Abstract
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 multivariable marine humidity product, gridded monthly at a
5∘×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 HadISDH.land, 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
digitized metadata. HadISDH.marine data, derived diagnostics, and plots are available at
http://www.metoffice.gov.uk/hadobs/hadisdh (last access: June 2019) and https://doi.org/10.5285/463b2fcd6a264a39b1e3249dab16c177 (Willett et
al., 2020).
Subject
General Earth and Planetary Sciences
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