Transcript The Rise of Solar Cycle 24

The Rise of Solar Cycle 24:
Magnetic Fields from the
Dynamo through the
Photosphere and Corona
and Connecting to the
Heliosphere
Part 2:
Corona & Heliophere
Importance of ‘Rush to Poles’: If this does not occur can the
poles reverse … will there be a solar cycle 25?
Northern hemisphere: there is some indication of a “Rush to the
Poles” signature
Southern hemisphere: “Rush to the Poles” is not apparent
CONTOURS: Smoothed negative latitude derivatives of GONG
torsional oscillation (removes the DC component)
("Shear") are superposed on shaded version of FeXIV obs.
ALTROCK
‘Rush to Poles’
• The Extended Solar Cycle appears to be associated with
Torsional Oscillation Shear. Extended cycle also appears in
orientation of ephemeral active regions
• Some signature of ‘Rush to Poles’ in north in FeXIV
• Other observations show ‘Rush to Poles’: 1) Polar crown
filament has moved up pole; 2) magnetic flux shows a
poleward motion;
• Is the weak signal in FeXIV due to lower coronal temperature
in cycle 24?
• Shift in FeXIV intensity to low latitudes: Are we in/near solar
maximum? (Maximum not expected until 2013)
LUHMANN
What PFSS models suggest
about the solar cycle variation of
IMF strength
Source Surface
• Identifies open/closed field
regions (e.g. coronal hole
footprints)
• Identifies location of base
of the heliospheric current
sheet
(Image from Yan Li)
One can obtain both good coronal hole and radial IMF matches with a PFSS model
and source surface ~1.8 Rsun around solar minimum. What about the rest of the cycle?
Based on MWO data archive
Rss=1.5 (red),1.8 (blue) ,2.5 (black)
C.Lee et al., Sol Phys 201
Are CMEs (or CME ‘legs’) for increase during maximum activity?
Or are there durable open flux changes related to the increased surface fields?
From C.Lee et al.
Sol Phys 2011
From Robbrecht et al., ApJ 2009
These are likely what produce the smaller
transients seen in images from STEREO HI
Fisk: Disconnected blobs
won’t account for increase
in IMF
(Cartoons from Wang et al., ApJ paper;
STEREO HI movie)
PFSS models:
•Unify solar-heliospheric observations
•Reproduce many features of the observed coronal holes and
radial interplanetary field (IMF)
•Suggest there are large variations of the open solar/coronal
flux that average out to a solar cycle change of about the right
magnitude. Are they the CMEs? JANET: probably
The observed ICMEs often include counterstreaming
suprathermal electrons that may represent in-situ sampling of
newly opening flux still attached to the Sun at both ends.
Where are their newly closing flux counterparts? Are some
of these connections to the CME shock? (may explain variety of
pitch angles in counterstreaming data)
SCHWADRON
Heliospheric Magnetic Flux Balance
• Correlation between CME
rate and field strength
– (neglects disconnection of
open magnetic flux)
• Note disagreement in the
extended minimum
Owens et al., 2009
How does the Sun lose open
flux?
• Open magnetic flux rooted at Sun
• Only two ways to lose it
U-shaped
blobs
visible in
STEREO
HI images.
Integration into Heliospheric Models
|B| = 2/4R12 where
R1 = 1 AU;
ICME = 1 x 1013 Wb;
D = 1/2;
ic = 40 days;
0 = 254 days;
d = 7.4 years;
flo = 0.5 day1;
fhi = 3 day1;
flr = 0
HOWEVER:
coronal
holes evolve
much more
rapidly
Offset due to flux conversion
Smith et al. Poster
Schwadron et al., Astrophys. J. Lett., 722, L132, 2010.
Hard to remove open flux, reconnection must happen
below alfven critical point
Recent Minimum: Very low CME rate: reconnection at the
current sheet which was thinner this past minimum: more
favorable for reconnection? U-shaped structures in
STEREO
Physical connection between open flux and photosphere
(disconnection or bipolar removal)
Floor (Open flux will not drop below this level)
Leif: Solar Mean Field: Measure the Sun as a star
Observed mean field does not include polar fields. Mean
field drops to nearly zero; therefore at minimum the origin
of the open flux is nearly entirely from the polar regions
SIZE OF POLAR REGIONS: S.A. Hess Webber
NOTE:
deToma /
Harvey gets
coronal hole
boundaries
twice as
large in
1996-97
Leif:
Different observatories have large differences in photospheric
magnetograms (factors of up to 4). We don’t know actual value
of magnetic fields at photosphere.
Alex Pestov:
Cross-calibration between HMI(MDI) vs. SOLIS fluxes
line-of-sight component
values depends on how many points you have in your
line (MDI had only 5 points); do you use avg. spectra? Derived
B? Need to account for different pixel sizes.
MDI about 20% too low
Strength of Cycle 24
Alex Pevstov: Cycle 23 similar to Cycle 24 based on
comparison of sunspot number during rise phase. Perhaps
this is not very weak cycle
Lan Jian: Compared rise of cycles 23 and 24:
Cycle 24: Lower geomagnetic activity
Only 2/3 as many ICMEs and they are slower, smaller
CIRs: Weaker peak field strengths, lower pressures