Using sunspot number data from 270 historical stations for the period 1981-2013, we investigate their personal reduction coefficients (k) statistically. Chang & Oh (2012) perform a simulation showing that the k varies with the solar cycle. We try to verify their results using observational data. For this, a weighted mean and weighted standard deviation of monthly sunspot number are used to estimate the error from observed data. We find that the observed error (noise) is much smaller than that used in the simulation. Thus no distinct k-variation with the solar cycle is observed contrary to the simulation. In addition, the probability distribution of k is determined to be non-Gaussian with a fat-tail on the right side. This result implies that the relative sunspot number after 1981 might be overestimated since the mean value of k is less than that of the Gaussian distribution.

Abstract
1. INTRODUCTION
2. METHOD AND RESULT
3. SUMMARY AND DISCUSSION
REFERENCES

• IL-HYUN CHO(Korea Astronomy and Space Science Institute, University of Science and Technology)
• SU-CHAN BONG(Korea Astronomy and Space Science Institute, University of Science and Technology)
• KYUNG-SUK CHO(Korea Astronomy and Space Science Institute, University of Science and Technology)
• JAEIN LEE(Korea Astronomy and Space Science Institute, University of Science and Technology)
• ROK-SOON KIM(Korea Astronomy and Space Science Institute)
• YOUNG-DEUK PARK(Korea Astronomy and Space Science Institute)
• YEON-HAN KIM(Korea Astronomy and Space Science Institute, University of Science and Technology, Big Bear Solar Observatory, New Jersey Institute of Technology) CORRESPONDING AUTHOR