Rigorous determination of stratospheric water vapor trends from MIPAS observations

The trend of stratospheric water vapor as a function of latitudeis estimated by the MIPAS measurements by means of a new method thatuses the measurement space solution. The method uses all the informationprovided by the observations avoiding the artifacts introduced by the apriori information and by the interpolation to different vertical grids. Theanalysis provides very precise values of the trends that, however, are limitedby a relatively large systematic error induced by the radiometric calibrationerror of the instrument. The results show in the five years from 2005 to2009 a dependence on latitude of the stratospheric (from 37 to 53 km) watervapor trend with a positive value of (0.41 ± 0.16)%yr-1 in the northernhemisphere and less than 0.16%yr-1 in the southern hemisphere.