Intro to magnetosphere (Chap. 8) Schematic of Bow Shock and Foreshock. Flow around planetary magnetic field obstacle. Homework #3 posted

Transcription

1 Intro to magnetosphere (Chap. 8) Homework #3 posted Reading: Finish Chap. 8 of Kallenrode Interaction with solar wind a. Magnetopause b. Structure of magnetosphere - open vs closed c. Convection d. Magnetotail Schematic of Bow Shock and Foreshock View of bow shock and foreshock region for a Parker spiral orientation for the IMF. Foreshock begins at the first tangent field line and is convected antisunward with solar wind. Yellow region is dominated by electrons, with ions entering in red region. Tsurutani and Rodriguez, 1981 Flow around planetary magnetic field obstacle

2 Hydrodynamic flow in Magnetosheath Parameters of hydrodynamic model of sheath flow: Top left: stream lines Top right: density enhancements Chapman-Ferraro current Using the single particle picture, what is the size of the current? What does Faraday s law tell us? Bottom left: velocity and temperature Botton rate: mass flux Spreiter and Stahara, 1995 Magnetopause Thickness of the Magnetopause: ISEE observations Russell, 1990 Otto, Chap. 7 The ISEE satellite mission flew two satellites through the magnetopause. From comparing the observations, the thickness and velocity of the magnetopause could be determined. For comparison, ion gyroradius is about 100 km (Berchem and Russell, 1982)

3 Magnetopause velocity Magnetopause crossing by ISEE satellite Magnetosheath: high density, low temperature, southward magnetic field Magnetosphere: low density, high temperature, northward magnetic field. Plascke et al., 2009 Russell, The Magnetopause, 1990 Dynamics of Solar Wind-Magnetosphere Coupling: The Dungey picture Magnetopause during northward IMF: Top: Southward IMF. Reconnection at the sub-solar magnetopause creates open field lines, which convect to the tail and reconnect again in the tail. Return flow takes place in the plasma sheet. Bottom: Northward IMF. The IMF drapes over the dayside magnetosphere and reconnects poleward of the cusps. Here the return flow is at higher latitudes. Lysak, 2009 Russell, The Magnetopause, 1990

4 Closed magnetosphere Alternative to Reconnection: Viscous Interaction Effective Viscosity to transfer momentum/energy Miura, 1995 Kelvin-Helmholtz instability: windover water instability due to velocity shear. Creates vortical structures that can transport momentum into the magnetosphere. Dynamic pressure variations: Fluctuations in solar wind dynamic pressure produce indentations in the magnetopause that convect antisunward with the solar wind Lysak et al., D MHD simulation of the Kelvin- Helmholtz instability shows forward and inverse energy cascades. The forward energy cascade is triggered by the secondary Rayleigh-Taylor instability [Matsumoto and Hoshino, GRL, 2004] and the inverse cascade is accomplished by nonlinear mode couplings between the fastest growing mode and other KH unstable modes [Matsumoto and Seki, JGR, 2010].

5 K-H simulation Magneto-Hydro Dynamic simulation result of the Kelvin-Helmholtz wave at t=410 s. The magnetic field (arrows) and the z-component of the current density Jz (colour coded) are plotted on the left panel. The right panel represents the velocity (arrows) and the density (colour coded). The black lines are magnetic field lines. Courtesy of Dr. Nykyri, Imperial College, UK Date: 06 Dec 2006 Copyright: K. Nykyri et al. Time evolution of the Kelvin-Helmholtz instability (KHI) at the dawnside magnetospheric flank. The colour code shows plasma density, where the higher density (orange) is in the magnetosheath and lower density (purple) is in the magnetospheric side. The Black arrows are the plasma velocity vectors and the black lines are the magnetic field lines projected into shear flow plane. When the Kelvin-Helmholtz wave passes by the Cluster spacecraft it generates quasi-periodic variations in the density, temperature, total pressure and normal component of the magnetic field. The initial configuration for the simulation is such that the magnetic fields are anti-parallel across the magnetopause in the shear flow plane. In this geometry the KHI can generate reconnection in two different regions within the vortex: A) reconnection occurs first in a current layer separating the anti-parallel magnetospheric and magnetosheath fields B) later the reconnection develops in a magnetospheric current layer generated by twisting of the magnetospheric field due to the KHI. Open vs closed

6 Anti-parallel vs. Subsolar Reconnection Magnetopause Boundary Layer Schematic of magnetopause boundary layer formed by particle entry across magnetopause during reconnection. Note that magnetosheath particles are colder and dense while magnetospheric particles are hotter but not as dense. Crooker, 1979 Laitinen et al., 2007 Where does reconnection occur at magnetopause? Antiparallel reconnection model (left) suggests reconnection occurs where IMF and geomagnetic field are antiparallel; Subsolar reconnection model (right) assumes reconnection is on line passing through sub-solar point (where Earth-Sun line intersects magnetopause) Gosling et al., 1990 Correlation of Solar Wind Parameters with Magnetospheric Activity Correlation of solar wind parameters with AE index, which is a measure of the strength of ionospheric currents. Parameters are: Akasofu! parameter:! = VB 2l 2 sin 4 (" / 2 ) Half-wave rectifier: VBS Dynamic pressure parameter: V2BS All parameters have similar correlations, with about 1 hour time lag

7 Direct connection to solar wind polar rain Wing et al. FAST 4/18 03:18-03:40 UT 03:38-03:58 UT How wide is the tail? Make what assumptions you need to. Figure out the diameter of the tail. Do you expect it to be constant?