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| Titel |
Longwave radiative effects of Saharan dust during the ICE-D campaign |
| VerfasserIn |
Jennifer Brooke, Stephan Havemann, Claire Ryder, Debbie O'Sullivan |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250148997
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| Publikation (Nr.) |
 EGU/EGU2017-13308.pdf |
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| Zusammenfassung |
| The Havemann-Taylor Fast Radiative Transfer Code (HT-FRTC) is a fast radiative
transfer model based on Principal Components. Scattering has been incorporated into
HT-FRTC which allows simulations of aerosol as well as clear-sky atmospheres. This
work evaluates the scattering scheme in HT-FRTC and investigates dust-affected
brightness temperatures using in-situ observations from Ice in Clouds Experiment – Dust
(ICE-D) campaign. The ICE-D campaign occurred during August 2015 and was
based from Cape Verde. The ICE-D campaign is a multidisciplinary project which
achieved measurements of in-situ mineral dust properties of the dust advected from the
Sahara, and on the aerosol-cloud interactions using the FAAM BAe-146 research
aircraft.
ICE-D encountered a range of low (0.3), intermediate (0.8) and high (1.3) aerosol optical
depths, AODs, and therefore provides a range of atmospheric dust loadings in the assessment
of dust scattering in HT-FRTC. Spectral radiances in the thermal infrared window region (800
– 1200 cm−1) are sensitive to the presence of mineral dust; mineral dust acts to reduce the
upwelling infrared radiation caused by the absorption and re-emission of radiation by the dust
layer. ARIES (Airborne Research Interferometer Evaluation System) is a nadir-facing
interferometer, measuring infrared radiances between 550 and 3000 cm−1. The ARIES
spectral radiances are converted to brightness temperatures by inversion of the Planck
function.
The mineral dust size distribution is important for radiative transfer applications as it
provides a measure of aerosol scattering. The longwave spectral mineral dust optical
properties including the mass extinction coefficients, single scattering albedos and the
asymmetry parameter have been derived from the mean ICE-D size distribution.
HT-FRTC scattering simulations are initialised with vertical mass fractions which can be
derived from extinction profiles from the lidar along with the specific extinction
coefficient, kext (m2/g) at 355 nm. In general the comparison between the lidar
retrieval of aerosol extinction coefficients and in-situ measurements show a good
agreement.
The root mean square of the brightness temperature residuals in the window region for
observations (ARIES) minus model simulations for i) clear-sky, ii) HT-FRTC ‘line-by-line’
scattering and, iii) HT-FRTC fast scattering are calculated. For the ICE-D case studies
mineral dust impacts on the brightness temperature of the background on the order of 1 – 1.5
K. |
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