Charles University, PragueCharles University, Prague Faculty of Mathematics and Physics Faculty of Mathematics and Physics

Position and velocity of Position and velocity of Earth’s bow shockEarth’s bow shock

Karel JelínekKarel Jelínek

Department of Electronics and Vacuum PhysicsDepartment of Electronics and Vacuum Physics

Supervisor:Supervisor: Prof. RNDr. Zdeněk Němeček, DrSc. Prof. RNDr. Zdeněk Němeček, DrSc.

motivationmotivation solar windsolar wind experimentexperimental setal set upup data sourcedata source current current model model of bow shockof bow shock aim of workaim of work statistical resultsstatistical results future planfuture plan

ContentContent

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.

MotivationMotivation

Solar windSolar wind

vsv 450 km s-1

p+ 6.6 cm-3

e- 7.2 cm-3

He2+ 0.25 cm-3

Te 1,4 .105K

Tp 1,2 .105K

D 1100 m

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

Magnetosphere of the Earth Magnetosphere of the Earth magnetopausemagnetopause

bbow shockow shock

magnetosheathmagnetosheath

solar windsolar wind

interplanetary interplanetary magnetic fieldmagnetic field

Classification of bow shockClassification of bow shockdefinition of the angledefinition of the angle BnBn

classification of BS accordingclassification of BS according BnBn

BS BS

bow shock

magnetopause

parallel BS perpendicular BSBS BS

quasiparalelquasiper-

pendicular

paralel pendicular

Current Earth’s bow shock Current Earth’s bow shock models (disadvantage)models (disadvantage)

set of crossings when the bow shock is in motion set of crossings when the bow shock is in motion (majority of these crossings are due to changes of solar (majority of these crossings are due to changes of solar wind parameters and BS changes its position from one wind parameters and BS changes its position from one to other stationary state, therefore, we observe BS to other stationary state, therefore, we observe BS during its motion and the observed position of BS does during its motion and the observed position of BS does not correspond to solar wind conditions) not correspond to solar wind conditions)

fitting of quadratic surface (paraboloid, ellipsoid, ...)fitting of quadratic surface (paraboloid, ellipsoid, ...) only dynamic pressure and Mach number are driving only dynamic pressure and Mach number are driving

parameters of fitted surface (magnetic field plays a parameters of fitted surface (magnetic field plays a small role in models)small role in models)

a shape of the magnetopause does not involve the cuspa shape of the magnetopause does not involve the cusp

Aim of workAim of work identification of exact time when BS crosses identification of exact time when BS crosses

through both of spacecraftsthrough both of spacecrafts Interball-IInterball-I aa Magion-4 Magion-4 .. estimation of the BS velocity (estimation of the BS velocity (vvBSBS) from timing and ) from timing and

location of observed BSlocation of observed BS.. determination of solar wind parameters for determination of solar wind parameters for

estimated estimated vvBSBS from satellite from satellite WINDWIND (e.g.(e.g. nn,, BB,, vvBSBS ,, T T )) and computation of and computation of BnBn,, MMAlfvén Alfvén andand , which are , which are the main parameters controlling processes on BS.the main parameters controlling processes on BS.

find out some dependencies between the BS find out some dependencies between the BS velocity and solar wind parameters.velocity and solar wind parameters.

Data Data sourcesource

For monitoring of the For monitoring of the solar wind, we have solar wind, we have used the WIND satellite.used the WIND satellite.

BS crossings were BS crossings were observed by observed by Interball-1 Interball-1 Magion-4Magion-4 spacecrafts spacecrafts

190 190 of events were observed by both spacecraftsof events were observed by both spacecrafts

1114 14 of events were identify only by one spacecraftof events were identify only by one spacecraft

