scholarly journals Modeled and observed properties related to the direct aerosol radiative effect of biomass burning aerosol over the Southeast Atlantic

2021 ◽  
Author(s):  
Sarah J. Doherty ◽  
Pablo E. Saide ◽  
Paquita Zuidema ◽  
Yohei Shinozuka ◽  
Gonzalo A. Ferrada ◽  
...  
Keyword(s):  
Optical Thickness ◽  
Cloud Fraction ◽  
Climate Forcing ◽  
Aerosol Extinction ◽  
Radiative Effect ◽  
Model Biases ◽  
Cloud Properties ◽  
Single Scatter ◽  
Aerosol Radiative ◽  
Vertical Gradients

Abstract. Biomass burning smoke is advected over the southeast Atlantic Ocean between July and October of each year. This smoke plume overlies and mixes into a region of persistent low marine clouds. Model calculations of climate forcing by this plume vary significantly, in both magnitude and sign. The NASA EVS-2 (Earth Venture Suborbital-2) ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) project deployed for field campaigns off the west coast of Africa in three consecutive years (Sept., 2016; Aug., 2017; and Oct., 2018) with the goal of better characterizing this plume as a function of the monthly evolution, by measuring the parameters necessary to calculate the direct aerosol radiative effect. Here, this dataset and satellite retrievals of cloud properties are used to test the representation of the smoke plume and the underlying cloud layer in two regional models (WRF-CAM5 and CNRM-ALADIN) and two global models (GEOS and UM-UKCA). The focus is on comparisons of those aerosol and cloud properties that are the primary determinants of the direct aerosol radiative effect, and on the vertical distribution of the plume and its properties. The representativeness of the observations to monthly averages are tested for each field campaign, with the sampled mean aerosol light extinction generally found to be within 20 % of the monthly mean at plume altitudes. When compared to the observations, in all models the simulated plume is too vertically diffuse, has smaller vertical gradients, and, in two of the models (GEOS and UM-UKCA), the plume core is displaced lower than in the observations. Plume carbon monoxide, black carbon, and organic aerosol masses indicate under-estimates in modeled plume concentrations, leading in general to under-estimates in mid-visible aerosol extinction and optical depth. Biases in mid-visible single scatter albedo are both positive and negative across the models. Observed vertical gradients in single scatter albedo are not captured by the models, but the models do capture the coarse temporal evolution, correctly simulating higher values in October (2018) than in August (2018) and September (2017). Uncertainties in the measured absorption Ångstrom exponent were large but propagate into a negligible (<4 %) uncertainty in integrated solar absorption by the aerosol and therefore in the aerosol direct radiative effect. Model biases in cloud fraction, and therefore the scene albedo below the plume, vary significantly across the four models. The optical thickness of clouds is, on average, well simulated in the WRF-CAM5 and ALADIN models in the stratocumulus region and is under-estimated in the GEOS model; UM-UKCA simulates significantly too-high cloud optical thickness. Overall, the study demonstrates the utility of repeated, semi-random sampling across multiple years that can give insights into model biases and how these biases affect modeled climate forcing. The combined impact of these aerosol and cloud biases on the direct aerosol radiative effect (DARE) is estimated using a first-order approximation for a sub-set of five comparison gridboxes. A significant finding is that the observed gridbox-average aerosol and cloud properties yield a positive (warming) aerosol direct radiative effect for all five gridboxes, whereas DARE using the gridbox-averaged modeled properties ranges from much larger positive values to small, negative values. It is shown quantitatively how model biases can offset each other, so that model improvements that reduce biases in only one property (e.g., single scatter albedo, but not cloud fraction) would lead to even greater biases in DARE. Across the models, biases in aerosol extinction and in cloud fraction and optical depth contribute the largest biases in DARE, with aerosol single scatter albedo also making a significant contribution.

scholarly journals Modeled and observed properties related to the direct aerosol radiative effect of biomass burning aerosol over the southeastern Atlantic

