Observing Water Vapour in the Planetary Boundary Layer from the Short-Wave Infrared

Tim Trent,Peter Somkuti,Noëlle Scott,Hartmut Boesch

doi:10.3390/rs10091469

Tim Trent, Peter Somkuti + Show 2 more

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https://doi.org/10.3390/rs10091469

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Abstract

Water vapour is a key greenhouse gas in the Earth climate system. In this golden age of satellite remote sensing, global observations of water vapour fields are made from numerous instruments measuring in the ultraviolet/visible, through the infrared bands, to the microwave regions of the electromagnetic spectrum. While these observations provide a wealth of information on columnar, free-tropospheric and upper troposphere/lower stratosphere water vapour amounts, there is still an observational gap regarding resolved bulk planetary boundary layer (PBL) concentrations. In this study we demonstrate the ability of the Greenhouse Gases Observing SATellite (GOSAT) to bridge this gap from highly resolved measurements in the shortwave infrared (SWIR). These new measurements of near surface columnar water vapour are free of topographic artefacts and are interpreted as a proxy for bulk PBL water vapour. Validation (over land surfaces only) of this new data set against global radiosondes show low biases that vary seasonally between −2% to 5%. Analysis on broad latitudinal bands show biases between −3% and 2% moving from high latitudes to the equatorial regions. Finally, with the extension of the GOSAT program out to at least 2027, we discuss the potential for a new GOSAT PBL water vapour Climate Data Record (CDR).

Highlights

Water vapour is arguably the most important greenhouse gas within the Earth climate system
By substituting this level for a Mixing Layer Height (MLH) derived from the radiosonde profile it can be shown that these different XH2O values are representative of one another
Another variable that contributes to the observed variability is the disparity between boundary layer height (BLH) values used in the Planetary Boundary Layer (PBL) XH2O (Figure 6c)

Summary

Introduction

Water vapour is arguably the most important (non anthropogenic) greenhouse gas within the Earth climate system. With a prevalent positive feedback in the order of 2 W m−2 K−1 (Dessler et al [2]), water vapour acts as the largest amplification mechanism for anthropogenic climate change compared to radiative forcing from greenhouse gases (Chung et al [3]). This makes water vapour critical for climate studies (Held and Soden [4], Trenberth et al [5]). Accurate characterisation of heat and water vapour transport is needed to fully describe coupling between surface hydrology, clouds and precipitation (Prieto et al [8])

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