VDS 2006 01

Charles University, Prague Faculty of Mathematics and Physics Position and velocity of Earth’s bow shock : 

Charles University, Prague Faculty of Mathematics and Physics Position and velocity of Earth’s bow shock Karel Jelínek Department of Electronics and Vacuum Physics Supervisor: Prof. RNDr. Zdeněk Němeček, DrSc.

Content: 

motivation solar wind experimental set up data source current model of bow shock aim of work statistical results future plan Content

Motivation: 

Collisionless bow shock attracts attention of many plasma physicist. Its ability of heating more ions then electrons can be helpful for thermonuclear fusion. The bow shock also accelerates particles on its front and therefore, it is a source of high energy particles. Such shocks often occur in space if a supersonic plasma flows onto obstacles like comets, planets and also galaxy. The Earth's bow shock provides necessary dissipation of kinetic energy of the solar wind (this occurs at a very short length). Many works deal with a study of shape and position of the bow shock but a systematic analysis of the bow shock velocity is still missing. Motivation

Solar wind: 

Solar wind averaged parameters of the solar wind in 1 AU distance from the Sun.

Magnetosphere of the Earth : 

Magnetosphere of the Earth solar wind

Classification of bow shock: 

Classification of bow shock definition of the angle Bn classification of BS according Bn BS BS bow shock magnetopause parallel BS perpendicular BS BS BS quasiparalel quasiper- pendicular paralel pendicular

Current Earth’s bow shock models (disadvantage): 

Current Earth’s bow shock models (disadvantage) set of crossings when the bow shock is in motion (majority of these crossings are due to changes of solar wind parameters and BS changes its position from one to other stationary state, therefore, we observe BS during its motion and the observed position of BS does not correspond to solar wind conditions) fitting of quadratic surface (paraboloid, ellipsoid, ...) only dynamic pressure and Mach number are driving parameters of fitted surface (magnetic field plays a small role in models) a shape of the magnetopause does not involve the cusp

Aim of work: 

Aim of work identification of exact time when BS crosses through both of spacecrafts Interball-I a Magion-4 . estimation of the BS velocity (vBS) from timing and location of observed BS. determination of solar wind parameters for estimated vBS from satellite WIND (e.g. n, B, vBS , T ) and computation of Bn, MAlfvén and , which are the main parameters controlling processes on BS. find out some dependencies between the BS velocity and solar wind parameters.

Data source: 

Data source For monitoring of the solar wind, we have used the WIND satellite. BS crossings were observed by Interball-1 Magion-4 spacecrafts 190 of events were observed by both spacecrafts 114 of events were identify only by one spacecraft BS crossing locations

Slide10: 

electron energy spectra ion energy spectra direction toward the Sun magnetometer Faraday’s cups 16. FEB 1996 23:00:07 – 00:00:12 ion energy spectra tailward direction electron energy spectra ion energy spectra tailward direction Faraday’s cups BSM4 BSM4 BSM4 BSIB Determination of the time of BS crossings

Slide11: 

electron energy spectra ion energy spectra direction toward the Sun magnetometer Faraday’s cups 16. FEB 1996 23:00:07 – 00:00:12 ion energy spectra tailward direction electron energy spectra ion energy spectra tailward direction Faraday’s cups BSM4 BSM4 BSM4 BSIB

BS velocity computation: 

BS velocity computation

Resulting histogram of BS speeds: 

Resulting histogram of BS speeds. The velocities range from 0 – 100 km/s but a majority of them (70%) is less than ~ 40 km/s – this is in agreement with previous studies. events Resulting histogram of BS speeds

Statistical results: 

Statistical results dependence of the BS velocity on its location one spacecraft both spacecrafts X direction distance to X axis

Slide15: 

dependence of the BS velocity on the solar wind velocity and on change of velocity velocity change of velocity both spacecrafts Statistical results one spacecraft

Slide16: 

density changes of density Statistical results one spacecraft both spacecrafts dependence of the BS velocity on particle density and on change of particle density

Slide17: 

change of IMF Statistical results one spacecraft both spacecrafts Bn dependence of the BS velocity on change of IMF and on angle Bn

Slide18: 

The histogram of shock velocities for quasiparallel and quasiperpendicular shocks. number of events vsh [km/s]

Conclusion: 

Conclusion The bow shock is in a permanent small-scale motion. The bow shock velocities are usually smaller than but velocities exceeding can be observed (these results are consistent with previous findings, e.g., Lepidi et al.,1996). We identify about 830 of the BS crossing. 114 of this events were observed only by one spacecraft. From 190 of the BS crossings which were observed by both spacecrafts we computed average velocity of the BS motion. We analyze how the BS velocity depends on the solar wind parameters, we find out: bigger velocity of SW => bigger velocity of the BS bigger change of SW velocity => bigger velocity of the BS bigger density of SW => smaller velocity of the BS bigger change of IMF => bigger velocity of the BS qvasiparallel BS is faster then quasiperpendicular other parameters of SW have not significant effect on BS velocity

Future plan: 

look for more BS crossings starts case study with interesting events employ statistical study of the BS velocity to improve model of BS location Future plan

Slide21: 

Positions of INTERBALL-1 and MAGION-4 spacecrafts during observations of BS crossings for 27 FEB 1997.

Thank you for your attention: 

Thank you for your attention