Comparison of Solar Wind and CME Data:
Current and Previous Solar Minima
David Webb1 & Sarah Gibson2
1 ISR,
Boston College, Chestnut Hill, MA
2 HAO/NCAR, Boulder, CO
Outline
•
The What and Why of the Whole Heliospheric Interval (WHI)?
•
Comparison of Current Solar Minimum (23/24) with
Previous Minimum (22/23):
- How typical was WHI (2008) of current minimum (~2009)?
- Previous minimum - Whole Sun Month (WSM - 1996)
- Unusually deep (and weak?) and complex
- How did it evolve?
- Including transients (CIRs and CMEs)
•
Summary & Future Plans
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Overview: What and Why WHI?
•
Internationally coordinated observing and modeling effort
Focus on observations originating from Carrington Rotation 2068:
March 20 - April 16, 2008
•
-
Synoptic observing programs: Broad heliospheric coverage, provide context and
baseline measurements
-
Targeted observing campaigns: Coordinated observations run during CROT 2068
-
Observational input from 27 solar, 19 heliospheric, and 21 geospace instruments
-
~200 people “officially registered” (still growing)
WHI Science Goals:
1. Connect the origins and effects of solar structure and activity through the solar wind
to the Earth and other planetary systems
2. Characterize the 3-D solar minimum heliosphere
Hope was WHI would be good example of ground-state solar minimum, but it was early.
But also we hoped for sufficient structure/activity to make the connections interesting….
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And2010
that is just what we got!
Overview: The Two Sides of WHI
• CMEs from the active regions
• CIRs from the low-latitude coronal holes (more later)
SOHO EIT
• Week20ofMay
WHI
Quiet Sun CampaignWebb-SORCE-Keystone, CO
2010
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• Sounding rocket (PI Woods) April 10, 2008, solar minimum irradiance spectrum (XUV/EUV)
Overview: The Two Sides of WHI
Active side
SOHO EIT
WHI Quiet side
Courtesy
Greg Kopp
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Comparison of Solar Minima
during WSM & WHI Periods
WSM
Magnetic Maps
Apr 09
WHI
Jul 08
WHI
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Time
Courtesy G. de Toma
6
Dec 07
How “typical” was WHI of Solar Minimum?
Depends what you look at, and how you define minimum
If minimum defined as a point in time, WHI was a bit early. But then where
exactly was that minimum point?
Oct 2008: minimum of 13-month
smoothed sunspot number
Aug 2008: minimum defined as point where
new cycle sunspot number (reversed polarity)
is greater than old cycle sunspots
WHI (March/April 2008)
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2010
Courtesy
Tom
Woods
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Courtesy David Hathaway
Comparison of Solar Minima: At the Sun
Low-latitude coronal holes more prevalent during WHI
N-S asymmetry due to solar B angle
microwave
EUV
WSM
WHI
Courtesy Giuliana de Toma
Courtesy Nat Gopalswamy
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Comparison of Solar Minima: At the Sun
Coronal streamer belt is wider
and more structured this
minimum compared to the last
two.
1980
1983
1986
1989
1992
1995
1998
2001
2004
2007
NORTH POLE
SOUTH POLE
NORTH POLE
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May 2010white
MLSO
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Webb-SORCE-Keystone,
COto Jan 2009 (Burkepile, 2010)
light (pB) 1.8 Solar
Radii, Jan 1980
Comparison of Solar Minima: At the Sun
• These differences are evident in comparing WHI to WSM:
- Similar low sunspot numbers
- Smaller polar coronal holes  dipole not as dominant
- Wider streamer belt  warped heliospheric current sheet (HCS) in solar wind
- Low-latitude open flux  more fast wind streams at low latitudes in solar wind
Cycle 22: Whole Sun Month (WSM)
NSO-GONG
Cycle 23: Whole Heliosphere Interval (WHI)
HAO/MLSO
NSO-GONG
Courtesy Gordon Petrie
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Evolution of Current
GONG synoptic polarity maps
from CR 2054 – 2083.
ThemisMinima:
Solar
Hinode
At the Sun
Towards the end of 2008, large low-latitude coronal
holes disappeared, and the HCS flattened
2054
Feb. 07
WHI
2064
Dec. 07
WHI
August 2009
2074
Sep. 08
2083
May 09
20 May 2010
Note that some small mid-latitude coronal
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holes were still present.
Comparison of Solar Minima: At the Sun...
More open magnetic flux at low latitudes in 2008 than in 1996.
The disappearance of large, low-latitude coronal holes in 2009 did not mean the global field became
completely dominated by the dipole, as in 1996. The MAS model above exhibited small open field
regions at all latitudes in 2009, possibly because of the weak polar field. Low latitude open flux may
May 2010
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still be20there,
but on smaller size scalesWebb-SORCE-Keystone,
implying less of impact
COon Earth.
Comparison of Solar Minima: In the solar wind
• B less, V similar but higher during WHI
• WHI vs current solar minimum:
- Dominance of high-speed streams during extended declining phase
- 2-stream structure weakened and disappeared, and radiation belt intensity
dropped soon after WHI
WHI
Courtesy Cristina Lee et al., SP, 2010
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Solar Wind Comparison:
Dominance of CIRs this Cycle
Hourly average Wind observations of solar wind protons (top) from the SWE instrument,
and suprathermal He (lower) from the EPACT/STEP instrument. Left: 1996-1997; Right:
2007-2008.
