Department of Physics, Division of atmospheric sciences and geophysics, University of Helsinki, Finland

Department of Physics, Division of atmospheric sciences and geophysics, University of Helsinki, Finland

Solar Physics Branch, Naval Research Laboratory, Washington, D.C. 20375, USA

Department of Physics, Division of atmospheric sciences and geophysics, University of Helsinki, Finland

Space Sciences Laboratory, University of California, Berkeley, CA, USA

Space Sciences Laboratory, University of California, Berkeley, CA, USA

Space Sciences Laboratory, University of California, Berkeley, CA, USA

Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH 03824, USA

Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH 03824, USA