Group A: S. Bale(Tutor), B. Engavale, W.L. Shi, W.L. Teh, L. Xie, L. Yang, and X.G. Zhang 13,May...

Group A: S. Bale(Tutor), B. Engavale, W.L. Shi, W.L. Teh, L. Xie, L. Yang, and X.G. Zhang 13,May 2004

3rd COSPAR Capacity Building Workshop3rd COSPAR Capacity Building Workshop, Beijing, China

Measuring the electric potential at the bow shock

Group A: Tutor: S. Bale Crew: L. Xie L. Yang B. Engavale W.-L. Teh

W.-L. Shi X.-G. Zhang



Outlines

Introduction Data and Analysis Techniques Present result Work to be done



Bow shock transition region from supersonic

upstream flow to subsonic downstream flow.

Density, temperature and fields changes rapidly

Shocks can be found everywhere, near the planets, stars, etc.



Bow shock of Earth magnetosphere

return



ukE

Solar wind Bow shock Magnetosheath

ukE

dkE

iKT

eKT

KT

e

Purpose of our project is to estimate potential energy in the bow shock region.



Energy distribution is earlier studied by J.D. Scudder(1986,1995), but it is not yet understood very clearly.

Very few measurements of potential at the bow shock are available.

Investigate the role of potential in the energy distribution and its dependence on solar wind properties(M, ,)

dei

dsw

uB

usw B

EKTemvEmv ),(

22

2

1

2

1



Sharp changing of Variables



Data And Analysis TechniquesData Description

FGM1. Magnetic Fields (FGM)

2. Electric Fields (EFW)

3. Plasma density (CIS)

4. Plasma velocity (CIS)



Analysis Methods

1. Shock identification

Some physical quantities, namely, B fields, plasma density, plasma velocity, will change rapidly when traversing the shock.

Cluster measures electric fields only in two directions, we want to computethe third component of E field by using this equation.

0 BE



One crossing of the shock

2001 Mar 31

Assumptions:

1. Quasi-perpendicular

shock

2. One-dimensional

structure of shock

3. Steady state



2. Shock Normal Estimate

Use crossing times approach to estimate the shock normal in our study.

2

1 1

])(ˆ[

N N

vtrrns

Method description:

n

v

rij

2

1 1

])([

N N

kkk trrms

0

km

s12 )]([1

nknnk RrrtNm

N

knnk rrNR1

/1

where

vnm /ˆ

||/1 mv

mvn

ˆ

n=[0.94,-0.2,0.28]



3. Coordinates transformation

Normal Incidence Frame

)ˆ(ˆ nVnV uNIF

In this frame, the flow will be directed along the shock normal.

Maximum variance analysis of electric field (MVAE)

3,2,1, 3

1

nnM E

EEEEM E

< > denotes the average



4. Electric potential calculation

After transforming the electric fields into the variance space, we integrate the maximum variance of the electric field, which is the normal electric component of the shock, to obtain the electric potential across the shock layer.

The estimate of the start time and end time becomes very important in this calculations of electric potential.

eV 1860Vup=670km/s, Vdn=263km/s, E=1974eV

Min

Int

Max

86BNU



Present result

Analyzed 8 shocks (21 Mar 2001)

as a function of Mach number.

2/2u

swmv

e

In order to study this further, we need to study more cases.



Work to be done

Cluster data available ⇒ 3 years(2000-2003)

∼100 orbits

200 to 2000 shocks

By assuming each event analysis take 30 min

6 person (8 hrs/day) ⇒ 1 months

back



PROJECT

GROUP_ A

GROUP_ B

GROUP_ C

Data analysis + programming

New interesting results,Need detailed analysis

Meeting for the discussion

Few months



LOOKING FORWARD FOR THIS PROJECT

THANKS FOR YOUR ATTENTIONS !

Group A: S. Bale(Tutor), B. Engavale, W.L. Shi, W.L. Teh, L. Xie, L. Yang, and X.G. Zhang 13,May...

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