scholarly journals Consistency of dimensional distributions and refractive indices of desert dust measured over Lampedusa with IASI radiances

2016 ◽  
Author(s):  
Giuliano Liuzzi ◽  
Guido Masiello ◽  
Carmine Serio ◽  
Daniela Meloni ◽  
Claudia Di Biagio ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Short Wave ◽  
Radiative Transfer Model ◽  
Refractive Indices ◽  
Transfer Model ◽  
Spectral Interval ◽  
Desert Dust ◽  
Microphysical Properties ◽  
Southern Mediterranean ◽  
The One

Abstract. In the context of the ChArMEx campaign, we present here some results concerning the quantitative comparison between simulated and observed radiances during a dust event occurred between June and July 2013 in the southern Mediterranean basin, involving the airmass above Lampedusa island. In particular, comparisons have been performed between radiances as observed by the Infrared Atmospheric Sounder Interferometer (IASI) and those simulated using the σ-IASI-as radiative transfer model, which takes into account aerosol extinction effect through a set of fast parameterizations. Simulations have been carried on with different sets of input complex refractive indices, which take into account the parent soils of the aerosols, and using the high-quality characterization of desert dust aerosol microphysical properties, achieved through direct measurements in the ChArMEx experiment; on the one hand, this comparison has offered the possibility to test the feasibility of the radiative transfer model. On the other hand, this work goes through a direct validation of different refractive indices sets for desert dust in the thermal infrared. Results show a good consistency between calculations and observations, especially in the spectral interval 800–1000 cm−1; moreover, the comparison between calculations and observations suggests that further efforts are needed to better characterize desert dust optical properties in the short wave (above 2000 cm−1). In any case, we show that it is necessary to properly tune the refractive indices according to the geographical origin of the observed aerosol.

scholarly journals Consistency of dimensional distributions and refractive indices of desert dust measured over Lampedusa with IASI radiances

2017 ◽  
Vol 10 (2) ◽  
pp. 599-615 ◽  
Author(s):  
Giuliano Liuzzi ◽  
Guido Masiello ◽  
Carmine Serio ◽  
Daniela Meloni ◽  
Claudia Di Biagio ◽  
...  
Keyword(s):  
Dust Particles ◽  
Radiative Transfer Model ◽  
Refractive Indices ◽  
Transfer Model ◽  
Spectral Interval ◽  
Desert Dust ◽  
Microphysical Properties ◽  
Southern Mediterranean ◽  
Dimensional Distribution ◽  
The One

Abstract. In the context of the ChArMEx campaign, we present here some results concerning the quantitative comparison between simulated and observed radiances in the presence of atmospheric desert dust, between June and July 2013 in the southern Mediterranean Basin, in the air mass above the island of Lampedusa. In particular, comparisons have been performed between radiances as observed by the Infrared Atmospheric Sounder Interferometer (IASI) and those simulated using the σ-IASI-as radiative transfer model, which takes into account aerosol extinction effect through a set of fast parameterizations. Simulations have been carried out using different sets of input complex refractive indices, which take into account the parent soils of the aerosols. Their accuracy also relies on the quality of the characterization of desert dust microphysical properties, achieved through direct measurements in the ChArMEx experiment. On the one hand, the fact that the model can ingest such a variable input proves its feasibility. On the other hand, this work goes through a direct validation of different refractive index sets for desert dust in the thermal infrared, and pursues an assessment of the sensitivity of IASI data with respect to the dimensional distribution of desert dust particles. Results show a good consistency between calculations and observations, especially in the spectral interval 800–1000 cm−1; further, the comparison between calculations and observations suggests that further efforts are needed to better characterize desert dust optical properties in the shortwave (above 2000 cm−1). Whatever the case, we show that it is necessary to properly tune the refractive indices according to the geographical origin of the observed aerosol.

scholarly journals Modeling the radiative effects of desert dust on weather and regional climate

2013 ◽  
Vol 13 (11) ◽  
pp. 5489-5504 ◽  
Author(s):  
C. Spyrou ◽  
G. Kallos ◽  
C. Mitsakou ◽  
P. Athanasiadis ◽  
C. Kalogeri ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Regional Climate ◽  
Lower Troposphere ◽  
Integrated Approach ◽  
Dust Particles ◽  
Radiative Transfer Model ◽  
Limited Area ◽  
Transfer Model ◽  
Radiative Effects ◽  
Desert Dust

