We investigate 20 post-coronal mass ejection (CME) blobs formed in the post-CME current sheet (CS) that were observed by K-Cor on 2017 September 10. By visual inspection of the trajectories and projected speed variations of each blob, we nd that all blobs except one show irregular \zigzag" trajectories resembling transverse oscillatory motions along the CS, and have at least one oscillatory pattern in their instantaneous radial speeds. Their oscillation periods are ranging from 30 to 91 s and their speed amplitudes from 128 to 902 kms􀀀1. Among 19 blobs, 10 blobs have experienced at least two cycles of radial speed oscillations with dierent speed amplitudes and periods, while 9 blobs undergo one oscillation cycle. To examine whether or not the apparent speed oscillations can be explained by vortex shedding, we estimate the quantitative parameter of vortex shedding, the Strouhal number, by using the observed lateral widths, linear speeds, and oscillation periods of the blobs. We then compare our estimates with theoretical and experimental results from MHD simulations and uid dynamic experiments. We nd that the observed Strouhal numbers range from 0.2 to 2.1, consistent with those (0.15{3.0) from uid dynamic experiments of blu spheres, while they are higher than those (0.15{0.25) from MHD simulations of cylindrical shapes. We thus nd that blobs formed in a post-CME CS undergo kinematic oscillations caused by uid dynamic vortex shedding. The vortex shedding is driven by the interaction of the outward-moving blob having a blu spherical shape with the background plasma in the post-CME CS.

Introduction
Data and Analysis
Results
Summary and Discussion
Acknowledgments
References

• Jae-Ok Lee(Korea Astronomy and Space Science Institute, Daejeon 34055, Korea) Corresponding author
• Kyung-Suk Cho(Korea Astronomy and Space Science Institute, Daejeon 34055, Korea, University of Science and Technology, Daejeon 34055, Korea)
• Valery M. Nakariakov(School of Space Research, Kyung Hee University, Yongin-si 17104, Korea, Centre for Fusion, Space and Astrophysics Department of Physics, University of Warwick, Coventry CV4 7AL, UK)
• Harim Lee(School of Space Research, Kyung Hee University, Yongin-si 17104, Korea)
• Rok-Soon Kim(Korea Astronomy and Space Science Institute, Daejeon 34055, Korea)
• Soojeong Jang(Korea Astronomy and Space Science Institute, Daejeon 34055, Korea)
• Heesu Yang(Korea Astronomy and Space Science Institute, Daejeon 34055, Korea)
• Sujin Kim(Korea Astronomy and Space Science Institute, Daejeon 34055, Korea)
• Yeon-Han Kim(Korea Astronomy and Space Science Institute, Daejeon 34055, Korea)