Observations and modelling of the solar and terrestrial radiative effects of Saharan dust: a radiative closure case‐study over oceans during the GERBILS campaign

Haywood, Jim M.; Johnson, Ben; Osborne, S.; Mulcahy, Jane; Brooks, M. E.; Harrison, Mark A.; Milton, Sean; Brindley, Helen E.

doi:10.1002/qj.770

Cited by 38 publications

(51 citation statements)

References 60 publications

(99 reference statements)

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“…These values are entirely plausible, given the analysis by Haywood et al (2005) and Allan et al (2011) and match reasonably well with values derived from GERBlike SEVIRI fluxes in the presence of aerosol (Brindley and Russell, 2008). The Balkanski et al (2007) refractive indices appear to perform reasonably in obtaining radiative closure in the LW region of the spectrum Haywood et al, 2011). Osborne et al (2011) suggest a diurnal average LW radiative impact of around 18 W m −2 /AOD 550 .…”

Section: Aircraft-based Assessments Of the Geographical Distribution supporting

confidence: 78%

“…Haywood et al (2011) clearly detect a significant upwelling SW direct radiative effect of 33 ± 3 W m −2 , which is reasonably represented by the SEVIRI retrievals developed by Brindley and Russell (2008). The corresponding measured reduction in the downwelling SW flux was around 47 ± 9 W m −2 .…”

Section: The Impact Of Mineral Dust On Radiation and Radiative Closuresupporting

confidence: 75%

“…Spectrally resolved upward and downward irradiances at a resolution of up to 0.0032 µm were determined from the Solar Hemispheric Integrating Measurement System (SHIMS), which consists of an integrating head coupled by fibre optics to Zeiss spectrometer units. A new 'pirouette' correction procedure detailed by Haywood et al (2011) was applied to account for pitch and roll variations for downwelling irradiances, while no correction was deemed necessary for upwelling irradiances. Spectral radiances at the same spectral resolution as SHIMS were also measured using a pointable narrow field of view short-wave spectrometer (SWS).…”

Section: Aircraft Instrumentation and Satellite Productsmentioning

confidence: 99%

“…While the majority of the GERBILS measurement campaign was performed over desert regions, Haywood et al (2011) perform a radiative closure study over ocean regions while the aircraft was on route to the campaign. Haywood et al (2011) clearly detect a significant upwelling SW direct radiative effect of 33 ± 3 W m −2 , which is reasonably represented by the SEVIRI retrievals developed by Brindley and Russell (2008).…”

Section: The Impact Of Mineral Dust On Radiation and Radiative Closurementioning

confidence: 99%

“…Subsequent to the DABEX campaign, the refractive indices of mineral dust were changed from those of the World Climate Program (1986) to those from Balkanski et al (2007) assuming 1.5% haematite content, similar to the 1-3% iron content suggested by Klaver et al (2011). Again, during GERBILS these refractive indices were found to better represent the absorption properties of mineral dust (see Haywood et al, 2011). Two dust uplift schemes were investigated.…”

Section: Validation and Improvement In Dust Modellingmentioning

confidence: 99%

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Motivation, rationale and key results from the GERBILS Saharan dust measurement campaign

Haywood

Johnson

Osborne

et al. 2011

Quart J Royal Meteoro Soc

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The Geostationary Earth Radiation Budget Intercomparison of Longwave and Shortwave radiation (GERBILS) was an observational field experiment over NorthAfrica during June 2007. The campaign involved 10 flights by the FAAM BAe-146 research aircraft over southwestern parts of the Sahara Desert and coastal stretches of the Atlantic Ocean. Objectives of the GERBILS campaign included characterisation of mineral dust geographic distribution and physical and optical properties, assessment of the impact upon radiation, validation of satellite remote sensing retrievals, and validation of numerical weather prediction model forecasts of aerosol optical depths (AODs) and size distributions. We provide the motivation behind GERBILS and the experimental design and report the progress made in each of the objectives. We show that mineral dust in the region is relatively nonabsorbing (mean single scattering albedo at 550 nm of 0.97) owing to the relatively small fraction of iron oxides present (1-3%), and that detailed spectral radiances are most accurately modelled using irregularly shaped particles. Satellite retrievals over bright desert surfaces are challenging owing to the lack of spectral contrast between the dust and the underlying surface. However, new techniques have been developed which are shown to be in relatively good agreement with AERONET estimates of AOD and with each other. This encouraging result enables relatively robust validation of numerical models which treat the production, transport, and deposition of mineral dust. The dust models themselves are able to represent largescale synoptically driven dust events to a reasonable degree, but some deficiencies remain both in the Sahara and over the Sahelian region, where cold pool outflow from convective cells associated with the intertropical convergence zone can lead to significant dust production.