2022 ◽  
Vol 22 (1) ◽  
pp. 1-46
Author(s):  
Sarah J. Doherty ◽  
Pablo E. Saide ◽  
Paquita Zuidema ◽  
Yohei Shinozuka ◽  
Gonzalo A. Ferrada ◽  
...  
Keyword(s):  
Cloud Fraction ◽  
Climate Forcing ◽  
Aerosol Extinction ◽  
Radiative Effect ◽  
Model Biases ◽  
Cloud Properties ◽  
Single Scatter ◽  
Aerosol Radiative ◽  
Vertical Gradients ◽  
Southeastern Atlantic

Abstract. Biomass burning smoke is advected over the southeastern Atlantic Ocean between July and October of each year. This smoke plume overlies and mixes into a region of persistent low marine clouds. Model calculations of climate forcing by this plume vary significantly in both magnitude and sign. NASA EVS-2 (Earth Venture Suborbital-2) ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) had deployments for field campaigns off the west coast of Africa in 3 consecutive years (September 2016, August 2017, and October 2018) with the goal of better characterizing this plume as a function of the monthly evolution by measuring the parameters necessary to calculate the direct aerosol radiative effect. Here, this dataset and satellite retrievals of cloud properties are used to test the representation of the smoke plume and the underlying cloud layer in two regional models (WRF-CAM5 and CNRM-ALADIN) and two global models (GEOS and UM-UKCA). The focus is on the comparisons of those aerosol and cloud properties that are the primary determinants of the direct aerosol radiative effect and on the vertical distribution of the plume and its properties. The representativeness of the observations to monthly averages are tested for each field campaign, with the sampled mean aerosol light extinction generally found to be within 20 % of the monthly mean at plume altitudes. When compared to the observations, in all models, the simulated plume is too vertically diffuse and has smaller vertical gradients, and in two of the models (GEOS and UM-UKCA), the plume core is displaced lower than in the observations. Plume carbon monoxide, black carbon, and organic aerosol masses indicate underestimates in modeled plume concentrations, leading, in general, to underestimates in mid-visible aerosol extinction and optical depth. Biases in mid-visible single scatter albedo are both positive and negative across the models. Observed vertical gradients in single scatter albedo are not captured by the models, but the models do capture the coarse temporal evolution, correctly simulating higher values in October (2018) than in August (2017) and September (2016). Uncertainties in the measured absorption Ångstrom exponent were large but propagate into a negligible (<4 %) uncertainty in integrated solar absorption by the aerosol and, therefore, in the aerosol direct radiative effect. Model biases in cloud fraction, and, therefore, the scene albedo below the plume, vary significantly across the four models. The optical thickness of clouds is, on average, well simulated in the WRF-CAM5 and ALADIN models in the stratocumulus region and is underestimated in the GEOS model; UM-UKCA simulates cloud optical thickness that is significantly too high. Overall, the study demonstrates the utility of repeated, semi-random sampling across multiple years that can give insights into model biases and how these biases affect modeled climate forcing. The combined impact of these aerosol and cloud biases on the direct aerosol radiative effect (DARE) is estimated using a first-order approximation for a subset of five comparison grid boxes. A significant finding is that the observed grid box average aerosol and cloud properties yield a positive (warming) aerosol direct radiative effect for all five grid boxes, whereas DARE using the grid-box-averaged modeled properties ranges from much larger positive values to small, negative values. It is shown quantitatively how model biases can offset each other, so that model improvements that reduce biases in only one property (e.g., single scatter albedo but not cloud fraction) would lead to even greater biases in DARE. Across the models, biases in aerosol extinction and in cloud fraction and optical depth contribute the largest biases in DARE, with aerosol single scatter albedo also making a significant contribution.

scholarly journals A Study of the Longer Term Variation of Aerosol Optical Thickness and Direct Shortwave Aerosol Radiative Effect Trends Using MODIS and CERES

