Adjustable magnetospheric event- oriented magnetic field models N. Yu. Ganushkina (1), M. V....

Adjustable magnetospheric event-oriented magnetic field models

N. Yu. Ganushkina (1), M. V. Kubyshkina (2), T. I. Pulkkinen (1)

(1) Finnish Meteorological Institute, Helsinki, Finland(2) University of St. Petersburg, Institute of Physics, St. Petersburg, Russia)

Event-oriented magnetospheric magnetic field modelling

- An accurate representation of magnetospheric configuration for a specific event (Ganushkina et al., JGR, 2002; Ganushkina et al., AnnGeo, 2004)

ICESTAR: Heliosphere Impact on Geospace, February 5-9, 2007, Helsinki, Finland

Global magnetospheric magnetic field models

- Most widely used (Tsyganenko [1987, 1989], Tsyganenko [1995])Good representation of average magnetospheric configuration, fine structure of magnetic field during substorms and large magnetic field changes during storms were not accounted for.

- Storm-time models (Alexeev et al. [1996], Tsyganenko [2002])model parameters for current systems fitted to entire data set,model magnetic field defined by assumed dependence on input parameters.

Event-oriented magnetospheric magnetic field models

- An accurate representation of magnetospheric configuration is of key importance for a specific event ADJUSTABLE!

- Study the evolution of different current systems during different storms and their relative contribution to Dst

Ganushkina et al., JGR, 2002; Ganushkina et al., AnnGeo, 2004

Magnetospheric magnetic field modelling approaches: Global and event-oriented


Why do we need Event-Oriented Models?Difference in mapping

Concept of magnetic conjugacy, crucial in interhemispheric comparisons


0 -2 -4 -6 -8 -10 -12 -14

-2-101234

65o

Kp=3 Kp=4

0 -2 -4 -6 -8 -10 -12 -14

-2

0

2

4

65o

Pdyn=3nPa; Dst=-30nT; ByIMF=0.0nT

BzIMF=-3nT

BzIMF=-4nT

T89

T96Magnetotail bending during substorm on Sep 14, 200410 deg to Sun-Earth lineLarge interhemispheric asymmetry

Event-oriented model may provide thenecessary accuracy

How to produce event-oriented model?


Choice of existing magnetospheric magnetic field model to modify:Any model easy to modify, simplest solution:

Tsyganenko T89, Kp =4 (for storm events) Replacing of T89 ring current with asymmetric bean-shaped ring current Varying the global intensity of T89 tail current Addition of thin current sheet Scaling of magnetopause currents

Determining free parameters for each current system

Collecting input data: All available magnetic field measurements during the modelled event in magnetosphere SYM-H measurements on the ground

Varying free parameters, we find the set of parameters that gives the best fit between model and all available in-situ field observations

Additional measurements for better model accuracy


Only several data points available.

Best model input, if satellites are at different locations

Measurements of point magnetic fields can be represented by different ways in models

Require additional measurements!They can be:

Isotropic boundaries

B-direction measured by LANL

Pressure value measured at magnetospheric spacecraft

Additional measurements for better model accuracy (1)


1. Isotropic boundaries (IB): available almost always, from IB to obtain curvature radius of magnetic field line, parameter characterising the field line, not the point measurement, in the most variable region of transition between dipole and stretched, tail-looking

field lines

Rc/

3 .6 3 .7 3 .8

1

1 0

1 0 0

1 0 00

1 0 0 0 0

coun

ts/s

ec

- 6 3 .8 1 3 .3 8

-6 8 .3 2 0 .5 6

-6 1 .4 2 1 .7 9

U TC G L a tM L T

0 3 :4 5 :5 8 -6 4 .7 2 2 .8

M ay 1 , 1 9 9 7

empty loss cone

isotropic boundariesfilling loss cone

polar cap flux B

flux II B

Additional measurements for better model accuracy (2)


2. B angle measured by LANL spacecraft:

angle between distribution symmetry axis and spin axis of the spacecraft

determines the B-direction: symmetry axis of electron temperature matrix T aligned with local magnetic field

