Large-scale structure of the sun's corona from radio observations using the Clark Lake Radioheliograph

We present meterwave maps of the solar corona made with the Clark Lake Radioheliograph at 30.9, 50, and 73.8 MHz for one solar rotation. We compare and contrast them with optical data: 10830 Å maps, white-light coronagraph images (SOLWIND and Mauna Loa K coronameter) and forbidden line scans. Most of the sources in the radio maps persist for two days or more, and appear to rotate approximately with the solar rate. A coronal hole seen against the disk at all three frequencies shows interesting similarities and significant differences with the optical signatures of the hole. Elongated features of the 50 MHz corona correspond rather well to the azimuthal position of white light streamers seen in SOLWIND images. Synoptic charts made from the radio maps show overall similarities to synoptic charts constructed from (limb) coronagraph data. Some of the differences may result from the different weightings given by the radio and optical data to density and temperature, or by the different sensitivities to non-radial geometries. We show that the combined use of meter wave and optical images provide considerable new insights into the three-dimensional structure of the low to middle corona.     

Comparison of the deflection of the vertical components computed by astro-geodetic, gravimetric and topographic-isostatic techniques

Three different types of deflection of the vertical components wre computed at a number of selected astronomical stations in the south central United States. Astro-geodetic deflections were obtained from the differences between the astronomical and geodetic coordinates of each station. Gravimetric deflections were computed from isostatic anomalies. The isostatic isoanomaly charts used in this computation were constructed from data obtained by correcting point values taken from existing free-air isoanomaly charts for the effects of the Bouguer reduction and the topographic-isostatic reduction. It is felt that this procedure substantially reduces the labor involved in making isostatic reductions without sacrificing accuracy appreciably. Topographic-isostatic deflections were computed by Hayford's Method as modified by Orlin. The differences between the three types of deflection components are compared and conclusions made concerning their accuracy and utility. Aerounautical Chart and Information Center