S. J. Doherty

• Doctor of Philosophy
• Senior Researcher at University of Washington

A modeling protocol (defined by a series of climate model simulations with specified model output) is introduced. Studies using these simulations are designed to improve the understanding of climate impacts using a strategy for climate intervention (CI) known as marine cloud brightening (MCB) in specific regions; therefore, the protocol is called M...

Low marine clouds and their response to aerosols are highly sensitive to ambient environmental conditions. To understand these responses across a broad spectrum of conditions, we introduce an innovative approach that encompasses the diverse environmental conditions prevalent in low marine cloud regions. This is achieved by creating a comprehensive...

As marine low clouds’ evolution is sensitive to the current state of the atmosphere and varying meteorological forcing, it is crucial to ascertain how cloud responses differ across a spectrum of those conditions. In this study, we introduce an innovative approach to encompass a wide array of conditions prevalent in low marine cloud regions by creat...

This study examines the impact of the interaction of cloud microphysics and macrophysics with the large-scale circulation on stratocumulus-to-cumulus transition (SCT) by combining large-eddy simulation (LES) with a parameterization of weak temperature gradient (WTG) stratified adjustment. The WTG approximates the interaction with the large-scale ci...

Atmospheric aerosols are an important component of the Earth’s climate system, contributing substantial uncertainties in predicting future climate change. In the southeast Atlantic, where expansive light-absorbing smoke aerosol plumes overlie semi-permanent stratocumulus clouds, the direct aerosol radiative effect (DARE) introduces warming in the r...

A modeling protocol is introduced (defined by a series of model simulations with specified model output). The protocol is designed to improve understanding of climate impacts from Marine Cloud Brightening (MCB) Climate Intervention. The model simulations are not intended to assess consequences from a realistic MCB deployment intended to achieve spe...

The Geoengineering Model Intercomparison Project (GeoMIP) has proposed multiple model experiments during phases 5 and 6 of the Climate Model Intercomparison Project (CMIP), with the latest set of model experiments proposed in 2015. With phase 7 of CMIP in preparation and with multiple efforts ongoing to better explore the potential space of outcome...

Research on Marine Cloud Brightening (MCB) shows the potential to cool the planet, yet uncertainties exist in predicting its efficacy within global climate models (GCMs), largely due to limitations in capturing complex low marine cloud mechanisms and associated aerosol-cloud interactions. As these clouds' evolution and their response to aerosols ar...

More than 2000 Lagrangian trajectories are developed, and then meteorological, cloud, and aerosol variables from reanalysis and satellite data are compiled along each trajectory.  Employing PCA reduces the dimensionality of the data needed to cover cloud field variability, and two PCs explain 43% of the variability among CCVs. PCA is useful in...

The Geoengineering Model Intercomparison Project (GeoMIP) has proposed multiple model experiments during the phases 5 and 6 of the Climate Model Intercomparison Project (CMIP), with the latest set of model experiment proposed in 2015. With phase 7 of CMIP in preparation, and with multiple efforts ongoing to better explore the potential space of out...

The southeastern Atlantic is home to an expansive smoke aerosol plume overlying a large cloud deck for approximately a third of the year. The aerosol plume is mainly attributed to the extensive biomass burning activities that occur in southern Africa. Current Earth system models (ESMs) reveal significant differences in their estimates of regional a...

Ship tracks in subtropical marine low clouds are simulated and investigated using large-eddy simulations. Five variants of a shallow subtropical stratocumulus-topped marine boundary layer (MBL) are chosen to span a range of background aerosol concentrations and variations in free-tropospheric moisture. Idealized time-invariant meteorological forcin...

Low marine clouds are a major source of uncertainty in cloud feedbacks across climate models and in forcing by aerosol-cloud interactions. The evolution of these clouds and their response to aerosol are sensitive to the ambient environmental conditions, so it is important to be able to determine different responses over a representative set of cond...

Observed stratocumulus to cumulus transitions (SCTs) and their sensitivity to aerosols are studied using a large‐eddy simulation (LES) model that simulates the aerosol lifecycle, including aerosol sources and sinks. To initialize, force, and evaluate the LES, we used a combination of reanalysis, satellite, and aircraft data from the 2015 Cloud Syst...

Observed stratocumulus to cumulus transitions (SCT) and their sensitivity to aerosols are studied using a Large-Eddy Simulation (LES) model that simulates the aerosol lifecycle, including aerosol sources and sinks. To initialize, force, and evaluate the LES, we used a combination of reanalysis, satellite, and aircraft data from the 2015 Cloud Syste...

Current impacts and escalating risks of climate change require strong and decisive action to reduce greenhouse gas (GHG) emissions. They also highlight the urgency of research to enhance safety for human and natural systems, especially for those most vulnerable. This is reflected in two recent US National Academies of Science, Engineering, and Medi...

