1. Magnetic Clouds: A Possibility of Forecasting Geomagnetic Storms I.ANTONIADOU (1), A.GERANIOS (1), Μ.VANDAS (2), O.MALANDRAKI (3) (1) University of Athens, Greece (2) Astronomical Institute, Academy of Sciences, Bocni II 1401, 14131 Praha 4, Czech Republic (3) Research and Support Department, ESTEC, European Space Agency, Noordwijk, Netherlands.

2. Subjects of Interest Introduction Introduction Magnetic Clouds Magnetic Clouds Geomagnetic storms and Dst index Geomagnetic storms and Dst index Simulations Simulations Conclusions Conclusions

3. Introduction Solar system is full of :  Solar Wind  Magnetic Fields  Structures ejected from the sun  There is a continual dynamic interaction and correlation between the Sun and the planets of our Solar System, through Solar Wind. Direct measurements in space : ► VELA, IMP-6 ► Confirmation of theoretical models about the propagation of Solar Wind ► Showed new properties of Solar Wind low plasma temperature PLASMA CLOUDS MAGNETIC CLOUDS

4. Magnetic Clouds Characteristics: To identify an interplanery structure as a Magnetic Cloud the following criteria must obeyed: Relatively strong magnetic field Relatively strong magnetic field Large and smooth rotation of the magnetic field Large and smooth rotation of the magnetic field Lower temperature than average Lower temperature than average Transient solar Transient solar mass ejections mass ejections

5. Magnetic clouds Propagation: → TOTAL PRESSURE: Ρ = Β 2 / 8π + nk(T e + T p ) magnetic thermal magnetic thermal pressure pressure pressure pressure Where Β : magnetic field n : density of electrons and protons n : density of electrons and protons k : Boltzmann’s constant k : Boltzmann’s constant Τ e,Τ p : electron and proton temperature respectively Τ e,Τ p : electron and proton temperature respectively  Pressure inside the cloud is greater than surroundings  the magnetic cloud is expanding  Reduction of particles density during the expansion

6. Magnetic Clouds → Cylindrical Model: ► Magnetic cloud forms a large loop (flux-ropes), which can be locally described as cylinder ► Magnetic field lines are attached to the sun surface ► Thermal connection with solar corona Helical magnetic field Helical magnetic field Structure of magnetic clouds

7. Magnetic Clouds Magnetic Clouds → Spheroid model: ► Disconnection of the magnetic loop from the solar corona ► Closed areas of magnetic field into the solar wind ► Thermal disconnection from the solar corona Structure of magnetic clouds poloidal magnetic field toroidal magnetic field

8. Simulations of Magnetic Clouds Measurements from satelliteSpheroid modelCylindrical model

9. Geomagnetic storms Interaction between Magnetic clouds and Earth’s Magnetosphere Geomagnetic storms : Geomagnetic storms : Disturbances in the Solar Wind and Earth’s Magnetosphere Disturbances in the Solar Wind and Earth’s Magnetosphere coupled system, caused by solar activity coupled system, caused by solar activity  Energetic particles are transferred from the solar wind to the magnetosphere Criterion: ► Bz < 0 : Southward magnetic field magnetic reconnection between the solar wind and the magnetosphere

10. Dst Index Calculation of Dst Index-Burton’s Model: Assumption:The strength of a geomagnetic storm can be study from the changes of the ring current changes of the ring current

11. Dst index BURTON’S MODEL BURTON’S MODEL b: Measures the changes of the P dyn of the Solar Wind. c: Measures the magnetic field at the quiet time of the ring current. F(E): Is the ring current injection rate and depends only from the E y (y-compoment of solar wind’s electric field) E y = -(VxB) y d: Measures the response of the injection rate 1/α: Measures the life-time of particles into the ring current. α→3 ή 5 hours,Εy > 4mV/m α→7,7 hours,Εy < 4mV/m b = 0,20 nT/(eV/cm 3 ) 1/2 c = 20 nT d = 1,2x10 -3 nT / (smV/m)

12. Simulations of Magnetic Clouds TIME (HOURS) FROM 19NOV.2003TIME (HOURS) FROM 6NOV.1997

13. Conclusions  Continuous studies and observations have shown two possible structures of magnetic clouds: cylindrical and spheroid.  When magnetic clouds interact with Earth’s magnetosphere it is possible to cause geomagnetic storms.  Study of these storms and forecasting of the space weather can be made using Dst index.

14. Acknowledgements The project is co-funded by the European Social Fund and National Resources (EPEAEK II) Pythagoras. References 1. Γεράνιος, Α., Μελέτη της χαμηλής θερμοκρασίας του ενδοπλανητικού πλάσματος από την μελέτη των δορυφόρων VELA, IMP και HELIOS, Διατριβή επί υφηγεσία, Αθήνα 1979 2. Buck, G.J, Forse-free Magnetic Field Solution in toroidal coordinates, Journal of applied Physics, Vol. 36, p.2231-2234, 1965 3. Burlaga, L.F, Magnetic clouds, Physics of the Inner Heliospere II, Vol. 21, p.9-17, 1991 4. Burton, R.K, Mc Pherron, R.L, Russel, C.T, An empirical relationship Between Interplanetary conditions and Dst, Geophysical Research Vol. 80, 1975 5. Chandrasechar, S., Kendall, P.C, On force-free magnetic fields, American Astronomical Society, p.457-460, 1957 6. Feldstein, Y.I, Pisarky, V.Y, Rudneva, N.M, Grafe, A., Ring Current Simulation in connection with interplanetary space conditions, Planet. Space Sci, Vol. 32, p.975-984, 1984 7. Fernich, F.R, Luhmann, J.G, Geomagnetic response to magnetic clouds of different polarity, Geophysical Research Letters, Vol. 25, p.2999-3002, 1998 8. Murayama, T., Coupling function between solar wind parameters and Geomagnetic indices, Rev. Geophys. Space Phys, Vol. 20, p.623-629, 1982 9. Vandas, M., Fischer, S., Geranios, A., Spherical and cylindrical Mondels of Magnetized Plasma Data and their Comparison with Spacecraft Data, Space Science, Vol. 39, p.1147-1154, 1991 10. Vandas, M., Fisher, S., Pelant, P., Geranios, A., Magnetic clouds:Comparison between spacecraft measurements and theoretical magnetic force-free solutions 11. Wilso, M.R., Geomagnetic response to magnetic clouds, Planetary Space Science, Vol. 35, 1987