scholarly journals Radiative effects of long-range-transported Saharan air layers as determined from airborne lidar measurements

2020 ◽  
Vol 20 (20) ◽  
pp. 12313-12327
Author(s):  
Manuel Gutleben ◽  
Silke Groß ◽  
Martin Wirth ◽  
Bernhard Mayer
Keyword(s):  
Water Vapor ◽  
Radiative Transfer ◽  
Heating Rate ◽  
Mineral Dust ◽  
Short Wave ◽  
Radiative Effect ◽  
Mixing Ratios ◽  
Long Wave ◽  
Lidar Measurements ◽  
Air Layers

Abstract. The radiative effect of long-range-transported Saharan air layers is investigated on the basis of simultaneous airborne high-spectral-resolution and differential-absorption lidar measurements in the vicinity of Barbados. Within the observed Saharan air layers, increased water vapor concentrations compared to the dry trade wind atmosphere are found. The measured profiles of aerosol optical properties and water vapor mixing ratios are used to characterize the atmospheric composition in radiative transfer calculations, to calculate radiative effects of moist Saharan air layers and to determine radiative heating rate profiles. An analysis based on three case studies reveals that the observed enhanced amounts of water vapor within Saharan air layers have a much stronger impact on heating rate calculations than mineral dust aerosol. Maximum mineral dust short-wave heating and long-wave cooling rates are found at altitudes of highest dust concentration (short wave: +0.5 K d−1; long wave: −0.2 K d−1; net: +0.3 K d−1). However, when considering both aerosol concentrations and measured water vapor mixing ratios in radiative transfer calculations, the maximum heating/cooling rates shift to the top of the dust layer (short wave: +2.2 K d−1; long wave: −6.0 to −7.0 K d−1; net: −4.0 to −5.0 K d−1). Additionally, the net heating rates decrease with height – indicating a destabilizing effect in the dust layers. Long-wave counter-radiation of Saharan air layers is found to reduce cooling at the tops of the subjacent marine boundary layers and might lead to less convective mixing in these layers. The overall short-wave radiative effect of mineral dust particles in Saharan air layers indicates a maximum magnitude of −40 W m−2 at surface level and a maximum of −25 W m−2 at the top of the atmosphere.

scholarly journals Radiative effects of long-range-transported Saharan air layers as determined from airborne lidar measurements

2020 ◽  
Author(s):  
Manuel Gutleben ◽  
Silke Groß ◽  
Martin Wirth ◽  
Bernhard Mayer
Keyword(s):  
Water Vapor ◽  
Radiative Transfer ◽  
Heating Rate ◽  
Mineral Dust ◽  
Short Wave ◽  
Radiative Effect ◽  
Mixing Ratios ◽  
Long Wave ◽  
Lidar Measurements ◽  
Air Layers

Abstract. The radiative effect of long-range-transported Saharan air layers is investigated on the basis of simultaneous airborne high spectral resolution and differential absorption lidar measurements in the vicinity of Barbados. Within the observed Saharan air layers increased water vapor concentrations compared to the dry trade wind atmosphere are found. The measured profiles of aerosol optical properties and water vapor mixing ratios are used to characterize the atmospheric composition in radiative transfer calculations, to calculate radiative effects of moist Saharan air layers and to determine radiative heating rate profiles. An analysis based on three case studies reveals that the observed enhanced amounts of water vapor within Saharan air layers have a much stronger impact on heating rate calculations than mineral dust aerosol. Maximum mineral dust short-wave heating and long-wave cooling rates are found in altitudes of highest dust concentration (short-wave: +0.5 Kd−1, long-wave: −0.2 Kd−1, net: +0.3 Kd−1). However, when considering both aerosol concentrations and measured water vapor mixing ratios in radiative transfer calculations the maximum heating/cooling rates shift to the top of the dust layer (short-wave: +2.2 Kd Kd−1, long-wave: −6.0 to −7.0 Kd−1, net: −5.0 to −4.0 Kd−1). Additionally, the net-heating rates decrease with height – indicating a destabilizing effect in the dust layers. Long-wave counter radiation of Saharan air layers is found to reduce cooling at the top of the subjacent marine boundary layers and might lead to less convective mixing in these layers. The overall short-wave radiative effect of mineral dust particles in Saharan air layers indicates a maximum magnitude of −40 Wm−2 at surface level and a maximum of −25 Wm−2 at the top of the atmosphere.

