Metrological challenges for measurements of key climatological observables, Part 4: Atmospheric relative humidity

Published

December 15, 2015

Author(s)

Allan H. Harvey, J W. Lovell-Smith, Rainer Feistel, Olaf Hellmuth, Stephanie A. Bell, M Heinonen, J R. Cooper

Abstract

Water in its three ambient phases plays the central thermodynamic role in the terrestrial climate system. Clouds control Earth’s radiation balance, atmospheric water vapour is the strongest “greenhouse” gas, and non-equilibrium relative humidity at the air-sea interface drives evaporation and latent heat export from the ocean. In this paper, we examine the climatologically relevant atmospheric relative humidity, noting fundamental deficiencies in the definition of this key observable. The metrological history of this quantity is reviewed, problems with its current definition and measurement practice are analysed, and options for future improvements are discussed in conjunction with the recent seawater standard TEOS-10. It is concluded that the International Bureau of Weights and Measures, (BIPM), in cooperation with the International Association for the Properties of Water and Steam, IAPWS, along with other international organisations and institutions, can make significant contributions by developing and recommending state-of-the-art solutions for this long standing metrological problem, such as are suggested here.

Citation

Metrologia

Volume

53

Issue

1

Pub Type

Journals

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DOI Link

Keywords

air, atmosphere, climate, humidity, metrology, water

Citation

Harvey, A. , Lovell-Smith, J. , Feistel, R. , Hellmuth, O. , Bell, S. , Heinonen, M. and Cooper, J. (2015), Metrological challenges for measurements of key climatological observables, Part 4: Atmospheric relative humidity, Metrologia, [online], https://doi.org/10.1088/0026-1394/53/1/R40 (Accessed October 28, 2025)