scholarly journals Effects of absorbing aerosols in cloudy skies: a satellite study over the Atlantic Ocean

2011 ◽  
Vol 11 (4) ◽  
pp. 1393-1404 ◽  
Author(s):  
K. Peters ◽  
J. Quaas ◽  
N. Bellouin
Keyword(s):  
Atlantic Ocean ◽  
Radiative Forcing ◽  
Liquid Water Path ◽  
Aerosol Absorption ◽  
Aerosol Effect ◽  
Direct Scattering ◽  
Planetary Albedo ◽  
Cloud Liquid Water Path ◽  
Absorbing Aerosols ◽  
Aerosol Effects

Abstract. We present a method for deriving the radiative effects of absorbing aerosols in cloudy scenes from satellite retrievals only. We use data of 2005–2007 from various passive sensors aboard satellites of the "A-Train" constellation. The study area is restricted to the tropical- and subtropical Atlantic Ocean. To identify the dependence of the local planetary albedo in cloudy scenes on cloud liquid water path and aerosol optical depth (AOD), we perform a multiple linear regression. The OMI UV-Aerosolindex serves as an indicator for absorbing-aerosol presence. In our method, the aerosol influences the local planetary albedo through direct- (scattering and absorption) and indirect (Twomey) aerosol effects. We find an increase of the local planetary albedo (LPA) with increasing AOD of mostly scattering aerosol and a decrease of the LPA with increasing AOD of mostly absorbing aerosol. These results allow us to derive the direct aerosol effect of absorbing aerosols in cloudy scenes, with the effect of cloudy-scene aerosol absorption in the tropical- and subtropical Atlantic contributing (+21.2 ± 11.1)×10−3 Wm−2 to the global top of the atmosphere radiative forcing.

scholarly journals Effects of absorbing aerosols in cloudy skies: a satellite study over the Atlantic Ocean

2009 ◽  
Vol 9 (5) ◽  
pp. 20853-20880 ◽  
Author(s):  
K. Peters ◽  
J. Quaas ◽  
N. Bellouin
Keyword(s):  
Atlantic Ocean ◽  
Radiative Forcing ◽  
Liquid Water Path ◽  
Aerosol Absorption ◽  
Planetary Albedo ◽  
Cloud Liquid Water Path ◽  
Absorbing Aerosols ◽  
Positive Direct ◽  
Aerosol Effects ◽  
Aerosol Radiative Effects

Abstract. Aerosol effects, direct as well as indirect, constitute one of the biggest sources of uncertainty when it comes to quantifying human forcing of climate change. Understanding these will thus increase the credibility of climate predictions. This study focuses on aerosol effects when absorbing aerosols reside in cloudy skies. In cloudfree conditions, aerosols usually exert a negative radiative forcing (RF) at the top of the atmosphere (TOA) due to their scattering properties. When located above clouds, absorbing aerosols can reduce the shortwave local planetary albedo α, resulting in an often significant local positive direct radiative forcing (DRF). A method for deriving the aerosol radiative effects of absorbing aerosols in cloudy situations from satellite retrievals is presented. Data of 2005 and 2006 from various sensors aboard satellites of the "A-Train" constellation, restricted to the tropical and subtropical Atlantic ocean, is used. A multiple linear regression is performed to identify the dependence of α in cloudy scenes on cloud liquid water path (LWP) and aerosol optical depth (AOD), using the OMI UV-Aerosolindex (UV-AI) as an indicator for absorbing aerosols. The results show an increase of α with increasing aerosol load, and a relative decrease of α with increasing amount of absorbing aerosols in cloudy scenes. This allows to derive the direct aerosol effect of absorbing aerosols above clouds, with the effect of aerosol absorption over clouds in the Atlantic contributing +0.08±1.2×10-3Wm-2 to the global TOA RF.

scholarly journals A 12-year long global record of optical depth of absorbing aerosols above the clouds derived from the OMI/OMACA algorithm

2018 ◽  
Vol 11 (10) ◽  
pp. 5837-5864 ◽  
Author(s):  
Hiren Jethva ◽  
Omar Torres ◽  
Changwoo Ahn
Keyword(s):  
Atlantic Ocean ◽  
Optical Depth ◽  
Frequency Of Occurrence ◽  
Cloud Optical Depth ◽  
Low Level ◽  
Aerosol Cloud ◽  
Aerosol Absorption ◽  
The World ◽  
Absorbing Aerosols

