  The solar inner corona is a region that plays a critical role in energizing
the solar wind and propelling it to supersonic and supra-Alfvenic velocities.
Despite its importance, this region remains poorly understood because of being
least explored due to observational limitations. The coronal radio sounding
technique in this context becomes useful as it helps in providing information
in parts of this least explored region. To shed light on the dynamics of the
solar wind in the inner corona, we conducted a study using data obtained from
coronal radio-sounding experiments carried out by the Akatsuki spacecraft
during the 2021 Venus-solar conjunction event. By analyzing X-band radio
signals recorded at two ground stations (IDSN in Bangalore and UDSC in Japan),
we investigated plasma turbulence characteristics and estimated flow speed
measurements based on isotropic quasi-static turbulence models. Our analysis
revealed that the speed of the solar wind in the inner corona (at heliocentric
distances from 5 to 13 solar radii), ranging from 220-550 km/sec, was higher
than the expected average flow speeds in this region. By integrating our
radio-sounding results with EUV images of the solar disk, we gained a unique
perspective on the properties and energization of high-velocity plasma streams
originating from coronal holes. We tracked the evolution of fast solar wind
streams emanating from an extended coronal hole as they propagated to
increasing heliocentric distances. Our study provides unique insights into the
least-explored inner coronal region by corroborating radio sounding results
with EUV observations of the corona.

Solar and Stellar Astrophysics;Space Physics