Ion Cyclotron Waves in the Solar Wind at 0.3 and 1 AU

A leading candidate to answer the mystery of what heats and accelerates the solar wind is the production and subsequent absorption of ion cyclotron waves. For the first time, we observed these waves in situ at 1 AU using the high-resolution magnetometer data from the STEREO spacecraft. They appear at times when solar wind conditions allow them to propagate to 1 AU. The waves are essentially left-handed polarized, propagating almost parallel to the magnetic field, and below the local proton gyro-frequency in the solar wind frame. Waves propagate both inward and outward from the Sun but are all carried out by the super-Alfvenic solar wind. We also extend our observations to the inner heliosphere based on the Helios data. We compare the properties of these waves at about 0.3 and 1 AU, to understand their radial evolution. Our study will help determine whether the power of these waves extrapolated to the corona is sufficient to accelerate the solar wind.