth radii (RE),
the Earth’s magnetic field can
be approximated as a dipole
tilted ~11 degrees from the
rotation axis
(RE = 6370 km)
• The Earth’s magnetic field is
confined by solar wind
plasma blowing outward from
the Sun.
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The Solar Wind
• Source of solar wind: hot plasma
(106 K) from the solar corona
• The coronal plasma is accelerated
and flows radially outward from the
sun, filling interplanetary space
• Solar wind properties at Earth:
• Speed ~400 km/s
• Speed range ~200-700 km/s
• Number density ~ 7 cm-3
• Magnetic field ~ 5 nT
• Electron temperature ~ 105 K
• Proton temperature ~3 x 104 K
Picture of a total solar eclipse: the solar
corona is visible
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The Magnetosphere
• The solar wind compresses the magnetic
field on the sun-side, creating a boundary
termed the magnetopause at ~10 RE.
Solar Wind
• Solar wind flows past Earth and is
deflected around Earth’s magnetic field.
• On the night side, the solar wind-dipole
field interaction results in a tail up to~60
RE.
• The magnetosphere is the region within
the magnetopause, from ~10 RE on the
sun side to ~60 RE on the night side.
• Plasma within ~4 – 6 RE rotates with the
Earth—a region called the plasmasphere.
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The Plasmasphere
• The plasmasphere is a region of
dense (101 – 104 electrons/cm3), ‘cold’
(energies < 1 eV) plasma located up to
~5 RE.
• The electron density drops by ~2 – 3
orders of magnitude outside the
plasmasphere. This density drop
occurs at a sharp boundary termed the
plasmapause.
plasmapause
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L-shell
• Specified distance from Earth in space and magnetospheric physics
• Describes a particular set of planetary magnetic field lines.
• Given L-value describes magnetic field line that crosses the magnetic equator
at a number of Earth-radii equal to the L-value.
• For example, "L = 2" describes the set of the Earth's magnetic field lines which
cross the Earth's magnetic equator at 2 RE from the center of the Earth.
• From this point, we will often specify geospace locations in terms of L-shell.
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L-shell mapped to ground
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Radiation Belts
• Within the cold plasma of the plasmasphere, there is a population of
energetic (from ~100 keV to several MeV) electrons and protons.
• These energetic particles comprise the radiation belts. There are two
belts—an inner radiation belt and an outer radiation belt.
• The inner electron radiation belt exists from L ~1.3 to L ~ 2. The outer
radiation belts extend beyond the plasmasphere.
• Between the two belts, there exists a slot region of depleted radiation
belt particles.
• The density of these ‘hot’ energetic particles is much lower than the 8
cold plasmaspheric density.
The Slot Region
• The slot region—a region
of depleted radiation belt
particles—exists from
approximately L = 2—3.
• Studying source and loss
processes in electron
radiation belts and formation
of slot region are major
research questions.
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The Ring Current
•The ring current is another population
of trapped, charged particles,
approximately located from 2 < L < 7.
• The ring current is a toroidally
shaped current that flows westward
(ions and electrons move in opposite
directions).
•Carried mainly by kilovolt protons.
•Particle motion is caused by gradient
and curvature drift induced by the
Earth’s magnetic field.
•The ring current is associated with
strong perturbations in the magnetic
field measured at Earth.
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Geomagnetic Storms
• Sharp temporary change occurring in Earth’s magnetic field.
• SC: caused by compression of Earth’s outer atmosphere by flareenhanced solar wind
• Initial phase: continued compression
• Main phase starts after plasma cloud passes Earth
• Reduction in surface field  increase in ring current particle fluxes
Mins-hours
H
10s of hours-1 week
1/2 hourseveral hours
F
Z
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Dst Index
• Geomagnetic index:
monitors world wide
magnetic storm level
• Based on the average
value of H measured
hourly at 4 nearequatorial geomagnetic
observatories.
main phase
recovery phase
• Negative values indicate
geomagnetic storm in
progress
• Negative deflections
caused by storm time
ring current
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Kp Index
• Measures magnetic activity based on value of H
• Combine data from 12 observatories to assign number
to disturbances
• Figure ranges from 0, 0+, 1-, 1, 1+, …, 9+
• Measured in 3-hour increments
• Quasi-logarithmic
February 1986
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References
Abel, B., and R. M. Thorne, Electron scattering loss in the Earth's inner
magnetosphere: 1. Dominant physical processes, J. Geophys. Res., 103, 2385,
1998a. (Correction, J. Geophys. Res., 104, 4627, 1999.)
Abel, B., and R. M. Thorne, Electron scattering loss in the Earth's inner
magnetosphere: 2. Sensitivity to model parameters, J. Geophys. Res., 103, 2397,
1998b. (Correction, J. Geophys. Res., 104, 4627, 1999.)
Carpenter, D., Whistler evidence of a ‘knee’ in the magnetospheric ionization density
profile, J. Geophy. Res., 68, 1675, 1963.
Li, X., and M. Temerin, The electron radiation belt, Space Science Reviews, 95,
January 2001.
Lyons, L. R., R. M. Thorne, and C. F. Kennel, Pitch angle diffusion of radiation
belt electrons within the plasmasphere, J. Geophys. Res., 77, 3455, 1972.
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