Discovery of Variation in Solar Coronal Rotation with Altitude

Here we report the first measure in radio emission of differential rotation as a function of height in the solar corona. This is derived from the disk-integrated simultaneous daily measurements of solar flux at 11 radio frequencies in the range of 275-2800 MHz. Based on the model calculations, these radio emissions originate from the solar corona in the estimated average height range of similar to (6-15)x 10(4)km above the photosphere. The investigations indicate that the sidereal rotation period at the highest frequency (2800 MHz), which originates from the lower corona around 6 x 10(4)km, is similar to 24.1 days. The sidereal rotation period decreases with height to similar to 23.7 days at the lower frequency (405 MHz), which originates at similar to 13 x 10(4)km. It is difficult to identify clearly the rotational modulation at 275 MHz, perhaps because these missions are significantly affected by the turbulence in the intervening medium. Since these investigations are based on disk-integrated solar flux at radio frequencies, it is difficult to say whether these systematic variations in sidereal rotation period are partly due to the latitudinal differential rotation of the solar corona. It will be interesting to investigate this possibility in the future.