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Extinction and optical depth retrievals for CALIPSO's Version 4 data release
摘要： The Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) on board the Cloud–Aerosol Lidar Infrared Pathfinder Satellite Observations (CALIPSO) satellite has been making near-global height-resolved measurements of cloud and aerosol layers since mid-June 2006. Version 4.10 (V4) of the CALIOP data products, released in November 2016, introduces extensive upgrades to the algorithms used to retrieve the spatial and optical properties of these layers, and thus there are both obvious and subtle differences between V4 and previous data releases. This paper describes the improvements made to the extinction retrieval algorithms and illustrates the impacts of these changes on the extinction and optical depth estimates reported in the CALIPSO lidar level 2 data products. The lidar ratios for both aerosols and ice clouds are generally higher than in previous data releases, resulting in generally higher extinction coefficients and optical depths in V4. A newly implemented algorithm for retrieving extinction coefficients in opaque layers is described and its impact examined. Precise lidar ratio estimates are also retrieved in these opaque layers. For semi-transparent cirrus clouds, comparisons between CALIOP V4 optical depths and the optical depths reported by MODIS collection 6 show substantial improvements relative to earlier comparisons between CALIOP version 3 and MODIS collection 5.
关键词： retrieval algorithms,clouds,CALIOP,lidar,optical depth,CALIPSO,aerosols,extinction,version 4
更新于2025-09-23 15:22:29
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A radiative transfer module for calculating photolysis rates and solar heating in climate models: Solar-J v7.5
摘要： Solar-J is a comprehensive radiative transfer model for the solar spectrum that addresses the needs of both solar heating and photochemistry in Earth system models. Solar-J is a spectral extension of Cloud-J, a standard in many chemical models that calculates photolysis rates in the 0.18–0.8 μm region. The Cloud-J core consists of an eight-stream scattering, plane-parallel radiative transfer solver with corrections for sphericity. Cloud-J uses cloud quadrature to accurately average over correlated cloud layers. It uses the scattering phase function of aerosols and clouds expanded to eighth order and thus avoids isotropic-equivalent approximations prevalent in most solar heating codes. The spectral extension from 0.8 to 12 μm enables calculation of both scattered and absorbed sunlight and thus aerosol direct radiative effects and heating rates throughout the Earth’s atmosphere. The Solar-J extension adopts the correlated-k gas absorption bins, primarily water vapor, from the shortwave Rapid Radiative Transfer Model for general circulation model (GCM) applications (RRTMG-SW). Solar-J successfully matches RRTMG-SW’s tropospheric heating profile in a clear-sky, aerosol-free, tropical atmosphere. We compare both codes in cloudy atmospheres with a liquid-water stratus cloud and an ice-crystal cirrus cloud. For the stratus cloud, both models use the same physical properties, and we find a systematic low bias of about 3 % in planetary albedo across all solar zenith angles caused by RRTMG-SW’s two-stream scattering. Discrepancies with the cirrus cloud using any of RRTMG-SW’s three different parameterizations are as large as about 20–40 % depending on the solar zenith angles and occur throughout the atmosphere. Effectively, Solar-J has combined the best components of RRTMG-SW and Cloud-J to build a high-fidelity module for the scattering and absorption of sunlight in the Earth’s atmosphere, for which the three major components – wavelength integration, scattering, and averaging over cloud fields – all have comparably small errors. More accurate solutions with Solar-J come with increased computational costs, about 5 times that of RRTMG-SW for a single atmosphere. There are options for reduced costs or computational acceleration that would bring costs down while maintaining improved fidelity and balanced errors.
