Solar eruptions
Solar eruptions
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Observable manifestations
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Prominences and filaments
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Flares
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Coronal mass ejections (CMEs)
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Interplanetary shocks
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Coronal waves
Measurable manifestations
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Interplanetary CMEs (ICMEs)
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Magnetic clouds
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Radio bursts (will be discussed on a seminar)
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Interplanetary shocks
Prominences
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Cool plasma (104K)
embedded in hot
corona (106K)
Above polarity
inversion lines
Filaments
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Top view of a
prominence
Co-aligned with
chromospheric
fibrils
Filaments
Dextral – axial field to the right from +
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Sinistral – axial field to the left from +
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Prominence model
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Legs extend into the
Sun
Exact support
mechanism is not
known. Could be:
twisted magnetic
field
→ magnetic pressure
→ magnetic buoyancy
Sources of plasma in prominences
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Too much plasma to be provided by the corona → the
sources are lower
Possible sources of cool plasma
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Radiative instabilities
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Magnetic levitation
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Injection of plasma from reconnection sites
Prominence eruption
Flux rope is held down by overlying magnetic arcades
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If force balance breaks → flux rope keeps expanding
→ CME
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Magnetic field reconnect below wrapping the fluxrope → solar flare
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Sigmoid signature of flux ropes
Sigmoid results from magnetic field lines twisting
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Sigmoid direction depends on flux rope chirality
(handedness)
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Formation of solar flux ropes
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For the first time observed by SDO spacecraft → flux
rope forms prior to eruption
Standard model of solar flares
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There is no 1-to-1
correspondence between
flares and eruptions
Post-eruption arcades and ribbons
ribbons
arcades
Initiation of CME. Breakout model
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Multipolar magnetic field configuration
Initiation of CME. Flux-rope eruption
Twisted flux rope is formed
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It lifts up due to plasma instabilities (kink and torus
instabilities)
→ flux rope
eruption
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Coronal mass ejections
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0.8 events/day to 3.5 events/days
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Up to 3000km/s when leaving the Sun
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200 – 800 km/s at 1 AU
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Reach 1 AU on average in 1-2 days
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~40% are associated with a flare
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~70% leave a signature on the solar disk
Coronal mass ejections
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5 (3) part structure:
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Ejecta – bright core
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Flux-rope – dark cavity
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Front – bright loop
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Sheath – diffuse emission
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Shock – faint loop
Coronal mass ejections
flux rope
Multipoint observations of CMEs
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Stereoscopic observations of CMEs allow to infer their
global structure and model them in 3D
Forward modeling of CMEs
Heliospheric imagers
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Allows observations of CMEs further from the Sun
Heliospheric imagers
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CMEs get distorted by interaction with background
solar wind – drag
Interplanetary
CMEs (ICMEs)
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Interplanetary
counterpart of a
CME
Definition came
from times when
association
between
phenomena
observed in whitelight and in-situ
measurements was
not certain
Interplanetary
CMEs (ICMEs)
Smooth magnetic
field
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Speed decrease
(deceleration or
expansion)
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Increased plasma
density
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Decreased plasma
temperature
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Small plasma beta
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Bi-directional
electrons
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Magnetic cloud =
magnetic field
rotation
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ICME modeling. Flux rope fitting
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Fitting magnetic field measurements with predefined
magnetic field configuration:
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Cylindrical Lundquist force-free solution
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Elliptical model
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Torus model
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Etc.
ICME modeling. Reconstruction
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Grad-Shafranov reconstruction. Assumed:
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Magnetohydrostatic equilibrium
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Invariant axis
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deHoffmann-Teller frame:
no electric field,
compensated by VxB
ICME modeling. Full 3D modeling
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Fitting to both white-light and in-situ measurements
→ less assumptions
→ possible to study CME evolution
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Deflections
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Rotations
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Deformations