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Accurate observations of near-infrared solar spectral irradiance and water vapour continuum

Elsey, J. D. C. (2019) Accurate observations of near-infrared solar spectral irradiance and water vapour continuum. PhD thesis, University of Reading

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To link to this item DOI: 10.48683/1926.00088668


This thesis contains analyses of the solar spectral irradiance (SSI) and near-infrared water vapour continuum from high-resolution observations by a ground-based, sun-pointing Fourier transform spectrometer in the wavenumber region 2000-10000 cm-1 (1-5 μm). This was performed primarily using the Langley method on observations during 18 September 2008. Particular focus was placed on a detailed assessment of the uncertainty budget for each of these analyses. The solar spectral irradiance was found to be ~8% lower than the commonly-used satellite-based ATLAS3 SSI in the region 4000-7000 cm-1 (where ATLAS3 is most uncertain). This disagreement with ATLAS3 is in line with several other modern analyses. There is good agreement with ATLAS3 and other spectra in the 7000-10000 cm-1 region (where these spectra are considered more accurate). This thesis contains the first published results of water vapour continuum absorption in the atmosphere in the 1.6 and 2.1 μm atmospheric windows (in which laboratory measurements show some significant disagreement) with robust uncertainties. The derived water vapour continuum in these windows is stronger than the widely-used MT_CKD model (v3.2) by a factor of ~100 and ~5 respectively. These results also show that MT_CKD is a reasonably accurate representation of the continuum in the 4 μm window. These results are broadly consistent with laboratory measurements of the foreign continuum, but are inconsistent with the highest such measurements of the self-continuum. The effect of the self and foreign continuum in atmospheric conditions is assessed, with comparisons to the Langley-derived spectra from this work. These results show that the difference between MT_CKD and this work in the 1.6 and 2.1 μm windows may come primarily from the observed differences in the foreign continuum, with a smaller contribution from the self-continuum. These results show inconsistency with several sets of laboratory room temperature spectra within the experimental uncertainties.

Item Type:Thesis (PhD)
Thesis Supervisor:Shine, K.
Thesis/Report Department:School of Mathematical, Physical and Computational Sciences
Identification Number/DOI:
Divisions:Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
ID Code:88668
Date on Title Page:2018


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