BS crossing locationsBS crossing locations

electron energy spectraelectron energy spectra

ionion energy spectra energy spectra direction toward the Sundirection toward the Sun

magnetometermagnetometer

FaradayFaraday’s cups’s cups

16. FEB 1996 23:00:07 – 00:00:12

ionion energy spectra energy spectra tailward directiontailward direction

electron energy spectraelectron energy spectra

ionion energy spectra energy spectra tailward directiontailward direction

FaradayFaraday’s cups’s cups

BSM4

BSM4 BSM4

BSIB

Determination of the time of BS crossings

electron energy spectraelectron energy spectra

ionion energy spectra energy spectra direction toward the Sundirection toward the Sun

magnetometermagnetometer

FaradayFaraday’s cups’s cups

16. FEB 1996 23:00:07 – 00:00:12

ionion energy spectra energy spectra tailward directiontailward direction

electron energy spectraelectron energy spectra

ionion energy spectra energy spectra tailward directiontailward direction

FaradayFaraday’s cups’s cups

BSM4

BSM4 BSM4

BSIB

BS velocity computationBS velocity computation

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.

even

ts

Resulting histogram of BS Resulting histogram of BS speedsspeeds

StatisticStatistical al resultsresults

dependence of the BS velocity dependence of the BS velocity on its locationon its location

one spacecraftone spacecraft both spacecraftsboth spacecrafts

XX direction direction

distance to distance to X axisX axis

dependence of the BS velocity on the solar dependence of the BS velocity on the solar wind velocity and on change of velocitywind velocity and on change of velocity

velocityvelocity

change ofchange ofvelocityvelocity

both spacecraftsboth spacecrafts

StatisticStatistical al resultsresults one spacecraftone spacecraft

densitydensity

changes ofchanges ofdensitydensity

StatisticStatistical al resultsresults one spacecraftone spacecraft both spacecraftsboth spacecrafts

dependence of the BS velocity on particle dependence of the BS velocity on particle density and on change of particle densitydensity and on change of particle density

change ofchange of IMFIMF

StatisticStatistical al resultsresults one spacecraftone spacecraft both spacecraftsboth spacecrafts

BnBn

dependence of the BS velocity on change of dependence of the BS velocity on change of

IMF and on angle IMF and on angle BnBn

The histogram of shock velocities for quasiparallel and quasiperpendicular shocks.

nu

mb

er o

f ev

ents

vsh [km/s]

ConclusionConclusion The bow shock is in a permanent small-scale motion.The bow shock is in a permanent small-scale motion. The bow shock velocities are usually smaller than but velocities The bow shock velocities are usually smaller than but velocities

exceeding can be observed (these results are consistent with exceeding can be observed (these results are consistent with previous findings, e.g., Lepidi et al.,1996).previous findings, e.g., Lepidi et al.,1996).

We identify about 830 of the BS crossing.We identify about 830 of the BS crossing. 114 of this events were observed only by one spacecraft.114 of this events were observed only by one spacecraft. From 190 of the BS crossings which were observed by both From 190 of the BS crossings which were observed by both

spacecrafts we computed average velocity of the BS motion.spacecrafts we computed average velocity of the BS motion.We analyze how the BS velocity depends on the solar wind We analyze how the BS velocity depends on the solar wind parameters, we find out:parameters, we find out:• bigger velocity of SWbigger velocity of SW ==> > bigger velocity of the BSbigger velocity of the BS• bigger change of SW velocity bigger change of SW velocity = => bigger velocity of the BS> bigger velocity of the BS• bigger density of SWbigger density of SW = => > smaller velocity of the BSsmaller velocity of the BS• bigger change ofbigger change of IMF = IMF => bigger velocity of the BS> bigger velocity of the BS • qqvavassiparaliparalllelel BS is faster then BS is faster then quasiperpendicularquasiperpendicular• other parameters of SW have not significant effect on BS velocityother parameters of SW have not significant effect on BS velocity

look for more BS crossingslook for more BS crossings starts case study with interesting starts case study with interesting

eventsevents employ statistical study of the BS employ statistical study of the BS

velocity to improve model of BS velocity to improve model of BS locationlocation

Future planFuture plan

Positions of Positions of INTERBALL-1INTERBALL-1 and and MAGION-4MAGION-4 spacecrafts spacecrafts during observations of during observations of BS crossings for 27 FEB BS crossings for 27 FEB 19971997.

Thank you for your Thank you for your attentionattention