Slow solar wind acceleration through the middle corona: Spacecraft radio studies

The “Middle Corona”, defined by recent consensus as the region spanning 1.5–6 solar radii (R ⊙ , heliocentric), is an important zone through which several structural and dynamic changes occur in coronal streamer regions. Among these a regime change from high density, closed magnetic field structures to open of much lower electron concentration. Along with this complex restructuring, forming slow wind channeled accelerated middle corona. Solar (SW) outflow speeds can be estimated trans-coronal radio observations. method frequency fluctuation (FF) analysis considers variations arising density inhomogeneities crossing sensing line-of-sight (LOS). Below 2 R where SW beginning form speed expected below acoustic wave speed, FF attributed oscillations waves path. With increasing helioaltitudes corona, are dominated disturbances advected across LOS. This property enables estimation at various heliodistances. plasma believed enter corona subsonic state, then accelerate exit generally supersonic, but sub-Alfvénic flows. Trans-coronal complements imaging other remote observations, helps bridge observational gap full distance range Radio techniques enrich study wind, should utilized next-generation, multiwavelength campaigns that tackle challenging physics acceleration.