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

Southern hemisphere: “Rush to the Poles” is not apparent

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

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)

• Identifies open/closed field regions (e.g. coronal hole footprints)

• Identifies location of base of the heliospheric current sheet

(Image from Yan Li)

Source Surface

What PFSS models suggest about the solar cycle variation of

IMF strengthLUHMANN

C.Lee et al., Sol Phys 2010

Rss=1.5 (red),1.8 (blue) ,2.5 (black)

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

From C.Lee et al. Sol Phys 2011

From Robbrecht et al., ApJ 2009

Are CMEs (or CME ‘legs’) for increase during maximum activity? Or are there durable open flux changes related to the increased surface fields?

These are likely what produce the smaller transients seen in images from STEREO HI

(Cartoons from Wang et al., ApJ paper;STEREO HI movie)

Fisk: Disconnected blobs won’t account for increase in IMF

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)

Owens et al., 2009

• Correlation between CME rate and field strength – (neglects disconnection of

open magnetic flux) • Note disagreement in the

extended minimum

SCHWADRON Heliospheric Magnetic Flux Balance

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| = 2/4R1

2 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

Smith et al. Poster

Schwadron et al., Astrophys. J. Lett., 722, L132, 2010.

Offset due to flux conversion

HOWEVER: coronal holes evolve much more rapidly

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 fluxesline-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

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, smallerCIRs: Weaker peak field strengths, lower pressures

Strength of Cycle 24