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Chromospheric Magnetic Field Measurements in a Flare and an Active Region Filament  

John Harvey   Submitted: 2012-03-08 14:41

Intensity (I) and circular polarization (V) spectra using the 854 nm line of Ca II with 3.65 pm spectral and 1 arcsecond spatial sampling were obtained with the SOLIS vector spectromagnetograph on 2011 November 8. An active region filament showing Doppler shifts as large as 50 km s-1 and an unrelated C1.8 flare were observed. Line-of-sight flux density estimates of the magnetic field (Blos) were mapped as a function of wavelength in both of these features using the weak-field Zeeman-splitting approximation that V is proportional to the first derivative of I. The filament had a large amount of structure in intensity and velocity but remarkably little Blos structure, which varied smoothly from 35 to 55 G. Two flare emission kernels showed average Blos values of 415 and -215 G, about 85% of the underlying photospheric fields. Counter to this modest strength decrease with increasing height, in nearly all parts of the brighter flare kernel there appears to be a substantial increase of Blos at the height corresponding to the central core of the 854 nm line. This increase, if verified, may be related to compression of the chromosphere associated with chromospheric evaporation. Alternatively, it might indicate that the profile of the line core is narrowed in the magnetic part of the flare kernel. The results presented here are generally similar to previous, rather sparse observations. Observations of the type reported here are made daily and could be used to greatly increase knowledge about the chromospheric magnetic field in active solar features.

Authors: Harvey, J.W.
Projects: None

Publication Status: Solar Physics (submitted)
Last Modified: 2012-03-09 21:05
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Sun-as-a-Star, Chromospheric Lines, 1974-2009  

John Harvey   Submitted: 2009-11-10 15:01

We update the McMath-Pierce spectral line scan archives for Ca II K, He I 10830 A, Ca II 8542 A, and H I 6562 A, both for full disk and center disk. The Ca K3 intensity feature displays a peak-to-peak activity cycle modulation of ~37% and He 10830 Å about 100%. SOLIS observations of the Ca K index suggest a cycle 23-24 minimum in late 2008 followed by a 0.7% rise by late 2009. Other McMath-Pierce indices display no evidence yet of cycle 24. Center-disk Ca K index measurements (optically averaged over the central 2-arcmin), show no particular response to cycle activity, i.e. the quiet disk is constant. A similar null response is found for the center-disk Wilson-Bappu effect.

Authors: Livingston, W., White, O. R., Wallace, L., Harvey, J.

Publication Status: NSO Workshop 25, to be published in Mem. S. A. It.
Last Modified: 2009-11-14 09:51
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Seething Horizontal Magnetic Fields in the Quiet Solar Photosphere  

John Harvey   Submitted: 2007-02-15 12:08

The photospheric magnetic field outside of active regions and the network has a ubiquitous and dynamic line-of-sight component that strengthens from disk center to limb as expected for a nearly horizontal orientation. This component shows a striking time variation with an average temporal rms near the limb of 1.7 G at ~3'' resolution. In our moderate resolution observations the nearly horizontal component has a frequency variation power law exponent of -1.4 below 1.5 mHz and is spatially patchy on scales up to ~15 arcsec. The field may be a manifestation of changing magnetic connections between eruptions and evolution of small magnetic flux elements in response to convective motions. It shows no detectable latitude or longitude variations.

Authors: J. W. Harvey, D. Branston, C. J. Henney, C. U. Keller, and the SOLIS and GONG Teams
Projects: None

Publication Status: ApJL (submitted)
Last Modified: 2007-02-16 10:16
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Abstracts by Author
Chromospheric Magnetic Field Measurements in a Flare and an Active Region Filament
Sun-as-a-Star, Chromospheric Lines, 1974-2009
Seething Horizontal Magnetic Fields in the Quiet Solar Photosphere

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