High-latitude solar rotation traced by magnetic elements

Abstract

Sequential observations at Huairou Solar Observation Station, China, and Kitt Peak, U.S.A., show that polar magnetic elements can live from several to more than 58 hours. This enables measurement of the solar rotation rate near the polar region by tracing magnetic element motions. With observations carried out on 8–15 July 1997, we identify and trace more than 1300 elements at north heliographic latitudes between 55°–85° using two methods, and fit the mean sidereal rotation rate as ω=14.0±0.54−(2.24±1.22)sin2θ−(1.78±0.79)sin4θ deg per day.