Abstract. Aerosol–cloud interaction continues to be one of the leading uncertain components of climate models, primarily due to the lack of adequate knowledge of the complex microphysical and radiative processes of the aerosol–cloud system. Situations when light-absorbing aerosols such as carbonaceous particles and windblown dust overlay low-level cloud decks are commonly found in several regions of the world. Contrary to the known cooling effects of these aerosols in cloud-free scenario over darker surfaces, an overlapping situation of the absorbing aerosols over the cloud can lead to a significant level of atmospheric absorption exerting a positive radiative forcing (warming) at the top of the atmosphere. We contribute to this topic by introducing a new global product of above-cloud aerosol optical depth (ACAOD) of absorbing aerosols retrieved from the near-UV observations made by the Ozone Monitoring Instrument (OMI) onboard NASA's Aura platform. Physically based on an unambiguous “color ratio” effect in the near-UV caused by the aerosol absorption above the cloud, the OMACA (OMI above-cloud aerosols) algorithm simultaneously retrieves the optical depths of aerosols and clouds under a prescribed state of the atmosphere. The OMACA algorithm shares many similarities with the two-channel cloud-free OMAERUV algorithm, including the use of AIRS carbon monoxide for aerosol type identification, CALIOP-based aerosol layer height dataset, and an OMI-based surface albedo database. We present the algorithm architecture, inversion procedure, retrieval quality flags, initial validation results, and results from a 12-year long OMI record (2005–2016) including global climatology of the frequency of occurrence, ACAOD, and aerosol-corrected cloud optical depth. A comparative analysis of the OMACA-retrieved ACAOD, collocated with equivalent accurate measurements from the HSRL-2 lidar for the ORACLES Phase I operation (August–September 2016), revealed a good agreement (R = 0.77, RMSE = 0.10). The long-term OMACA record reveals several important regions of the world, where the carbonaceous aerosols from the seasonal biomass burning and mineral dust originated over the continents are found to overlie low-level cloud decks with moderate (0.3 < ACAOD < 0.5, away from the sources) to higher levels of ACAOD (> 0.8 in the proximity to the sources), including the southeastern Atlantic Ocean, southern Indian Ocean, Southeast Asia, the tropical Atlantic Ocean off the coast of western Africa, and northern Arabian sea. No significant long-term trend in the frequency of occurrence of aerosols above the clouds and ACAOD is noticed when OMI observations that are free from the “row anomaly” throughout the operation are considered. If not accounted for, the effects of aerosol absorption above the clouds introduce low bias in the retrieval of cloud optical depth with a profound impact on increasing ACAOD and cloud brightness. The OMACA aerosol product from OMI presented in this paper offers a crucial missing piece of information from the aerosol loading above cloud that will help us to quantify the radiative effects of clouds when overlaid with aerosols and their resultant impact on cloud properties and climate.

scholarly journals The effects of timing and rate of marine cloud brightening aerosol injection on albedo changes during the diurnal cycle of marine stratocumulus clouds

2013 ◽  
Vol 13 (3) ◽  
pp. 1659-1673 ◽  
Author(s):  
A. K. L. Jenkins ◽  
P. M. Forster ◽  
L. S. Jackson
Keyword(s):  
Point Source ◽  
Diurnal Cycle ◽  
Radiative Forcing ◽  
Early Morning ◽  
Injection Time ◽  
Liquid Water Path ◽  
Marine Stratocumulus ◽  
Cloud Albedo ◽  
Aerosol Effect ◽  
Early Afternoon