关键词： solar heating,clouds,Cloud-J,climate models,radiative transfer,photolysis rates,scattering,aerosols,RRTMG-SW,Solar-J
更新于2025-09-23 15:22:29
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Improving direct normal irradiance retrieval in cloud-free, but high aerosol load conditions by using aerosol optical depth
摘要： Measurements of the global surface solar irradiation and its direct and diffuse components performed at three Egyptian sites (Aswan, Cairo, and Port Said) are used to test the ability of two published decomposition models to estimate the hourly direct normal irradiance from the measured global horizontal one in cloud-free conditions. The tested models failed to reproduce the temporal variability of the measurements, which we show to be partly induced by the large variability of the atmospheric content in aerosols. We propose a revised formulation of the decomposition models that takes into account the aerosol optical depth (AOD) at 1000 nm derived from onsite measurements. It leads to a significant reduction of the bias and root mean square deviation of the original models and this at the three Egyptian sites. However, because the AOD is rarely measured at the meteorological stations, we also quantify the performance of the revised models when the AOD is either derived from the MODIS observations or obtained by the products from Copernicus Atmospheric Monitoring Service (CAMS). Probably because of their finer temporal resolution that makes them more apt to reproduce the rapid variations of the AOD, the best results are obtained with the CAMS products. Therefore, we recommend using a combination of the revised decomposition models and these CAMS products to estimate the hourly direct normal irradiance in areas such as Egypt where aerosols are ubiquitous. Note that the improved decomposition models are generally applicable in all-sky conditions, although their benefit has been demonstrated to be significant, and probably limited to, cloud-free conditions.
关键词： Egypt,Direct normal irradiance,Aerosols,MENA
更新于2025-09-23 15:22:29
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Atmospheric response to the 20 March 2015 solar eclipse along the whole aerosol column by lidar measurements
摘要： Lidar measurements at 355, 532, and 1064 nm have been performed at Lecce (40.3°N, 18.1°E), in south-eastern Italy, to investigate for the first time the impact of the 20 March 2015 solar eclipse on both the planetary boundary layer (PBL) height and the aerosol optical and microphysical properties along the whole aerosol column. The partial solar eclipse lasted from 08:30 up to 10:47 UTC and reached the full phase at 09:37 UTC. The maximum percentage obscuration of the solar disk was 43.6%. The eclipse cooling effect was responsible at the full phase time (tF) for the downward solar irradiance decrease at the top of the atmosphere, at the surface, and within the atmosphere of 429.2 ± 0.6, 373 ± 25, and 56 ± 26 W m-2, respectively. The turbulent kinetic energy, the potential temperature flux, the sensible heat flux, the variance of air temperature, and the vertical wind speed at the surface revealed that the turbulence activity reached the maximum weakening at the time tF. The standard deviation (SD) technique has been applied to both the lidar range corrected signals (RCS) at 1064 nm and the linear volume depolarization ratio (δV) profiles at 355 nm to determine the time evolution of the shallow PBL height and the aloft aerosol layers. The SD technique applied to RCS and δV profiles revealed similar results within experimental uncertainties. The PBL height, which was equal to 380 ± 40 m above ground level (AGL) at the eclipse full phase (09:37 UTC), decreased up to 220 ± 20 m at 09:45 UTC because of the eclipse cooling effect, and then increased up to 320 ± 30 m at 10:17 UTC. The determined PBL height time evolution was in good agreement with the ones of the main turbulence parameters at the surface after tF. The vertical profiles of the aerosol backscatter coefficient (β), the δV at 355 nm, and the extinction-related ?ngstr?m exponent (?), calculated at the 355-1064 nm wavelength pair revealed a marked decrease of β, δV, and ? at the eclipse full phase, within the aloft aerosol layers. The abrupt β, δV, and ? decrease due to the aerosol concentration and type changes has mainly been associated with the decrease of the fine-mode particle contribution.
关键词： solar irradiance,Solar eclipse,lidar measurements,atmospheric aerosols,turbulence parameters,planetary boundary layer
更新于2025-09-23 15:21:01
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Visualizing Speech-Generated Oral Fluid Droplets with Laser Light Scattering
摘要： Aerosols and droplets generated during speech have been implicated in the person-to-person transmission of viruses, and there is current interest in understanding the mechanisms responsible for the spread of Covid-19 by these means. The act of speaking generates oral fluid droplets that vary widely in size, and these droplets can harbor infectious virus particles. Whereas large droplets fall quickly to the ground, small droplets can dehydrate and linger as “droplet nuclei” in the air, where they behave like an aerosol and thereby expand the spatial extent of emitted infectious particles. We report the results of a laser light-scattering experiment in which speech-generated droplets and their trajectories were visualized.
