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1、Magnetospheric MorphologyPrepared by Prajwal Kulkarni and Naoshin HaqueStanford University, Stanford, CAIHY Workshop on Advancing VLF through the Global AWESOME NetworkWhat is the Magnetosphere? Magnetosphere is region of space controlled by the Earths magnetic field. Within 5 - 6 Earth radii (RE),
2、the Earths magnetic field can be approximated as a dipole tilted 11 degrees from the rotation axis(RE = 6370 km) The Earths magnetic field is confined by solar wind plasma blowing outward from the Sun.The Solar Wind Source of solar wind: hot plasma (106 K) from the solar corona The coronal plasma is
3、 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 KPicture of a total solar eclipse: the solar coro
4、na is visibleThe MagnetosphereSolar Wind Solar wind flows past Earth and is deflected around Earths magnetic field. The solar wind compresses the magnetic field on the sun-side, creating a boundary termed the magnetopause at 10 RE. On the night side, the solar wind-dipole field interaction results i
5、n a tail up to60 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 Eartha region called the plasmasphere.The Plasmasphere The plasmasphere is a region of dense (101 104 electrons/cm3), cold (energ
6、ies 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. plasmapauseL-shell Specified distance from Earth in space and magnetospheric physics Describes a particular set of
7、 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 Earths magnetic field lines which cross the Earths magnetic equator at 2 RE from the center of t
8、he Earth. From this point, we will often specify geospace locations in terms of L-shell.L-shell mapped to groundRadiation 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 r
9、adiation belts. There are two beltsan 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 de
10、nsity of these hot energetic particles is much lower than thecold plasmaspheric density. The Slot Region The slot regiona region of depleted radiation belt particlesexists from approximately L = 23. Studying source and loss processes in electron radiation belts and formation of slot region are major
11、 research questions.The Ring CurrentThe 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
12、 motion is caused by gradient and curvature drift induced by the Earths magnetic field.The ring current is associated with strong perturbations in the magnetic field measured at Earth.Geomagnetic StormsSharp temporary change occurring in Earths magnetic field.SC: caused by compression of Earths oute
13、r atmosphere by flare-enhanced solar windInitial phase: continued compressionMain phase starts after plasma cloud passes EarthReduction in surface field increase in ring current particle fluxesHFZMins-hours1/2 hour-several hours10s of hours-1 weekDst IndexGeomagnetic index: monitors world wide magne
14、tic storm levelBased on the average value of H measured hourly at 4 near-equatorial geomagnetic observatories. Negative values indicate geomagnetic storm in progressNegative deflections caused by storm time ring currentmain phaserecovery phaseKp Index Measures magnetic activity based on value of H C
15、ombine data from 12 observatories to assign number to disturbances Figure ranges from 0, 0+, 1-, 1, 1+, , 9+ Measured in 3-hour increments Quasi-logarithmicFebruary 1986ReferencesAbel, B., and R. M. Thorne, Electron scattering loss in the Earths inner magnetosphere: 1. Dominant physical processes, J
16、. Geophys. Res., 103, 2385,1998a. (Correction, J. Geophys. Res., 104, 4627, 1999.)Abel, B., and R. M. Thorne, Electron scattering loss in the Earths inner magnetosphere: 2. Sensitivity to model parameters, J. Geophys. Res., 103, 2397, 1998b. (Correction, J. Geophys. Res., 104, 4627, 1999.)Carpenter,
17、 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 radiationbelt electrons within the plasmasphere, J. Geophys. Res., 77, 3455, 1972.
