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FORUM: Unique Far-Infrared Satellite Observations to Better Understand How Earth Radiates Energy to Space

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  • 1 National Institute of Optics, CNR, Florence, Italy
  • | 2 National Centre for Earth Observation, Imperial College London, London, United Kingdom
  • | 3 Universität Hamburg, Hamburg, Germany
  • | 4 IPSL–Sorbonne Université, UPMC, Paris, France
  • | 5 Institute of Applied Physics, CNR, Florence, Italy
  • | 6 National Institute of Optics, CNR, Florence, Italy
  • | 7 Institute of Atmospheric Sciences and Climate, CNR, Bologna, Italy
  • | 8 Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California
  • | 9 Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, Michigan
  • | 10 Laboratoire d’Optique Atmosphérique, Université de Lille, France
  • | 11 CNRM, Université de Toulouse, Météo-France, CNRS, Toulouse, France
  • | 12 Department of Physics and Astronomy, University of Bologna, Bologna, Italy
  • | 13 NASA Langley Research Center, Hampton, Virginia
  • | 14 Space and Atmospheric Physics Group, Imperial College London, London, United Kingdom
  • | 15 ESTEC, ESA, Noordwijk, Netherlands
  • | 16 National Institute of Optics, CNR, Florence, Italy
  • | 17 IEK-7, Forschungszentrum Jülich, Germany
  • | 18 Space and Atmospheric Physics Group, Imperial College London, London, United Kingdom
  • | 19 Met Office, Exeter, United Kingdom
  • | 20 Scuola di Ingegneria, Università degli Studi della Basilicata, Potenza, Italy
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Abstract

The outgoing longwave radiation (OLR) emitted to space is a fundamental component of the Earth’s energy budget. There are numerous, entangled physical processes that contribute to OLR and that are responsible for driving, and responding to, climate change. Spectrally resolved observations can disentangle these processes, but technical limitations have precluded accurate space-based spectral measurements covering the far infrared (FIR) from 100 to 667 cm−1 (wavelengths between 15 and 100 µm). The Earth’s FIR spectrum is thus essentially unmeasured even though at least half of the OLR arises from this spectral range. The region is strongly influenced by upper-tropospheric–lower-stratospheric water vapor, temperature lapse rate, ice cloud distribution, and microphysics, all critical parameters in the climate system that are highly variable and still poorly observed and understood. To cover this uncharted territory in Earth observations, the Far-Infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission has recently been selected as ESA’s ninth Earth Explorer mission for launch in 2026. The primary goal of FORUM is to measure, with high absolute accuracy, the FIR component of the spectrally resolved OLR for the first time with high spectral resolution and radiometric accuracy. The mission will provide a benchmark dataset of global observations which will significantly enhance our understanding of key forcing and feedback processes of the Earth’s atmosphere to enable more stringent evaluation of climate models. This paper describes the motivation for the mission, highlighting the scientific advances that are expected from the new measurements.

© 2020 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Luca Palchetti, luca.palchetti@cnr.it

Abstract

The outgoing longwave radiation (OLR) emitted to space is a fundamental component of the Earth’s energy budget. There are numerous, entangled physical processes that contribute to OLR and that are responsible for driving, and responding to, climate change. Spectrally resolved observations can disentangle these processes, but technical limitations have precluded accurate space-based spectral measurements covering the far infrared (FIR) from 100 to 667 cm−1 (wavelengths between 15 and 100 µm). The Earth’s FIR spectrum is thus essentially unmeasured even though at least half of the OLR arises from this spectral range. The region is strongly influenced by upper-tropospheric–lower-stratospheric water vapor, temperature lapse rate, ice cloud distribution, and microphysics, all critical parameters in the climate system that are highly variable and still poorly observed and understood. To cover this uncharted territory in Earth observations, the Far-Infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission has recently been selected as ESA’s ninth Earth Explorer mission for launch in 2026. The primary goal of FORUM is to measure, with high absolute accuracy, the FIR component of the spectrally resolved OLR for the first time with high spectral resolution and radiometric accuracy. The mission will provide a benchmark dataset of global observations which will significantly enhance our understanding of key forcing and feedback processes of the Earth’s atmosphere to enable more stringent evaluation of climate models. This paper describes the motivation for the mission, highlighting the scientific advances that are expected from the new measurements.

© 2020 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Luca Palchetti, luca.palchetti@cnr.it
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