2017 ◽  
Author(s):  
Ricardo Alfaro-Contreras ◽  
Jianglong Zhang ◽  
Jeffrey S. Reid ◽  
Sundar Christopher
Keyword(s):  
Optical Thickness ◽  
Broad Band ◽  
Radiant Energy ◽  
Energy System ◽  
Short Wave ◽  
Aerosol Optical Thickness ◽  
Radiative Effect ◽  
Distribution Models ◽  
Direct Forcing ◽  
Aerosol Radiative

Abstract. By combining Collection 6 Moderate Resolution and Imaging Spectroradiometer (MODIS) and Version 22 Multi-angle Imaging Spectroradiometer (MISR) aerosol products with Cloud and Earth’s Radiant Energy System (CERES) flux products, the aerosol optical thickness (AOT, at 0.55 µm) and Short-Wave Aerosol Radiative Effect (SWARE) trends are studied over ocean for the near full Terra (2000–2015) and Aqua (2002–2015) data records. Despite differences in sampling methods, regional SWARE and AOT trends are highly correlated with one another. Over global oceans, weak SWARE (cloud free SW flux) and AOT trends of 0.5–0.6 W m−2 (−0.5 to −0.6 W m−2) and 0.002 AOT decade−1 were found using Terra data. Near zero AOT and SWARE trends are also found for using Aqua data, regardless of Angular Distribution Models (ADMs) used. Regionally, positive SWARE and AOT trends are found over the Bay of Bengal, Arabian Sea, Arabian/Persian Gulf and the Red Sea, while statistically significant negative trends are derived over the Mediterranean Sea and the eastern US coast. In addition, the global mean instantaneous SW aerosol direct forcing efficiencies are found to be ~ −60 W m−2 per AOT, with corresponding SWARE values of ~ −7 W m−2 from both Aqua and Terra data, and again, regardless of CERES ADMs used. Regionally, SW aerosol direct forcing efficiency values of ~ −40 W m−2 per AOT are found over the southwest coast of Africa where smoke aerosol particles dominate in summer. Larger (in magnitude) SW aerosol direct forcing efficiency values of −50 to −80 W m−2 per AOT are found over several other dust and pollutant aerosol dominated regions. Lastly, the AOT and SWARE trends from this study are also inter-compared with aerosol trends (such as active-based) from several previous studies. Findings suggest that a cohesive understanding of the changing aerosol skies can be achieved through the analysis of observations from both passive- and active-based analyses, as well as at both narrow-band and broad-band data sets.

A Climatology of Clouds in Marine Cold Air Outbreaks in Both Hemispheres

2016 ◽  
Vol 29 (18) ◽  
pp. 6677-6692 ◽  
Author(s):  
Jennifer K. Fletcher ◽  
Shannon Mason ◽  
Christian Jakob
Keyword(s):  
Climate Models ◽  
Cloud Fraction ◽  
Satellite Observations ◽  
Radiative Effect ◽  
Cold Air ◽  
Cloud Properties ◽  
Cold Air Outbreak ◽  
Cloud Radiative Effect ◽  
Cold Air Outbreaks

Abstract A climatology of clouds within marine cold air outbreaks, primarily using long-term satellite observations, is presented. Cloud properties between cold air outbreaks in different regions in both hemispheres are compared. In all regions marine cold air outbreak clouds tend to be low level with high cloud fraction and low-to-moderate optical thickness. Stronger cold air outbreaks have clouds that are optically thicker, but not geometrically thicker, than those in weaker cold air outbreaks. There is some evidence that clouds deepen and break up over the course of a cold air outbreak event. The top-of-the-atmosphere longwave cloud radiative effect in cold air outbreaks is small because the clouds have low tops. However, their surface longwave cloud radiative effect is considerably larger. The rarity of cold air outbreaks in summer limits their shortwave cloud radiative effect. They do not contribute substantially to global shortwave cloud radiative effect and are, therefore, unlikely to be a major source of shortwave cloud radiative effect errors in climate models.