Available if Tpar/Tperp far from 1, for anisotropic plasma:

2 0 2 0 . 5 2 1 2 1 . 5 2 2 2 2 . 5 2 3U T, hours

0

40

80

120

160

200

d

egre

es

0.5

1

1.5

2

2.5

3

3.5

Tpar

/Tpe

rp

Ring current representation (1)

2/A0

2

2R

west0eqwest0

2/A0

2

2R

east0eqeast0

SYM0 B/B

2

RRexpJB/B

2

RRexpJB/B,RJ

eqeq

Symmetric ring current = eastward + westward:

cosC1B/B

2

RRexpJ,B/B,RJ 2A

02qRe

2part0eq

part0ASYM

0

Asymmetric ring current = partial + closing Region 2 field-aligned currents :

Local time asymmetry gives rise to field-aligned currents (calculated numerically)


,,,

,,,

,,,

0

0

0

0

0

0

CA

JJJ

RRR

R

part

west

east

part

west

east

Free parameters:

mean radius

max current density

width of J distr.

anisotropy indexconstantduskward shift anglefor partial RC

- 5051 0

X , R e

- 1 0

- 5

0

5

Y, R

e

- 5051 0

X , R e

- 1 0

- 5

0

5

Y, R

e

Jr

- 5051 0

X , R e

- 1 0

- 5

0

5

Z, R

e

- 5051 0

X , R e

- 1 0

- 5

0

5

Z, R

e

J y ( a )

( b )

Ring current representation (2)


Global changes:intensification of the tail current (T89) as a whole with amplification factor (1+ATS).

Local changes:Adding a new thin tail current sheet.

Addition of a new tail current sheet (1)

Two vector potentials, similar to T89:

,

D,a,zSCC

D,zaD,a,zSy,xWA

0TT

21

0TT0TT

2T1

,

D,a,zSCC

D,zaD,a,zSy,xWA

0TT

21

0TT0TT

2T2

With truncation factors:

,Dy1Dxx

xx1Ay,xW12

y2

212xntc1

ntc1ntc1

,Dy1Dxx

xx1Ay,xW12

y2

212xntc2

ntc2ntc2


thin current sheet intensity

X0 - location of steepest decrease of W(x,y)

D0 - half-thickness of current sheet

Addition of a new tail current sheet (2)

0

21 ,,

,

D

xx

A

ntcntc

ntc

Free parameters:

2 0 1 0 0 - 1 0 - 2 0 - 3 0 - 4 0X g s m , R e

- 1 5 0

- 1 0 0

- 5 0

0

5 0

1 0 0

1 5 0

2 0 0

2 5 0

Inte

gral

cur

rent

, mA

/m

T 8 9

th in C S

T 8 9 + th in C S

Subtracting yxWyxWAA TT ,, 2121 gives a thin current sheet with finite x-scale, zero outside 25 Re.


Scaling factor AMP=3 for the magnetic field of Chapman-Ferraro currents at magnetopause, determined from solar wind pressure variations PSW:

Storm-time magnetic field modelling: Magnetopause currents

Parameter RT , characteristic scale size of magnetotail, defined by solar wind parameters:

.6/1k,P/P,BB kSWSWCF

3CF 89T

,ZZ

R30R89T,T

Shue,TET

30 RE - parameter RT in T89 Kp=4, ZT, Shue - magnetopause position given by Shue et al [1998] model dependent on PSW and IMF Bz at X= - 20 RE , Y = 0,ZT, T89 - ‘magnetopause’ position given by T89 Kp= 4 model at X= - 20 RE , Y = 0.


Baseline model: Tsyganenko T89 Kp=4

Varying free parameters, we find the set of parameters that gives the best fit between model and all available in-situ field observations, for example, by GOES, Polar, CLUSTER, LANL satellites and Dst (SYM-index) measurements.