Abstract. The marine-cloud brightening geoengineering technique has been suggested as a possible means of counteracting the positive radiative forcing associated with anthropogenic atmospheric CO2 increases. The focus of this study is to quantify the albedo response to aerosols injected into marine stratocumulus cloud from a point source at different times of day. We use a cloud-resolving model to investigate both weakly precipitating and non-precipitating regimes. Injection into both regimes induces a first indirect aerosol effect. Additionally, the weakly precipitating regime shows evidence of liquid water path gain associated with a second indirect aerosol effect that contributes to a more negative radiative forcing, and cloud changes indicative of a regime change to more persistent cloud. This results in a cloud albedo increase up to six times larger than in the non-precipitating case. These indirect effects show considerable variation with injection at different times in the diurnal cycle. For the weakly precipitating case, aerosol injection results in domain average increases in cloud albedo of 0.28 and 0.17 in the early and mid morning (03:00:00 local time (LT) and 08:00:00 LT respectively) and 0.01 in the evening (18:00:00 LT). No cloud develops when injecting into the cloud-free early afternoon (13:00:00 LT). However, the all-sky albedo increases (which include both the indirect and direct aerosol effects) are highest for early morning injection (0.11). Mid-morning and daytime injections produce increases of 0.06, with the direct aerosol effect compensating for the lack of cloud albedo perturbation during the cloud-free early afternoon. Evening injection results in an increase of 0.04. For the weakly precipitating case considered, the optimal injection time for planetary albedo response is the early morning. Here, the cloud has more opportunity develop into a more persistent non-precipitating regime prior to the dissipative effects of solar heating. The effectiveness of the sea-spray injection method is highly sensitive to diurnal injection time and the direct aerosol effect of an intense aerosol point source. Studies which ignore these factors could overstate the effectiveness of the marine cloud brightening technique.

scholarly journals A 12-Year Long Global Record of Optical Depth of Absorbing Aerosols above the Clouds Derived from OMI/OMACA Algorithm

2018 ◽  
Author(s):  
Hiren Jethva ◽  
Omar Torres ◽  
Changwoo Ahn
Keyword(s):  
Atlantic Ocean ◽  
Optical Depth ◽  
Frequency Of Occurrence ◽  
Cloud Optical Depth ◽  
Low Level ◽  
Aerosol Cloud ◽  
Aerosol Absorption ◽  
The World ◽  
Absorbing Aerosols

Abstract. Aerosol-cloud interaction continues to be one of the leading uncertain components of the climate models, primarily due to the lack of adequate knowledge of the complex microphysical and radiative processes of the aerosol-cloud system. Situations when the light-absorbing aerosols such as carbonaceous particles and windblown dust overlay low-level cloud decks are commonly found in several regions of the world. Contrary to the known cooling effects of these aerosols in cloud-free scenario over darker surfaces, an overlapping situation of the absorbing aerosols over the cloud can lead to a significant level of atmospheric absorption exerting a positive radiative forcing (warming) at the top-of-atmosphere. We contribute to this topic by introducing a new global product of the above-cloud aerosol optical depth (ACAOD) of absorbing aerosols retrieved from the near-UV observations made by the Ozone Monitoring Instrument (OMI) onboard NASA's Aura platform. Physically based on an unambiguous color ratio effect in the near-UV caused by the aerosol absorption above the cloud, the OMACA (OMI Above-Cloud Aerosols) algorithm simultaneously retrieves the optical depths of aerosols and clouds under a prescribed state of the atmosphere. The OMACA algorithm shares many similarities with the two-channel cloud-free OMAERUV algorithm, including the use of AIRS carbon monoxide for the aerosol type identification, CALIOP-based aerosol layer height dataset, and OMI-based surface albedo database. We present the algorithm architecture, inversion procedure, retrieval quality flags, initial validation results, and results from a 12-year long OMI record (2005–2016) including global climatology of the frequency of occurrence, ACAOD, and aerosol-corrected cloud optical depth. A comparative analysis of the coincident and collocated OMACA-retrieved ACAOD and equivalent accurate measurements from the HSRL-2 lidar for the ORACLES phase I operation (August-September 2016) revealed a good agreement (R=0.77, RMSE=0.10). The long-term OMACA record reveals several important regions of the world, including Southeastern Atlantic Ocean, southern Indian Ocean, South-East Asia, tropical Atlantic Ocean off the coast of western Africa, and northern Arabian sea where the carbonaceous aerosols from the seasonal biomass burning and mineral dust originated over the continents are found to overlie low-level cloud decks with moderate (0.30.8 in the proximity to the sources). No significant long-term trend in the frequency of occurrence of aerosols above the clouds and ACAOD is noticed when OMI observations that are free from the row anomaly throughout the operation are considered. If not accounted, the effects of aerosol absorption above the clouds introduce low bias in the retrieval of cloud optical depth with a profound impact at increasing ACAOD and cloud brightness. The OMACA aerosol product from OMI presented in this paper offers a crucial missing piece of information of the aerosol loading above cloud that will help us to quantify the radiative effects of clouds when overlaid with aerosols and its resultant impact on cloud properties and climate.

