Space Science
Solar wind driving of space weather
Prof. Tuija Pulkkinen (elec.aalto.fi)
The continuous, highly variable solar wind flows through the heliosphere and drives space weather in space environments of the Earth and other planets. The solar wind influence on the magnetosphere is not instantaneous; solar wind properties are altered at the bow shock and further modified in the magnetosheath between the shock and the magnetospheric boundary (Fig. 1). The magnetosheath plasma and magnetic field determine the efficiency of mechanisms governing solar wind energy and plasma entry to the magneto-sphere: magnetic reconnection, Kelvin-Helmholtz instability, and kinetic Alfvén waves. Within hours, the coupling leads to magnetotail reconfigurations and over days, acceleration of relativistic electrons in the van Allen belts.
Increasing evidence suggests that interplanetary magnetic field fluctuations enhance the solar wind–magnetosphere coupling efficiency: A significant portion of the largest magnetospheric disturbances are associated with turbulent sheath regions, fluctuating stream interaction regions drive radiation belt electron enhancements, and strong ULF waves are associated with strong ionospheric convection. We use space observations and numerical modeling methods to investigate how the solar wind and interplanetary magnetic field and their variability drive geomagnetic activity in the magnetotail, in the inner magnetosphere, and in the ionosphere.
Two Radiation Belt Storm Probes (RBSP) (nasa.gov), were launched on Aug 30, 2012 to the inner magnetosphere to monitor the ring current and radiation belts. The European four Cluster (sci.esa.int) craft have been in orbit since 2000 and the NASA Five Themis (nasa.gov) spacecraft since 2007 providing an unprecedented opportunity of frequent simultaneous measurements from the near-Earth solar wind, shocked magnetosheath plasma, and consequences in the magnetotail and inner magnetosphere (Fig. 2).
Local (Fig. 3) and global (Fig. 4) magnetohydrodynamic simulations are used to examine the plasma transport and dynamic processes in the magnetosphere. While the local models can address many details of the instability development, the global simulations address the large-scale dynamics of the entire system. The GUMICS global MHD simulation developed in Finland is one of 5 actively used simulations globally, and the only one in Europe.
The increased dependence of modern society on space technology has generated a need for targeted space weather studies, which aim at predicting the space environment and estimating worst-case scenarios for technology development and asset protection purposes.
Research is carried out in collaboration with the University of Helsinki (physics.helsinki.fi) and the Finnish Meteorological Institute (en.ilmatieteenlaitos.fi) under the auspices of the Kumpula Space Centre (kumpulaspace.fi).
Recent publications
K. Nykyri, A. Otto, Lavraud B., Mouikis C., Kistler L., Balogh A., Reme H, “Cluster Observations of Reconnection due to the Kelvin-Helmholtz Instability at the Dawnside Magnetospheric Flank,” Annales Geophysicae 24, 2619, 2006
T. I. Pulkkinen, M. Palmroth, E. I. Tanskanen, N. Yu. Ganushkina, M. A. Shukhtina, and N. P. Dmitrieva, Large-scale solar wind - magnetosphere coupling, J. Atmos. Solar-Terr. Phys., 69, 256-264, doi:10.1016/j.jastp.2006.05.029, 2007
E.K.J. Kilpua, J. Pomoell, A. Vourlidas, R. Vainio, J. Luhmann, Y. Li, P. Schroeder, A.B. Galvin, and K. Simunac, STEREO observations of interplanetary coronal mass ejections and prominence deflection during solar minimum period, Annales Geophysicae, 27, 4491-4503, 2009
T. I. Pulkkinen, M. Palmroth, N. Partamies, H. E. J. Koskinen, T. V. Laitinen, C. C. Goodrich, J. G. Lyon, and V. G. Merkin, Magnetospheric modes and solar wind energy coupling efficiency, J. Geophys. Res., 115, A03207, doi:10.1029/2009JA014737, 2010
T. I. Pulkkinen, E. I. Tanskanen, A. Viljanen, N. Partamies, K. Kauristie, Auroral electrojets during deep solar minimum at the end of solar cycle 23, J. Geophys. Res., 116, A04207, doi:10.1029/2010JA016098
N. Yu. Ganushkina, M. W. Liemohn, and T. I. Pulkkinen, Storm-time ring current: Model-dependent results, Ann. Geophys., 30, 177–202, doi:10.5194/angeo-30-177-2012, 2012
E.K.J Kilpua, Y. Li, J.G. Luhmann, L.K. Jian, and C. T. Russell. On the relationship between magnetic cloud field polarity and geoeffectiveness, Annales Geophysicae, 30, 1037-1050, 2012
K. Nykyri, Otto, A., Adamson E., Kronberg E., Daly P., On the Origin of High-Energy Particles in the Cusp Diamagnetic Cavity, JASTP, doi:10.1016/j.jastp.2011.08.012, 2012
Figure captions
Fig. 1. Magnetosphere and its plasma regions. Distance to Sun is not to scale.
Fig. 2. Wave power measured by Cluster and Geotail satellites during 2.5 hours on May 15, 2005.
Top: Solar wind, Bottom: Magnetosheath, Left: Wavelet analysis, Right: Integrated ULF power. (E. Kilpua)
Fig. 3. 2-D local simulation of the Kelvin-Helmholtz Instability at the dusk-side flank magnetopause. The simulation geometry (left panel) and evolution of the plasma density and velocity field (right panel). The background color is the number density, arrows are velocity vectors, black lines are magnetic field lines and yellow line is marking the boundary between magnetosheath and magnetospheric plasma (Nykyri et al., 2006).
Fig. 4. A 3-D view of the magnetosphere in two cut planes from the GUMICS-4 global MHD simulation (Janhunen et al., 2012). Pressure is colour coded along with a pressure isosurface drawn at 0.4 nPa. Flowlines from the solar wind boundary and traces of the night-side magnetic field are also shown.
