A method of evolving synoptic maps of the solar magnetic field, II. Comparison with observations of the polar fields

• Published in: Solar physics 2004-01, Vol.219 (1), p.55-78
• Main Authors: Durrant, C.J., Mccloughan, J.
• Format: Article
• Language: English
• Subjects: Fluctuations; Latitude; Magnetic fields
• ISSN: 0038-0938; 1573-093X
• DOI: 10.1023/B:SOLA.0000021830.88336.86

We describe the application of the synoptic transport equation to simulate the temporal evolution of the magnetic flux over the solar surface. This provides a means of predicting each day both the synoptic maps for the Carrington rotation starting the next day and the instantaneous map of the solar flux over the whole solar surface for the next day. The reliability of the predicted synoptic maps is tested by comparing the locations of the zero-flux contour with those of the observed maps produced by the National Solar Observatory, Kitt Peak and with the locations of Hα filaments measured on filtergrams obtained by the Big Bear Solar Observatory. We conclude that the best match at high latitudes is obtained by long-term simulations (over 20 rotations) with flux updates each rotation between latitudes ±60°. We illustrate the use of the simulations to describe the evolution of the polar fields at the time of the polarity reversals in Cycle 23. The reconstruction of the instantaneous maps is tested by comparison with full-disk magnetograms. The method provides a simple means of estimating the large-scale flux distribution over the whole surface. It does not take account of flux emerging after the central meridian passage each rotation so it is only approximate in the activity belts but provides a reliable map beyond those latitudes.[PUBLICATION ABSTRACT]