Introduction to Space Weather Magnetosphere: Topology Oct. 22, 2009 CSI 662 / PHYS 660 Fall, 2009 Jie Zhang Copyright ©

Roadmap Part 1: The Sun Part 2: The Heliosphere Part 3: The Magnetosphere Part 4: The Ionsophere Part 5: Space Weather Effects Part 3: The Magnetosphere Topology Plasmas and Currents Geomagnetic Activities

CSI 662 / PHYS 660 October 22 2009 The Magnetosphere: Earth Magnetic Field and Topology of the Magnetosphere References: Kallenrode: Chap. 8.1 and 8.2 Prolss: Chap. 5

Plasma Physics

Magnetosphere Fast and Slow Wind As a result of interaction between Earth magnetic field and solar wind Highly structured Elements: magnetic fields Plasma electric current energetic particles. Fast and Slow Wind

Geomagnetic Field Fast and Slow Wind Magnetic dipole axis is inclined by 12° Magnetic North Pole: 78°N 69°W (Greenland) Magnetic South Pole: 78°S 111°E The dipole moment: http://www.birdgeo.com/images/CTE1810.jpg Fast and Slow Wind

Geomagnetic Field Kallenrode: Chap. 8.1 L-shell parameter and the dipole field line

Geomagnetic Field South Magnetic Pole South Atlantic Anomaly North Magnetic Pole Geomagnetic Reference Field http://www.ngdc.noaa.gov/geomag/icons/Obs1999_lg.gif

South Atlantic Anomaly (SAA) The center of the geomagnetic dipole is offset by 436 km relative to the center of the Earth in the direction of westerly Pacifics. This offset leads to a region of unusually small magnetic flux density in the south Atlantic, just off the coast of Brazil: the SAA. Radiation belts comes close to the Earth’s space at this region, making it a radiation risk for satellites and manned-space flight. Fast and Slow Wind

Terrestrial Dynamo Earth Layers

Terrestrial Dynamo Earth magnetic field is generated in a similar way as the Sun’s magnetic field, through a MHD dynamo process Ω effect: the differential rotation in the outer liquid core produced a strengthened toroidal field from a seed poloidal field α effect: the convection motion causes the rising motion, resulting in the twist of magnetic field by the Coriolis force, which produces a poloidal field, amplifying the original seed field

Topology Fast and Slow Wind The geomagnetic dipole is distorted by the solar wind. The magnetosphere is divided into two parts: Dayside: ellipsoidal shape, subsolar point at L ~10 RE Nightside: greatly extended, magnetotail ~ 200 RE Magnetotail Plasma Sheet Noon-Midnight Cross-section of magnetosphere Fast and Slow Wind

Magnetopause Fast and Slow Wind Magnetopause is the boundary layer between the solar wind regime and the terrestrial regime controlled by the geomagnetic field. The stand-off distance of the sub-solar point of the magnetopause The pressure balance point between the solar wind dynamic pressure (=ρu2)and the Earth magnetic pressure Fast and Slow Wind

Magnetopause Fast and Slow Wind Due to deflection of solar wind plasma or magnetic gradient drift, electric current forms within the magnetopause; the current is so-called Chapman-Ferraro current The current is from dawn to dusk Also interpreted as the presence of dawn-to-dusk electric field Deflection of solar wind electrons and protons (Fig. 8.9) Fast and Slow Wind

Polar Cusp Fast and Slow Wind Polar cusps are magnetic singularities in the dayside magnetosphere It separates the closed field lines on the dayside magnetosphere from open field lines swept to the nightside All field lines of the magnetopause converge at the cusps At geomagnetic latitude of ~78° At the cusp, solar wind plasma and energetic particles can penetrate deep into the Earth’s atmosphere Fast and Slow Wind

Polar Cap Fast and Slow Wind Within polar cap, all magnetic field lines are swept by the solar wind into the night side and are open Polar cap is a high-latitude region, above 78° of geomagnetic latitude Fast and Slow Wind

Magnetotail Fast and Slow Wind Earth’s high latitude magnetic fields are swept open downstream by the solar wind, forming a long magnetotail. To determine the cross-section size of the magnetotail, one uses the fact that the magnetic flux from the polar cap equals the magnetic flux in the tail Fast and Slow Wind

Bow Shock Fast and Slow Wind Bow shock forms where the supersonic solar wind is slowed down to subsonic speed in front of the magnetopause. Bow shock is a standing shock; on the other hand, the CME-driven interplanetary shock is a travelling shock Fast and Slow Wind

Shock Fast and Slow Wind Shock front Rankine-Hugoniot relations: 2: down stream 1: upper stream M: Mach number Ref: Prolss A.9, P468-471 Also see kallenrode Chap 6.8 Fast and Slow Wind

Bow Shock For the bow shock of the Earth’s magnetosphere, typically U2:U1 = 1:4 n2:n1 = 4:1 T2:T1 = 30:1 P2:P1 = 125:1

Magnetosheath Fast and Slow Wind Magnetosheath: the region between the bow shock and magnetopause Filled with down stream solar wind plasma Along the Sub-Earth line, sheath size is about 1/3 of the geocentric distance of the magnetopause Flow become supersonic again down the stream Plasma Flow Inside the Magnetosphere (Fig. 8.15) Fast and Slow Wind

The End