Comparison of precipitable water via JRA-55 and GPS in Japan considering different elevations

Abstract

This study compared precipitable water vapor (PWV) of JRA-55 and GPS in Japan by considering different elevations in JRA-55 (geopotential height) and GPS (antenna height) because JRA-55’s PWV is pointed out to be underestimated as a result of dry bias in the middle and upper troposphere in the forecast model. We selected 26 grid points of JRA-55 over Japanese islands and the respective nearest 26 GPS stations operated by the Geospatial Information Authority of Japan. First, we linearly converted the geopotential height of 26 grid points to air pressure at the antenna height, assuming the sea surface and 1500-m height corresponding to 1013.25 hPa and 850 hPa, respectively. We then calculated JRA-55’s PWV by vertically integrating specific humidity in the pressure coordinate system using the antenna height from July 2010 through December 2012 (designated as “corrected PWV”). At 22 grid points among the 26, the geopotential height is higher than the antenna height, where the majority of the data of PWV provided by the JRA project was smaller than that retrieved from GPS. The underestimation of the corrected PWV decreased, although 65% of them remained underestimated. The underestimation of the corrected PWV increased in winter and decreased in summer.