Geomagnetic Indices in a SW Perspective: Improved Description of the Magnetosphere

Geomagnetic indices in a SW perspective M. Menvielle(1) and A. Marchaudon(2) (1) Centre d’études des Environnements Terrestre et PlanétairesUMR 8615 IPL/CNRS/UVSQ4, Avenue de NeptuneF-94100 Saint Maur des Fossés, France (2) Laboratoire de Physique et Chimie de l’Environnement3-A Avenue de la recherche scientifiqueF-45071 Orléans Cedex 2, France M. Menvielle and A. MarchaudonESWW2 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 M. Menvielle and A. MarchaudonESWW2

X Mantle Polar Cusp LLBL X Tail Plasma Sheet X Polar Cusp X Mantle The Earth’s magnetosphere and its key regions M. Menvielle and A. MarchaudonESWW2

Magnetosphere R1 J// R2 J// R2 J// R1 J// J//-Region1 Jp Jp Edawn-dusk J//-Region2 Jp JH JH Cross-Tail Current Sheet Ionosphere East Electrojet West Electrojet Sun 1200 MLT Dawn 0600 MLT Dusk 1800 MLT Z, North X, Sun Y, dusk The large-scale currents in the magnetosphere and their closure in the ionosphere Dawn-dusk cut of theionosphere-magnetosphere system M. Menvielle and A. MarchaudonESWW2

The geomagnetic activity Magnetic signaturesat the Earth surface auroral latitudes:currents, convection… AE, PC indices Solar wind parametersat the magnetosphereboundaries K-derived indices sub-auroral latitudes low latitude:ring current, … Magnetosphere-ionosphere filter Dst, SYM indices Pulsations Values measuredin situ at L1 SR variation … M. Menvielle and A. MarchaudonESWW2

J//-Region1 J//-Region2 Cross-Tail Current Sheet The geomagnetic indices DH envelopes PC AE f(DH, DD, t) Kp K-derived ASY-H DH range am Dst SYM-H DH weightedaverage M. Menvielle and A. MarchaudonESWW2

PC and AE indices Increasing magnetosphere activity results in an expansion of the auroral oval AE indices – minute values Maximum intensity in Eastwards (AU: upper envelope) and Westwards (AL: lower envelope) auroral electrojets 12 stations (among them, one is closed)  no data from southern hemisphere  non-linear response wrt activity level  non-linear response wrt local time red ovals correspond to 70° and 60° geomagnetic latitudes PC – minute values North (PCN) and South (PCS) transpolar convection currents 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 M. Menvielle and A. MarchaudonESWW2

Observed and Computed am-indices 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 magnetosphereover the 3-hour interval. • Estimation by a semi-empiric equation(Svalgaard, 1978) SW dynamical Pressure Flux of reconnected field lines Geometric effect am M. Menvielle and A. MarchaudonESWW2

Region 1 Current Partial Ring Current Region 2 Current Ring Current Region 2 Current Region 1 Current to the Sun  Dst, SYM-H and ASY-H indices Dst – hourly values SYM-H – minute values Intensity of the axi-symmetric currents having a P10 geometry {Br(q) ~ cos(q); Bq(q) ~ sin(q)}, 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 M. Menvielle and A. MarchaudonESWW2

ACE IMF (GSM) – Solar Wind – Delay: 36 min Magnetic clouds By int. (nT) Bz int. (nT) PP SW pressure (nPa) AE(nT) Substorms SYM-H(nT) ASY-H(nT) The storm history (Hanuise et al., 2003) 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) Typical quiet time R-1 value: 0.25 A/m (Potemra, 1994) Latitudinal extent of the R-1 current sheet PCN index (Hanuise et al., 2003) 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

5 4 3 2 1 Longitude dependence 1000 nT 1 0 1000 nT 3 0 4 1000 nT 0 5 1000 nT 0 am M. Menvielle and A. MarchaudonESWW2

Planetary scale – Kp Regional scale – al DTM MSIS SW application Thermosphere temperature disturbances al smoother curves: importance of the magnetic activity longitude dependence UT - 3h for d < 30° UT - 6h for d  30° DT is clearly observeddown to d = 40° DT = WINDII temperature – Computed model temperature for quiet magnetic situations Observed WINDII temperature disturbance DT as a function of the distance to the oval auroral (d) and of the magnetic activity (al or Kp) M. Menvielle and A. MarchaudonESWW2

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). M. Menvielle and A. MarchaudonESWW2

t = 180 min. 100 nT t = 30 min. 100 nT A possible rms-based aa-like index First half of July 2000 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

aday Polar cap anight Better magnetic description of the magnetosphere-ionosphere activity Future work Definition of 2 new magnetic indices describing the magnetic perturbations in the dayside aday and in the nightside anight auroral zones independently. Magnetometers distribution in and around the Northern auroral oval M. Menvielle and A. MarchaudonESWW2

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? M. Menvielle and A. MarchaudonESWW2

B/t at OTT B/t at FRD A global B/t index? (from C. Balch, 2004) 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) 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

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. M. Menvielle and A. MarchaudonESWW2

Geomagnetic Indices in a SW Perspective: Improved Description of the Magnetosphere

Geomagnetic Indices in a SW Perspective: Improved Description of the Magnetosphere

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