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Comparison of spectrally resolved outgoing longwave radiation between 1970 and 2003: The ν4 band of methane

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  • JA Griggs
  • JE Harries
Original languageEnglish
Number of pages12
JournalProceedings of SPIE
StatePublished - 29 Aug 2005


Measurements of spectrally resolved outgoing longwave radiation recorded in 1970, 1997 and 2003 are compared to determine the change in radiative forcing over that period. The changes are shown to be in agreements with that simulated by MODTRAN, a band model, using the known changes in atmospheric temperature and greenhouse gas concentrations when the effects of noise in the observed spectra are considered. The only region where the simulations are unable to reproduce the observations is in the v4 band of methane around 1306cm-1. The methane profiles used to simulate this region of the spectrum are shown to be in good agreement with all available data and the noise levels on the spectra are small. Therefore, it is proposed that the inability to model this region lies in the model formulation. Genln2, a line-by-line model, is shown to give very different results in this particular band to those obtained using MODTRAN. Sensitivity studies show that Genln2 is also not able to fully reproduce the spectrum observed. Errors in the spectroscopic parameters are shown to be smaller than the observed discrepancy and line mixing in methane is suggested as a possible cause of the discrepancy.

Additional information

Rose publication type: Journal article Sponsorship: This work was supported by a NERC studentship. Terms of use: Copyright 2005 Society of Photo-Optical Instrumentation Engineers. This paper was published in Proceedings of SPIE Volume: 5883 and is made available as an electronic reprint (preprint) with permission of SPIE. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.

    Research areas

  • outgoing longwave radiation, spectrum, greenhouse gases, simulation, infrared, methane, HITRAN

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