scholarly journals Comparing ERA-Interim clouds with satellite observations using a simplified satellite simulator

2018 ◽  
Author(s):  
Martin Stengel ◽  
Cornelia Schlundt ◽  
Stefan Stapelberg ◽  
Oliver Sus ◽  
Salomon Eliasson ◽  
...  
Keyword(s):  
Optical Thickness ◽  
Reanalysis Data ◽  
Cloud Fraction ◽  
Satellite Observations ◽  
Vertical Position ◽  
Polar Regions ◽  
Cloud Properties ◽  
Low Clouds ◽  
Low Cloud ◽  
Cloud Optical Thickness

Abstract. An evaluation of the ERA-Interim clouds using satellite observations is presented. To facilitate such an evaluation in a proper way, a simplified satellite simulator has been developed and applied to six-hourly ERA-Interim reanalysis data covering the period 1982 to 2014. The simulator converts modelled cloud fields, for example those of the ERA-Interim reanalysis, to simulated cloud fields by accounting for specific characteristics of passive imaging satellite sensors such as the Advanced Very High Resolution Radiometer (AVHRR), which form the basis of many long-term observational datasets of cloud properties. It is attempted to keep the simulated cloud fields close to the original modelled cloud fields to allow a quality assessment of the latter based on comparisons of the simulated clouds fields with the observations. Applying the simulator to ERA-Interim data, this study firstly focuses on spatial distribution and frequency of clouds (total cloud fraction) and on their vertical position, using cloud top pressure to express the cloud fraction of high, mid-level and low clouds. Furthermore, the cloud-top thermodynamic phase is investigated. All comparisons incorporate knowledge of systematic uncertainties in the satellite observations and are further stratified by accounting for the limited sensitivity of the observations to clouds with very low cloud optical thickness (COT). The comparisons show that ERA-Interim has generally too low cloud fraction – nearly everywhere on the globe except in the polar regions. This underestimation is caused by a lack of mid-level and/or low clouds – for which the comparisons only show a minor sensitivity to cloud optical thickness thresholds applied. The amount of ERA-Interim high clouds, being higher than in the observations, agrees to the observations within their estimated uncertainties. Removing the optically very thin clouds (COT 

scholarly journals Shortwave Radiative Effect of Arctic Low-Level Clouds: Evaluation of Imagery-Derived Irradiance with Aircraft Observations

2019 ◽  
Author(s):  
Hong Chen ◽  
Sebastian Schmidt ◽  
Michael D. King ◽  
Galina Wind ◽  
Anthony Bucholtz ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Optical Thickness ◽  
Surface Albedo ◽  
Detection Threshold ◽  
The Arctic ◽  
Radiative Effect ◽  
Cloud Detection ◽  
Study Region ◽  
Low Level ◽  
Cloud Properties

Abstract. Cloud optical properties such as optical thickness along with surface albedo are important inputs for deriving the shortwave radiative effects of clouds from space-borne remote sensing. Owing to insufficient knowledge about the snow or ice surface in the Arctic, cloud detection and the retrieval products derived from passive remote sensing, such as from the Moderate Resolution Imaging Spectroradiometer (MODIS), are difficult to obtain with adequate accuracy – especially for low-level thin clouds, which are ubiquitous in the Arctic. This study aims at evaluating the spectral and broadband irradiance calculated from MODIS-derived cloud properties in the Arctic using aircraft measurements collected during the Arctic Radiation-IceBridge Sea and Ice Experiment (ARISE), specifically using the upwelling and downwelling shortwave spectral and broadband irradiance measured by the Solar Spectral Flux Radiometer (SSFR) and the BroadBand Radiometer system (BBR). This entails the derivation of surface albedo from SSFR/BBR and camera imagery for heterogeneous surfaces in the marginal ice zone (MIZ), as well as subsequent measurement-model inter-comparisons in the presence of thin clouds. In addition to MODIS cloud retrievals and surface albedo from SSFR, we used temperature and humidity data from in-situ data and reanalysis (MERRA-2). The spectral surface albedo derived from the airborne radiometers is consistent with prior ground-based measurements, and adequately represents the surface variability for the study region and time period. Somewhat surprisingly, the primary error in MODIS-derived irradiance fields for this study stems from undetected clouds, rather than from the retrieved cloud properties. In our case studies, about 22 % of clouds remained undetected (cloud optical thickness less than 0.5). The radiative effect of clouds above the detection threshold was −40 W m−2 above cloud, and −39 W m−2 below the cloud layer, and the optical thickness from the MODIS "1621" cloud product was consistent with the reflected and transmitted irradiance observations. This study suggests that passive imagery cloud detection could be improved through a multi-pixel approach, that would make it more dependable in the Arctic. Regardless of the cloud retrieval method, there is a need for an operational imagery-based surface albedo product for the polar regions that adequately captures its temporal, spatial, and spectral variability to estimate cloud radiative effect from space-borne remote sensing.

