Quantitative Measurements of CME-driven Shocks from LASCO Observations

TL;DR

This study demonstrates that CME-driven shocks can be detected and characterized in white light coronagraph images, providing measurements of shock properties and propagation directions, with results aligning well with theoretical models.

Contribution

The paper introduces a method to detect and measure CME-driven shocks in coronagraph images, including their density compression, shape, and orientation, using simple modeling techniques.

Findings

Shock signatures detected in 86% of high-speed CMEs

Measured shock density ratios agree with theoretical predictions

3D shock shapes estimated with simple forward modeling

Abstract

In this paper, we demonstrate that CME-driven shocks can be detected in white light coronagraph images and in which properties such as the density compression ratio and shock direction can be measured. Also, their propagation direction can be deduced via simple modeling. We focused on CMEs during the ascending phase of solar cycle 23 when the large-scale morphology of the corona was simple. We selected events which were good candidates to drive a shock due to their high speeds (V>1500 km/s). The final list includes 15 CMEs. For each event, we calibrated the LASCO data, constructed excess mass images and searched for indications of faint and relatively sharp fronts ahead of the bright CME front. We found such signatures in 86% (13/15) of the events and measured the upstream/downstream densities to estimate the shock strength. Our values are in agreement with theoretical expectations and show good correlations with the CME kinetic energy and momentum. Finally, we used a simple forward modeling technique to estimate the 3D shape and orientation of the white light shock features. We found excellent agreement with the observed density profiles and the locations of the CME source regions. Our results strongly suggest that the observed brightness enhancements result from density enhancements due to a bow-shock structure driven by the CME.