A benchmark for testing the accuracy and computational cost of shortwave top-of-atmosphere reflectance calculations in clear-sky aerosol-laden atmospheres

Escribano, Jerónimo; Bozzo, Alessio; Dubuisson, Philippe; Flemming, Johannes; Hogan, Robin J.; C.‐Labonnote, Laurent; Boucher, Oliviér

doi:10.5194/gmd-12-805-2019

Cited by 8 publications

(4 citation statements)

References 56 publications

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“…Tabulated results can be found for homogeneous atmospheres containing molecules only [12,34,35,36,37], for (in-) homogeneous atmospheres containing (molecules and) aerosols [38,39,40], and for homogeneous atmospheres consisting of cloud droplets [40]. However, while Escribano et al [41] do consider an ocean surface below an atmosphere for testbed results, there exist no such tables for the polarization of light computed for atmosphere-ocean system (AOS) models that include water-leaving radiance. Comparisons for polarized light computations using different RT codes have been reported for such models [42,43,44,45,46], but the results are drawn as a function of viewing angle which limits the accuracy that can be extracted to validate other RT codes.…”

Section: Introductionmentioning

confidence: 99%

Testbed results for scalar and vector radiative transfer computations of light in atmosphere-ocean systems

Chowdhary

Zhai

et al. 2020

Journal of Quantitative Spectroscopy and Radiative Transfer

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Section: Introductionmentioning

confidence: 99%

Testbed results for scalar and vector radiative transfer computations of light in atmosphere-ocean systems

Chowdhary

Zhai

et al. 2020

Journal of Quantitative Spectroscopy and Radiative Transfer

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“…The two-stream source-function (TSSF; Toon et al, 1989) approach is used for thermal infrared radiances, and has also been applied to model passive microwave radiances, although such measurements are not used in this study. For solar wavelengths the Forward-Lobe Two-Stream Radiance Model (FLOTSAM; Escribano et al, 2019) is used, wherein forward scattered solar radiation either remains close to the angle of incidence (the narrow forward-lobe), or is scattered into the wide forward-lobe at angles around 15 • ; additional diffuse fluxes are calculated using the two-stream method, so FLOTSAM can be thought of as the equivalent of TSSF for solar wavelengths.…”

Section: Radiative Transfermentioning

confidence: 99%

A unified synergistic retrieval of clouds, aerosols and precipitation from EarthCARE: the ACM-CAP product

Mason

Hogan

Bozzo

et al. 2022

Preprint

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Abstract. The ATLID-CPR-MSI retrieval of Clouds, Aerosols and Precipitation (ACM-CAP) product provides a synergistic “best-estimate” retrieval of the quantities and properties of all aerosols and hydrometeors detected by EarthCARE. While synergistic retrieval algorithms are now mature in many contexts, ACM-CAP is unique in providing a single unified retrieval product for all classes of hydrometeor—ice cloud and snow, drizzle and rain, and liquid clouds—and aerosol species, informed by the synergistic target classification (AC-TC). The simultaneous retrieval of the entire atmosphere with a single optimal estimation retrieval, called Cloud, Aerosol and Precipitation from mulTiple Instruments using a VAriational TEchnique (CAPTIVATE), allows for a robust accounting of observational and retrieval errors and the contributions of passive and integrated measurements in the context of layered and complex regimes, and for enforcing physical relationships between components (e.g. the conservation of precipitating mass flux through the melting layer). We have demonstrated and evaluated the ACM-CAP product as applied to the three EarthCARE test scenes simulated from numerical weather model forecasts, using both case studies and statistical evaluation against the simulated measurements and the “true” quantities from the numerical model. We show that the retrievals are both strongly constrained by the observations from the active and passive instruments, and overall closely resemble the underlying model fields in terms of bulk quantities (e.g. cloud water content, precipitation mass flux, and aerosol extinction) and microphysical properties (e.g. cloud effective radius, median volume diameter, and aerosols lidar ratio). The retrieval performs best where the active instruments have strong and unambiguous signal: in ice clouds and snow, which is observed by both ATLID and CPR, and in light to moderate rain, where CPR signal is strong. In precipitation, CPR's Doppler capability permits enhanced retrievals of snow particle density and raindrop size. In complex and layered scenes where ATLID is obscured, we have shown that making a simple assumption about the presence and vertical distribution of liquid cloud in rain and mixed-phase clouds allows improved assimilation of MSI solar radiances. In combination with a constraint on CPR path-integrated attenuation from the ocean surface, this leads to improved retrievals of both liquid cloud and rain in mid-latitude stratiform precipitation. In the heaviest convective precipitation (i.e. greater than around 10 mm h-1), both active instruments are strongly attenuated and dominated by multiple scattering; in these situations ACM-CAP provides a seamless retrieval of cloud and precipitation, but one which is subject to a high degree of uncertainty. ACM-CAP's aerosol retrieval, constrained by ATLID and MSI solar radiances, is performed in hydrometeor-free parts of the atmosphere. The lidar backscatter is subject to high noise, while the solar radiances are expected to be dominated by uncertainties in surface properties especially over land. While the aerosol optical depth is well-constrained in the test scenes, there is a high degree of noise at the ~1 km resolution of the ACM-CAP product. The use of numerical forecast models to simulate test scenes for testing and evaluation puts EarthCARE L2 processors at an unprecedented degree of readiness ahead of launch. While exposure to further simulated test scenes, campaign data, and ultimately in-flight EarthCARE measurements will motivate ongoing improvements to the representation of cloud and precipitation, the instrument forward-models, and their uncertainties, the present evaluation demonstrates that ACM-CAP will provide a novel unified and synergistic retrieval of clouds, aerosols and precipitation of high quality, including a robust accounting of the contributions of observations, and of measurement and retrieval errors.

