Coronal holes at 11.5 and 21 cm observed with the Arecibo radio telescope

Abstract

CORONAL holes have been seen in several regions of the electromagnetic spectrum. Observations have been made in the X-ray and UV (ultraviolet) regions by several groups^1,2. These observations, however, can be made only from space and are not always available. Coronal holes have also been identified from spectroheliograms made from the ground³ at the 10,830 Å line of He. The 10,830 Å spectroheliograms are now obtained on a regular basis at Kitt Peak. In the radio domain several groups have attempted to identify coronal holes. These include observations at 80 and 160 MHz with the Culgoora radio heliograph⁴, at 10.7 GHz with the Bonn 100m antenna⁵, and at 85 GHz with the NRAO 11 m antenna⁶. Our observations reported here made at 1,420 and 2,600 MHz with the 1,000ft Arecibo radio telescope show the presence of coronal holes very clearly and provide for the first time an excellent matching of coronal hole images obtained from decimetre solar radio maps and 10,830 Å spectroheliograms.