Abstract. Mineral dust aerosols exert a significant effect on both solar and terrestrial radiation. By absorbing and scattering, the solar radiation aerosols reduce the amount of energy reaching the surface. In addition, aerosols enhance the greenhouse effect by absorbing and emitting outgoing longwave radiation. Desert dust forcing exhibits large regional and temporal variability due to its short lifetime and diverse optical properties, further complicating the quantification of the direct radiative effect (DRE). The complexity of the links and feedbacks of dust on radiative transfer indicate the need for an integrated approach in order to examine these impacts. In order to examine these feedbacks, the SKIRON limited area model has been upgraded to include the RRTMG (Rapid Radiative Transfer Model – GCM) radiative transfer model that takes into consideration the aerosol radiative effects. It was run for a 6 year period. Two sets of simulations were performed, one without the effects of dust and the other including the radiative feedback. The results were first evaluated using aerosol optical depth data to examine the capabilities of the system in describing the desert dust cycle. Then the aerosol feedback on radiative transfer was quantified and the links between dust and radiation were studied. The study has revealed a strong interaction between dust particles and solar and terrestrial radiation, with several implications on the energy budget of the atmosphere. A profound effect is the increased absorption (in the shortwave and longwave) in the lower troposphere and the induced modification of the atmospheric temperature profile. These feedbacks depend strongly on the spatial distribution of dust and have more profound effects where the number of particles is greater, such as near their source.

scholarly journals Technical Note: A novel parameterization of the transmissivity due to ozone absorption in the <i>k</i>-distribution method and correlated-<i>k</i> approximation of Kato et al. (1999) over the UV band

2015 ◽  
Vol 15 (13) ◽  
pp. 7449-7456 ◽  
Author(s):  
W. Wandji Nyamsi ◽  
A. Arola ◽  
P. Blanc ◽  
A. V. Lindfors ◽  
V. Cesnulyte ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Solar Spectrum ◽  
Ground Level ◽  
Technical Note ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Spectral Interval ◽  
Computationally Efficient ◽  
Ozone Absorption ◽  
Distribution Method

Abstract. The k-distribution method and the correlated-k approximation of Kato et al. (1999) is a computationally efficient approach originally designed for calculations of the broadband solar radiation at ground level by dividing the solar spectrum in 32 specific spectral bands from 240 to 4606 nm. Compared to a spectrally resolved computation, its performance in the UV band appears to be inaccurate, especially in the spectral intervals #3 [283, 307] nm and #4 [307, 328] nm because of inaccuracy in modeling the transmissivity due to ozone absorption. Numerical simulations presented in this paper indicate that a single effective ozone cross section is insufficient to accurately represent the transmissivity over each spectral interval. A novel parameterization of the transmissivity using more quadrature points yields maximum errors of respectively 0.0006 and 0.0143 for intervals #3 and #4. How to practically implement this new parameterization in a radiative transfer model is discussed for the case of libRadtran (library for radiative transfer). The new parameterization considerably improves the accuracy of the retrieval of irradiances in UV bands.

scholarly journals Estimating bias in the OCO-2 retrieval algorithm caused by 3-D radiation scattering from unresolved boundary layer clouds

2015 ◽  
Vol 8 (4) ◽  
pp. 1641-1656 ◽  
Author(s):  
A. Merrelli ◽  
R. Bennartz ◽  
C. W. O'Dell ◽  
T. E. Taylor
Keyword(s):  
Radiative Transfer ◽  
Scattering Problem ◽  
Three Dimensional ◽  
Co2 Concentration ◽  
Bare Soil ◽  
Short Wave ◽  
Radiative Transfer Model ◽  
Retrieval Algorithm ◽  
Transfer Model ◽  
Retrieval Algorithms

Abstract. Due to the complexity of the multiple scattering problem for shortwave radiative transfer in Earth's atmosphere, operational physical retrieval algorithms commonly use a plane parallel radiative transfer model (RTM). This so-called one-dimensional (1-D) assumption allows practical retrieval algorithms to be implemented. In order to understand the impacts of this assumption for low altitude, unresolved clouds observed by OCO-2, the three-dimensional (3-D) radiative transfer model SHDOM is used to generate synthetic observations which are then processed by the operational retrieval algorithm based on a 1-D RTM. Simulations are performed over three realistic surface spectral albedos, corresponding to snow, vegetation, and bare soil. The results show that the existing cloud screening algorithm has difficulty identifying sub-field of view (FOV), unresolved clouds that fill less than half of the FOV. The unresolved clouds introduce a bias in the retrieved CO2 concentration, as quantified by the dry air mole fraction (XCO2). The biases are relatively small (less than 1 ppm) when the albedo at 2.1 μm is high, which is common over bare land surfaces. For cases with low 2.1 μm albedo, such as snow, the bias becomes much larger, up to 5 ppm. These results indicate that the XCO2 retrieval appears robust to 3-D scattering effects from unresolved low level clouds when the short wave infrared surface albedo is large, but for darker surfaces these clouds can introduce significant biases.

