The role of aerodynamic drag in propagation of interplanetary coronal mass ejections

B. Vršnak¹, T. Žic¹, T. V. Falkenberg², C. Möstl^3,4, S. Vennerstrom² and D. Vrbanec¹

¹ Hvar Observatory, Faculty of Geodesy, University of Zagreb, Kačićeva 26, 10000 Zagreb, Croatia e-mail: bvrsnak@geof.hr
² National Space Institute, Technical University of Denmark, Juliane Maries vej 30, 2100 København, Denmark
³ Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
⁴ Institute for Physics, University of Graz, Universitätsplatz 5, 8010 Graz, Austria

Received: 15 October 2009
Accepted: 17 December 2009

Abstract

Context. The propagation of interplanetary coronal mass ejections (ICMEs) and the forecast of their arrival on Earth is one of the central issues of space weather studies.

Aims. We investigate to which degree various ICME parameters (mass, size, take-off speed) and the ambient solar-wind parameters (density and velocity) affect the ICME Sun-Earth transit time.

Methods. We study solutions of a drag-based equation of motion by systematically varying the input parameters. The analysis is focused on ICME transit times and 1 AU velocities.

Results. The model results reveal that wide ICMEs of low masses adjust to the solar-wind speed already close to the sun, so the transit time is determined primarily by the solar-wind speed. The shortest transit times and accordingly the highest 1 AU velocities are related to narrow and massive ICMEs (i.e. high-density eruptions) propagating in high-speed solar wind streams. We apply the model to the Sun-Earth event associated with the CME of 25 July 2004 and compare the results with the outcome of the numerical MHD modeling.