23 Feb 2022
23 Feb 2022
Status: this preprint is currently under review for the journal ACP.

Analysis of global trends of total column water vapour from multiple years of OMI observations

Christian Borger, Steffen Beirle, and Thomas Wagner Christian Borger et al.
  • Satellite Remote Sensing Group, Max Planck Institute for Chemistry, Mainz, Germany

Abstract. In this study, we investigate trends in total column water vapour (TCWV) retrieved from measurements of the Ozone Monitoring Instrument (OMI) for the time range between January 2005 to December 2020. The trend analysis reveals on global average an annual increase in the TCWV amount of approximately +0.056 kg m−2 y−1 or +0.24 % y−1. After the application of a Z-test (to the significance level of 5 %) and a false discovery rate test to the results of the trend analysis, mainly positive trends remain, in particular over the Northern subtropics in the East Pacific.

Combining the relative TCWV trends with trends in air temperature, we also analyze trends in relative humidity (RH) on local scale. This analysis reveals that the assumption of temporally invariant RH is not always fulfilled: we obtain increasing and decreasing RH trends over large areas of the ocean and land surface and also observe that these trends are not limited to arid and humid regions, respectively. For instance, we find decreasing RH trends over the (humid) tropical Pacific ocean in the region of the intertropical convergence zone. Interestingly, these decreasing RH trends in the tropical Pacific ocean coincide well to decreasing trends in precipitation.

Additional investigations of the global response of TCWV to changes in (surface) air temperature show that the relative TCWV trends do not follow a Clausius-Clapeyron response (i.e. 6–7 % K−1) and are about 2 to 3 times higher even for the case of global averages. Moreover, by combining the trends of TCWV, surface temperature, and precipitation we derive trends for the global water vapour turnover time (TUT) of approximately +0.02 d y−1. Also, we obtain a TUT rate of change of around 11 % K−1 which is 2 to 4 times higher than the values obtained in previous studies.

Christian Borger et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-149', Kevin Trenberth, 03 Mar 2022
  • RC2: 'Comment on acp-2022-149', Chunlüe Zhou, 06 Apr 2022

Christian Borger et al.

Christian Borger et al.


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Short summary
In this study, we analyze trends of total column water vapour (TCWV) using multiple years of satellite observations and find on global average an increase in the TCWV amount by about 0.24 % per year. Further investigations of the hydrological cycle reveal that the assumption of temporally invariant relative humidity is not always fulfilled and that its responses to global warming are 2 to 4 times higher than theoretically expected or previously reported values.