On the limitations of using metric radio bursts as diagnostic tools for interplanetary coronal mass ejections

Aims. Metric radio bursts are often said to be valuable diagnostic tools for studying the near-sun kinematics and energetics of the interplanetary coronal mass ejections (ICMEs). Radio observations also serve as indirect tools to estimate the coronal magnetic fields. However, how these estimated coronal magnetic fields are related to the magnetic field strength in the ICME at 1 AU has rarely been explored. Our aim was to establish a relation between the coronal magnetic fields obtained from the radio observations very close to the Sun and the magnetic field measured at 1 AU when the ICME arrives at the Earth. Methods. We performed statistical analyses of all metric type II radio bursts in solar cycles 23 and 24 that were found to be associated with ICMEs. We estimated the coronal magnetic field associated with the corresponding CME near the Sun (middle corona) using a split-band radio technique and compared them with the magnetic fields recorded at 1 AU with in situ observations. Results. We found that the estimated magnetic fields near the Sun using radio techniques are not well correlated with the magnetic fields measured at 1 AU using in situ observations. This could be due to the complex evolution of the magnetic field as it propagates through the heliosphere. Conclusions. Our results suggest that while metric radio observations can serve as effective proxies for estimating magnetic fields near the Sun, they may not be as effective close to the Earth. At least, no linear relation could be established using metric radio emissions to estimate the magnetic fields at 1 AU with acceptable error margins.