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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.
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The Rise of Solar Cycle 24: Magnetic Fields from the Dynamo through the Photosphere and Corona and Connecting to the Heliosphere
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.
‘Rush to Poles’
What PFSS models suggest about the solar cycle variation of IMF strength
(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 2010
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
Fisk: Disconnected blobs won’t account for increase in IMF
(Cartoons from Wang et al., ApJ paper;
STEREO HI movie)
U-shaped blobs visible in STEREO HI images.
|B| = 2/4R12 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 day1;
fhi = 3 day1;
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)
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
Different observatories have large differences in photospheric magnetograms (factors of up to 4). We don’t know actual value of magnetic fields at photosphere.
Cross-calibration between HMI(MDI) vs. SOLIS fluxes
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
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