scholarly journals Exploring the differences in cloud properties observed by the Terra and Aqua MODIS sensors

2009 ◽  
Vol 9 (1) ◽  
pp. 1489-1520
Author(s):  
N. Meskhidze ◽  
L. A. Remer ◽  
S. Platnick ◽  
R. Negrón Juárez ◽  
A. M. Lichtenberger ◽  
...  
Keyword(s):  
Diurnal Variation ◽  
Optical Thickness ◽  
Deep Convection ◽  
Cloud Fraction ◽  
Trade Wind ◽  
Clear Correlation ◽  
Remotely Sensed Data ◽  
Diurnal Variability ◽  
Cloud Properties ◽  
Different Parts

Abstract. The aerosol-cloud interaction in different parts of the globe is examined here using multi-year statistics of remotely sensed data from two MODIS sensors aboard NASA's Terra (morning) and Aqua (afternoon) satellites. Simultaneous retrievals of aerosol loadings and cloud properties by the MODIS sensor allowed us to explore intra-diurnal variation of liquid cloud fraction (CF) and optical thickness (COT) for clean, moderately polluted and heavily polluted clouds in different seasons. Data analysis for six-years of MODIS retrievals revealed strong temporal and spatial patterns in intra-diurnal variation of cloud fraction and optical thickness over different parts of the global oceans and the land. For the vast areas of stratocumulus cloud regions, the data shows that the presence of aerosols can more than double afternoon reduction of CF and COT pointing to the possible predominance of semi-direct over the indirect effects of aerosols in stratocumulus clouds. A positive relationship between AOD and morning-to-afternoon variation of trade wind cumulus cloud cover was also found over the northern Indian Ocean, though no clear correlation between the concentration of Indo-Asian haze and intra-diurnal variation of COT was established. Over the Amazon region during wet conditions, aerosols are associated with an enhanced convective process in which morning shallow warm clouds are organized into afternoon deep convection with greater ice cloud coverage. Analysis presented here demonstrates that the new technique for exploring intra-diurnal variability in cloud properties by using the differences in data products from the two daily MODIS overpasses is capable of capturing some of the major features of morning-to-afternoon variations in cloud properties and can be used for improved understanding of aerosol radiative effects.

scholarly journals A long-term time series of global and diffuse photosynthetically active radiation in the Mediterranean: interannual variability and cloud effects

2017 ◽  
Author(s):  
Pamela Trisolino ◽  
Alcide di Sarra ◽  
Fabrizio Anello ◽  
Carlo Bommarito ◽  
Tatiana Di Iorio ◽  
...  
Keyword(s):  
Optical Thickness ◽  
Annual Cycle ◽  
Cloud Fraction ◽  
Radiative Effect ◽  
Diffuse Component ◽  
Active Radiation ◽  
Cloud Radiative Effect ◽  
Cloud Optical Thickness ◽  
Cloud Top Pressure

