Mirror mode waves: Messengers from the coronal heating region

An ongoing problem in heliospheric physics is the mechanism for the heating and acceleration of the solar wind. One process that has been identified as a potentially important source of energy input is ion cyclotron waves, but except for some evidence of perpendicular heating of heavy ions obtained by remote sensing, it has proven difficult to establish their overall effectiveness. We suggest that mirror mode waves in the solar wind may be a signature of the presence of these waves in the corona. Mirror mode waves and ion cyclotron waves can be cogenerated by anisotropic ion distribution functions as demonstrated by their joint growth in the low beta conditions of Saturn's inner magnetosphere. We infer from this example and from the high occurrence rates of mirror mode waves at the closest distances to the Sun probed by spacecraft that the inner corona is also replete with ion cyclotron waves. Understanding quantitatively how these two wave modes share the free energy of the corona could help us to understand the ion‐cyclotron wave generation process and its role in solar wind heating and acceleration.