scholarly journals THE SENSITIVITY OF THE GREENHOUSE EFFECT TO CHANGES IN THE CONCENTRATION OF GASES IN PLANETARY ATMOSPHERES

2013 ◽  
Vol 53 (A) ◽  
pp. 832-838
Author(s):  
Smadar Bressler ◽  
Giora Shaviv ◽  
Nir J. Shaviv
Keyword(s):  
Radiative Transfer ◽  
Surface Temperature ◽  
Greenhouse Effect ◽  
Central Star ◽  
Temperature Limit ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Long Wavelength ◽  
Earth Like Planets ◽  
The One

We present a radiative transfer model for Earth-Like-Planets (ELP). The model allows the assessment of the effect of a change in the concentration of an atmospheric component, especially a greenhouse gas (GHG), on the surface temperature of a planet. The model is based on the separation between the contribution of the short wavelength molecular absorption and the long wavelength one. A unique feature of the model is the condition of energy conservation at every point in the atmosphere. The radiative transfer equation is solved in the two stream approximation without assuming the existence of an LTE in any wavelength range. The model allows us to solve the Simpson paradox, whereby the greenhouse effect (GHE) has no temperature limit. On the contrary, we show that the temperature saturates, and its value depends primarily on the distance of the planet from the central star. We also show how the relative humidity affects the surface temperature of a planet and explain why the effect is smaller than the one derived when the above assumptions are neglected.

scholarly journals Aerosol radiative forcing during African desert dust events (2005–2010) over South-Eastern Spain

2012 ◽  
Vol 12 (3) ◽  
pp. 6593-6622 ◽  
Author(s):  
A. Valenzuela ◽  
F. J. Olmo ◽  
H. Lyamani ◽  
M. Antón ◽  
A. Quirantes ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Radiative Forcing ◽  
Single Scattering ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Aerosol Radiative Forcing ◽  
Desert Dust ◽  
Aerosol Parameter ◽  
Dust Events ◽  
Aerosol Radiative

Abstract. The instantaneous values of the aerosol radiative forcing (ARF) at the surface and the top of the atmosphere (TOA) were calculated during desert dust events occurred at Granada (Southeastern Spain) from 2005 to 2010. For that, the SBDART radiative transfer model was utilized to simulate the global irradiance values (0.3–2.8 μm) at the surface and TOA using as input the aerosol properties derived from a CIMEL sun-photometer measurements and an inversion methodology that uses the sky radiance measurements in principal plane configuration and non-spherical particle shapes approximation. The SBDART modeled global irradiances at surface have been successfully validated against experimental measurements obtained by CM-11 pyranometer, indicating the reliability of the radiative transfer model used in this work for the ARF calculations. The monthly ARF values at surface ranged from −32 W m−2 to −46 W m−2, being larger in April and July than in the rest of months. The seasonal ARF evolution was inconsistent with seasonal aerosol optical depth (AOD) variation due to the effects induced by other aerosol parameter such as the single scattering albedo. The ARF at TOA changed from −9 W m−2 to −29 W m−2. Thus, the atmospheric ARF values (ARF at TOA minus ARF at surface) ranged from +15 to +35 W m−2. These results suggest that the African dust caused local atmospheric heating over the study location. The instantaneous aerosol radiative forcing efficiency (ARFE), aerosol radiative forcing per unit of AOD (440 nm), at surface and TOA during African desert dust events was evaluated according to the desert dust source origins. The ARFE values at surface were relatively high (in absolute term) and were −157 ± 20 (Sector A), −154 ± 23 (Sector B), and −147 ± 23 (Sector C) W m−2. These values were larger than many of the values found in literature which could be due to the presence of more absorbing atmospheric particles during African desert dust intrusions over our study area. Finally, our ARF computations showed good agreement with the corresponding ARF calculated by AERONET network.

scholarly journals Airborne validation of radiative transfer modelling of ice clouds at millimetre and sub-millimetre wavelengths

