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Radiative Transfer in the Earth Atmosphere

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A special issue of Atmosphere (ISSN 2073-4433). This special issue belongs to the section "Meteorology".

Deadline for manuscript submissions: closed (20 December 2020) | Viewed by 56558

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Prof. Dr. Irina N. Sokolik

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School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA

Special Issue Information

Dear Colleagues,

Electromagnetic radiation, propagating thought the Earth's atmosphere, plays many important roles in controlling the environment and climate. It provides light to support human life, and also provides PAR radiation to support vegetation growth.

Originating from the sun, solar radiation is a main source of energy, followed by the thermal IR radiation emitted by the Earth–atmosphere system. The radiative budget is a sum of solar and IR radiation, and it controls the Earth climate system, affecting all major dynamics and thermodynamic processes that occur in the system. Major radiative quantities include the surface radiation budget, the profile of heating/cooling radiative rates, radiative forcing at the top of the atmosphere, and actinic fluxes. The latter plays an important role in atmospheric chemistry by controlling photochemical reaction rates, which are important in ozone production.

There have been a great many efforts directed at the measurement and modeling of electromagnetic radiation. This Special Issue provides a summary of recent accomplishments in studying the diverse impacts of electromagnetic radiation, including recent progress in modeling, as well as measurements. The fast growth of satellite remote sensing, which is based on measurements of electromagnetic radiation in different parts of the spectrum of electromagnetic energy, has provided significant progress in the understanding of the properties, life-cycles, and diverse impacts of aerosol and clouds. In addition, aircraft measurements of radiation have provided an important understanding of the impact of aerosol and clouds on the propagation of electromagnetic radiation under different cloudy and aerosol-laden conditions.

Aerosols, clouds, and some gases are major atmospheric components that strongly influence the propagation of electromagnetic radiation through the atmosphere. Because the properties of aerosols and clouds are highly variable in space and time, predictions of their radiative impacts have been difficult make. The major types of atmospheric aerosols that affect electromagnetic radiation include mineral dust aerosols, smoke aerosols, including black carbon, organic carbon, sea-salt, and various sulfate and nitrate compounds. They all have distinct physical and chemical properties that affect their interactions with electromagnetic radiation. Given that these properties vary strongly during aerosol and cloud lifetimes in the atmosphere, their quantitative characterization has been particularly difficult.

There are a variety of clouds that all interact with radiation, depending on the concentrations and size distributions of cloud drops. The presence of ice crystals adds an additional complexity to the prediction of their radiative impacts. Although they are made from ice, the single species, their optical properties, and, thus, radiative impacts are strongly dependent on their various shapes.

Representations of aerosols and clouds in general circulation models and regional transport models have been exploited as a powerful tool to estimate the radiative impacts of aerosol and cloud through a detailed representation of their major processes, such as their emissions, formation in the atmosphere, and transport (including the evolution of their physical and chemical properties that affect their optical properties and radiative impacts).

This Special Issue aims at addressing some of the recent developments towards improving our understanding of the diverse radiative impact of different types of aerosols and clouds.

Prof. Dr. Irina N. Sokolik
Guest Editor

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Keywords

electromagnetic radiation
scattering
absorption
emission
surface reflection and emission
radiative fluxes
heating/cooling radiative rates
radiative forcing
radiative budget
satellite remote sensing

Published Papers (14 papers)

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Editorial

Jump to: Research, Review

3 pages, 164 KiB

Open AccessEditorial

Introduction to the Special Issue “Radiative Transfer in the Earth Atmosphere”

by Irina Sokolik

Atmosphere 2021, 12(4), 479; https://doi.org/10.3390/atmos12040479 - 09 Apr 2021

Cited by 1 | Viewed by 1245

Abstract

This Special Issue aims at addressing the recent developments towards improving our understanding of the diverse radiative impact of different types of aerosols and clouds [...] Full article

(This article belongs to the Special Issue Radiative Transfer in the Earth Atmosphere)

Research

Jump to: Editorial, Review

20 pages, 24977 KiB

Open AccessArticle

The Impact of Aerosols on Satellite Radiance Data Assimilation Using NCEP Global Data Assimilation System

by Shih-Wei Wei, Cheng-Hsuan (Sarah) Lu, Quanhua Liu, Andrew Collard, Tong Zhu, Dustin Grogan, Xu Li, Jun Wang, Robert Grumbine and Partha S. Bhattacharjee