scholarly journals Multi-Satellite Retrieval of SSA using OMI-MODIS algorithm

2018 ◽  
Author(s):  
Kruthika Eswaran ◽  
Sreedharan Krishnakumari Satheesh ◽  
Jayaraman Srinivasan
Keyword(s):  
Radiative Forcing ◽  
Single Scattering ◽  
Retrieval Algorithm ◽  
Ozone Monitoring Instrument ◽  
Aerosol Composition ◽  
Aerosol Radiative Forcing ◽  
Aerosol Absorption ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Absorbing Aerosols ◽  
Aerosol Type

Abstract. Single scattering albedo (SSA) represents a unique identification of aerosol type and aerosol radiative forcing. However, SSA retrievals are highly uncertain due cloud contamination and aerosol composition. Recent improvement in the SSA retrieval algorithm has combined the superior cloud masking technique of Moderate Resolution Imaging Spectroradiometer (MODIS) and the better sensitivity of Ozone Monitoring Instrument (OMI) to aerosol absorption. The combined OMI-MODIS algorithm has been validated over a small spatial and temporal scale only. The present study validates the algorithm over global oceans for the period 2008–2012. The geographical heterogeneity in the aerosol type and concentration over the Atlantic Ocean, the Arabian Sea and the Bay of Bengal was useful to delineate the effect of aerosol type on the retrieval algorithm. We also noted that OMI overestimates SSA when absorbing aerosols were present closer to the surface. We attribute this overestimation to data discontinuity in the aerosol height climatology derived from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite. OMI uses pre-defined aerosol heights over regions where CALIPSO climatology is not present leading to overestimation of SSA. The importance of aerosol height was also studied using the Santa Barbara DISORT radiative transfer (SBDART) model. The results from the joint retrieval were validated with ground-based measurements and it was seen that OMI-MODIS SSA retrievals were better constrained than OMI only retrieval.

scholarly journals Effects of model resolution on entrainment (inversion heights), cloud-radiation interactions, and cloud radiative forcing

2008 ◽  
Vol 8 (6) ◽  
pp. 20399-20425 ◽  
Author(s):  
H. Guo ◽  
Y. Liu ◽  
P. H. Daum ◽  
X. Zeng ◽  
X. Li ◽  
...  
Keyword(s):  
Liquid Water ◽  
Radiative Forcing ◽  
Horizontal Resolution ◽  
Vertical Resolution ◽  
Model Resolution ◽  
Liquid Water Path ◽  
Cloud Liquid Water ◽  
Cloud Radiative Forcing ◽  
Water Path ◽  
Cloud Liquid Water Path

Abstract. We undertook three-dimensional numerical studies of a marine stratus deck under a strong inversion using an interactive shortwave- and longwave-radiation module. A suite of sensitivity tests were conducted to address the effects of model resolution on entrainment (inversion heights), cloud-radiation interactions, and cloud radiative-forcings by varying model horizontal resolution only, varying vertical resolution only, and varying horizontal- and vertical-resolution simultaneously but with a fixed aspect ratio of 2.5. Our results showed that entrainment (inversion height) is more sensitive to vertical- than to horizontal-resolution. A vertical resolution finer than 40 m can simulate spatial- and temporal-variations in the inversion height well. The inversion height decreases with increasing vertical resolution, but tends to increase with increasing horizontal resolution. Cloud liquid water path doubles after refining both the vertical- and horizontal-resolution by a factor of four. This doubling is associated with a positive feedback between cloud water and cloud top radiative cooling, which amplifies small differences initiated by changes in the model resolution. The magnitude of the cloud radiative-forcing tends to increase with increasing model resolution, mainly attributable to the increase in the cloud liquid water path. Shortwave radiative forcing is dominant, and more sensitive to model resolution than the longwave counterpart.

scholarly journals The scale problem in quantifying aerosol indirect effects

2011 ◽  
Vol 11 (9) ◽  
pp. 26741-26789 ◽  
Author(s):  
A. McComiskey ◽  
G. Feingold
Keyword(s):  
Indirect Effects ◽  
Radiative Forcing ◽  
Liquid Water Path ◽  
Aerosol Indirect Effects ◽  
Remote Sensors ◽  
Cloud Properties ◽  
Wide Range ◽  
Albedo Effect ◽  
Cloud Liquid Water Path ◽  
The Impact

