chromospheric magnetic reconnection from an observer’s point of view jongchul chae seoul national...
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Chromospheric Magnetic Chromospheric Magnetic Reconnection Reconnection
from an Observer’s Point of Viewfrom an Observer’s Point of View
Jongchul ChaeJongchul Chae
Seoul National University, KoreaSeoul National University, Korea
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What is Chromospheric What is Chromospheric Reconnection ?Reconnection ?
Magnetic reconnection occurring in the chromosphere and photosphere, not in the corona
Lower Alitudes: 0 to 104 km Lower temperatures: a few 103 K to a few 105 KHigher densitiesSmall-scale low altitudeDiversities in flow speed, density and temperature strong stratification Driven reconnection
Flux emergenceSupergranular flow
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Observational SignaturesObservational Signatures
Canceling Magnetic FeaturesJet-like Features seen in H and UV/FUV/EUV
UV/EUV jets, UV explosive eventsH alpha jets/ surges/ H alpha upflow events
Chromospheric Brightenings Ellerman bombsOther brightenings in UV/EUV/ H alpha
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Canceling Magnetic Canceling Magnetic FeaturesFeatures
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Canceling Magnetic FeatureCanceling Magnetic Feature
From Chae, Moon, Park 2003, JKAS 36, S13
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Interior
CMF as a CMR eventCMF as a CMR event
cv Photosphere
Chromosphere
Corona
ivDOWNFLOW
UPFLOW
FLUX CANCELLATIONCONVERGING MOTION
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Does the flux submerge in Does the flux submerge in CMFs?CMFs?
YES! The ASP observations produced the evidence for it.
From Chae, Moon, Pevtsov 2004, ApJL, 602, L65
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Observables of CMFObservables of CMF
Rate of Magnetic Flux Loss
Half length of interface between two poles
Specific flux loss rate
Converging speed of each pole toward PIL
d
dt
cv
cL
From Chae, Moon, Park 2003, JKAS 36, S13
obsc
dr
L dt
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Summary of CMF Summary of CMF ObservationsObservations
Chae et al. 2002 Case A
Chae et al. 2002 Case B
Chae et al. 2003
Chae et al.1998
Flux loss rate Mx/h
3.4 x 1018
2.5 x 1018
1.8x101
8
2x101
7
Contact length Mm
7.8 3.3 2.5 3
Specific flux loss rate G cm/s
1.2 x 106
1.1x106 2.0x106
2x105
Converging speed km/s
0.27 0.35 0.22
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Chromospheric Jets in Active Chromospheric Jets in Active RegionsRegions
EUV Jets
-1 5 10 -3150 250 km s , 2 3 10 K, 1 10 cmev T n From Chae, J. 2003, ApJ 584, 1084
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HH Jets in the same active Jets in the same active regionregion
-1 410 40 km s , 10 Kv T
Chae, J. et al. 2000, Solar Physics 195, 333
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EUV/HEUV/H Jets in another AR Jets in another AR
-1 550 100 km s , 2 3 10 Kv T
-1 430 km s , 10 Kv T
From Chae et al. 1999 ApJ 513, L75
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Jet-like features in the Jet-like features in the quiet Sunquiet Sun
H upflow events
-1 420 km s , 10 Kv T
From Chae et al. 1998, ApJ, 504, L123
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Jet-like in the quiet SunJet-like in the quiet Sun
UV explosive events
-1 570 km s , 10 Kv T
From Chae et al. 1998, ApJ, 479, L109
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Summary of Jet Summary of Jet Observations Observations
Jet-like features occur in strong association with canceling magnetic features.There is a good correlation between speed and temperature in jet-like features.Jet-like features with different temperatures often occur together at the same place.
