Thin‐Plate Spline Interpolation Spatial Modelling of <scp>GNSS</scp> Retrieved Water Vapour Over Northeast Japan

ABSTRACT The study investigated precipitable water vapour (PWV) variation over Northeast Japan by using more than two decades (2000 to 2022) of measurements. These data have been extracted from 36 Global Navigation Satellite System (GNSS) networks and interpolated with thin‐plate spline interpolation to understand its spatial variation over the region. PWV annual and seasonal variation is studied and correlated with ERA5 reanalysis observations. These PWV variation shows that the northern part of Northeast Japan which is located at higher latitudes showed a smaller magnitude compared to PWV magnitude in the southern part of low latitudes. This is possible because the cold air is drier and the warm air holds more moisture in the lower southern part. The correlation coefficient variation based on geographical area is visible which quantifies the consistency between GNSS PWV and ERA5 and visualises the effects in sampling. The southern part, where the correlation coefficients are very high (more than 0.80), indicates good agreements between GNSS PWV and ERA5 values and can be considered well‐sampled observations. Moreover, the correlation coefficients drop the values to approximately 0.40–0.60 for poorly sampled observations on the northern coast, pointing out the interannual inconsistency of PWV measurements, which are loosely related to ERA5 observations. Finally, the correlation coefficient between PWV with surface temperature and atmospheric pressure over Northeast Japan is investigated. This is clear from the results that the correlation coefficient between PWV and temperature is around 0.98 for each site, indicating that PWV has a very high dependency on surface temperature. The correlation coefficient between PWV and pressure is highly negative around −0.80, indicating their inverse relationship. We believe the outcomes from this study will contribute to a better understanding of PWV over Japan and the future refinements of atmospheric models over the East Asian region.