Abstract. A wide range of estimates exists for the radiative forcing of the aerosol effect on cloud albedo. We argue that a component of this uncertainty derives from the use of a wide range of observational scales and platforms. Aerosol affects cloud properties at the microphysical scale, or the "process scale" but observations are most often made of bulk properties over a wide range of resolutions, or "analysis scales". We show that differences between process and analysis scales incur biases in quantification of the albedo effect through the impact that data aggregation has on statistical properties of the aerosol or cloud variable, and their covariance. Measures made within this range of scales are erroneously treated as equivalent, leading to a large uncertainty in associated radiative forcing estimates. Issues associated with the coarsening of observational resolution particular to quantifying the albedo effect are discussed. Specifically, the omission of the constraint on cloud liquid water path and the separation in space of cloud and aerosol properties from passive, space-based remote sensors dampen the measured strength of the albedo effect. Based on our understanding of these biases we propose a new approach for an observationally-based, robust method for estimating aerosol indirect effects that can be used for radiative forcing estimates as well as a better characterization of the uncertainties associated with those estimates.

scholarly journals Satellite observations of aerosols and clouds over southern China from 2006 to 2015: analysis of changes and possible interaction mechanisms

2018 ◽  
Author(s):  
Nikos Benas ◽  
Jan Fokke Meirink ◽  
Karl-Göran Karlsson ◽  
Martin Stengel ◽  
Piet Stammes
Keyword(s):  
Southern China ◽  
Liquid Water Path ◽  
Cloud Droplets ◽  
Emission Data ◽  
Cloud Properties ◽  
Main Driver ◽  
Satellite Sensors ◽  
Cloud Liquid Water Path ◽  
Aerosol Cloud Interactions ◽  
Absorbing Aerosols

Abstract. Aerosol and cloud properties over southern China during the 10-year period 2006–2015 are analysed based on observations from passive and active satellite sensors and emission data. The results show a decrease in aerosol optical depth over the study area by about 20 % on average, accompanied by an increase in liquid cloud cover and cloud liquid water path (LWP) by 5 % and 13 %, respectively. Analysis of aerosol types and emissions suggests that the main driver for their reduction is a decrease in biomass burning aerosols. These changes occurred mainly in late autumn and early winter months and coincided with changes in cloud properties. For the latter, possible explanatory mechanisms were examined, including changes in circulation patterns and aerosol-cloud interactions. Further analysis of changes in aerosol vertical profiles demonstrates a consistency of the observed aerosol and cloud changes with the aerosol semi-direct effect, which depends on their relative heights. Based on this mechanism, fewer absorbing aerosols in the cloud layer would lead to an overall decrease in evaporation of cloud droplets, thus increasing cloud LWP and cover.

scholarly journals Biomass burning aerosols in most climate models are too absorbing

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Hunter Brown ◽  
Xiaohong Liu ◽  
Rudra Pokhrel ◽  
Shane Murphy ◽  
Zheng Lu ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Climate Models ◽  
Carbonaceous Aerosol ◽  
Mixing State ◽  
Aerosol Composition ◽  
Aerosol Absorption ◽  
Aerosol Effect ◽  
Community Atmosphere Model ◽  
Aerosol Effects ◽  
Aerosol Mixing State

AbstractUncertainty in the representation of biomass burning (BB) aerosol composition and optical properties in climate models contributes to a range in modeled aerosol effects on incoming solar radiation. Depending on the model, the top-of-the-atmosphere BB aerosol effect can range from cooling to warming. By relating aerosol absorption relative to extinction and carbonaceous aerosol composition from 12 observational datasets to nine state-of-the-art Earth system models/chemical transport models, we identify varying degrees of overestimation in BB aerosol absorptivity by these models. Modifications to BB aerosol refractive index, size, and mixing state improve the Community Atmosphere Model version 5 (CAM5) agreement with observations, leading to a global change in BB direct radiative effect of −0.07 W m−2, and regional changes of −2 W m−2 (Africa) and −0.5 W m−2 (South America/Temperate). Our findings suggest that current modeled BB contributes less to warming than previously thought, largely due to treatments of aerosol mixing state.

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