= 0.8A = 1

,DstDst

tanh2 0

Dst0 = 40 nT

.6/1k,P/PAMP kSWSW

,ZZ

R30R89T,T

Shue,TET

Current system Parameter StatusEastward RC Roeast 2 Re

Joeast 1.5 nA/m2

Westward RC Rowest 2.5 – 4.5 ReJowest 1.5 – 15 nA/m2

Partial RC Ropart 5 – 6.5 ReJopart 0.5 - 7 nA/m2

C 1 From Dst

Tail current ATS -0.5 – 2Antc 0.1 – 2.4X1ntc - 2 ReX2ntc - 10 ReDo 0.2 Re

Magnetopausecurrents

AMP From SW

RT From SW & IMF

Event-oriented magnetospheric magnetic field modelling


Storm on Oct 21-22, 2001

Magnetic cloud arrival Oct 21, 2001, 1645 UT

Cloud sheath region driver for storm main phase

At cloud leading edge IMF Bz ~ 0

At cloud trailing edge IMF Bz < 0

Wind, ACE measurements almost identical despite large distance between s/c



Storm on Oct 21-22, 2001: Magnetotail behavior

Strong sawtooth-like injections at geosynchronous

Dipolarization events simultaneous at GOES and POLAR and with injections

October 22, 1000-2000 UT: Magnetic field during saw-tooth eventG O ES 10G O ES8 PO LAR

1 0 1 2 1 4 1 6 1 8 2 0

- 1 5 0

- 1 0 0

- 5 0

0

5 0

1 0 0

Bz, n

T

1 0 1 2 1 4 1 6 1 8 2 0

- 8 0

- 4 0

0

4 0

8 0

Bx, n

T

1 0 1 2 1 4 1 6 1 8 2 0

- 4 0

- 3 0

- 2 0

- 1 0

0

1 0

2 0

Bx, n

T

1 0 1 2 1 4 1 6 1 8 2 0

- 8 0

- 4 0

0

4 0

8 0

Bz, n

T

1 0 1 2 1 4 1 6 1 8 2 0UT

-40

0

40

80

By (G

SM)

1 0 1 2 1 4 1 6 1 8 2 0

- 1 0

0

1 0

2 0

3 0

4 0

BY(G

SM)

1 0 1 2 1 4 1 6 1 8 2 0

- 2 0 0

- 1 0 0

0

1 0 0

2 0 0

Bx, n

T

1 0 1 2 1 4 1 6 1 8 2 0

- 8 0

- 6 0

- 4 0

- 2 0

0

2 0

Bz, n

T

1 0 1 2 1 4 1 6 1 8 2 0

- 8 0

- 4 0

0

4 0

8 0

BY G

SM

ev en t-o r ien ted

T 01 s


+ Allows to play easily with current systems, their location and parameters, to get better agreement with data + Good representation of smaller scale variations in magnetic field: substorm-associated, saw-tooth events etc. + Good representation of local magnetic field variations (observations at a specific satellite)

To get detailed magnetic field variations for a specific event, time period, magnetospheric region use event-oriented model

- Only for specific events, when magnetic field data are available at least at 3 satellites in different magnetospheric regions - Requires some work for determination of model parameters

To get magnetic field quickly, for several storms, over a large region in magnetosphere,good in average use T01s model

Event-oriented magnetospheric magnetic field modelling: Advantages and disadvantages


Isotropic boundary position depends only on magnetotail magnetic field for a given particle.

Isotropic boundary provides a method of remote-sensing of magnetospheric magnetic field by low-latitude spacecraft measurements.

Isotropic boundary is an additional input into event-oriented model construction.

Isotropic boundary can be used as an indirect indicator of the accuracy of magnetospheric magnetic field models.

Accurate magnetic field model is highly needed for interhemispheric studies.

Usefulness of isotropic boundaries concept for event-oriented modelling and

event-oriented modelling for interhemispheric studies


Adjustable magnetospheric event- oriented magnetic field models N. Yu. Ganushkina (1), M. V....

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