The old calcium plages differential rotation latitudinal profile: Its gross and fine structure evolution with the solar cycle
✍ Scribed by Maurizio Ternullo
- Publisher
- Springer
- Year
- 1987
- Tongue
- English
- Weight
- 504 KB
- Volume
- 112
- Category
- Article
- ISSN
- 0038-0938
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✦ Synopsis
This work is a study of the rotational properties of the solar calcium plages, during the time interval 1967-1977; only plages older than 4 days have been the object of this research. We have looked systematically for any significant change occurring during the course of the solar cycle, and any kind of 'anomaly' or fine structure in the differential rotation latitudinal profile. We find that such a profile undergoes a cyclic transformation, making it assume the highest steepness at the solar maximum; a sudden flattening then occurs in the first years of declining activity; the last years of the cycle, as the first years of the next one, are characterized by intermediate steepness values.
Moreover, we find that, in spite of the general belief that the angular rotation rate is continuously decreasing with increasing heliographic latitude, at least two inversions do exist of such an overall tendency:
(i) A narrow, minimal angular-rotation-rate strip lies very close to the equatorward margin of the plage production band; this feature shifts continuously, in a wave-like manner, throughout the solar cycle, from 15/18 ~ to 3/6 ~ latitude.
(ii) A narrow, maximal angular-rotation-rate strip has been observed lying in the neighbourhood of the poleward margin of the activity band; a process of continuous transformation of the rotation rate profile is always active, in a narrow latitude strip on the equatorward side of such a feature, generating new features of the same kind, which replace the older ones, that disappeared due to the equatorward shift of the plage zone. All that simulates an equatorward shift of the observed 'anomalies'; we observed them until the minimum activity epoch (1976), at 15/18 ~ latitude. Some relations of these features with both torsional waves (Howard and LaBonte, 1980) and magnetic activity are briefly discussed.