Currently, there is no continuous water vapor sensor which can observe water vapor amount over the ocean.
One of the methods is to assimilate PWV as observation data at the surface where water vapor amount is large.
Then spatial distribution of temperature and adsorbed vapor amount are obtained with respect to time in adsorption desorption cycles.
Water vapor absorption bands tend to exhibit larger differences between model and measurement as uncertainties in temperature and water vapor amount increase model errors.
Therefore, as a height correction, the radiosonde observed water vapor amount between the radiosonde launching point to the GNSS antenna was removed from radiosonde observations.
This method modifies water vapor amount mainly near the surface by using the vertical localization because the sampling error in the background error correlation between PWV and water vapor amount generally becomes larger as the layer of the model is distant from the surface.
As a result, GNSS-derived PWV is estimated as a spatially averaged water vapor amount within an inverse cone defined by the elevation cutoff angle, resulting in smoothed local-scale PWV fluctuations.
In the upper part of trapped mountain waves, there were little difference of water vapor amount between heights of peaks and troughs, resulting in smaller perturbation refractivity at that height than that in the lower part of trapped waves.
The ΔPWV maps, representing the time differences of the PWV, highlight both positive and negative time differences, corresponding to an increase and decrease in the water vapor amount in the atmosphere, respectively, and help to interpret the PWV evolution.
As already explained in section "GNSS-derived PWV observed by the Uji network", PWVCON is estimated as a spatially averaged water vapor amount within an inverse cone defined by the low elevation cutoff angle.
However, we needed to modify the water vapor amount of the model also at the middle troposphere because Uji was located at the south side of a stationary front and the middle troposphere was very humid during the Uji heavy rainfall event.
