Two modes of rotation in the solar corona

The pattern of emission coronal green line brightness (Fe XIV 530.3 nm) has been used as a tracer to determine differential rotation of the solar corona. Detailed knowledge of the solar rotation seems to be crucial for understanding of the magnetic field generation within the sun's convection zone and for explanation of the cyclic evolution of solar activity. Spectral variation analysis (SVAN) was applied to our own database of the coronal green line brightness (CGLB) covering almost six solar cycles (1939-2001). It was found that the period of rotation increases from 27 days at the solar equator to a little more than 29 days within the latitudes +/- 40 degrees, displaying in this way much less pronounced differential rotation than the majority of the photospheric phenomena do. At the higher latitudes the rotation period changes very slowly and its value of about 29 days remains up to the polar regions. An assumption on the presence of two modes in the coronal rotation seems to be feasible to explain the results obtained. Comparison of the found results with the latest helioscismic measurements is discussed. (c) 2006 COSPAR. Published by Elsevier Ltd. All rights reserved.