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Theoretical Considerations of Theoretical Considerations of Chromospheric ReconnectionChromospheric Reconnection
Adiabatic Current Sheet of Sweet-Parker typeInsights on Chromospheric Reconnection from Observations of Jet-like Features Insights on Chromospheric Reconnection from Observations of Canceling Magnetic Features
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Adiabatic Current Sheet Model Adiabatic Current Sheet Model
of Sweet-Parker typeof Sweet-Parker type
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width (inflowing length)2 : L
thickness (outflowing length)2 : l
length (in the third direction): zL
Current Sheet Model of Current Sheet Model of CMRCMR
o o z
dv B L
dt
Supposing z cL L
6 -12 10 G cm so oz
dr v B
L dt
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Steady-state Current Sheet Steady-state Current Sheet ModelModel
Sweet-Parker Model
Incompressible flow
Litvinenko (1999)Compressible, isothermal flow
Chae et al. (2003)Adiabatic flowA generalized approach
i oT T
i o
i i o 1 i oT T
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Steady-state EquationsSteady-state Equations
Induction equation
Mass conservation
Momentum conservation
Adiabatic energy equation
ii i o o c
Bv B v B
l
i i o ov L v l 2
21
8 2i
i i i c
Bv p p
21
2 8i o
o o o c
B B Lv p p
l
2 22 21 1
2 1 4 2 1 4i o
i i i i o o o o
B Bv p v L v p v l
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SolutionsSolutions
Basic assumptions
Density compression factor
Outflow speed
Temperature Excess -outflow speed relation
2 2; ; , / 8c o i i i ip p l L v p B
4i
o Ai
i
Bv v
21
2H
o i oB
mT T T v
k
11
1o
i i
f
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Insights on Chromospheric Insights on Chromospheric Reconnection from Reconnection from Observations of Observations of Jet-like FeaturesJet-like Features
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Are observed jet-like features Are observed jet-like features chromospheric reconnection chromospheric reconnection
jets?jets?Temperature excess-outflow speed relation
H jets
UV Explosive events in the quiet Sun
EUV Jets
21
2H
o i oB
mT T T v
k
-1 5
5
5
70 km s , 10 K
=5/3, =0.6 0.7 10 K
=4/3, =0.6 0.4 10 K
v T
T
T
-1 5
5
200 km s , 2 3 10 K
=4/3, =0.6 3.6 10 K
v T
T
-1 4
4
4
20 km s , 10 K
=5/3, =1.0 1 10 K
=4/3, =1.0 0.6 10 K
v T
T
T
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Are observed jet-like features Are observed jet-like features chromospheric reconnection chromospheric reconnection
jets? jets? Yes, very likely as seen from the temperature-speed relation.Hotter jets are better explained with a smaller value of (~ closer to isothermal process ) =4/3 fairly well explains the observed temperature-speed relations in jet-like features.
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Are Ellerman bombs Are Ellerman bombs chromospheric reconnection chromospheric reconnection
events?events?Ellerman bombs: Brightening in the far wing of H alpha line profile Heating events in the low chromosphere T=2000 K
They may be reconnection events. If so, we have a prediction
It would be important to measure the flow associated with Ellerman bombs.Note: Shimizu et al. 2005 “Extremely red-shifted magnetic features” as high as 10 km/s
-1~ 8 km s with =1.3, =5/3 v
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What determines jet What determines jet temperatures?temperatures?
Temperature excess Outflow speed Alfven speed of inflowing region magnetic field strength and density Atmospheric level
The temperature and speed of reconnection jets strongly depend on the atmospheric level where reconnection occurs.
Higher Atmospheric level Lower density Higher Alfven speed Higher outflow speed Hotter jets
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What determines the degree What determines the degree of compression?of compression?
Specific heat ratio the efficiency of radiative cooling
=1 restores the Litvinenko’s (1999) result. This is an unrealistic assumption. In general , 1 (isothermal) < <5/3 (adiabatic)It is likely that gets bigger with higher levels where the medium is more transparent.
