Hale long sought the polar field, and its presence was detected by the Babcocks and by Howard in the form of a conglomeration of fairly strong field elements of like polarity. While a NASA panel recently pronounced that the polar field cannot be measured, it is easily detected and has been studied by various groups. The "polar field" is a crown of strong magnetic elements that appears at each minimum coextensive with the polar coronal holes (indeed, apparently producing them). In between is an irregular continuous background field of about 0.05 gauss, which Zhang and Zirin recently found had a net polarity opposite the dominant field in that hemisphere. This is the first detection of a continuous field on the Sun, all others being concentrated in small elements. This field is not seen in equatorial unipolar regions. Despite its wide extent, the uniform field has less flux than a single unipolar element. The location of zero is crucial to these measurements. The above detection depended on the difference of sign between the two poles. We have carried forward these measurements by regularly reversing the polarity of the modulator of the Leighton-Smithson videomagnetograph at BBSO, which fixes the zero. So far the results are mixed, favoring the presence of the background fields but with some negative results. The complete results to date will be present. Other parts of the Sun give zero uniform field down to the 0.05 gauss limit.
AAS/Solar Physics Division Meeting #28
- Pub Date:
- May 1997