M. Menvielle and A. Marchaudon ESWW2 M. Menvielle (1) and A. Marchaudon (2) (1) Centre d’études des Environnements Terrestre et Planétaires UMR 8615 IPL/CNRS/UVSQ

M. Menvielle and A. MarchaudonESWW2

M. Menvielle(1) and A. Marchaudon(2)

(1) Centre d’études des Environnements Terrestre et Planétaires

UMR 8615 IPL/CNRS/UVSQ4, Avenue de Neptune

F-94100 Saint Maur des Fossés, France(2) Laboratoire de Physique et Chimie de

l’Environnement3-A Avenue de la recherche scientifique

F-45071 Orléans Cedex 2, France

Geomagnetic indices in a SW perspective

ESWW2, November 22nd, 2005


The Earth’ magnetosphere

Magnetosphere activity and geomagnetic indices

An example: the late May 2003 event

Geomagnetic indices in a Space Weather perspective: improved description of the magnetosphere

Geomagnetic indices in a Space Weather perspective: magnetic indices dedicated to SW applications

Conclusion







Conclusion


The Earth’s magnetosphere and its key regions

Mantle

XMantle

X

Polar Cusp

Polar Cusp

LLBL

X Tail Plasma Sheet

X


The large-scale currents in the magnetosphere and their closure in the ionosphere

Cross-Tail Current Sheet

J//-Region1

J//-Region2

Z, North

X, Sun Y, dusk

Ionosphere

Magnetosphere

Sun1200 MLT

R1J//

R2J//

R1J//

R2J//

Dusk 1800 MLT

Dawn0600 MLT

Jp

JH

East Electrojet

Jp

Jp

JH

Edawn-dusk

West Electrojet

Dawn-dusk cut of theionosphere-magnetosphere system


The geomagnetic activity

Solar wind parametersat the magnetosphere

boundaries

Values measuredin situ at L1 M

agne

tosp

here

-io

nosp

here

filt

er

Magnetic signaturesat the Earth surface

auroral latitudes: currents, convection…

AE, PC indices

sub-auroral latitudes K-derived indices

low latitude:ring current, … Dst, SYM indices

Pulsations

SR variation

…







Conclusion


The geomagnetic indices

Cross-Tail Current Sheet

J//-Region1

J//-Region2

Dst SYM-H

ASY-H

AE

Kp

am

K-derived

H envelopes

H weightedaverage

H range

PCf(H, D, t)


AE indices – minute valuesMaximum intensity in Eastwards (AU: upper envelope) and Westwards (AL: lower envelope) auroral electrojets

PC and AE indices

PC – minute valuesNorth (PCN) and South (PCS) transpolar convection currents

12 stations (among them, one is closed) no data from southern hemisphere non-linear response wrt activity level non-linear response wrt local time

Increasing magnetosphere activity results in an expansion of

the auroral oval

red ovals correspond to 70° and 60°

geomagnetic latitudes

PCN and PCS rely on statistical estimate of parameters used for index derivationEach of them is based upon data from only one near-pole magnetic observatory


am indices: physical interpretation• Experimental estimation

K : code characterising the magnetic energy density at the station where it is measured (Menvielle, 1979).

am : estimate of the energy status of the magnetosphere over the 3-hour interval.

• Estimation by a semi-empiric equation (Svalgaard, 1978)

322

31

200

31

1571

1052166

cos

,,q,nVBV

fam

Flux of reconnected field lines

Geometric effect

SW dynamical Pressure

Observed and Computed am-indices


Dst, SYM-H and ASY-H indices

Partial RingCurrent

RingCurrent

Region 1Current

Region 2Current

Region 1Current

Region 2Current

to the Sun

Dst – hourly valuesSYM-H – minute valuesIntensity of the axi-symmetric currents having a P1

0 geometry {Br() ~ cos(); B() ~ sin()}, mostly Chapman-Ferraro magnetopause and Ring currents

ASY-H – minute valuesPresence of non axi-symmetric current flows, corresponding to e.g., partial ring current.

Dst: 4 stations – SYM-/ASY-H: 6 groups large scale resolution in longitude (120 to 160°) axi-symmetric currents contain part of the partial ring current Dst and SYM-H mostly capture the magnetic signature of the Ring Current, but are sensitive to other magnetosphere currents







Conclusion


The storm history

(Hanuise et al., 2003)

Magnetic clouds

PP

ACE IMF (GSM) – Solar Wind – Delay: 36 min

Substorms

AE

(nT

)S

YM

-H(n

T)

AS

Y-H

(nT

)S

W p

ress

ure

(n

Pa

)B

z in

t. (n

T)

By

int.