Atmosphere 2021, 12(4), 432; https://doi.org/10.3390/atmos12040432 - 28 Mar 2021

Cited by 7 | Viewed by 2370

Abstract

Aerosol radiative effects have been studied extensively by climate and weather research communities. However, aerosol impacts on radiance in the context of data assimilation (DA) have received little research attention. In this study, we investigated the aerosol impacts on the assimilation of satellite radiances by incorporating time-varying three-dimensional aerosol distributions into the radiance observation operator. A series of DA experiments was conducted for August 2017. We assessed the aerosol impacts on the simulated brightness temperatures (BTs), bias correction and quality control (QC) algorithms for the assimilated infrared sensors, and analyzed temperature fields. We found that taking the aerosols into account reduces simulated BT in thermal window channels (8 to 13 μm) by up to 4 K over dust-dominant regions. The cooler simulated BTs result in more positive first-guess departures, produce more negative biases, and alter the QC checks about 20%/40% of total/assimilated observations at the wavelength of 10.39 μm. As a result, assimilating aerosol-affected BTs produces a warmer analyzed lower atmosphere and sea surface temperature which have better agreement with measurements over the trans-Atlantic region. Full article

(This article belongs to the Special Issue Radiative Transfer in the Earth Atmosphere)

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18 pages, 3726 KiB

Open AccessEditor’s ChoiceArticle

Regional Distribution of Net Radiation over Different Ecohydrological Land Surfaces

by Md Masudur Rahman, Wanchang Zhang and Arfan Arshad

Atmosphere 2020, 11(11), 1229; https://doi.org/10.3390/atmos11111229 - 14 Nov 2020

Cited by 3 | Viewed by 3007

Abstract

Net radiation is an important component of the earth’s surface energy balance, which plays a vital role in the evolution of regional climate or climate change. The estimation of this component at regional or global scales is critical and challenging due to the sparse and limited ground-based observations. This paper made an attempt to analyze the feasibility of a remote sensing-based surface energy balance model using satellite (TERRA/MODIS) data to derive the net radiation (R_n). In the present study, MODIS data at 15 different days of the year (DOY) were utilized to visualize the spatial pattern of net radiation flux over three versatile and heterogeneous ecohydrological land surfaces (upstream, midstream, and downstream) of northwest China (Heihe river basin). The results revealed that the estimated net radiation from the satellite data agrees well with the ground-based measurements over three different surfaces, with a mean relative error of 9.33% over the upstream superstation (grasslands), 13.95% over the middle stream superstation (croplands), and 11.63% over the downstream superstation (mixed forests), where the overall relative error was 11.64% with an overall rmse of 29.36 W/m² in the study area. The regional distribution of net radiation over the versatile land surfaces was validated well at a large scale during the five-month period and over different land surfaces. It was also observed that the spatial pattern of net radiation varies spatially over three different landscape regions during four different days of the year, which might be associated with different climatic conditions and landscape features in these regions. The overall findings of this study concluded that satellite-derived net radiation can rationally be obtained using a single-source remote sensing model over different land surfaces. Full article

(This article belongs to the Special Issue Radiative Transfer in the Earth Atmosphere)

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27 pages, 13072 KiB

Open AccessArticle

Weather Effects of Aerosols in the Global Forecast Model

by Gill-Ran Jeong

Atmosphere 2020, 11(8), 850; https://doi.org/10.3390/atmos11080850 - 12 Aug 2020

Cited by 5 | Viewed by 2702

Abstract

The weather effects of aerosol types were investigated using well-posed aerosol climatology through the aerosol sensitivity test of thermodynamic and hydrometeor fields, and the weather forecast performances in July of 2017. The largest aerosol direct radiative forcing (ADRF) in July was due to dust aerosols at the surface and atmosphere, and sulfate at the top of the atmosphere (TOA), respectively. The ADRF of total aerosols had unilateral tendencies in thermodynamic and hydrometeor fields. The contribution of individual aerosols was linearly additive to those of total aerosols in the heat fluxes, heating rates, humidity, and convective precipitation. However, no such linearity existed in temperature, geopotential height, cloud liquid or ice contents, and large-scale precipitation. Dust was the most influential forcing agent in July among five aerosol types due to the largest light-absorption capacity. Such unilateral tendencies of total aerosols and a part of the linearity of individual aerosols were exerted on the weather systems. The verification of medium-range forecasts showed that aerosols alleviated the overestimation of surface shortwave (SW) downward fluxes, the negative biases of temperature and geopotential heights at TOA and surface, and the underestimation in light and moderate precipitation. In contrast, they enhanced warm biases at the mid-atmosphere and underestimation in heavy precipitations, particularly negative biases in the intertropical convergence zone (ITCZ). Weather forecast scores including current aerosol information were improved in geopotential height (GPH) of the northern hemisphere (NH); however, they got worse in the temperature and the upper atmosphere GPH of the southern hemisphere (SH), which was mostly due to black carbon (BC) aerosols in the tropical regions. The missing mechanisms such as aerosol–cloud interactions, better aerosol spectral optical properties including mixing states and aging, and the near-real-time (NRT) based aerosol loading data are worthwhile to be tried in the near future for fixing the intrinsic underestimation of precipitation in ITCZ and surface radiative fluxes in the desert and biomass burning area. Full article