关键词： Covid-19,speech,virus transmission,laser light-scattering,droplets,aerosols
更新于2025-09-23 15:19:57
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Future evolution of surface solar radiation and photovoltaic potential in Europe: investigating the role of aerosols
摘要： In recent decades, trends in photovoltaic (PV) technology deployment have shown an overall increase across the world. Comprehensive knowledge of the solar resource and its future evolution is demanded by the energy sector. Solar resource and PV potential have been estimated in several studies using both the global climate model (GCM) and regional climate model (RCM), revealing a GCM–RCM discrepancy in the projected change over Europe. An increase in surface solar radiation (SSR) (and therefore in PV potential production) is projected by GCMs, whereas most RCM simulations project a decrease in SSR over Europe. In this work, we investigate the role of aerosol forcing in RCMs as a key explaining factor of this inconsistency. The results show that RCM simulations including evolving aerosols agree with GCMs in the sign and amplitude of the SSR change over Europe for mid-21st century projections (2021–2050 compared to 1971–2000 for representative concentration pathway climate change scenario RCP8.5). The opposite signal is projected by the rest of the RCMs. The amplitude of the changes likely depends on the RCM and on its aerosol forcing choice. In terms of PV potential, RCMs including evolving aerosols simulate an increase, especially in summer for Central and Eastern Europe, with maximum values reaching +10% in some cases. This study illustrates the key role of the often-neglected aerosol forcing evolution in RCMs. It also suggests that it is important to be very careful when using the multi-model Coordinated Regional Climate Downscaling Experiment (CORDEX) projections for solar radiation and related variables, and argues for the inclusion of aerosol forcing evolution in the next generation of CORDEX simulations.
关键词： regional climate modeling,photovoltaic future projections,aerosols,photovoltaic energy
更新于2025-09-23 15:19:57
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A novel single-cavity three-wavelength photoacoustic spectrometer for atmospheric aerosol research
摘要： The spectral light-absorbing behavior of carbonaceous aerosols varies depending on the chemical composition and structure of the particles. A new single-cavity three-wavelength photoacoustic spectrometer was developed and characterized for measuring absorption coefficients at three wavelengths across the visible spectral range. In laboratory studies, several types of soot with different organic content were generated by a diffusion flame burner and were investigated for changes in mass-specific absorption cross section (MAC) values, absorption and scattering ?ngstr?m exponents (αabs and αsca), and single scattering albedo (ω). By increasing the organic carbonaceous (OC) content of the aerosol from 50 to 90 % of the total carbonaceous mass, for 660 nm nearly no change of MAC was found with increasing OC content. In contrast, for 532 nm a significant increase, and for 445 nm a strong increase of MAC was found with increasing OC content of the aerosol. Depending on the OC content, the ?ngstr?m exponents of absorption and scattering as well as the single scattering albedo increased. These laboratory results were compared to a field study at a traffic-dominated urban site, which was also influenced by residential wood combustion. For this site a daily average value of αabs(445–660) of 1.9 was found.
关键词： light absorption,carbonaceous aerosols,organic carbon,photoacoustic spectrometer,black carbon,single scattering albedo,?ngstr?m exponents
更新于2025-09-23 15:19:57
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Echo characteristics of polarized heterodyne lidar in nonspherical aerosol environments
摘要： Heterodyne lidar echoes in atmospheric detection are greatly affected by the shapes of aerosols. With the aid of T-matrix and vector Monte Carlo simulation, we investigated the properties of lidar echoes backscattered by randomly oriented polydisperse aerosols, including the soot, sea salt and mineral aerosols. The degree of polarization (DoP) and backscattered photon numbers in different range bins are calculated when the launched laser pulses are linearly polarized light and circularly polarized light at 1.55 μm. There are reductions of DoP along the 10 km detection path, which vary with aspect ratios (AR) and aerosol types. The ARs are chosen within 0.5–2.0 for cylinders and 0.3–1.0 for spheroids. The lidar echoes in soot aerosols have the largest DoP which is higher than 0.8. Moreover, the shape fading factor and polarization fading factor are defined and calculated based on the effective backscattered photon numbers, which shows that the mineral aerosols in nuc.mode (MINM) is less affected by aerosol shapes and laser polarization states, and that the LPL is suitable for the heterodyne detection of nonspherical atmospheric aerosols. The results provide echo characteristic deviations from the spherical particle scattering, which can be used in the practical modeling of atmospheric echoes and designs of heterodyne lidars.