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“…However, the manufacturer provides a software that allows to convert the obtained PSDs with PSLs to PSDs of spherical particles assuming 16 different refractive indices. We used this information, the information on the scattering angle, and the Lorenz-Mie code used in Escribano et al (2019) to infer a light spectrum that can best reproduce the software conversions between spherical aerosol types. Our optimization problem was constrained to fit a sum of Gaussian spectra over the wavelength domain.…”

Section: Size-resolved Dust Concentration Measurementsmentioning

confidence: 99%

Insights into the size-resolved dust emission from field measurements in the Moroccan Sahara

González-Flórez

Klose²,

Alastuey³

et al. 2022

Preprint

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Abstract. Mineral dust effects upon climate are strongly affected by its particle size distribution (PSD). In particular, the emitted dust PSD partly controls the dust lifetime and its global distribution. Despite the extensive research performed on this topic over the last decades, there are still substantial gaps in our understanding of the emitted PSD along with its potential variability and associated causes. In this study, we provide insights into the saltation and size-resolved dust emission process based on measurements obtained during a comprehensive wind erosion and dust emission field campaign that took place in the Moroccan Sahara in September 2019 in the context of the FRontiers in dust minerAloGical coMposition and its Effects upoN climaTe (FRAGMENT) project. The measurement site located in a remote ephemeral lake, consisting of a smooth hard-crusted paved sediment surface surrounded by small sand dunes, is characterized by strong and frequent saltation and dust emission conditions, and relatively low sandblasting efficiencies. Our study, which thoroughly analyses the number and mass PSDs of both the concentration and diffusive flux (the latter typically assumed to be equivalent to the emitted dust PSD), detects statistically significant dependencies upon friction velocity (u*), wind direction and type of event (regular events vs haboob events). We discuss the potential underlying causes of such variability, including the effect of dry deposition, an enhanced fragmentation of aggregates, and the impact of the haboob gust front. We clearly identify and quantify the major role played by dry deposition in shaping the diffusive flux PSD variations, modulated by the wind direction-dependent fetch length of our measurement location and u*. Our estimates show the importance of dry deposition relative to emission, representing up to ∼40 % for super-coarse particles (> 10 μm) and up to ∼20 % for particles as small as ∼5 μm in diameter. While we attribute the enhancement (reduction) in submicron (supermicron) particles with u* to the effect of dry deposition, an enhanced fragmentation of aggregates with u* could still play a complementary yet arguably smaller role. We additionally find clear differences in the PSDs associated to haboob events in comparison with the regular events, i.e., a higher (lower) proportion of supermicron (submicron) particles for equivalent or higher u* values, and more vigorous dry deposition and variability in the coarse and super-coarse dust mass fractions. We hypothesize that these differences are due to 1) a smaller horizontal (spatial) extent of the haboob events (which is equivalent to the effect of a smaller fetch), 2) the effect of the moving haboob gust front, where u* and dust emission are maximized, along with its changing proximity to the measurement site (which is equivalent to a variable fetch), and/or 3) the increased resistance of soil aggregates to fragmentation associated to the observed increases in relative humidity along the haboob outflow. We finally compare the obtained PSDs with both the PSDs predicted by the original and a recently updated version Brittle Fragmentation Theory (BFT), the latter accounting for super-coarse dust emission. For the comparison with the updated BFT we transform our optical diameters into geometric diameter PSDs, assuming dust particles are tri-axial ellipsoids with an index of refraction consistent with measured optical properties during the campaign. We obtain a substantially lower (higher) proportion of submicron (supermicron) particles in the diffusive flux PSDs in comparison with the original BFT PSDs. Also, our PSDs show a higher proportion of particles above ∼2 μm and a higher mass fraction of super-coarse particles, despite large effect of dry deposition upon this fraction. All in all, our results indicate that dry deposition needs to be adequately considered to estimate the emitted PSD, even in studies limited to the fine and coarse size ranges (< 10 μm), and particularly in measurement locations with long fetches.

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A benchmark for testing the accuracy and computational cost of shortwave top-of-atmosphere reflectance calculations in clear-sky aerosol-laden atmospheres

Cited by 8 publications

References 56 publications

Testbed results for scalar and vector radiative transfer computations of light in atmosphere-ocean systems

Testbed results for scalar and vector radiative transfer computations of light in atmosphere-ocean systems

A unified synergistic retrieval of clouds, aerosols and precipitation from EarthCARE: the ACM-CAP product

Insights into the size-resolved dust emission from field measurements in the Moroccan Sahara

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