Radio and EUV measurements of the equatorial coronal hole of February 25, 1999

Abstract

We present here the observations of the equatorial coronal hole made at 109 MHz on February 25, 1999 with the Gauribidanur Radioheliograph. The brightness temperature of this coronal hole is about 1:7£105 K.We compare our observations with EUV measurements of EIT onboard SOHO. Ray-tracing calculations show that the observed brightness temperature of this coronal hole can be due a decrement in density by factor of 4 compared to the Newkirk's density model.