Abstract. Measurements of global and diffuse photosynthetically active radiation (PAR) have been carried out on the island of Lampedusa, in the central Mediterranean Sea, since 2002. PAR is derived from observations made with multi filter rotating shadowband radiometers (MFRSRs) by comparison with a freshly calibrated PAR sensor and by relying on the on-site Langley plots. In this way, a long-term calibrated record covering the period 2002–2016 is obtained and is presented in this work. The monthly mean global PAR peaks in June, with about 160 W m−2, while the diffuse PAR reaches 60 W m−2 in some cases in spring or summer. The global PAR displays a clear annual cycle with a semi amplitude of about 52 W m−2. The diffuse PAR annual cycle has a semi amplitude of about 12 W m−2 (about 23 % of the annual mean value). The diffuse PAR is about 39 % of the global, with a marked seasonal variation, between about 25–30 % in winter and about 50 % in summer. A simple method to retrieve the cloud-free PAR global and diffuse irradiances in days characterized by partly cloudy conditions has been implemented and applied to the dataset. This method allows to retrieve the cloud-free evolution of PAR, and to calculate the cloud radiative effect. CRE, for downwelling PAR. The cloud-free monthly mean global PAR reaches 175 W m−2 in summer, and the diffuse PAR about 40 W m−2. The annual semi amplitudes are similar for all-sky and cloud-free data. The diffuse PAR for the cloud-free cases is about 24 % of the global. The cloud radiative effect, CRE, on global and diffuse PAR is calculated as the difference between all-sky and cloud-free measurements. The average CRE is about −14.7 W m−2 for the global, and +8.1 W m−2 for the diffuse PAR. The smallest CRE is observed in July, due to the high cloud-free conditions frequency. Maxima (negative for the global, and positive for the diffuse component) occur in March–April and in October, due to the combination of elevated PAR irradiances and high occurrence of cloudy conditions. Largest monthly mean values of CRE are at about −31 W m−2 for the global (April 2007), and +18 W m−2 for the diffuse component (April 2010). Summer clouds appear to be characterized by a low frequency of occurrence, low altitude, and low optical thickness, possibly linked to the peculiar marine boundary layer structure. These properties also contribute to produce small radiative effects on PAR in summer. The cloud radiative effect has been de-seasonalized to remove the influence of annual irradiance variations. The monthly mean normalized CRE for global PAR shows a statistically significant high correlation with monthly cloud fraction, cloud top pressure, and cloud optical thickness, as determined from satellite MODIS observations. The normalized CRE for diffuse PAR show lower correlations, although still statistically significant, with cloud fraction and cloud top pressure, while displays a limited correlation with cloud optical thickness. Cloud fraction seems to be the most relevant parameter driving the cloud radiative effects. Normalized CRE data have been de-seasonalized and related with variations of the de-seasonalized PAR. A statistically significant correlation is found between the de-seasonalized PAR and the de-seasonalized normalized CRE. This correlation is seasonally dependent, and suggests that about 77 % of the global PAR interannual variability may be ascribed to clouds variability in winter.

scholarly journals Empirically derived parameterizations of the direct aerosol radiative effect based on ORACLES aircraft observations

2021 ◽  
Vol 14 (1) ◽  
pp. 567-593
Author(s):  
Sabrina P. Cochrane ◽  
K. Sebastian Schmidt ◽  
Hong Chen ◽  
Peter Pilewskie ◽  
Scott Kittelman ◽  
...  
Keyword(s):  
Asymmetry Parameter ◽  
Single Scattering ◽  
Radiative Effect ◽  
Study Region ◽  
Clear Sky ◽  
Microphysical Properties ◽  
Cloud Properties ◽  
Aerosol Property ◽  
532 Nm ◽  
Aerosol Radiative

