Download
1 / 18
180 likes | 190 Views
This text delves into the intricacies of the magnetosphere dynamics, focusing on key phenomena like bow shock, substorms, and storms. Learn about the formation of bow shock, solar wind interaction, plasma convection, and the phases of magnetospheric substorms. Discover how solar wind energy is transferred into the Earth's magnetosphere and the impact of magnetospheric storms. Gain insights into the solar wind dynamo, magnetosheath, and the open magnetosphere model. Explore topics such as magnetic reconnection, plasma convection, and the behaviors of the magnetospheric substorm and storm phases. Dive deep into the workings and complexities of Earth's magnetic field interactions with the solar wind.
E N D
CSI 662 / ASTR 769 Lect. 09 Spring 2007 April 03, 2007 Magnetosphere: Bow ShockSubstorm and Storm • References: • Prolss: Chap. 6.4, P. 325-336; Chap. 7.6, P381 – 394; Chap. 8.3, P415-422 (main reference) • Tascione: Chap. 5.7 – 5.10, P. 69 – 76 (supplement) • Gombosi: Chap. 14.4 – 14.6, P292 – P312 (supplement)
Fast and Slow Wind Magnetosphere • Formation of Bow Shock • Solar Wind Dynamo • Plasma Convection • Magnetospheric Substorm • Growth phase • Expansion phase • Recovery phase • Magnetospheric Storm
Fast and Slow Wind Bow Shock • Shock forms in front of supersonic objects, e.g., CME • Shock also forms in front of obstacles placed in supersonic flows, e.g., bow shock of Earth’s magnetosphere • Magnetosheath: the region between bow shock and magnetopause
Fast and Slow Wind Shock Shock front • Rankine-Hugoniot relations: 2: down stream 1: upper stream M: Mach number Ref: Prolss A.9, P468-471
Bow Shock • Typically • M1=10 • M2=0.5 • U2:U1 = 1:4 • n2:n1 = 4:1 • P2:P1 = 125:1 • T2:T1 = 30:1 • E.g. Proton temperature • Tp = 105K (SW) • Tp = 2 X 106K (sheath)
Fast and Slow Wind Magnetosheath • 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
Fast and Slow Wind Solar Wind Dynamo • How is solar wind energy transferred into the Earth magnetosphere? • Energy must be from the kinetic energy of solar wind flow • In quiet condition, solar wind plasma and magnetic field simply “slip” through around the magnetopause. There is no connection between solar wind magnetic field and Earth magnetic field • In storm condition, reconnection opens the Earth magnetic field. The flow generates the electric dynamo field (or convection electric field) that powers the systems
Solar Wind Energy Transfer • How is solar wind energy transferred into the Earth magnetosphere? • Energy must be from the kinetic energy of solar wind flow • In quiet condition, solar wind plasma and magnetic field simply “slip” through around the magnetopause. There is no connection between solar wind magnetic field and Earth magnetic field. Closed magnetosphere • In storm condition, reconnection opens the Earth magnetic field. The flow generates the electric dynamo field (or convection electric field) that powers the systems. Open magnetosphere
Fast and Slow Wind Solar Wind Dynamo • Electric dynamo field, driven by SW flow, is given by Edyn • Electric dynamo field enters the magnetosphere when Earth magnetic field line is open • One footpoint rooted on the surface of the Earth • One footpoint connected with the solar wind magnetic field • Because Bs, Electric dynamo field always points from dawn to dust
Fast and Slow Wind Open Magnetosphere • The Dungey reconnection model • When SW B field is southward, magnetic reconnection causes the dayside closed field to open up, and connect with SW B field. Open field Magnetic reconnection
Plasma Convection • (1) -> (9), a cycle of magnetic field transport, along with a large scale plasma convection (or transport) • (1) create partially IP and partially magnetosphere field • (6) create purely IP and purely magnetospheric field
Plasma Convection • In the magnetosphere, plasma drifts back in the anti-Sun direction, drive • The return flow is driven by E X B drift
Magnetospheric Substorm • Geomagnetic perturbation lasting a few hours, which tends to occur during local post-midnight nighttime. • A substorm corresponds to an injections of charged particles from the magnetotail into the auroral oval. • Growth phase • About 1 hour • Energy accumulation • Magnetic reconnection on the dayside • Enhanced magnetic field in the magneto-tail lobes • Narrowing of the plasma sheet thickness
Magnetospheric Substorm • During the substorm, instability causes current disruption in the neutral sheet • Neutral sheet current is diverted through the ionosphere, producing strong polar electrojet • Current disruption causes strong electric field to energize particles. Substorm Current Wedge
Magnetospheric Substorm • Expansion phase • also called “dipolarization” • About 1- 2 hour • Aurora brightening • Depression of geomagnetic field • Energy release through night side reconnection • Injection energetic particles into the inner magnetosphere • Plasma sheet heating • Bursty bulk flow • Tailward plasmoid release
Magnetospheric storm • Large and prolonged disturbances of the magnetosphere • Main phase lasts for several hours • Recovery phase lasts for several days • Due to the increase of ring current • Geogagnetic storm main phase may have several substorms superposed.
