Μάθημα : Ενημέρωση φοιτητών κατεύθυνσης Αστροφυσικής

Την Παρασκευή, 8 Νοεμβρίοθ 2024, ώρα 5-6μμ, θα πραγματοποιηθεί το 25ο διαδικτυακό σεμινάριο του διεθνούς προγράμματος SCOSTEP/PRESTO από τον Dr. Jie Zhang, καθηγητή του George Mason University (ΗΠΑ), με τίτλο:
Solar Eruptions: Initiation, Propagation and Their Earth Impact

Ακολουθούν οδηγίες για την παρακολούθηση και περίληψη

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Abstract:
Flares and coronal mass ejections (CMEs) are the two largest energetic phenomena
originating in the Sun’s atmosphere. They are different in observations: flares are
manifested as a spontaneous release of EM radiations in almost all wavelengths
through the acceleration of non-thermal particles and plasma heating, while CMEs,
equally energetic, are observed as the eruption and ejection of a large-scale
organized magnetic structure into the outer corona.  In this talk, I will first reflect
on the debate in the 1990s on the so-called “solar flare myth”, which initiated the
paradigm shift on the cause of space weather from a flare-centered view to a
CME-centered view. Secondly, a comprehensive overview of our improved
understanding of the relationship between flares and CMEs will be made.  
Thanks to the advancement in observations made by a series of modern space
observatories, including SOHO, STEREO and SDO, it has been found that mostly
the energetic process of a flare (e.g., the increase of X-ray flux) and the accompanying
CME (e.g., the increase of the CME velocity) is highly synchronized in time.
They are intimately coupled in the energy release process; thus, they should be
collectively called a solar eruption. On the other hand, the Sun shows a zoology
of the phenomena, as they can also occur independently from each other,
namely confined flares and “stealthy” CMEs, respectively. The physical causes
of the coupling and the diversity will be discussed in this talk. Lastly, how and
what solar eruptions affect the geo-space, i.e., the Sun-to-Earth chain activities,
will be presented, with a focus on the in-situ solar wind properties from two types
of CMEs, i.e., originated from active regions versus those from quiescent regions.