Abstract. In this paper, we use observations from the NASA ORACLES (ObseRvations of CLouds above Aerosols and their intEractionS) aircraft campaign to develop a framework by way of two parameterizations that establishes regionally representative relationships between aerosol-cloud properties and their radiative effects. These relationships rely on new spectral aerosol property retrievals of the single scattering albedo (SSA) and asymmetry parameter (ASY). The retrievals capture the natural variability of the study region as sampled, and both were found to be fairly narrowly constrained (SSA: 0.83 ± 0.03 in the mid-visible, 532 nm; ASY: 0.54 ± 0.06 at 532 nm). The spectral retrievals are well suited for calculating the direct aerosol radiative effect (DARE) since SSA and ASY are tied directly to the irradiance measured in the presence of aerosols – one of the inputs to the spectral DARE. The framework allows for entire campaigns to be generalized into a set of parameterizations. For a range of solar zenith angles, it links the broadband DARE to the mid-visible aerosol optical depth (AOD) and the albedo (α) of the underlying scene (either clouds or clear sky) by way of the first parameterization: P(AOD, α). For ORACLES, the majority of the case-to-case variability of the broadband DARE is attributable to the dependence on the two driving parameters of P(AOD, α). A second, extended, parameterization PX(AOD, α, SSA) explains even more of the case-to-case variability by introducing the mid-visible SSA as a third parameter. These parameterizations establish a direct link from two or three mid-visible (narrowband) parameters to the broadband DARE, implicitly accounting for the underlying spectral dependencies of its drivers. They circumvent some of the assumptions when calculating DARE from satellite products or in a modeling context. For example, the DARE dependence on aerosol microphysical properties is not explicit in P or PX because the asymmetry parameter varies too little from case to case to translate into appreciable DARE variability. While these particular DARE parameterizations only represent the ORACLES data, they raise the prospect of generalizing the framework to other regions.

scholarly journals Exploring the differences in cloud properties observed by the Terra and Aqua MODIS Sensors

2009 ◽  
Vol 9 (10) ◽  
pp. 3461-3475 ◽  
Author(s):  
N. Meskhidze ◽  
L. A. Remer ◽  
S. Platnick ◽  
R. Negrón Juárez ◽  
A. M. Lichtenberger ◽  
...  
Keyword(s):  
Optical Thickness ◽  
Deep Convection ◽  
Cloud Fraction ◽  
Trade Wind ◽  
Remotely Sensed Data ◽  
Ice Cloud ◽  
Cloud Properties ◽  
Different Seasons ◽  
Convective Process ◽  
Different Parts

Abstract. The aerosol-cloud interaction in different parts of the globe is examined here using multi-year statistics of remotely sensed data from two MODIS sensors aboard NASA's Terra (morning) and Aqua (afternoon) satellites. Simultaneous retrievals of aerosol loadings and cloud properties by the MODIS sensor allowed us to explore morning-to-afternoon variation of liquid cloud fraction (CF) and optical thickness (COT) for clean, moderately polluted and heavily polluted clouds in different seasons. Data analysis for seven-years of MODIS retrievals revealed strong temporal and spatial patterns in morning-to-afternoon variation of cloud fraction and optical thickness over different parts of the global oceans and the land. For the vast areas of stratocumulus cloud regions, the data shows that the days with elevated aerosol abundance were also associated with enhanced afternoon reduction of CF and COT pointing to the possible reduction of the indirect climate forcing. A positive correlation between aerosol optical depth and morning-to-afternoon variation of trade wind cumulus cloud cover was also found over the northern Indian Ocean, though no clear relationship between the concentration of Indo-Asian haze and morning-to-afternoon variation of COT was established. Over the Amazon region during wet conditions, aerosols are associated with an enhanced convective process in which morning shallow warm clouds are organized into afternoon deep convection with greater ice cloud coverage. Analysis presented here demonstrates that the new technique for exploring morning-to-afternoon variability in cloud properties by using the differences in data products from the two daily MODIS overpasses is capable of capturing some of the major features of diurnal variations in cloud properties and can be used for better understanding of aerosol radiative effects.

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