View
222
Download
1
Category
Preview:
Citation preview
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
M. Menvielle and A. MarchaudonESWW2
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
M. Menvielle and A. MarchaudonESWW2
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
M. Menvielle and A. MarchaudonESWW2
The Earth’s magnetosphere and its key regions
Mantle
XMantle
X
Polar Cusp
Polar Cusp
LLBL
X Tail Plasma Sheet
X
M. Menvielle and A. MarchaudonESWW2
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
M. Menvielle and A. MarchaudonESWW2
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
…
M. Menvielle and A. MarchaudonESWW2
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
M. Menvielle and A. MarchaudonESWW2
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)
M. Menvielle and A. MarchaudonESWW2
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
M. Menvielle and A. MarchaudonESWW2
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
M. Menvielle and A. MarchaudonESWW2
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
M. Menvielle and A. MarchaudonESWW2
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
M. Menvielle and A. MarchaudonESWW2
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
)
M. Menvielle and A. MarchaudonESWW2
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)
M. Menvielle and A. MarchaudonESWW2
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
M. Menvielle and A. MarchaudonESWW2
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
M. Menvielle and A. MarchaudonESWW2
Longitude dependence
5 4 3 2 1
1
3
4
5
am
0
1000 nT
0
1000 nT
0
1000 nT
0
1000 nT
M. Menvielle and A. MarchaudonESWW2
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)
M. Menvielle and A. MarchaudonESWW2
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)
M. Menvielle and A. MarchaudonESWW2
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
M. Menvielle and A. MarchaudonESWW2
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
M. Menvielle and A. MarchaudonESWW2
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
M. Menvielle and A. MarchaudonESWW2
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?
M. Menvielle and A. MarchaudonESWW2
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)
M. Menvielle and A. MarchaudonESWW2
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.
M. Menvielle and A. MarchaudonESWW2
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
M. Menvielle and A. MarchaudonESWW2
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, …
M. Menvielle and A. MarchaudonESWW2
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.
Recommended