scholarly journals LASE Measurements of Water Vapor, Aerosol, and Cloud Distributions in Saharan Air Layers and Tropical Disturbances

2010 ◽  
Vol 67 (4) ◽  
pp. 1026-1047 ◽  
Author(s):  
Syed Ismail ◽  
Richard A. Ferrare ◽  
Edward V. Browell ◽  
Gao Chen ◽  
Bruce Anderson ◽  
...  
Keyword(s):  
Water Vapor ◽  
High Water ◽  
Aerosol Extinction ◽  
African Easterly Waves ◽  
Easterly Waves ◽  
Mixing Ratios ◽  
Aerosol Scattering ◽  
Lidar Measurements ◽  
Air Layers ◽  
Eastern North Atlantic

Abstract The Lidar Atmospheric Sensing Experiment (LASE) on board the NASA DC-8 measured high-resolution profiles of water vapor and aerosols, and cloud distributions in 14 flights over the eastern North Atlantic during the NASA African Monsoon Multidisciplinary Analyses (NAMMA) field experiment. These measurements were used to study African easterly waves (AEWs), tropical cyclones (TCs), and the Saharan air layer (SAL). These LASE measurements represent the first simultaneous water vapor and aerosol lidar measurements to study the SAL and its interactions with AEWs and TCs. Three case studies were selected for detailed analysis: (i) a stratified SAL, with fine structure and layering (unlike a well-mixed SAL), (ii) a SAL with high relative humidity (RH), and (iii) an AEW surrounded by SAL dry air intrusions. Profile measurements of aerosol scattering ratios, aerosol extinction coefficients, aerosol optical thickness, water vapor mixing ratios, RH, and temperature are presented to illustrate their characteristics in the SAL, convection, and clear air regions. LASE extinction-to-backscatter ratios for the dust layers varied from 35 ± 5 to 45 ± 5 sr, well within the range of values determined by other lidar systems. LASE aerosol extinction and water vapor profiles are validated by comparison with onboard in situ aerosol measurements and GPS dropsonde water vapor soundings, respectively. An analysis of LASE data suggests that the SAL suppresses low-altitude convection. Midlevel convection associated with the AEW and transport are likely responsible for high water vapor content observed in the southern regions of the SAL on 20 August 2008. This interaction is responsible for the transfer of about 7 × 1015 J (or 8 × 103 J m−2) latent heat energy within a day to the SAL. Initial modeling studies that used LASE water vapor profiles show sensitivity to and improvements in model forecasts of an AEW.

scholarly journals Estimation of mineral dust long-wave radiative forcing: sensitivity study to particle properties and application to real cases in the region of Barcelona

2014 ◽  
Vol 14 (17) ◽  
pp. 9213-9231 ◽  
Author(s):  
M. Sicard ◽  
S. Bertolín ◽  
M. Mallet ◽  
P. Dubuisson ◽  
A. Comerón
Keyword(s):  
Spectral Range ◽  
Radiative Forcing ◽  
Mineral Dust ◽  
Opposite Sign ◽  
Sensitivity Study ◽  
Short Wave ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Radiative Effect ◽  
Long Wave

Abstract. The aerosol radiative effect in the long-wave (LW) spectral range is sometimes not taken into account in atmospheric aerosol forcing studies at local scale because the LW aerosol effect is assumed to be negligible. At regional and global scale this effect is partially taken into account: aerosol absorption is taken into account but scattering is still neglected. However, aerosols with strong absorbing and scattering properties in the LW region, like mineral dust, can have a non-negligible radiative effect in the LW spectral range (both at surface and top of the atmosphere) which can counteract their cooling effect occurring in the short-wave spectral range. The first objective of this research is to perform a sensitivity study of mineral dust LW radiative forcing (RF) as a function of dust microphysical and optical properties using an accurate radiative transfer model which can compute vertically resolved short-wave and long-wave aerosol RF. Radiative forcing simulations in the LW range have shown an important sensitivity to the following parameters: aerosol load, radius of the coarse mode, refractive index, aerosol vertical distribution, surface temperature and surface albedo. The scattering effect has been estimated to contribute to the LW RF up to 18% at the surface and up to 38% at the top of the atmosphere. The second objective is the estimation of the short-wave and long-wave dust RF for 11 dust outbreaks observed in Barcelona. At the surface, the LW RF varies between +2.8 and +10.2 W m−2, which represents between 11 and 26% (with opposite sign) of the SW component, while at the top of the atmosphere the LW RF varies between +0.6 and +5.8 W m−2, which represents between 6 and 26% (with opposite sign) of the SW component.