2018 ◽  
Author(s):  
Stuart Fox ◽  
Jana Mendrok ◽  
Patrick Eriksson ◽  
Robin Ekelund ◽  
Sebastian J. O'Shea ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Cloud Microphysics ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Atmospheric Measurements ◽  
Microphysical Properties ◽  
Cloud Properties ◽  
Research Aircraft ◽  
Cloud Ice ◽  
Ice Water

Abstract. The next generation of European polar orbiting weather satellites will carry a novel instrument, the Ice Cloud Imager (ICI), which uses passive observations between 183 and 664 GHz to make daily global observations of cloud ice. Successful use of these observations requires accurate modelling of cloud ice scattering, and this study uses airborne observations from two flights of the Facility for Airborne Atmospheric Measurements (FAAM) BAe-146 research aircraft to validate radiative transfer simulations of cirrus clouds at frequencies between 325 and 664 GHz using the Atmospheric Radiative Transfer Simulator (ARTS) and a state-of-the-art database of cloud ice optical properties. Particular care is taken to ensure that the inputs to the radiative transfer model are representative of the true atmospheric state by combining both remote-sensing and in-situ observations of the same clouds to create realistic vertical profiles of cloud properties that are consistent with both observed particle size distributions and bulk ice mass. The simulations are compared to measurements from the International Submillimetre Airborne Radiometer (ISMAR), which is an airborne demonstrator for ICI. It is shown that whilst they are generally able to reproduce the observed cloud signals, for a given ice water path (IWP) there is considerable sensitivity to the cloud microphysics including the distribution of ice mass within the cloud and the ice particle habit. Accurate retrievals from ICI will therefore require realistic representations of cloud microphysical properties.

scholarly journals Diffusion approximation in a radiative transfer model for astrophysical flows

2018 ◽  
Vol 64 ◽  
pp. 78-92
Author(s):  
Laurent Di Menza ◽  
Claire Michaut ◽  
Océane Saincir
Keyword(s):  
Radiative Transfer ◽  
Diffusion Approximation ◽  
Low Cost ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Asymptotic Model ◽  
Low Cost Strategy ◽  
Volume Algorithm ◽  
The One ◽  
Astrophysical Flows

In this work, we present the diffusion approximation model for radiative transfer when we deal with optically thick astrophysical flows. Since the initial model is high CPU time demanding when dealing with its numerical approximation, solving this simpler system can provide a low cost strategy for the simulation of radiative media. We then use a finite-volume algorithm coupled with an implicit scheme for radiative contributions to solve this simplified system. Numerical experiments in the one-dimensional and two dimensional cases are presented to validate our numerical strategy and to prove the relevance of this asymptotic model.

scholarly journals Estimating bias in the OCO-2 retrieval algorithm caused by 3-D radiation scattering from unresolved boundary layer clouds

2014 ◽  
Vol 7 (11) ◽  
pp. 11547-11591
Author(s):  
A. Merrelli ◽  
R. Bennartz ◽  
C. W. O'Dell ◽  
T. E. Taylor
Keyword(s):  
Radiative Transfer ◽  
Scattering Problem ◽  
Three Dimensional ◽  
Co2 Concentration ◽  
Bare Soil ◽  
Short Wave ◽  
Radiative Transfer Model ◽  
Retrieval Algorithm ◽  
Transfer Model ◽  
Retrieval Algorithms

Abstract. Due to the complexity of the multiple scattering problem for shortwave radiative transfer in Earth's atmosphere, operational physical retrieval algorithms commonly use a plane parallel Radiative Transfer Model (RTM). This so-called One-Dimensional (1-D) assumption allows practical retrieval algorithms to be implemented. In order to understand the impacts of this assumption for low altitude, unresolved clouds observed by OCO-2, the Three-Dimensional (3-D) radiative transfer model SHDOM is used to generate synthetic observations which are then processed by the operational retrieval algorithm based on a 1-D RTM. Simulations are performed over three realistic surface spectral albedos, corresponding to snow, vegetation, and bare soil. The results show that the existing cloud screening algorithm has difficulty identifying sub-Field of View (FOV), unresolved clouds that fill less than half of the FOV. The unresolved clouds introduce a bias in the retrieved CO2 concentration, as quantified by the dry air mole fraction (XCO2). The biases are relatively small (less than 1 ppm) when the albedo at 2.1 μm is high, which is common over bare land surfaces. For cases with low 2.1 μm albedo, such as snow, the bias becomes much larger, up to 5 ppm. These results indicate that the XCO2 retrieval appears robust to 3-D scattering effects from unresolved low level clouds when the short wave infrared surface albedo is large, but for darker surfaces these clouds can introduce significant biases.

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