Propagation of density fluctuations in the near-Sun environment inferred from radio sounding during Tianwen-1 solar conjunction

The near-Sun environment is the critical region for the acceleration of the primary solar wind. Thanks to a growing number of radio telescopes worldwide, we are able to conduct simultaneous observations of the near-Sun envirnoment with high spatial and temporal resolution using radio sounding. During Tianwen-1 solar conjunction in 2021, we estimate the propagation velocity of density fluctuations using time lag analyses, and track their propagations with ray tracing method. We obtain the radial projected velocity profile, and the distribution of projected velocity regarding the baseline direction and the coherence scale. Further, we determine the wave vector of propagating compressible fluctation by multi-baseline analysis, and find that it may be the slow modes generating from the solar surface by ray tracing. Our results present the unique advantage of radio sounding, and enhance our understanding of the complex picture of fluctuations propagation in the near-Sun environment.