Impacts of long-range-transported Saharan dust layers on atmospheric stability and turbulence in the trades

2021 ◽  
Author(s):  
Manuel Gutleben ◽  
Silke Groß ◽  
Martin Wirth
Keyword(s):  
Water Vapor ◽  
Radiative Transfer ◽  
Mineral Dust ◽  
Atmospheric Stability ◽  
Power Spectra ◽  
Saharan Dust ◽  
Dust Particles ◽  
Boreal Summer ◽  
The Caribbean ◽  
Wavelet Analyses

<p>Aeolian Saharan mineral dust particles can be transported over long distances. Great amounts of Saharan mineral dust particles are transported westwards over the Atlantic Ocean towards the Caribbean islands especially during the boreal summer months. During the transport they can either have a direct environmental effect by absorbing, emitting and scattering radiation or an indirect effect by changing cloud micro-physical properties and by modifying cloud lifetime or formation.</p><p>Our recent studies indicate that elevated transported Saharan dust layers, so-called Saharan Air Layers (SALs), come along with enhanced concentrations of water vapor compared to the surrounding atmosphere. Radiative transfer simulations reveal that not the dust particles inside the SALs but the enhanced concentrations of water vapor play the dominant role for atmospheric heating in dust-laden subtropical regions. In this way water vapor has the potential to impact both atmospheric stability and turbulent properties not only inside the SALs but also at lower atmospheric levels.  To study the effects of water vapor on atmospheric turbulence and stability in SAL-regions, we performed wavelet analyses as well as calculations of power spectra on the basis of airborne lidar backscatter and water vapor measurements by the DLR lidar system WALES during the NARVAL-II research campaign. For an in-depth investigation of SAL-properties, several research flights during NARVAL-II were designed to lead over dust-laden regions upstream the Caribbean island of Barbados. Our analysis shows that water vapor heating does not only have an effect on the stability and turbulence of SALs by maintaining their confining inversions and promoting vertical mixing in their interior, but also hinders the development of shallow marine convection below.</p><p>In our presentation we will give an overview of the performed measurements and radiative transfer simulations as well as of the conducted stability and turbulence analyses by means of calculated power spectra and wavelet analyses.</p>

scholarly journals First-Year Operation of a New Water Vapor Raman Lidar at the JPL Table Mountain Facility, California

2008 ◽  
Vol 25 (8) ◽  
pp. 1454-1462 ◽  
Author(s):  
Thierry Leblanc ◽  
I. Stuart McDermid ◽  
Robin A. Aspey
Keyword(s):  
Water Vapor ◽  
Current System ◽  
First Year ◽  
Raman Lidar ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
Table Mountain ◽  
Lidar Measurements ◽  
Better Than ◽  
Good Agreement

Abstract A new water vapor Raman lidar was recently built at the Table Mountain Facility (TMF) of the Jet Propulsion Laboratory (JPL) in California and more than a year of routine 2-h-long nighttime measurements 4–5 times per week have been completed. The lidar was designed to reach accuracies better than 5% anywhere up to 12-km altitude, and with the capability to measure water vapor mixing ratios as low as 1 to 10 ppmv near the tropopause and in the lower stratosphere. The current system is not yet fully optimized but has already shown promising results as water vapor profiles have been retrieved up to 18-km altitude. Comparisons with Vaisala RS92K radiosondes exhibit very good agreement up to at least 10 km. They also revealed a wet bias in the lidar profiles (or a dry bias in the radiosonde profiles), increasing with altitude and becoming significant near 10 km and large when approaching the tropopause. This bias cannot be explained solely by well-known too-dry measurements of the RS92K in the upper troposphere and therefore must partly originate in the lidar measurements. Excess signal due to residual fluorescence in the lidar receiver components is among the most likely candidates and is subject to ongoing investigation.

