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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 27, issue 11
Ann. Geophys., 27, 4281–4291, 2009
https://doi.org/10.5194/angeo-27-4281-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 27, 4281–4291, 2009
https://doi.org/10.5194/angeo-27-4281-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.

  16 Nov 2009

16 Nov 2009

Different magnetospheric modes: solar wind driving and coupling efficiency

N. Partamies1, T. I. Pulkkinen1, R. L. McPherron2, K. McWilliams3, C. R. Bryant3, E. Tanskanen4, H. J. Singer5, G. D. Reeves6, and M. F. Thomsen6 N. Partamies et al.
  • 1Finnish Meteorological Institute, Helsinki, Finland
  • 2University of California, Los Angeles, USA
  • 3University of Saskatchewan, Saskatoon, Canada
  • 4University of Bergen, Bergen, Norway
  • 5NOAA, Space Weather Prediction Center, Boulder, CO, USA
  • 6Los Alamos National Laboratory, NM, USA

Abstract. This study describes a systematic statistical comparison of isolated non-storm substorms, steady magnetospheric convection (SMC) intervals and sawtooth events. The number of events is approximately the same in each group and the data are taken from about the same years to avoid biasing by different solar cycle phase. The very same superposed epoch analysis is performed for each event group to show the characteristics of ground-based indices (AL, PCN, PC potential), particle injection at the geostationary orbit and the solar wind and IMF parameters. We show that the monthly occurrence of sawtooth events and isolated non-stormtime substorms closely follows maxima of the geomagnetic activity at (or close to) the equinoxes. The most strongly solar wind driven event type, sawtooth events, is the least efficient in coupling the solar wind energy to the auroral ionosphere, while SMC periods are associated with the highest coupling ratio (AL/EY). Furthermore, solar wind speed seems to play a key role in determining the type of activity in the magnetosphere. Slow solar wind is capable of maintaining steady convection. During fast solar wind streams the magnetosphere responds with loading–unloading cycles, represented by substorms during moderately active conditions and sawtooth events (or other storm-time activations) during geomagnetically active conditions.

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