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THE SPECTROVIDEOMAGNETOGRAPH REVEALS THE TRUE STRENGTH OF WEAK SOLAR FIELDS  

Hal Zirin   Submitted: 2000-05-17 18:03

  ABSTRACT We present new observations of weak solar magnetic fields with a technique, which we term the spectro-videomagnetograph (SP-VMG). We apply tests to hundreds of measurements of the Stokes V-component both for the 5250 line (y=3) and the 5247 line (y=2) and show that the filling factor of the magnetic measurements is near unity, that is the field strengths are actually what we measure them to be for fields above 500 gauss. This contradicts the commonly held belief that the fields are much stronger, but only fill a fraction of the optical resolution element. While we cannot specify the filling factor for fields below 500 gauss, there is now no evidence for a lower limit.

Authors: Harold Zirin and Robert Cameron ;;Solar Astronomy, California Institute of Technology, Pasadena, CA 91125
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Publication Status: Ap J letters (submitted) Preprint is at
Last Modified: 2000-05-17 18:03
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WHICH REGIONS WILL FLARE?  

Hal Zirin   Submitted: 1999-10-27 18:01

We have studied 8 years of active region observations from the USAF/Mt. Wilson data set supplied by the NOAA World Data Center (WDC) to confirm the relation between delta spots and large flares. We found that after correcting errors, we were able to describe relationships between active region size, peak flare SXR flux (measured by GOES 1-8 Å flux), and magnetic classification. We found the Solar Optical Observing Network (SOON) magnetic classification to be reasonably accurate with a few exceptions, but its area measures to be inaccurate for many of the regions. This is partly due to transcription errors and partly, wrong correction for limb projection. Errors could, however, be repaired by intercomp- intercomparison of multiple observations. We confirm Künzel's original idea that regions classified bgd produce many more flares than other regions of comparable size. Almost all substantial flares occurred in regions classified bgd by the Air Force sites. The regions larger than 1000 microhemispheres (mh) classified bgd had nearly 100% probability of producing flares classified X1 or greater. Yet only a half-dozen of those, showing the "island delta" configuration, produced really great activity. There is a general trend for large regions to produce large flares, but it is less significant than the dependence on magnetic class.

Authors: SAMMIS, I., TANG, F. AND ZIRIN, H.
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Publication Status: Solar Physics (submitted)
Last Modified: 1999-10-27 18:01
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THE SPECTROVIDEOMAGNETOGRAPH REVEALS THE TRUE STRENGTH OF WEAK SOLAR FIELDS
WHICH REGIONS WILL FLARE?

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