(This article belongs to the Special Issue Radiative Transfer in the Earth Atmosphere)

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36 pages, 30886 KiB

Open AccessArticle

A Geostationary Instrument Simulator for Aerosol Observing System Simulation Experiments

by Patricia Castellanos, Arlindo M. Da Silva, Anton S. Darmenov, Virginie Buchard, Ravi C. Govindaraju, Pubu Ciren and Shobha Kondragunta

Atmosphere 2019, 10(1), 2; https://doi.org/10.3390/atmos10010002 - 21 Dec 2018

Cited by 11 | Viewed by 5110

Abstract

In the near future, there will be several new instruments measuring atmospheric composition from geostationary orbit over North America, East Asia, and Europe. This constellation of satellites will provide high resolution, time resolved measurements of trace gases and aerosols for monitoring air quality and tracking pollution sources. This paper describes a detailed, fast, and accurate (less than 1.0% uncertainty) method for calculating synthetic top of the atmosphere (TOA) radiances from a global simulation with a mesoscale free running model, the GEOS-5 Nature Run, for remote sensing instruments in geostationary orbit that measure in the ultraviolet-visible spectral range (UV-Vis). Generating these synthetic observations is the first step of an Observing System Simulation Experiment (OSSE), a framework for evaluating the impact of a new observation or algorithm. This paper provides details of the model sampling, aerosol and cloud optical properties, surface reflectance modeling, Rayleigh scattering calculations, and a discussion of the uncertainties of the simulated TOA radiance. An application for the simulated TOA radiance observations is demonstrated in the manuscript. Simulated TEMPO (Tropospheric Emissions: Monitoring of Pollution) and GOES-R (Geostationary Operational Environmental Satellites) observations were used to show how observations from the two instruments could be combined to facilitate aerosol type discrimination. The results demonstrate the viability of a detailed instrument simulator for radiance measurements in the UV-Vis that is capable of accurately simulating high resolution, time-resolved measurements with reasonable computational efficiency. Full article

(This article belongs to the Special Issue Radiative Transfer in the Earth Atmosphere)

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15 pages, 2268 KiB

Open AccessArticle

Response of Surface Ultraviolet and Visible Radiation to Stratospheric SO₂ Injections

by Sasha Madronich, Simone Tilmes, Ben Kravitz, Douglas G. MacMartin and Jadwiga H. Richter

Atmosphere 2018, 9(11), 432; https://doi.org/10.3390/atmos9110432 - 07 Nov 2018

Cited by 19 | Viewed by 6161

Abstract

Climate modification by stratospheric SO₂ injections, to form sulfate aerosols, may alter the spectral and angular distributions of the solar ultraviolet and visible radiation that reach the Earth’s surface, with potential consequences to environmental photobiology and photochemistry. We used modeling results from the CESM1(WACCM) stratospheric aerosol geoengineering large ensemble (GLENS) project, following the RCP8.5 emission scenario, and one geoengineering experiment with SO₂ injections in the stratosphere, designed to keep surface temperatures at 2020 levels. Zonally and monthly averaged vertical profiles of O₃, SO₂, and sulfate aerosols, at 30 N and 70 N, served as input into a radiative transfer model, to compute biologically active irradiances for DNA damage (i_DNA), UV index (UVI), photosynthetically active radiation (PAR), and two key tropospheric photodissociation coefficients (j_O1D for O₃ + hν (λ < 330 nm) → O(¹D) + O₂; and j_NO2 for NO₂ + hν (λ < 420 nm) → O(³P) + NO). We show that the geoengineering scenario is accompanied by substantial reductions in UV radiation. For example, comparing March 2080 to March 2020, i_DNA decreased by 25% to 29% in the subtropics (30 N) and by 26% to 33% in the polar regions (70 N); UVI decreased by 19% to 20% at 30 N and 23% to 26% at 70 N; and j_O1D decreased by 22% to 24% at 30 N and 35% to 40% at 70 N, with comparable contributions from sulfate scattering and stratospheric O₃ recovery. Different responses were found for processes that depend on longer UV and visible wavelengths, as these are minimally affected by ozone; PAR and j_NO2 were only slightly lower (9–12%) at 30 N, but much lower at 70 N (35–40%). Similar reductions were estimated for other months (June, September, and December). Large increases in the PAR diffuse-direct ratio occurred in agreement with previous studies. Absorption by SO₂ gas had a small (~1%) effect on j_O1D, i_DNA, and UVI, and no effect on j_NO2 and PAR. Full article