(nT

)


Large scale high-latitude currents

15:00 – 16:00 MLT sector

R-1 current intensity (latitudinally integrated current density from CHAMP magnetic measurements)

Latitudinal extent of the R-1 current sheet

PCN index

Typical quiet time R-1 value:0.25 A/m (Potemra, 1994)

(Hanuise et al., 2003)







Conclusion


Complexity of the magnetosphere-ionosphere coupling

• Dayside coupling: magnetopause reconnection and plasma injections with respect to IMF conditions

• Nightside coupling: tail reconnection especially during substorm events (causes and effects)

• Magnetic storm events: - global or local impact with respect to solar wind conditions- propagation in the magnetosphere-ionosphere system

(temporal and spatial scales)

Necessity of new indices:- to better estimate the temporal scale of the solar events- to better estimate the spatial propagation of the solar events in the magnetosphere- to separate the effects of the day side and night side processes


Longitude dependence

5 4 3 2 1

1

3

4

5

am

0

1000 nT

0

1000 nT

0

1000 nT

0

1000 nT


SW applicationThermosphere temperature disturbances

DTM

MSIS

Planetary scale – KpRegional scale – a

a smoother curves:importance of the magnetic

activity longitude dependence

T is clearly observed

down to d = 40°

T = WINDII temperature – Computed model temperature for quiet magnetic situations

UT - 3h for d < 30°UT - 6h for d 30°

Observed WINDII temperature disturbance T as a function of the distance to the oval auroral (d) and of the magnetic activity (a or Kp)


The time resolution

301 302 303 304Julian day (2003)

0

250

500

750

aa in

dic

es(n

T)

301 302 303 304

S. h

emis

ph

ere

(CN

B)

301 302 303 304

N. h

emis

ph

ere

(HA

D)

Present time resolution for Kp, am, and aa3-hour, imposed by the K-index definition

How to improve it?Define a new index:- based upon a proxy of the energy- that keep the same physical meaning for different length of the time interval

Since the pioneer work of Joselyn (1970), different index definition have been proposed, based on e.g., power spectra (Reda and Jankowski, 2004), or rms (Menvielle, 2003).

301 302 303 304Julian day (2003)

0

250

500

750

aa in

dic

es(n

T)

301 302 303 304

S. h

emis

ph

ere

(CN

B)

301 302 303 304

N. h

emis

ph

ere

(HA

D)


A possible rms-based aa-like index

First half of July 2000

= 180 min.

200 201 202 203 204 205 206 207 208 209 210 211 212 213 214

0

10

20

30

40

50

60

70

80

90

100

a a a

200 201 202 203 204 205 206 207 208 209 210 211 212 213 214

0

10

20

30

40

50

60

70

80

90

100

a a a

= 30 min.100 nT 100 nT

A rms-based geomagnetic index is consistent with the classical planetary geomagnetic indices while computed using 3-hour

intervals, and makes it possible to monitor the magnetic activity with a better – and flexible – time resolution


Better magnetic description of the magnetosphere-ionosphere activity

Definition of 2 new magnetic indices describing the magnetic perturbations in the dayside aday and in the nightside anight auroral zones independently.

aday

anight

Polar cap

Magnetometers distribution in and around the Northern

auroral oval

Future work







Conclusion


The case of GICThe key physical quantity is

the locally induced geoelectric field over the

region of the conductordriven by both the time rate of change of

magnetic field, and properties of the medium (described in terms of e.g., surface

impedance)

Using global indices?

Will the index contain information about the rate of change of the magnetic field?

Will local variations of B/t be properly accounted by a global index?


A global B/t index?

B/ t at OTT B/t at FRD

The differences between B/t observed at OTTAWA (OTT) and FREDERICKSBURG (FRD), illustrate the necessity of ‘regional’ indices deduced from a rather dense network of

magnetic stations at a ‘regional’ scale (typically 100 km spacing between stations)

(from C. Balch, 2004)


Local issues

• User needs are very different, depending on the application: e.g., aeromagnetic surveys, oil drilling, …

• The best solution is using information on the magnetic activity from nearby geomagnetic station(s), for deriving an index which answer the specific user needs. Such index turns out to be a compromise between what should be an ideal index and the available data.







Conclusion


Magnetosphere description

• Indices aiming at describing the magnetosphere are basic data for both Solar-Terrestrial physics investigations and Space Weather applications

• They should have a clear physical meaning; reference data series should exist, as it is the case at present; free of charge access is mandatory

• Present situation: – magnetosphere description at a planetary scale, with a time

resolution of 1 minute (AE, PC, SYM/ASY), 1 hour (Dst) or 3-hour (Kp, am, aa)

– ground based magnetic observatory data

• Future issues: – improvement of the longitude resolution; development of new

indices similar to am with a better time resolution– development of indices based upon in situ measurements: solar

wind at L1, field aligned currents from LEO magnetic satellites, …


SW applications

Indices defined to answer a specific user need.

• In practice they result from a compromise between what should be an ideal index and the available data

• No need of reference data series; since they are “added value” quantities derived for specific applications, they may be charged.

• Their definition generally takes benefit from results of academic research activities.

Documents

M. Menvielle and A. Marchaudon ESWW2 M. Menvielle (1) and A. Marchaudon (2) (1) Centre d’études des Environnements Terrestre et Planétaires UMR 8615 IPL/CNRS/UVSQ