Plasma beta of inflow restores the incompressible flow assumption of the original Sweet-Parker model In practice, this assumption is hard to achieve in solar atmosphere, and hence unrealistic.
11
1o
i i
f
i
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What determines the degree What determines the degree of compression?of compression?
Near the photosphere
In the upper chromosphere
5/ 3, 1 1.6i f
11
1o
i i
f
4 / 3, 0.1 3.3i f
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Insights on Chromospheric Insights on Chromospheric Reconnection from Reconnection from
Observations of Canceling Observations of Canceling Magnetic FeaturesMagnetic Features
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Linking observed parameters Linking observed parameters of CMF and physical of CMF and physical parameters of CMFparameters of CMF1
o oz
dr v B
L dt
1/ 3 2 / 3 1/ 3
1/ 3 1/ 3 1/ 3
( 4 / )
( 4 / )
i i c
i i c
B L r f
v L r f
( : anomalous resitivity factor)
ipi
i
c i
pL H
g
q q
, : VAL 81
: Kubat & Karlicky 1986i i
i
z p
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Do CMFs result from Do CMFs result from reconnection in the reconnection in the
temperature minimum?temperature minimum?Sturrock (1999) and Litvinenko (1999) YES We have to say NOT necessarily.
The speed of reconnection using classical conductivity of the inflow region is too slow to explain the observed converging speed in canceling magnetic features. The resistivity of the current sheet should be much bigger than that of inflowing region. anomalous resistivity
The molecular resistivity of the inflowing region is no longer the most important parameter characterizing chromospheric reconnection.
6
9 3
8
-1
-1
2 10 cgs
5 10 cgs, 1.3 10 cgs 100 km
7 10 cgs
1 0.10 km s
10 0.22 km s
i i
i
i
i
r
p L
q v
q v
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Observational constraints Observational constraints on on qq
Too small values of q yield too low inflow speeds and too high outflow speedsToo big values of q yield too high inflow speeds and too low inflow speeds The observed inflow speeds and outflow speeds constrains the anomalous resistivity factor q
1/ 3 1/ 3
1/ 3 1/ 3,c ci o
i i
v q v q
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A reference model A reference model 6 -11.5 10 G cm s , 50, 4 3r q
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Is there any preferred height Is there any preferred height for chromospheric magnetic for chromospheric magnetic
reconnection?reconnection?No!Classical resistivity is not the major factor.Reconnection may occur at any height. It may be the geometry of two interacting flux systems that determines the reconnection height.
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What we have learned so farWhat we have learned so far
Canceling magnetic features, H jets, UV explosive events, EUV jets are nicely fit into the picture of chromospheric reconnection.An adiabatic current sheet with anomalous resistivity factor of about 50 and specific ratio of 4/3 may serve as a reference model for chromospheric reconection.There may be no preferred height of chromospheric reconnection, and it may be the geometry of two interacting flux systems that determines the reconnection height.
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Observational Challenges of Observational Challenges of Solar-BSolar-B
Fine-scale structure of canceling magnetic features new and more reliable measurements of specific cancellation rates and converging speeds (SOT)Discovery of reconnection outflows in the low chromosphere: v~10 km/s, T~103 K (SOT)Simultaneous observations of canceling magnetic features, low chromosphere reconnection flows, H alpha flows, UV jets, EUV jets, X-ray jets that cover diverse speeds, temperatures and atmospheric levels (SOT, EIS, XRT)
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Theoretical ChallengesTheoretical ChallengesImpulsive, recurrent (often bursty) occurrence (Chae et al. 1998a, b)
existence of elementary non-steady reconnection events ? formation of a number of magnetic islands via tearing instability?
Co-occurrence of hot jets and cool jets (Chae etal. 1998b, 1999)
Two step reconnection (formation of magnetic islands in the lower atmosphere followed by its destruction in the upper atmosphere, Chae 1999)?Multi-site reconnection of many thin shredded flux sheets at different atmospheric heights (in a stratified medium)?