(This article belongs to the Special Issue Radiative Transfer in the Earth Atmosphere)

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17 pages, 3343 KiB

Open AccessArticle

Modeling of Aerosol Radiation-Relevant Parameters in the Troposphere of Siberia on the Basis of Empirical Data

by Mikhail V. Panchenko, Svetlana A. Terpugova, Victor V. Pol’kin, Valerii S. Kozlov and Dmitry G. Chernov

Atmosphere 2018, 9(11), 414; https://doi.org/10.3390/atmos9110414 - 23 Oct 2018

Cited by 10 | Viewed by 2596

Abstract

The paper presents the generalized empirical model of the aerosol optical characteristics in the lower 5-km layer of the atmosphere of West Siberia. The model is based on the data of long-term airborne sensing of the vertical profiles of the angular scattering coefficient, aerosol disperse composition, as well as the content of absorbing particles. The model provides for retrieval of the aerosol optical characteristics in visible and near IR wavelength ranges (complex refractive index, scattering and absorption coefficients, optical depth, single scattering albedo, and asymmetry factor of the scattering phase function). The main attention in the presented version of the model is given to two aspects: The study of the effect of the size spectrum of the absorbing substance in the composition of aerosol particles on radiative-relevant parameters (the single scattering albedo (SSA) and the asymmetry factor (AF)) and the consideration of different algorithms for taking into account the relative humidity of air. The ranges of uncertainty of SSA and AF at variations in the modal radius of the absorbing fraction at different altitudes in the troposphere are estimated. Full article

(This article belongs to the Special Issue Radiative Transfer in the Earth Atmosphere)

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13 pages, 15586 KiB

Open AccessArticle

The Impacts of Smoke Emitted from Boreal Forest Wildfires on the High Latitude Radiative Energy Budget—A Case Study of the 2002 Yakutsk Wildfires

by Zheng Lu and Irina N. Sokolik

Atmosphere 2018, 9(10), 410; https://doi.org/10.3390/atmos9100410 - 19 Oct 2018

Cited by 7 | Viewed by 2643

Abstract

We examine the 2002 Yakutsk wildfire event and simulate the impacts of smoke aerosols on local radiative energy budget, using the WRF-Chem-SMOKE model. When comparing satellite retrievals (the Surface Radiation Budget (SRB) dataset) with model simulations, we found that the agreement is generally good, except for the regions where the model predicts too few clouds or SRB misclassifies strong smoke plumes as clouds. We also found that the smoke-induced changes in upward shortwave fluxes at top of atmosphere (TOA) vary under different burning and meteorological conditions. In the first period of the fire season (9–12 August), smoke particles cause a warming effect around 3 W/m², mainly through functioning as ice nuclei, which deplete the cloud water amount in the frontal system. At the beginning of the second period of the fire season (19–20 August), large amounts of pre-existing smoke particles cause a strong cooling effect of −8 W/m². This is offset by the warming effect caused by relatively small amounts of cloud condensation nuclei increases, which promotes the rain formation and depletes the cloud water amount. After the cloud decks are well mixed with smoke plumes (21–22 August), the first indirect and direct effects of smoke together lead to a cooling of −10 W/m². These results highlight the importance of meso-scale modeling efforts in estimating the smoke-induced changes in the radiative energy budget over high latitudes. Full article

(This article belongs to the Special Issue Radiative Transfer in the Earth Atmosphere)

