Solar Cycle 24 Group C
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from a combination of both effects. | from a combination of both effects. | ||
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MDI: Saturation in sunspots (MDI underestimates LOS field in sunspots) | MDI: Saturation in sunspots (MDI underestimates LOS field in sunspots) | ||
Revision as of 18:09, 8 January 2009
Tue III
Aimee Norton:
Emergence of sunspots early in a solar cycle might be tipped, evidence for Cycle 23, not known for earlier cycles (or for Cycle 24). Norton & Gilman (2005), and Norton, Raouafi & Petrie (2008).
Evidence is that dipole is always tipped for previous minimum, from streamer locations from LASCO. Generally agrees with PFSS-style models.
Is there evidence for off-axis polar cap? Hard to tell from magnetograms due to incomplete coverage of polar fields (especially for the one pole that tilted away from earth). From PFSS models, tilt ranged form 2 to 6 degrees. Was the azimuthal angle stable? For isolated periods (e.g., CR1915-1919), yes.
Todd: New cycle fields emerge with a pattern that suggests a systematic asymmetry, and it might not be related to the polar cap arrangement of flux, and so the dipole tilt angles shown here results from a combination of both effects.
Magnetogram calibration discussion:
MDI: Saturation in sunspots (MDI underestimates LOS field in sunspots)
MDI: Zero-point issues, maybe related to secular trends in monopole component of surface field configuration.
Hinode is showing us that fields are complicated! HMI line selection paper gives some idea of uncertainties in, say, MDI measurements of LOS field. In many cases, there are many field components in even a Hinode pixel.
Polar fields are particularly troublesome, given their steep viewing angle, and particularly important given that they determine the heliospheric flux during solar minimum.
A study comparing MDI and Hinode B_LOS should probably be done. Recent MDI recalibration was due to multiple line studies by Roger Ulrich at UCLA, and resulted in slightly weaker fields at poles.
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