A new method to retrieve the aerosol layer absorption coefficient from airborne flux density and actinic radiation measurements

Bierwirth, Eike; Wendisch, Manfred; Jäkel, Evelyn; Ehrlich, André; Schmidt, S.; Stark, Harald; Pilewskie, P.; Esselborn, Michael; Gobbi, Gian Paolo; Ferrare, R. A.; Müller, Thomas; Clarke, A. D.

doi:10.1029/2009jd013636

Cited by 13 publications

(9 citation statements)

References 52 publications

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“…It would be negative over dark surfaces such as the ocean. • Development of a new method to combine airborne radiation measurements of irradiance and actinic flux density to derive the absorption coefficient of an aerosol layer (Bierwirth et al, 2010). • Significant differences (10-20% at top and bottom of the atmosphere) in solar and thermal radiative transfer calculations when considering more realistic dust particle shapes (spheroidal instead of spherical shape), more realistic aspect ratios (size-dependent versus size-independent), and refractive index characteristics (from SAMUM-1 observations, Otto et al, 2009;.…”

Section: Samum-1mentioning

confidence: 99%

Saharan Mineral Dust Experiments SAMUM–1 and SAMUM–2: what have we learned?

Ansmann¹,

Petzold²,

Kandler³

et al. 2011

Tellus B

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111

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The relationship between chemical composition, shape morphology, size distribution and optical effects of the dust particles was investigated. The impact of Saharan dust on radiative transfer and the feedback of radiative effects upon dust emission and aerosol transport were studied. Field observations (ground-based, airborne and remote sensing) and modelling results were compared within a variety of dust closure experiments with a strong focus on vertical profiling. For the first time, multiwavelength Raman/polarization lidars and an airborne high spectral resolution lidar were involved in major dust field campaigns and provided profiles of the volume extinction coefficient of the particles at ambient conditions (for the full dust size distribution), of particle-shape-sensitive optical properties at several wavelengths, and a clear separation of dust and smoke profiles allowing for an estimation of the single-scattering albedo of the biomass-burning aerosol. SAMUM-1 took place in southern Morocco close to the Saharan desert in the summer of 2006, whereas SAMUM-2 was conducted in Cape Verde in the outflow region of desert dust and biomass-burning smoke from western Africa in the winter of 2008. This paper gives an overview of the SAMUM concept, strategy and goals, provides snapshots (highlights) of SAMUM-2 observations and modelling efforts, summarizes main findings of SAMUM-1 and SAMUM-2 and finally presents a list of remaining problems and unsolved questions.

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Section: Samum-1mentioning

confidence: 99%

Saharan Mineral Dust Experiments SAMUM–1 and SAMUM–2: what have we learned?

Ansmann¹,

Petzold²,

Kandler³

et al. 2011

Tellus B

Self Cite

111

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“…2b) are equivalent. Since meteorological and air-quality experiments are not designed with the same aim in mind (Bierwirth et al 2010;Wong et al 2012), synchronized and reliable measurements of net radiative flux density and actinic flux are difficult to obtain. The results showed in Fig.…”

Section: Design Of Numerical Experimentsmentioning

confidence: 99%

Impacts of Aerosol Shortwave Radiation Absorption on the Dynamics of an Idealized Convective Atmospheric Boundary Layer

