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

Why do we need Event-Oriented Models? Difference in mapping Concept of magnetic conjugacy, crucial in interhemispheric comparisons ICESTAR: Heliosphere Impact on Geospace, February 5-9, 2007, Helsinki, Finland Magnetotail bending during substorm on Sep 14, deg to Sun-Earth line Large interhemispheric asymmetry Event-oriented model may provide the necessary accuracy

How to produce event-oriented model? ICESTAR: Heliosphere Impact on Geospace, February 5-9, 2007, Helsinki, Finland 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 ICESTAR: Heliosphere Impact on Geospace, February 5-9, 2007, Helsinki, Finland 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) ICESTAR: Heliosphere Impact on Geospace, February 5-9, 2007, Helsinki, Finland 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 empty loss cone isotropic boundaries filling loss cone polar cap flux  B flux II B

Additional measurements for better model accuracy (2) ICESTAR: Heliosphere Impact on Geospace, February 5-9, 2007, Helsinki, Finland 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:

Ring current representation (1) Symmetric ring current = eastward + westward: Asymmetric ring current = partial + closing Region 2 field-aligned currents : Local time asymmetry gives rise to field-aligned currents (calculated numerically) ICESTAR: Heliosphere Impact on Geospace, February 5-9, 2007, Helsinki, Finland

Free parameters: mean radius max current density width of J distr. anisotropy index constant duskward shift angle for partial RC Ring current representation (2) ICESTAR: Heliosphere Impact on Geospace, February 5-9, 2007, Helsinki, Finland

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

thin current sheet intensity X 0 - location of steepest decrease of W(x,y) D 0 - half-thickness of current sheet Addition of a new tail current sheet (2) Free parameters: Subtractinggives a thin current sheet with finite x-scale, zero outside 25 Re. ICESTAR: Heliosphere Impact on Geospace, February 5-9, 2007, Helsinki, Finland

Scaling factor AMP=  3 for the magnetic field of Chapman-Ferraro currents at magnetopause, determined from solar wind pressure variations P SW : Storm-time magnetic field modelling: Magnetopause currents Parameter R T, characteristic scale size of magnetotail, defined by solar wind parameters: 30 R E - parameter R T in T89 Kp=4, Z T, Shue - magnetopause position given by Shue et al [1998] model dependent on P SW and IMF Bz at X= - 20 R E, Y = 0, Z T, T89 - ‘magnetopause’ position given by T89 Kp= 4 model at X= - 20 R E, Y = 0. ICESTAR: Heliosphere Impact on Geospace, February 5-9, 2007, Helsinki, Finland

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.  = 0.8 A = 1 Dst 0 = 40 nT Event-oriented magnetospheric magnetic field modelling ICESTAR: Heliosphere Impact on Geospace, February 5-9, 2007, Helsinki, Finland

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

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, UT: Magnetic field during saw-tooth event ICESTAR: Heliosphere Impact on Geospace, February 5-9, 2007, Helsinki, Finland

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

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