A comparison of CME expansion speeds between solar cycles 23 and 24

Fithanegest K Dagnew,Nat Gopalswamy,Solomon B Tessema

doi:10.1088/1742-6596/1620/1/012003

Abstract

We report on a comparison of the expansion speeds of limb coronal mass ejections (CMEs) between solar cycles 23 and 24. We selected a large number of limb CME events associated with soft X-ray flare size greater than or equal to M1.0 from both cycles. We used data and measurement tools available at the online CME catalog (https://cdaw.gsfc.nasa.gov) that consists of the properties of all CMEs detected by the Solar and Heliospheric Observatory’s (SOHO) Large Angle and Spectrometric Coronagraph (LASCO). We found that the expansion speeds in cycle 24 are higher than those in cycle 23. We also found that the relation between radial and expansion speeds has different slopes in cycles 23 and 24. The cycle 24 slope is 45% higher than that in cycle 23. The expansion speed is also higher for a given radial speed. The difference increases with speed. For a 2000 km/s radial speed, the expansion speed in cycle 24 is ∼48% higher. These results present additional evidence for the anomalous expansion of cycle 24-CMEs, which is due to the reduced total pressure in the heliosphere.

Highlights

The expansion speed (Vexp) of a coronal mass ejections (CMEs) is the rate at which the lateral dimension of a CME at its widest part changes with time
The lateral CME expansion speed is the only parameter that can be uniquely measured for any CME, be it on the limb or pointed along the Sun-Earth line, on the front or back side [2,3]
We report on a comparison of the expansion speeds of limb CMEs between solar cycles 23 and 24 and its implications for the state of the heliosphere

Summary

Introduction

The expansion speed (Vexp) of a CME is the rate at which the lateral dimension of a CME at its widest part changes with time. Schwenn et al [2,3] define the expansion speed as the speed at which the CME expands in a direction perpendicular to its direction of propagation. The sky plane speed varies considerably with the viewing angle, the expansion speed is independent of the direction of motion of the CME relative to the viewer’s line of sight. The lateral CME expansion speed is the only parameter that can be uniquely measured for any CME, be it on the limb or pointed along the Sun-Earth line, on the front or back side [2,3]

Methods

Findings

Conclusion