关键词： Nonspherical aerosols,T-matrix,Heterodyne lidar,Polarization
更新于2025-09-19 17:15:36
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An LM-BP Neural Network Approach to Estimate Monthly-Mean Daily Global Solar Radiation Using MODIS Atmospheric Products
摘要： Solar energy is one of the most widely used renewable energy sources in the world and its development and utilization are being integrated into people’s lives. Therefore, accurate solar radiation data are of great significance for site-selection of photovoltaic (PV) power generation, design of solar furnaces and energy-efficient buildings. Practically, it is challenging to get accurate solar radiation data because of scarce and uneven distribution of ground-based observation sites throughout the country. Many artificial neural network (ANN) estimation models are therefore developed to estimate solar radiation, but the existing ANN models are mostly based on conventional meteorological data; clouds, aerosols, and water vapor are rarely considered because of a lack of instrumental observations at the conventional meteorological stations. Based on clouds, aerosols, and precipitable water-vapor data from Moderate Resolution Imaging Spectroradiometer (MODIS), along with conventional meteorological data, back-propagation (BP) neural network method was developed in this work with Levenberg-Marquardt (LM) algorithm (referred to as LM-BP) to simulate monthly-mean daily global solar radiation (M-GSR). Comparisons were carried out among three M-GSR estimates, including the one presented in this study, the multiple linear regression (MLR) model, and remotely-sensed radiation products by Cloud and the Earth’s radiation energy system (CERES). The validation results indicate that the accuracy of the ANN model is better than that of the MLR model and CERES radiation products, with a root mean squared error (RMSE) of 1.34 MJ·m?2 (ANN), 2.46 MJ·m?2 (MLR), 2.11 MJ·m?2 (CERES), respectively. Finally, according to the established ANN-based method, the M-GSR of 36 conventional meteorological stations for 12 months was estimated in 2012 in the study area. Solar radiation data based on the LM-BP method of this study can provide some reference for the utilization of solar and heat energy.
关键词： precipitable water vapor,solar radiation,LM-BP neural network,aerosols,clouds
更新于2025-09-19 17:15:36
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Comparison and evaluation of MODIS Multi-angle Implementation of Atmospheric Correction (MAIAC) aerosol product over South Asia
摘要： The Multiangle Implementation of Atmospheric Correction (MAIAC) is a new generic algorithm applied to collection 6 (C6) MODIS measurements to retrieve Aerosol Optical Depth (AOD) over land at high spatial resolution (1 km). This study is the first evaluation of the MAIAC AOD from MODIS Aqua (A) and Terra (T) satellites between 2006 and 2016 over South Asia. The retrieval accuracy of MAIAC was assessed by comparing it to ground-truth AErosol RObotic NETwork (AERONET) AOD, as well as to AOD retrieved by the two operational MODIS algorithms: Dark Target (DT) and Deep Blue (DB). MAIAC AOD showed higher spatial coverage and retrieval frequency than either the DT or the DB AOD retrievals. The high spatial resolution of the MAIAC retrievals enhances the capability to distinguish aerosol sources and to determine fine aerosol features, such as wildfire smoke plumes and haze over complex geographical regions, and provides more retrievals in conditions that are cloudy or when the surface is partially covered by snow. In comparison to AERONET AOD, MAIAC AOD shows a better accuracy than both DT and DB AOD. A higher number of MAIAC-AERONET AOD matchups demonstrate the capability of MAIAC to retrieve AOD over varied surfaces, different aerosol types and loadings. Our results demonstrate high retrieval accuracy in term of the Expected Error (EE) (A/T, EE: 72.22%, 73.50%), and low root mean square error (A/T, RMSE: 0.148, 0.164), root mean bias (RMB) (A/T, RMB: 0.978, 1.049) and mean absolute error (MAE) (A/T, MAE: 0.098, 0.096). Moreover, MAIAC has a lower bias as a function of the viewing geometry and the aerosol type among the three retrieval algorithms. MAIAC performed well over bright and vegetated land surfaces, showing the highest retrieval accuracy over dense vegetation and particularly well in retrieving smoke AOD, yet it underestimated dust AOD. In conclusion, MAIAC's ability to provide AOD at high spatial resolution appears promising over South Asia, thus having advantage over contemporary aerosol retrieval algorithms for epidemiological and climatological studies.
关键词： South Asia,AOD,MODIS,IGP,Aerosols,AERONET,MAIAC
更新于2025-09-19 17:15:36