far-infrared spectral radiance observations of the arctic atmosphere neil humpage, paul green:...
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![Page 1: Far-infrared Spectral Radiance Observations of the Arctic Atmosphere Neil Humpage, Paul Green: Imperial College London Dave D. Turner: University of Wisconsin](https://reader034.vdocument.in/reader034/viewer/2022051819/5515fe81550346a2308b4ad8/html5/thumbnails/1.jpg)
Far-infrared Spectral Radiance Observations of the Arctic Atmosphere
Neil Humpage, Paul Green: Imperial College London
Dave D. Turner: University of Wisconsin – Madison
Eli Mlawer: AER Inc, Lexington, Massachusetts
Ed Westwater: Cooperative Institute for Research in Environmental Sciences, Boulder, Colorado
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Overview
Why make far-infrared observations of the arctic atmosphere?
Description of RHUBC:• Spectrometers – TAFTS and AERI-ER• Other instruments
Line-by-line radiative transfer modelling using LBLRTM
Case study: 10th March 2007• Sensitivity of modelled radiance spectra to column water vapour and foreign broadened H2O continuum strength
• Comparison with TAFTS and AERI-ER observed spectra
Summary
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Why make far-infrared observations of the arctic atmosphere?
• The Earth’s radiative emission spectrum peaks in the FIR
• 27-35% of clear sky OLR is at far-infrared wavelengths (Sinha and Harries 1995)
• Cooling of the upper troposphere to space is predominantly via the H2O rotation band (Clough et al 1992)• Strength and nature of the water vapour continuum remains uncertain – few atmospheric observations to date (Tobin et al 1999, Serio et al 2008)• Very dry arctic winter atmosphere enables ground based observations of water vapour absorption spectroscopy
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Radiative Heating in Under-explored Bands Campaign
• RHUBC aims:• Water vapour spectroscopy
through clear sky observations• Instrument cross-calibration and
validation (TAFTS vs. AERI-ER)• Investigation of radiative
properties of sub-arctic cirrus
• February 22nd – March 14th 2007
• Typical temperatures of -30°C
• Low PWV• February 2007 median: 1.76mm• March 2007 median: 1.47mm
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Spectrometers involved in RHUBC
• TAFTS• 80 – 600 cm-1 spectral range• 0.12 cm-1 resolution• 2 second scan time• Higher resolution, range extends
further into far-infrared
• AERI-ER• 400 – 3300 cm-1 spectral range• 1.0 cm-1 resolution• 20 second scan time• Range includes mid-infrared
window region and CO2 absorption band
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Auxiliary data available during RHUBC
• Vaisala RS-92 sondes• Twice a day, up to once
every 2 hours in low PWV conditions
• Temperature and RH profiles
• GSR• Ground-based Scanning
Radiometer• Measures 183 GHz water
vapour absorption line (PWV retrieval)
• Retrieved PWV within 5% of sonde observations (Westwater et al 2008 ARM Science Meeting)
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Line-by-line radiative transfer modelling using LBLRTM
LBLRTM(S. Clough et al)
WV profileT profile Other absorbing gases
Clear sky radiances
HITRAN 2004database
Water vapour continuum model (MT_CKDv2.0)
Instrument response function
MODELLED RADIANCESPECTRUM
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10th March 2007 1401 UTC TAFTS vs. LBLRTM
• Water vapour profile taken from RS-92 launched at 1333 UTC
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10th March 2007 1401 UTC – PWV sensitivity
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10th March 2007 1401 UTC – Cfgn sensitivity
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Sensitivity to PWV and Cfgn
0.75
0.95
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10th March 2007 1401 UTC AERI-ER vs. LBLRTM
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Sensitivity to PWV and Cfgn
0.72
1.17
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TAFTS and AERI-ER vs. LBLRTM – PWV and Cfgn rescaled
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Summary
• The far-infrared is a significant yet under-studied component of the Earth’s radiative energy budget
• High resolution spectral measurements important for validating line-by-line radiative transfer models
• In dry conditions, the far-infrared spectrum observed from the ground is highly sensitive to changes in PWV and foreign broadened continuum strength
• Further observations of this kind required to validate (and if necessary revise) the foreign broadened continuum formulation at far-infrared wavelengths (e.g. Serio et al 2008)
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Acknowledgements
The RHUBC team:• Dave Turner (U. Wisconsin)• Eli Mlawer (AER Inc.)• Ed Westwater (CIRES)• Jeff Zirzow (Sandia Labs)• Mark Ivey (Sandia Labs)• Nico Cimini (CIRES)
… plus many more, including all the staff based at the ARM-NSA site
The TAFTS team (Imperial):• Paul Green• Caroline Cox• Juliet Pickering• Alan Last• John Harries
Campaign website: www.science.arm.gov/rhubcInitial RHUBC results:
http://www.arm.gov/publications/proceedings/conf18/[email protected]