scholarly journals The Full-Spectrum Correlated-k Method for Longwave Atmospheric Radiative Transfer Using an Effective Planck Function

2010 ◽  
Vol 67 (6) ◽  
pp. 2086-2100 ◽  
Author(s):  
Robin J. Hogan
Keyword(s):  
Water Vapor ◽  
Radiative Transfer ◽  
Heating Rate ◽  
Rank Correlation ◽  
Quadrature Point ◽  
Atmospheric Models ◽  
Heating Rates ◽  
Full Spectrum ◽  
Clear Sky ◽  
Different Gases

Abstract The correlated-k-distribution (CKD) method is widely used in the radiative transfer schemes of atmospheric models; it involves dividing the spectrum into a number of bands and then reordering the gaseous absorption coefficients within each one. The fluxes and heating rates for each band may then be computed by discretizing the reordered spectrum into O(10) quadrature points per major gas and performing a pseudomonochromatic radiation calculation for each point. In this paper it is first argued that for clear-sky longwave calculations, sufficient accuracy for most applications can be achieved without the need for bands: reordering may be performed on the entire longwave spectrum. The resulting full-spectrum correlated-k (FSCK) method requires significantly fewer pseudomonochromatic calculations than standard CKD to achieve a given accuracy. The concept is first demonstrated by comparing with line-by-line calculations for an atmosphere containing only water vapor, in which it is shown that the accuracy of heating rate calculations improves approximately in proportion to the square of the number of quadrature points. For more than around 20 points, the root-mean-square error flattens out at around 0.015 K day−1 due to the imperfect rank correlation of absorption spectra at different pressures in the profile. The spectral overlap of m different gases is treated by considering an m-dimensional hypercube where each axis corresponds to the reordered spectrum of one of the gases. This hypercube is then divided up into a number of volumes, each approximated by a single quadrature point, such that the total number of quadrature points is slightly fewer than the sum of the number that would be required to treat each of the gases separately. The gaseous absorptions for each quadrature point are optimized such that they minimize a cost function expressing the deviation of the heating rates and fluxes calculated by the FSCK method from line-by-line calculations for a number of training profiles. This approach is validated for atmospheres containing water vapor, carbon dioxide, and ozone, in which it is found that in the troposphere and most of the stratosphere, heating rate errors of less than 0.2 K day−1 can be achieved using a total of 23 quadrature points, decreasing to less than 0.1 K day−1 for 32 quadrature points. It would be relatively straightforward to extend the method to include other gases.

Maintenance of Lower Tropospheric Temperature Inversion in the Saharan Air Layer by Dust and Dry Anomaly

2009 ◽  
Vol 22 (19) ◽  
pp. 5149-5162 ◽  
Author(s):  
Sun Wong ◽  
Andrew E. Dessler ◽  
Natalie M. Mahowald ◽  
Ping Yang ◽  
Qian Feng
Keyword(s):  
Water Vapor ◽  
Radiative Transfer ◽  
Heating Rate ◽  
Temperature Inversion ◽  
Dust Content ◽  
Radiative Heating ◽  
Specific Humidity ◽  
Transfer Model ◽  
Tropospheric Temperature ◽  
Saharan Air Layer

Abstract The role of Saharan dust and dry anomaly in maintaining the temperature inversion in the Saharan air layer (SAL) is investigated. The dust aerosol optical thickness (AOT) in the SAL is inferred from the measurements taken by Aqua Moderate Resolution Imaging Spectroradiometer (MODIS), and the corresponding temperature and specific humidity anomalies are identified using the National Centers for Environmental Prediction (NCEP) data in August–September over the North Atlantic tropical cyclone (TC) main development region (MDR; 10°–20°N, 40°–60°W). The authors also study the SAL simulated in the National Center of Atmospheric Research (NCAR) Community Atmosphere Model, version 3 (CAM3), coupled with dust radiative effect. It is found that higher AOT is associated with warmer and dryer anomalies below 700 hPa, which increases the atmospheric stability. The calculated instantaneous radiative heating anomalies from a radiative transfer model indicate that both the dust and low humidity are essential to maintaining the temperature structure in the SAL against thermal relaxation. At 850 hPa, heating anomalies caused by both the dust and dry anomalies (for AOT > 0.8) are 0.2–0.4 K day−1. The dust heats the atmosphere below 600 hPa, while the dry anomaly cools the atmosphere below 925 hPa, resulting in a peak of heating rate anomaly located at 700–850 hPa. In the eastern Atlantic, dust contributes about 50% of the heating rate anomaly. Westward of 40°W, when the dust content becomes small (AOT < 0.6), the heating rates are more sensitive to the water vapor profile used in the radiative transfer calculation. Retrieving or simulating correct water vapor profiles is essential to the assessment of the SAL heating budgets in regions where the dust content in the SAL is small.

