Investigating Remote-Sensing Techniques to Reveal Stealth Coronal Mass Ejections

Nariaki V Nitta,Nandita Srivastava,Tamitha Mulligan,Andrei N Zhukov,Suvadip Sinha,Erika Palmerio,Ian G Richardson,Jennifer O’Kane,Marilena Mierla,Stephanie L Yardley

doi:10.3389/fspas.2021.695966

Abstract

Eruptions of coronal mass ejections (CMEs) from the Sun are usually associated with a number of signatures that can be identified in solar disc imagery. However, there are cases in which a CME that is well observed in coronagraph data is missing a clear low-coronal counterpart. These events have received attention during recent years, mainly as a result of the increased availability of multi-point observations, and are now known as “stealth CMEs.” In this work, we analyze examples of stealth CMEs featuring various levels of ambiguity. All the selected case studies produced a large-scale CME detected by coronagraphs and were observed from at least one secondary viewpoint, enabling a priori knowledge of their approximate source region. To each event, we apply several image processing and geometric techniques with the aim to evaluate whether such methods can provide additional information compared to the study of “normal” intensity images. We are able to identify at least weak eruptive signatures for all events upon careful investigation of remote-sensing data, noting that differently processed images may be needed to properly interpret and analyze elusive observations. We also find that the effectiveness of geometric techniques strongly depends on the CME propagation direction with respect to the observers and the relative spacecraft separation. Being able to observe and therefore forecast stealth CMEs is of great importance in the context of space weather, since such events are occasionally the solar counterparts of so-called “problem geomagnetic storms.”

Highlights

Coronal mass ejections (CMEs) are powerful solar eruptions containing large amounts of plasma and magnetic field that are regularly expelled from the Sun into the heliosphere
The latitude of ∼S02° is rather consistent with the dimming locations, but less compatible with the Graduated Cylindrical Shell (GCS) reconstruction shown in the middle row of Figure 8, which gives a CME apex propagation direction of N12°E05°, indicating a significant deflection and/or non-radial propagation of the structure toward the north after eruption
As was the case for Event 2 and Event 3, this eruption can be convincingly linked to low-coronal signatures, and as was the case for Event 1, relying uniquely on coronagraph imagery and GCS reconstructions would have resulted in a somewhat misleading estimated source region

Summary

Introduction

Coronal mass ejections (CMEs) are powerful solar eruptions containing large amounts of plasma and magnetic field that are regularly expelled from the Sun into the heliosphere. They were first identified in white light in the early 1970s (Tousey, 1973; Gosling et al, 1974) in images from the 7th Orbiting Solar Observatory (OSO-7) coronagraph (Koomen et al, 1975) and the coronagraph onboard the Skylab space station that formed part of the Apollo Telescope Mount (ATM; Tousey, 1977) suite of solar instruments. The whole Sun-to-Earth picture of CMEs was seemingly quite clear: The presence of low-coronal signatures preceding a halo CME observed by LASCO would signify that the CME is Earth-directed, whereas the lack of visible activity on the solar disc would indicate that the CME was associated with a far-sided eruption

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Conclusion