insight from the outside: the solar cycle from a ... · insight from the outside: the solar cycle...
TRANSCRIPT
![Page 1: Insight from the outside: The solar cycle from a ... · Insight from the outside: The solar cycle from a heliospheric perspective M. Owens 1, N. Crooker 2 N. Schwadron 2 and T. Horbury](https://reader035.vdocuments.net/reader035/viewer/2022071119/6018c5a07d71101a3a4e4d6d/html5/thumbnails/1.jpg)
Insight from the outside:
The solar cycle from a
heliospheric perspective
M. Owens1, N. Crooker2,M. Owens , N. Crooker ,
N. Schwadron2 and T. Horbury1
1Imperial College London2Boston University
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Overview
• A quick summary of the solar cycle
• Probing the heliosphere with electrons
• Interplanetary coronal mass ejections
• Evolution of the coronal/heliospheric field
• Summary
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Sunspots
[Greenwich sunspot data]
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Photospheric flux
[Top: David Hathaway, Goddard]
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Heliospheric flux
[Updated regularly at:
http://www.sp.ph.ic.ac.uk/~mowens/helioflux.htm]
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[Adapted from
Jones et al.,
2003]
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A snapshot of solar maximum
[Top: Mt. Wilson
magnetogram
Bottom: Jones et Bottom: Jones et
al., 2003
Both at solar
maximum]
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Solar cycle:
corona
Yang Liu, SHINE 2006
Riley et al., 2006
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How does the coronal field
evolve?• Wang & Sheeley: Emerging active region loops bring
about field reversal by destruction of existing open flux
– Series of PFSS solutions
• Fisk & Schwadron: Open flux is conserved, but reconfigured by reconnectionreconfigured by reconnection
• B.C. Low: Magnetic helicity conservation means potential state cannot be reached by reconnection alone
– CMEs required to shed the helicity
– CMEs bodily remove flux to allow field reversal
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Heliospheric magnetic fields
• Only have local measure of magnetic field
• Electrons can tell us about topology and connectivityconnectivity
– Suprathermal electrons
– Jovian electrons
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Suprathermal electrons
[Stverak et al., 2009] [Hammond et al., 1996]
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Suprathermal electrons
Owens and Crooker, 2008
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Suprathermal electron evolution
[Hammond et al.,1996]
[Maksimovic et al.,2005]
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Explaining electron evolution
• Two competing effects:
– Adiabatic focussing
(conservation of magnetic
moment) – R dependent
– Pitch angle scattering –
constant in time?constant in time?
• Close to the Sun, focussing
wins out
• Far from the Sun, scattering
dominates
[Owens et al.,2008]
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Modelling electron evolution
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Coronal mass ejections
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Flux ropes in CMEs?
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Flux ropes in ICMEs?
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Field-line length
Some evidence from solar electron bursts [e.g., Larson et
al., 1997], but sparse data
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Expected electron profile
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Analysis of ~100 magnetic clouds
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Solar connectivity
Crooker et al., 2004
Marubashi., 1997
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CMEs add flux to the heliosphere
Owens and Crooker, JGR, 2006
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Estimating the CME flux
contribution
• Need values for:
1. Flux contained in a typical CME
2. CME rate over the solar cycle2. CME rate over the solar cycle
3. Background “open” flux (i.e., non-CME flux)
4. Timescale for CME flux removal
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Cross-sectional elongation
• Radial motion will distort flux rope [Riley and
Crooker, 2004]
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Cross-sectional elongation
[Owens, 2008]
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Combining remote and in situ
observations
• LASCO/Ulysses
– x5 more flux than
force-free suggests
• ~1012-1013 Wb of • ~1012-1013 Wb of axial flux
• How important a source of magnetic flux are ICMEs?
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CME rates
Owens et al., GRL, 2008
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Removing CME fluxSimple picture:
– Disconnection: EDs, no decay in CSE
– Interchange: no EDs, decay in CSE
Owens and Crooker, JGR, 2007
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Both reduce flux at same rate
Owens and Crooker, 2007
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Model estimates: 40-day
timescale?
Model of Owens and Crooker [2006]
using updated data
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Long CME
opening times?
• How quickly is the CSE
signature removed due
to scattering?
[Owens and Crooker, 2007]
to scattering?
• 8 AU?
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Evidence for CME
loop opening
1 AU: Shodhan et al., 2002
Riley et al., 20045 AU: Crooker et al., 2002
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Evidence for CME loop opening
Crooker et al, JGR, 2008Owens et al., GRL, 2007
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Transport of open flux
Owens and Crooker, JGR, 2007
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CME footpoint orientations
Bothmer and Schwenn, 1998
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Polarity reversal
TimeOwens et al, GRL, 2007
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Declining phase
Time
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• Number of CMEs required to reverse polarity:
Is there sufficient flux?
• Timescale for such a reversal
d > 5o
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Observations
Owens et al, 2007 Crooker and Webb, 2006
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In summary...
• CMEs add flux to the heliosphere
– May explain solar cycle variation in |B|
• CME flux removed by opening closed loops
– Open flux is transported across foot points– Open flux is transported across foot points
• Coronal and heliospheric polarity reversal can be explained in this way
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Still to be done
• Better estimates of CME flux content need to combine remote and in situ observations
• Open flux transport by CMEs
– Identify sources of CMEs and location of – Identify sources of CMEs and location of
reconnection
– Compare with polarity of open flux in ICMEs
• Look for reconfiguration of closed flux in observations and PFSS solutions
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Flux excess
[Lockwood et al., 2009]
R [AU]
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Reconnection?
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Owens and Crooker, 2007