Courtesy G. Mason
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Comparison of Solar Minima: In the solar wind
WHI min
WSM min
CR 1888-1914
CR 2038-2088
V
N
T
Na
/N
p
P
Decline of ecliptic parameters this cycle: N by 45%,
B by 15%
Ulysses during polar passes: lower magnetic
field (35%),
(20%), speed (3%)
20 May density
2010
McComas et al., GRL, 35, L18103, 2008
Courtesy Cristina Lee et al., 2010, Possible Influence
of the Source Surface Changes on the IMF
Magnitude”, in prep.
Comparison of Solar Minima: In the wind
Black = 2008
White = 1996
Tokumaru et al., JGR, 2010
Left: STEL IPS solar wind speed distr. over 2
full cycles w/WSO neutral lines
Right: Comparison of speed vs latitude
16 bins
at last two minima.
Comparison of Solar Minima: In the wind
For last 2 cycles:
Top: SSN
Middle: WSO polar field
Bottom: STEL speeds as f(area)
Tokumaru et al., JGR, 2010
STEL IPS map showing start
in 2003 of high speed wind at
low latitudes.
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Comparison of Solar Minima: At the Earth
Because of recurring high-speed streams, relativistic electrons in outer radiation
belt (GOES geosynchronous orbit) were elevated for much of 2008
• 340 % increase (71% log) for WHI vs. WSM (faster wind)
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Gibson et al., JGR, 114, A09105, 2009
Hinode
Comparison of Solar Themis
Minima: At the Earth
As the high-speed streams disappeared, radiation belts fell to record
lows, and cosmic rays reached record highs
WHI
Courtesy Dan Baker
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Courtesy R. Mewaldt
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Comparison of
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SolarThemis
Minima:
Hinode
Summary
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Gibson et al., JGR, 114, A09105,
2009
Variation of Coronal Mass Ejections
at Solar Minima
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Total Coronal Mass - MLO MK;
Burkepile et al., SOHO23, 2009
Minimim coronal mass similar in 1986 and 2009: ~ 5 x 1016 g.
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CME Occurrence Rate over
the Solar Cycle
Robbrecht et al., ApJ, 2009
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STEREO and SOHO CME Rates
Jan
1996
Jan
1997
Jan
1998
Courtesy C. St Cyr
& H. Xie
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Total LASCO CME Mass Per Rotation;
Howard et al., SOHO23, 2009
Note: Total mass at solar max ~100x that at minimum.
No significant difference at beginning and end of cycle 23
(red horizontal line is to guide the eye)
CME Rates: WHI vs WSM
Cremades et al.
CME
(day-1)
Faint CME
(day-1)
Jet
(day-1)
Str. Swell
(day-1)
Total
(day-1)
WHI
(LASCO)
0.93
0.71
1.3
0.04
3.0
WHI
(COR1)
0.93
0.50
2.1
-
3.5
WHI (total)
1.14
0.82
2.2
0.04
4.2
WSM
(LASCO)
0.50
0.22
0.54
0.25
1.5
A really different
minimum?
Dissimilar
cadence - FOV?
Instrumental
limitations + projection
issues
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Summary: WHI vs. WSM
Cremades et al.
WHI
WSM
• More ejecta
• More jets
• Less ejecta
• More streamer swelling events
•
•
•
Less ambiguity in source identification
Less than 20% produced by Ars
•
Large uncertainties due to poor coverage,
bad cadence
More than 40% produced by ARs
• Ejecta at all position angles
• Predominance at equatorial
latitudes
•
•
•
•
Jets at polar latitudes
Less “Parkerian” solar wind
Non-radial jets
Alignment at 135º and 315º
• No significant MCs or ICMEs at Earth. No strong magnetic field or flux.
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Solar Minima Studies: Summary
•
The current solar minimum is not just long and deep, but also extended and complex
•
WHI illustrates certain aspects of this solar minimum well:
-
•
•
“Quiet” side irradiance (as low as any this minimum)
Low-latitude coronal holes  high-speed streams  geospace periodicities
The length of this cycle allows us to probe Sun-Earth physical processes
1.
In 2008 geospace was forced by high-speed streams, even though solar irradiance,
activity, and IMF were lower than 1996 – allows us to isolate the effects of fast
solar wind
2.
In 2009 solar magnetic flux moved to smaller spatial scales; high-speed streams
no longer periodically forced the Earth – allows us to study the Sun-Earth system
at its “quietest”
Coronal density/mass was similar at last two minima
CME rates and masses were similar
CME mass/year less at end of SC 23
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Solar Minima Studies: Future Plans
• Modeling and connecting observations post-WHI via internet:
http://ihy2007.org/WHI/WHI.shtml
• New IAU International Working Group on Comparative Solar Minima:
http://ihy2007.org/IAUWG/WEBPAGES/IAUWG.shtml
• IAU Proceedings of JD 16 in Highlights of Astronomy, Vol. 15, 2010:
http://ihy2007.org/WHI/jd16.shtml
• Upcoming special issue of Solar Physics on WHI/Minima-related topics
• IAU Symposium 286 on Comparative Magnetic Minima: Characterizing Quiet Times
in the Sun and Stars; Mendoza, ARG, October 2011.
http://www.iau.org/science/meetings/future/symposia/999/
WHI continue to encourage new participants!
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