Internal rotation of the Sun

Internal rotation of the Sun

. The rotation rate inside the Sun, determined from helioseismology. The outer parts of the Sun exhibit differential rotation, with high latitudes rotating more slowly than equatorial ones. This differential rotation persists to the bottom of the convective zone at 28.7 percent of the way down. The rotation period in days is given at the left axis, and the corresponding angular velocity scale is on the right axis in units of nanoHertz, abbreviated nHz, where 1 nHz = 10-9, or a billionth, of a cycle per second. A rotation rate of 320 nHz corresponds to a period of about 36 days (solar poles), and a rate of 460 nHz to a period of about 25 days (solar equator). The rotation in the outer parts of the Sun, at latitudes of zero (solar equator), 30, 45, 60 and 75 degrees, has been inferred from 144 days of data using the Michelson Doppler Imager, abbreviated MDI, aboard the SOlar and Heliospheric Observatory, or SOHO for short. Just below the convective zone, the rotational speed changes markedly, and shearing motions along this interface may be the dynamo source of the Sun’s magnetism. By examining more than five years of low-order acoustic modes, obtained using the GOLF and MDI instruments aboard SOHO, the rotation rate has been inferred for the deep solar layers (error bars), mainly along the solar equator. There is uniform rotation in the radiative zone, from the base of the convective zone at 0.713 solar radii to about 0.25 solar radii. The acoustic modes (sound waves) do not reach the central part of the energy-generating core. (Courtesy of Alexander G. “Sasha” Kosovichev for the MDI data showing differential rotation in the convective zone, and Sebastien Couvidat, Rafael García and Sylvaine Turck-Chièze for the GOLF/MDI data in the radiative zone. SOHO is a project of international cooperation between ESA and NA)

Copyright 2010, Professor Kenneth R. Lang, Tufts University