Magnetic Clouds: A Possibility of Forecasting Geomagnetic Storms

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 • Magnetic Clouds • Geomagnetic storms andDst index • Simulations • Conclusions

3. Solar system is full of : Solar Wind Magnetic Fields Structures ejected from the sun There is a continual dynamicinteraction and correlation between theSun 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 Introduction

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

5. Magnetic clouds Propagation: • TOTAL PRESSURE: Ρ = Β2 / 8π + nk(Te+ Tp) magneticthermal pressurepressure Where Β : magnetic field n : density of electrons and protons k: Boltzmann’s constant Τe,Τp : 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 Structure of 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

7. Magnetic Clouds Structure of 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 toroidal magnetic field poloidal magnetic field

8. Simulations of Magnetic Clouds Measurements from satellite Cylindrical model Spheroid model

9. Geomagnetic storms Interaction between Magnetic clouds and Earth’s Magnetosphere Geomagnetic storms: Disturbances in the Solar Wind and Earth’s Magnetosphere 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

11. Dst index BURTON’S MODEL b: Measures the changes of the Pdyn 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 Ey (y-compoment of solar wind’s electric field) Ey = -(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/mα→7,7 hours ,Εy <4mV/m b = 0,20 nT/(eV/cm3)1/2 c = 20 nT d = 1,2x10-3 nT / (smV/m)

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