scholarly journals Using aircraft measurements to determine the refractive index of Saharan dust during the DODO Experiments

2010 ◽  
Vol 10 (6) ◽  
pp. 3081-3098 ◽  
Author(s):  
C. L. McConnell ◽  
P. Formenti ◽  
E. J. Highwood ◽  
M. A. J. Harrison
Keyword(s):  
Refractive Index ◽  
Iron Oxide ◽  
Radiative Transfer ◽  
Size Distribution ◽  
Imaginary Part ◽  
Mineral Dust ◽  
Refractive Indices ◽  
Aircraft Measurements ◽  
Radiative Effect ◽  
Radiative Transfer Modeling

Abstract. Much uncertainty in the value of the imaginary part of the refractive index of mineral dust contributes to uncertainty in the radiative effect of mineral dust in the atmosphere. A synthesis of optical, chemical and physical in-situ aircraft measurements from the DODO experiments during February and August 2006 are used to calculate the refractive index mineral dust encountered over West Africa. Radiative transfer modeling and measurements of broadband shortwave irradiance at a range of altitudes are used to test and validate these calculations for a specific dust event on 23 August 2006 over Mauritania. Two techniques are used to determine the refractive index: firstly a method combining measurements of scattering, absorption, size distributions and Mie code simulations, and secondly a method using composition measured on filter samples to apportion the content of internally mixed quartz, calcite and iron oxide-clay aggregates, where the iron oxide is represented by either hematite or goethite and clay by either illite or kaolinite. The imaginary part of the refractive index at 550 nm (ni550) is found to range between 0.0001 i to 0.0046 i, and where filter samples are available, agreement between methods is found depending on mineral combination assumed. The refractive indices are also found to agree well with AERONET data where comparisons are possible. ni550 is found to vary with dust source, which is investigated with the NAME model for each case. The relationship between both size distribution and ni550 on the accumulation mode single scattering albedo at 550 nm (ω0550) are examined and size distribution is found to have no correlation to ω0550, while ni550 shows a strong linear relationship with ω0550. Radiative transfer modeling was performed with different models (Mie-derived refractive indices, but also filter sampling composition assuming both internal and external mixing). Our calculations indicate that Mie-derived values of ni550 and the externally mixed dust where the iron oxide-clay aggregate corresponds to the goethite-kaolinite combination result in the best agreement with irradiance measurements. The radiative effect of the dust is found to be very sensitive to the mineral combination (and hence refractive index) assumed, and to whether the dust is assumed to be internally or externally mixed.

scholarly journals Combining atmospheric and snow layer radiative transfer models to assess the solar radiative effects of black carbon in the Arctic

2020 ◽  
Author(s):  
Tobias Donth ◽  
Evelyn Jäkel ◽  
André Ehrlich ◽  
Bernd Heinold ◽  
Jacob Schacht ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Black Carbon ◽  
Heating Rate ◽  
Mass Concentration ◽  
Early Spring ◽  
Early Summer ◽  
The Arctic ◽  
Radiative Effect ◽  
Snow Layer ◽  
Surface Snow

