This repository archives codes for analysis and plot presented in Abdillah et al. (2018): "Strong linkage of El Niño-Southern Oscillation to the polar cold air mass in the Northern Hemisphere". The codes are written in GrADS, Octave, and NCL format. The repository also includes a Fortran package for isentropic polar cold air mass diagnosis as in Iwasaki et al. (2014). The package was specifically created by Dr. Y. Kanno. Reference: Abdillah, M. R., Kanno, Y., Iwasaki, T. (2018). Strong linkage of El Niño‐Southern Oscillation to the polar cold air mass in the Northern Hemisphere. Geophysical Research Letters, in press. https://doi.org/10.1029/2018GL077612 Iwasaki, T., Shoji, T., Kanno, Y., Sawada, M., Ujiie, M., & Takaya, K. (2014). Isentropic Analysis of Polar Cold Airmass Streams in the Northern Hemispheric Winter. Journal of the Atmospheric Sciences, 71(6), 2230–2243. https://doi.org/10.1175/JAS-D-13-058.1