Barbaro

Arellano

Krol

et al. 2013

Boundary-Layer Meteorol

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We investigated the impact of aerosol heat absorption on convective atmospheric boundary-layer (CBL) dynamics. Numerical experiments using a large-eddy simulation model enabled us to study the changes in the structure of a dry and shearless CBL in depthequilibrium for different vertical profiles of aerosol heating rates. Our results indicated that aerosol heat absorption decreased the depth of the CBL due to a combination of factors: (i) surface shadowing, reducing the sensible heat flux at the surface and, (ii) the development of a deeper inversion layer, stabilizing the upper CBL depending on the vertical aerosol distribution. Steady-state analytical solutions for CBL depth and potential temperature jump, derived using zero-order mixed-layer theory, agreed well with the large-eddy simulations. An analysis of the entrainment zone heat budget showed that, although the entrainment flux was controlled by the reduction in surface flux, the entrainment zone became deeper and less stably stratified. Therefore, the vertical profile of the aerosol heating rate promoted changes in both the structure and evolution of the CBL. More specifically, when absorbing aerosols were present only at the top of the CBL, we found that stratification at lower levels was the mechanism responsible for a reduction in the vertical velocity and a steeper decay of the turbulent kinetic energy throughout the CBL. The increase in the depth of the inversion layer also modified the potential temperature variance. When aerosols were present we observed that the potential temperature variance became significant already around 0.7z i (where z i is the CBL height) but less intense at the entrainment zone due to the smoother potential temperature vertical gradient.

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“…1). The system is similar to the Spectral Modular RAdiation measurement sysTem (SMART)-Albedometer introduced by Wendisch et al (2001) and further developed by Bierwirth et al (2010). It monitors a spectral range from 350 to 2000 nm with a spectral resolution of 2 to 3 nm (full width at half maximum, FWHM) for the wavelength range between 350 and 1000 nm and FWHM of 9 to 16 nm for the near-infrared (NIR) wavelength range 1000 to 2000 nm.…”

Section: Airborne Remote Sensing Of Cirrus Using Halo-sr and Hsrlmentioning

confidence: 99%

Influence of local surface albedo variability and ice crystal shape on passive remote sensing of thin cirrus

et al. 2014

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Abstract. Airborne measurements of solar spectral radiance reflected by cirrus are performed with the HALO-Solar Radiation (HALO-SR) instrument onboard the High Altitude and Long Range Research Aircraft (HALO) in November 2010. The data are used to quantify the influence of surface albedo variability on the retrieval of cirrus optical thickness and crystal effective radius. The applied retrieval of cirrus optical properties is based on a standard two-wavelength approach utilizing measured and simulated reflected radiance in the visible and near-infrared spectral region. Frequency distributions of the surface albedos from Moderate resolution Imaging Spectroradiometer (MODIS) satellite observations are used to compile surface-albedo-dependent lookup tables of reflected radiance. For each assumed surface albedo the cirrus optical thickness and effective crystal radius are retrieved as a function of the assumed surface albedo. The results for the cirrus optical thickness are compared to measurements from the High Spectral Resolution Lidar (HSRL). The uncertainty in cirrus optical thickness due to local variability of surface albedo in the specific case study investigated here is below 0.1 and thus less than that caused by the measurement uncertainty of both instruments. It is concluded that for the retrieval of cirrus optical thickness the surface albedo variability is negligible. However, for the retrieval of crystal effective radius, the surface albedo variability is of major importance, introducing uncertainties up to 50 %. Furthermore, the influence of the bidirectional reflectance distribution function (BRDF) on the retrieval of crystal effective radius was investigated and quantified with uncertainties below 10 %, which ranges below the uncertainty caused by the surface albedo variability. The comparison with the independent lidar data allowed for investigation of the role of the crystal shape in the retrieval. It is found that if assuming aggregate ice crystals, the HSRL observations fit best with the retrieved optical thickness from HALO-SR.

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A new method to retrieve the aerosol layer absorption coefficient from airborne flux density and actinic radiation measurements

Cited by 13 publications

References 52 publications

Saharan Mineral Dust Experiments SAMUM–1 and SAMUM–2: what have we learned?

Saharan Mineral Dust Experiments SAMUM–1 and SAMUM–2: what have we learned?

Impacts of Aerosol Shortwave Radiation Absorption on the Dynamics of an Idealized Convective Atmospheric Boundary Layer

Influence of local surface albedo variability and ice crystal shape on passive remote sensing of thin cirrus

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