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19 pages, 4171 KiB

Open AccessArticle

Large-Scale Modeling of Absorbing Aerosols and Their Semi-Direct Effects

by Ina Tegen and Bernd Heinold

Atmosphere 2018, 9(10), 380; https://doi.org/10.3390/atmos9100380 - 28 Sep 2018

Cited by 15 | Viewed by 4420

Abstract

Radiative effects of absorbing black carbon and mineral dust aerosols are estimated from global aerosol climate model simulations with fixed sea surface temperatures as a boundary condition. Semi-direct effects are approximated as the residual between the total direct radiative effect and the instantaneous direct radiative effect of the simulated absorbing aerosol species. No distinction is made for aerosols from natural and anthropogenic sources. Results for global average are highly uncertain due to high model variability, but consistent with previous estimates. The global average results for black carbon aerosol semi-direct effects are small due to cancellation of regionally positive or negative effects, and may be positive or negative overall, depending on the model setup. The presence of mineral dust aerosol above dark surfaces and below a layer containing black carbon aerosol may enhance the reflectivity and act to enhance the positive radiative effect of black carbon aerosol. When mineral dust is absent the semi-direct effect at the top-of-atmosphere of black carbon aerosol from both anthropogenic and natural sources is −0.03 Wm⁻², while averaging to +0.09 Wm⁻² if dust is included. Full article

(This article belongs to the Special Issue Radiative Transfer in the Earth Atmosphere)

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28 pages, 7450 KiB

Open AccessArticle

Analysis of Dust Aerosol Retrievals Using Satellite Data in Central Asia

by Longlei Li and Irina N. Sokolik

Atmosphere 2018, 9(8), 288; https://doi.org/10.3390/atmos9080288 - 24 Jul 2018

Cited by 26 | Viewed by 4853

Abstract

Several long-term monitoring of aerosol datasets from the Moderate Resolution Imaging Spectroradiometer (MODIS) on board Terra/Aqua, Multi-angle Imaging SpectroRadiometer (MISR), Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) were used to derive the dust aerosol optical depth (DOD) in Central Asia based on the Angstrom exponent parameter and/or the particle shape. All sensors agree very well on the interannual variability of DOD. The seasonal analysis of DOD and dust occurrences identified the largest dust loading and the most frequent dust occurrence in the spring and summer, respectively. No significant trend was found during the research period in terms of both DOD and the dust occurrence. Further analysis of Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) aerosol products on a case-by-case basis in most dust months of 2007 suggested that the vertical structure is varying in terms of the extension and the dust loading from one event to another, although dust particles of most episodes have similar physical characteristics (particle shape and size). Our analysis on the vertical structure of dust plumes, the layer-integrated color ratio and depolarization ratio indicates a varied climate effect (e.g., the direct radiative impact) by mineral dust, dependent on the event being observed in Central Asia. Full article

(This article belongs to the Special Issue Radiative Transfer in the Earth Atmosphere)

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17 pages, 2356 KiB

Open AccessArticle

Assessment of Aerosol Radiative Forcing with 1-D Radiative Transfer Modeling in the U. S. South-East

by Erica J. Alston and Irina N. Sokolik

Atmosphere 2018, 9(7), 271; https://doi.org/10.3390/atmos9070271 - 17 Jul 2018

Cited by 3 | Viewed by 3677

Abstract

Aerosols and their radiative properties play an integral part in understanding Earth’s climate. It is becoming increasingly common to examine aerosol’s radiative impacts on a regional scale. The primary goal of this research is to explore the impacts of regional aerosol’s forcing at the surface and top-of-atmosphere (TOA) in the south-eastern U.S. by using a 1-D radiative transfer model. By using test cases that are representative of conditions common to this region, an estimate of aerosol forcing can be compared to other results. Speciation data and aerosol layer analysis provide the basis for the modeling. Results indicate that the region experiences TOA cooling year-round, where the winter has TOA forcings between −2.8 and −5 W/m², and the summer has forcings between −5 and −15 W/m² for typical atmospheric conditions. Surface level forcing efficiencies are greater than those estimated for the TOA for all cases considered i.e., urban and non-urban background conditions. One potential implication of this research is that regional aerosol mixtures have effects that are not well captured in global climate model estimates, which has implications for a warming climate where all radiative inputs are not well characterized, thus increasing the ambiguity in determining regional climate impacts. Full article

(This article belongs to the Special Issue Radiative Transfer in the Earth Atmosphere)