Abstract. Solar radiative effects (cooling or warming) of black carbon (BC) particles suspended in the Arctic atmosphere and surface snow layer were explored by radiative transfer simulations on the basis of BC mass concentrations measured in pristine early summer and polluted early spring conditions under cloudless and cloudy conditions. To account for the radiative interactions between the black carbon containing snow surface layer and the atmosphere, a snow layer and an atmospheric radiative transfer model were coupled iteratively. For pristine summer conditions (no atmospheric BC) and a representative BC particle mass concentration of 5 ng g−1 in the surface snow layer, a positive solar radiative effect of +0.2 W m−2 was calculated for the surface radiative budget. Contrarily, a higher load of atmospheric BC representing springtime conditions, results in a slightly negative radiative effect of about −0.05 W m−2, even when the same BC mass concentration is suspended in the surface snow layer. This counteracting of atmospheric BC and BC suspended in the snow layer strongly depends on the snow optical properties determined by the snow specific surface area. However, it was found, that the atmospheric heating rate by water vapor or clouds is one to two orders of magnitude larger than that by atmospheric BC. Similarly, the total heating rate (6 K day−1) within a snow pack due to absorption by the ice water, was found to be more than one order of magnitude larger than the heating rate of suspended BC (0.2 K day−1). The role of clouds in the estimation of the combined direct radiative BC effect (BC in snow and in atmosphere) was analyzed for the pristine early summer and the polluted early spring BC conditions. Both, the cooling effect by atmospheric BC, as well as the warming effect by BC suspended in snow are reduced in the presence of clouds.

scholarly journals Aerosol properties and aerosol–radiation interactions in clear-sky conditions over Germany

2021 ◽  
Vol 21 (19) ◽  
pp. 14591-14630
Author(s):  
Jonas Witthuhn ◽  
Anja Hünerbein ◽  
Florian Filipitsch ◽  
Stefan Wacker ◽  
Stefanie Meilinger ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Radiative Transfer ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Short Wave ◽  
Radiative Effect ◽  
Radiation Model ◽  
Clear Sky ◽  
Solar Radiation Model ◽  
Level Of Agreement

Abstract. The clear-sky radiative effect of aerosol–radiation interactions is of relevance for our understanding of the climate system. The influence of aerosol on the surface energy budget is of high interest for the renewable energy sector. In this study, the radiative effect is investigated in particular with respect to seasonal and regional variations for the region of Germany and the year 2015 at the surface and top of atmosphere using two complementary approaches. First, an ensemble of clear-sky models which explicitly consider aerosols is utilized to retrieve the aerosol optical depth and the surface direct radiative effect of aerosols by means of a clear-sky fitting technique. For this, short-wave broadband irradiance measurements in the absence of clouds are used as a basis. A clear-sky detection algorithm is used to identify cloud-free observations. Considered are measurements of the short-wave broadband global and diffuse horizontal irradiance with shaded and unshaded pyranometers at 25 stations across Germany within the observational network of the German Weather Service (DWD). The clear-sky models used are the Modified MAC model (MMAC), the Meteorological Radiation Model (MRM) v6.1, the Meteorological–Statistical solar radiation model (METSTAT), the European Solar Radiation Atlas (ESRA), Heliosat-1, the Center for Environment and Man solar radiation model (CEM), and the simplified Solis model. The definition of aerosol and atmospheric characteristics of the models are examined in detail for their suitability for this approach. Second, the radiative effect is estimated using explicit radiative transfer simulations with inputs on the meteorological state of the atmosphere, trace gases and aerosol from the Copernicus Atmosphere Monitoring Service (CAMS) reanalysis. The aerosol optical properties (aerosol optical depth, Ångström exponent, single scattering albedo and asymmetry parameter) are first evaluated with AERONET direct sun and inversion products. The largest inconsistency is found for the aerosol absorption, which is overestimated by about 0.03 or about 30 % by the CAMS reanalysis. Compared to the DWD observational network, the simulated global, direct and diffuse irradiances show reasonable agreement within the measurement uncertainty. The radiative kernel method is used to estimate the resulting uncertainty and bias of the simulated direct radiative effect. The uncertainty is estimated to −1.5 ± 7.7 and 0.6 ± 3.5 W m−2 at the surface and top of atmosphere, respectively, while the annual-mean biases at the surface, top of atmosphere and total atmosphere are −10.6, −6.5 and 4.1 W m−2, respectively. The retrieval of the aerosol radiative effect with the clear-sky models shows a high level of agreement with the radiative transfer simulations, with an RMSE of 5.8 W m−2 and a correlation of 0.75. The annual mean of the REari at the surface for the 25 DWD stations shows a value of −12.8 ± 5 W m−2 as the average over the clear-sky models, compared to −11 W m−2 from the radiative transfer simulations. Since all models assume a fixed aerosol characterization, the annual cycle of the aerosol radiation effect cannot be reproduced. Out of this set of clear-sky models, the largest level of agreement is shown by the ESRA and MRM v6.1 models.

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