The file contains the S4 data for 340GHz wave through the clear air. The data are obtained by a experimental setup working at 340 GHz, and the wave propagates throug the outdoor atmosphere, and the measured data are processed to the scintillation index data S­4, the meteorogical data are given, too. The meteorogical data includes temperature with the unit of ℃，the water vapour density in unit of g/m3, and the wind speed in unit of m/s. the S4 data is in the last row in the dataset.