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10866 KiB

Open AccessArticle

Comparison of Five Modeling Approaches to Quantify and Estimate the Effect of Clouds on the Radiation Amplification Factor (RAF) for Solar Ultraviolet Radiation

by Eric S. Hall

Atmosphere 2017, 8(8), 153; https://doi.org/10.3390/atmos8080153 - 18 Aug 2017

Cited by 4 | Viewed by 6511

Abstract

A generally accepted value for the Radiation Amplification Factor (RAF), with respect to the erythemal action spectrum for sunburn of human skin, is −1.1, indicating that a 1.0% increase in stratospheric ozone leads to a 1.1% decrease in the biologically damaging UV radiation in the erythemal action spectrum reaching the Earth. The RAF is used to quantify the non-linear change in the biologically damaging UV radiation in the erythemal action spectrum as a function of total column ozone (O₃). Spectrophotometer measurements recorded at ten US monitoring sites were used in this analysis, and over 71,000 total UVR measurement scans of the sky were collected at those 10 sites between 1998 and 2000 to assess the RAF value. This UVR dataset was examined to determine the specific impact of clouds on the RAF. Five de novo modeling approaches were used on the dataset, and the calculated RAF values ranged from a low of −0.80 to a high of −1.38. Full article

(This article belongs to the Special Issue Radiative Transfer in the Earth Atmosphere)

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Review

Jump to: Editorial, Research

31 pages, 8717 KiB

Open AccessReview

A Review of Ice Cloud Optical Property Models for Passive Satellite Remote Sensing

by Ping Yang, Souichiro Hioki, Masanori Saito, Chia-Pang Kuo, Bryan A. Baum and Kuo-Nan Liou

Atmosphere 2018, 9(12), 499; https://doi.org/10.3390/atmos9120499 - 17 Dec 2018

Cited by 41 | Viewed by 5914

Abstract

The current wealth of spaceborne passive and active measurements from ultraviolet to the infrared wavelengths provides an unprecedented opportunity to construct ice cloud bulk optical property models that lead to consistent ice cloud property retrievals across multiple sensors and platforms. To infer the microphysical and radiative properties of ice clouds from these satellite measurements, the general approach is to assume an ice cloud optical property model that implicitly assumes the habit (shape) and size distributions of the ice particles in these clouds. The assumption is that this ice optical property model will be adequate for global retrievals. In this review paper, we first summarize the key optical properties of individual particles and then the bulk radiative properties of their ensemble, followed by a review of the ice cloud models developed for application to satellite remote sensing. We illustrate that the random orientation condition assumed for ice particles is arguably justified for passive remote sensing applications based on radiometric measurements. The focus of the present discussion is on the ice models used by the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Clouds and Earth’s Radiant Energy System (CERES) science teams. In addition, we briefly review the ice cloud models adopted by the Polarization and Directionality of the Earth’s Reflectance (POLDER) and the Himawari-8 Advanced Himawari Imager (AHI) for ice cloud retrievals. We find that both the MODIS Collection 6 ice model and the CERES two-habit model result in spectrally consistent retrievals. Full article

(This article belongs to the Special Issue Radiative Transfer in the Earth Atmosphere)

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17 pages, 10438 KiB

Open AccessReview

Satellite Observations of Cloud-Related Variations in Aerosol Properties

by Tamás Várnai and Alexander Marshak

Atmosphere 2018, 9(11), 430; https://doi.org/10.3390/atmos9110430 - 07 Nov 2018

Cited by 20 | Viewed by 3897

Abstract

This paper presents an overview of our efforts to characterize and better understand cloud-related changes in aerosol properties. These efforts primarily involved the statistical analysis of global or regional datasets of Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol and cloud observations. The results show that in oceanic regions, more than half of all aerosol measurements by passive satellite instruments come from near-cloud areas, where clouds and cloud-related processes may significantly modify aerosol optical depth and particle size. Aerosol optical depth is also shown to increase systematically with regional cloud amount throughout the Earth. In contrast, it is shown that effective particle size can either increase or decrease with increasing cloud cover. In bimodal aerosol populations, the sign of changes depends on whether coarse mode or small mode aerosols are most affected by clouds. The results also indicate that over large parts of Earth, undetected cloud particles are not the dominant reason for the satellite-observed changes with cloud amount, and that 3D radiative processes contribute about 30% of the observed near-cloud changes. The findings underline the need for improving our ability to accurately measure aerosols near clouds. Full article

(This article belongs to the Special Issue Radiative Transfer in the Earth Atmosphere)

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