Multi-Wavelength Studies of Dynamic Events in the Solar Corona From Space-Based and Total Solar Eclipse Observations

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Student thesis: Doctoral ThesisDoctor of Philosophy

Original languageEnglish
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Award date2017
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Abstract

Total solar eclipse observations were the first to raise fundamental questions
about the Sun’s atmosphere, or corona. Instruments and analysis tools have
been developed (and continue to be developed) to address questions regarding
the temperature and structure of the corona, the underlying mechanisms responsible for coronal activity and the effects of the Sun on the heliosphere and
on Earth. The development of modern imaging instrumentation, with optics
designed for a broad range of wavelengths and detector arrays, has led to new
understanding of the dynamic nature of the corona. The new image processing
techniques described in Chapter 2 are essential to fully exploit data from coronagraphs and EUV imagers. In order to explore the broader range of dynamic events in the corona that differ from typical coronal mass ejections (CMEs) in structure and behavior, this thesis focuses on three main areas: 1) CME-type (jet-like) events, 2) low-coronal signatures (LCSs) of ‘stealth’ CMEs and 3) dynamic events captured during total solar eclipse observations. Jets have a huge variation of observational characteristics and can arise from many different regions at the Sun. Chapter 3 describes observations of recurring jetting activity from an active region (AR). During a period of three days beginning 2013 January 17, twelve recurrent reconnection events occurred within a small region of opposing flux embedded within one footpoint of an AR, accompanied by flares and jets observed in EUV and fast and faint structureless ‘puffs’ observed by coronagraphs. During the same period a slow structured CME gradually erupts, with one end anchored close to, or within, the jetting region. Four of the jet events occur in pairs (a narrow, primary jet followed by
a spray-like jet). The puffs are disturbances caused by the initial reconnection
event, which also drives the first narrow jet. The primary jet, the associated
flaring activity, and the puffs are all symptoms of magnetic reconnection. The
source of the fast events observed in LASCO/C2 is a region of positive magnetic
flux at the footpoint of a large AR. This work shows that propagating
disturbances, without an accompanying flow of material, are clearly observable
in the extended corona. CMEs are generally associated with LCSs such
as flares, filament eruptions, EUV waves or jets. Recent published works have
observed CMEs without LCSs, leading scientists to refer to them as ‘stealth’
CMEs. The study described in Chapter 4 focuses on a set of 40 stealth CMEs
identified from a study by D’Huys et al. 2014. Application of advanced image
processing reveals activity in the lower corona that are the LCSs associated
with these so-called stealth events. Many of these LCSs were missed because
vi of data and image processing limitations. Twenty-three of these events are
identified as small, low-mass, unstructured blobs or puffs, often occurring in
the aftermath of a large CME, but associated with LCSs such as small flares,
jets or filament eruptions. Of the larger CMEs, 7 are associated with jets
and 8 with filament eruptions. The main conclusion reached is that stealth
CMEs are a misconception arising from observational and processing limitations.
Total solar eclipse observations are essential in coronal studies because
they provide a full map of the extent of the corona from the solar surface out to
several solar radii. When total solar eclipse images are processed, these high
resolution images reveal the finest details of coronal structures down to the
spatial resolution of the instrument (1-2 arcsec). The 2012 and 2013 eclipse
observations described in Chapter 5 were acquired at the peak of solar activity.
The study of the dynamic events captured in the eclipse images are
complemented by time-series observations from space, taken prior to and during totality. The focus of the study is on the source of ‘atypical’ large-scale
structures captured in these images. The two events described show the impact
of flaring activity from ARs, and their association with sprays, jets and
CMEs. All three studies described in this thesis rely on new state-of-the-art
image processing techniques applied mainly to satellite data from LASCO/C2,
SDO, EUVI, and SWAP. Reliable image processing has opened up new venues
for studying dynamic coronal events. Using multi-wavelength EUV (SDO/AIA
and STEREO/EUVI), complemented by coronagraph data (LASCO/C2 and
COR2) and total solar eclipse images, we have created an extensive catalog of
CMEs based on their LCSs seen in EUV and their overall behavior in coronagraph
and eclipse images

Documents

  • Alzate_Nathalia

    Thesis, 32 MB, PDF

    Embargo end date: 31 Dec 2099

    Embargo reason: Extensive 3rd Party Copyright Included

Documents

  • Alzate_Nathalia

    Thesis, 32 MB, PDF

    Embargo end date: 31 Dec 2099

    Request copy