Download
1 / 17
170 likes | 180 Views
This research delves into Solar Cycle 24 magnetic field dynamics through the photosphere and corona, exploring correlations with the heliosphere and potential implications for Solar Cycle 25. Analysis includes observations of the Rush to the Poles signature in the Northern hemisphere, while the absence of this phenomenon is noted in the Southern hemisphere. Utilizing smoothed GONG torsional oscillation data and FeXIV observations, the study investigates the connection between Torsional Oscillation Shear and the Extended Solar Cycle. Observations of polar crown filaments, magnetic flux movements, and FeXIV intensity shifts prompt questions about coronal temperature effects and solar maximum timing. Models examining the solar cycle variation of Interplanetary Magnetic Field (IMF) strength shed light on potential flux variations and CME occurrences throughout the solar cycle. The study also discusses open magnetic flux dynamics, CME rates, and the role of heliospheric magnetic balance in shaping solar activity peaks.
E N D
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)
What PFSS models suggest about the solar cycle variation of IMF strength LUHMANN 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 2010
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| = 2/4R12 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)
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
