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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

  28 Nov 2019

28 Nov 2019

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A revised version of this preprint is currently under review for the journal ESSD.

Development of the HadISDH marine humidity climate monitoring dataset

Kate Willett1, Robert Dunn1, John Kennedy1, and David Berry2 Kate Willett et al.
  • 1Met Office Hadley Centre, Exeter, UK
  • 2National Oceanography Centre, Southampton, UK

Abstract. Atmospheric humidity plays an important role in climate analyses. Here we describe the production and key characteristics of a new quasi-global marine humidity product intended for climate monitoring, HadISDH.marine. It is an in-situ based multi-variable marine humidity product, gridded monthly at a 5° by 5° spatial resolution from January 1973 to December 2018 with annual updates planned. Currently, only reanalyses provide up to date estimates of marine surface humidity but there are concerns over their long-term stability. As a result, this new product makes a valuable addition to the climate record and will help address some of the uncertainties around recent changes (e.g. contrasting land and sea trends, relative humidity drying). Efforts have been made to quality control the data, ensure spatial and temporal homogeneity as far as possible, adjust for known biases in non-aspirated instruments and ship heights, and also estimate uncertainty in the data. Uncertainty estimates for whole-number reporting and for other measurement errors have not been quantified before for marine humidity. This is a companion product to, which, when combined will provide methodologically consistent land and marine estimates of surface humidity. The spatial coverage of HadISDH.marine is good over the Northern Hemisphere outside of the high latitudes but poor over the Southern Hemisphere, especially south of 20° S. The trends and variability shown are in line with overall signals of increasing moisture and warmth over oceans from theoretical expectations and other products. Uncertainty in the global average is larger over periods where digital ship metadata are fewer or unavailable but not large enough to cast doubt over trends in specific humidity or air temperature. Hence, we conclude that HadISDH.marine is a useful contribution to our understanding of climate change. However, we note that our ability to monitor surface humidity with any degree of confidence depends on the continued availability of ship data and provision of digitised metadata.

HadISDH.marine data, derived diagnostics and plots can be found at

Kate Willett et al.

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Kate Willett et al.

Kate Willett et al.


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Latest update: 10 Aug 2020
Short summary
We describe the development and validation of a new near-global gridded marine humidity monitoring product, HadISDH.marine, from air temperature and dew point temperature reported by ships. Erroneous data, biases and inhomogeneities have been removed where possible through checks for outliers, supersaturated values, repeated values, and adjustments for known biases in non-aspirated instruments and ship heights. We have also estimated uncertainty in the data at the gridbox and regional level.
We describe the development and validation of a new near-global gridded marine humidity...