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Section: Aircraft-based Assessments Of the Geographical Distribution supporting

confidence: 78%

Section: The Impact Of Mineral Dust On Radiation and Radiative Closuresupporting

confidence: 75%

Section: Aircraft Instrumentation and Satellite Productsmentioning

confidence: 99%

Section: The Impact Of Mineral Dust On Radiation and Radiative Closurementioning

confidence: 99%

Section: Validation and Improvement In Dust Modellingmentioning

confidence: 99%

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Motivation, rationale and key results from the GERBILS Saharan dust measurement campaign

Haywood

Johnson

Osborne

et al. 2011

Quart J Royal Meteoro Soc

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Aerosol direct radiative effect of smoke over clouds over the southeast Atlantic Ocean from 2006 to 2009

Graaf

Bellouin

Tilstra

et al. 2014

Geophysical Research Letters

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The aerosol direct radiative effect (DRE) of African smoke was analyzed in cloud scenes over the southeast Atlantic Ocean, using Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) satellite observations and Hadley Centre Global Environmental Model version 2 (HadGEM2) climate model simulations. The observed mean DRE was about 30–35 W m−2 in August and September 2006–2009. In some years, short episodes of high‐aerosol DRE can be observed, due to high‐aerosol loadings, while in other years the loadings are lower but more prolonged. Climate models that use evenly distributed monthly averaged emission fields will not reproduce these high‐aerosol loadings. Furthermore, the simulated monthly mean aerosol DRE in HadGEM2 is only about 6 W m−2 in August. The difference with SCIAMACHY mean observations can be partly explained by an underestimation of the aerosol absorption Ångström exponent in the ultraviolet. However, the subsequent increase of aerosol DRE simulation by about 20% is not enough to explain the observed discrepancy between simulations and observations.

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Altitude‐resolved shortwave and longwave radiative effects of desert dust in the Mediterranean during the GAMARF campaign: Indications of a net daily cooling in the dust layer

et al. 2015

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Desert dust interacts with shortwave (SW) and longwave (LW) radiation, influencing the Earth radiation budget and the atmospheric vertical structure. Uncertainties on the dust role are large in the LW spectral range, where few measurements are available and the dust optical properties are not well constrained. The first airborne measurements of LW irradiance vertical profiles over the Mediterranean were carried out during the Ground-based and Airborne Measurements of Aerosol Radiative Forcing (GAMARF) campaign, which took place in spring 2008 at the island of Lampedusa. The experiment was aimed at estimating the vertical profiles of the SW and LW aerosol direct radiative forcing (ADRF) and heating rates (AHR), taking advantage of vertically resolved measurements of irradiances, meteorological parameters, and aerosol microphysical and optical properties. Two cases, characterized respectively by the presence of a homogeneous dust layer (3 May, with aerosol optical depth, AOD, at 500 nm of 0.59) and by a low aerosol burden (5 May, with AOD of 0.14), are discussed. A radiative transfer model was initialized with the measured vertical profiles and with different aerosol properties, derived from measurements or from the literature. The simulation of the irradiance vertical profiles, in particular, provides the opportunity to constrain model-derived estimates of the AHR. The measured SW and LW irradiances were reproduced when the model was initialized with the measured aerosol size distributions and refractive indices. For the dust case, the instantaneous (solar zenith angle, SZA, of 55.1°) LW-to-SW ADRF ratio was 23% at the surface and 11% at the top of the atmosphere (TOA), with a more significant LW contribution on a daily basis (52% at the surface and 26% at TOA), indicating a relevant reduction of the SW radiative effects. The AHR profiles followed the aerosol extinction profile, with comparable peaks in the SW (0.72 ± 0.11 K d À1) and in the LW (À0.52 ± 0.12 K d À1) for the considered SZA. On a daily basis, the absolute value of the heating rate was larger in the LW than in the SW, producing a net cooling effect at specific levels. These are quite unexpected results, emphasizing the important role of LW radiation.

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Observations and modelling of the solar and terrestrial radiative effects of Saharan dust: a radiative closure case‐study over oceans during the GERBILS campaign

Cited by 38 publications

References 60 publications

Motivation, rationale and key results from the GERBILS Saharan dust measurement campaign

Motivation, rationale and key results from the GERBILS Saharan dust measurement campaign

Aerosol direct radiative effect of smoke over clouds over the southeast Atlantic Ocean from 2006 to 2009

Altitude‐resolved shortwave and longwave radiative effects of desert dust in the Mediterranean during the GAMARF campaign: Indications of a net daily cooling in the dust layer

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