1. 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 4, Avenue de Neptune F-94100 Saint Maur des Fossés, France (2) Laboratoire de Physique et Chimie de l’Environnement 3-A Avenue de la recherche scientifique F-45071 Orléans Cedex 2, France Geomagnetic indices in a SW perspective ESWW2, November 22 nd, 2005

2. M. Menvielle and A. Marchaudon ESWW2 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

3. M. Menvielle and A. Marchaudon ESWW2 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

4. M. Menvielle and A. Marchaudon ESWW2 The Earth’s magnetosphere and its key regions Mantle X X Polar Cusp LLBL X Tail Plasma Sheet X

5. M. Menvielle and A. Marchaudon ESWW2 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 Sun 1200 MLT R1 J // R2 J // R1 J // R2 J // Dusk 1800 MLT Dawn 0600 MLT JpJp JHJH East Electrojet JpJp JpJp JHJH E dawn-dusk West Electrojet Dawn-dusk cut of the ionosphere-magnetosphere system

6. M. Menvielle and A. Marchaudon ESWW2 The geomagnetic activity Solar wind parameters at the magnetosphere boundaries Values measured in situ at L1 Magnetosphere- ionosphere filter Magnetic signatures at the Earth surface auroral latitudes: currents, convection… AE, PC indices sub-auroral latitudes K-derived indices low latitude: ring current, … Dst, SYM indices Pulsations S R variation …

7. M. Menvielle and A. Marchaudon ESWW2 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

8. M. Menvielle and A. Marchaudon ESWW2 The geomagnetic indices Cross-Tail Current Sheet J // -Region1 J // -Region2 Dst SYM-H ASY-H AE Kp am K-derived  H envelopes  H weighted average  H range PC f (  H,  D, t)

9. M. Menvielle and A. Marchaudon ESWW2 AE indices – minute values Maximum intensity in Eastwards (AU: upper envelope) and Westwards (AL: lower envelope) auroral electrojets PC and AE indices PC – minute values North (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 derivation Each of them is based upon data from only one near-pole magnetic observatory

10. M. Menvielle and A. Marchaudon ESWW2 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 ) am Flux of reconnected field lines Geometric effect SW dynamical Pressure Observed and Computed am-indices

11. M. Menvielle and A. Marchaudon ESWW2 Dst, SYM-H and ASY-H indices Partial Ring Current Ring Current Region 1 Current Region 2 Current Region 1 Current Region 2 Current  to the Sun Dst – hourly values SYM-H – minute values Intensity of the axi-symmetric currents having a P 1 0 geometry {B r (  ) ~ cos(  ); B  (  ) ~ sin(  )}, mostly Chapman-Ferraro magnetopause and Ring currents ASY-H – minute values Presence 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

12. M. Menvielle and A. Marchaudon ESWW2 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

13. M. Menvielle and A. Marchaudon ESWW2 The storm history (Hanuise et al., 2003) Magnetic clouds PP ACE IMF (GSM) – Solar Wind – Delay: 36 min Substorms AE (nT) SYM-H (nT) ASY-H (nT) SW pressure (nPa) Bz int. (nT) By int. (nT)

14. M. Menvielle and A. Marchaudon ESWW2 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)

15. M. Menvielle and A. Marchaudon ESWW2 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

16. M. Menvielle and A. Marchaudon ESWW2 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

17. M. Menvielle and A. Marchaudon ESWW2 Longitude dependence 54321 1 3 4 5 am 0 1000 nT 0 0 0

18. M. Menvielle and A. Marchaudon ESWW2 SW application Thermosphere temperature disturbances DTM MSIS Planetary scale – Kp Regional scale – al 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 l or Kp )

19. M. Menvielle and A. Marchaudon ESWW2 The time resolution Present time resolution for Kp, am, and aa 3-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).

20. M. Menvielle and A. Marchaudon ESWW2 A possible rms -based aa-like index First half of July 2000  = 180 min.  = 30 min. 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

21. M. Menvielle and A. Marchaudon ESWW2 Better magnetic description of the magnetosphere-ionosphere activity Definition of 2 new magnetic indices describing the magnetic perturbations in the dayside a day and in the nightside a night auroral zones independently. a day a night Polar cap Magnetometers distribution in and around the Northern auroral oval Future work

22. M. Menvielle and A. Marchaudon ESWW2 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

23. M. Menvielle and A. Marchaudon ESWW2 The case of GIC The key physical quantity is the locally induced geoelectric field over the region of the conductor driven 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?

24. M. Menvielle and A. Marchaudon ESWW2 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)

25. M. Menvielle and A. Marchaudon ESWW2 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.

26. M. Menvielle and A. Marchaudon ESWW2 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

27. M. Menvielle and A. Marchaudon ESWW2 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, …

28. M. Menvielle and A. Marchaudon ESWW2 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.