Smoke from southern Africa blankets the southeastern Atlantic Ocean from June to October, producing strong and competing aerosol radiative effects. Smoke effects on the transition between overcast stratocumulus and scattered cumulus clouds are investigated along a Lagrangian (air-mass-following) trajectory in regional climate and large eddy simulat...

This dataset contains observational/reanalysis data, input forcing files, LES model setup scripts, LES outputs, and Python scripts regarding the paper: Erfani et al., 2022: Simulating aerosol lifecycle impacts on the subtropical stratocumulus-to-cumulus transition using large-eddy simulations, J. Geophys. Res. Atmos. https://doi.org/10.1029/2022J...

The southeast Atlantic is home to an expansive smoke aerosol plume overlying a large cloud deck for approximately a third of the year. The aerosol plume is mainly attributed to the extensive biomass burning activity that occurs in southern Africa. Current Earth system models (ESMs) reveal significant differences in their estimates of regional aeros...

Observed stratocumulus to cumulus transitions (SCT) and their sensitivity to aerosols are studied using a Large-Eddy Simulation (LES) model that simulates the aerosol lifecycle, including aerosol sources and sinks. To initialize, force, and evaluate the LES, we used a combination of reanalysis, satellite, and aircraft data from the 2015 Cloud Syste...

Smoke from southern Africa blankets the southeast Atlantic Ocean from June–October, producing strong and competing aerosol radiative effects. Smoke effects on the transition between overcast stratocumulus and scattered cumulus clouds are investigated along a Lagrangian (air-mass-following) trajectory in regional climate and large eddy simulation mo...

Ship tracks in subtropical marine low clouds are simulated and investigated using large eddy simulations. Five variants of a shallow subtropical stratocumulus-topped marine boundary layer (MBL) are chosen to span a range of background aerosol concentrations and variations in free-tropospheric (FT) moisture. Idealized time-invariant meteorological f...

We developed and performed Lagrangian Large Eddy Simulation (LES) experiments that explore the aerosol-cloud-precipitation interactions in the marine boundary layer (MBL) for case studies taken from the Cloud System Evolution in the Trades (CSET) campaign, which took place in summer 2015 over the Northeast Pacific. Our LES is coupled to an aerosol...

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 (ObseRvati...

Low marine clouds are a major source of uncertainty in cloud simulations across models from LES to global scale. To address this issue, we conducted Lagrangian LES experiments that explore the aerosol-cloud interactions for case studies covering a spectrum of observed ambient conditions, and evaluated the model against observations. Our LES benefit...

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 (ObseRva...

Modern climate models were designed to simulate natural systems and changes mainly due to atmospheric carbon dioxide, rather than to predict effects of deliberate climate interventions.

Southern Africa produces almost a third of the Earth's biomass burning (BB) aerosol particles, yet the fate of these particles and their influence on regional and global climate is poorly understood. ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) is a 5-year NASA EVS-2 (Earth Venture Suborbital-2) investigation with three in...

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 spectr...

In the southeast Atlantic, well-defined smoke plumes from Africa advect over marine boundary layer cloud decks; both are most extensive around September, when most of the smoke resides in the free troposphere. A framework is put forth for evaluating the performance of a range of global and regional atmospheric composition models against observation...

Aviation is one of the most important global economic activities in the modern world. Aviation emissions of CO2 and non-CO2 aviation effects result in changes to the climate system (Fig. 1). Both aviation CO2 and the sum of quantified non-CO2 contributions lead to surface warming. The largest contribution to anthropogenic climate change across all...

This work establishes an observationally-driven link from mid-visible aerosol optical depth (AOD) and other scene parameters to broadband shortwave irradiance (and by extension, the direct aerosol radiative effect, DARE), based on observations from the 2016 and 2017 field campaigns of ORACLES (ObseRvations of Aerosols above CLouds and their intErac...

Southern Africa produces almost a third of the Earth’s biomass burning (BB) aerosol particles, yet the fate of these particles and their influence on regional and global climate is poorly understood. ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) is a five-year NASA EVS-2 (Earth Venture Suborbital-2) investigation with three...

Determining the direct aerosol radiative effect (DARE) of absorbing aerosols above clouds from satellite observations alone is a challenging task, in part because the radiative signal of the aerosol layer is not easily untangled from that of the clouds below. In this study, we use aircraft measurements from the NASA ObseRvations of CLouds above Aer...

The southeast Atlantic is home to well-defined smoke outflow from Africa coinciding vertically with extensive marine boundary-layer cloud decks, both reaching their climatological maxima in spatial extent around September. A framework is put forth for evaluating the performance of a range of global and regional aerosol models against observations m...

The total effect of aerosols, both directly and on cloud properties, remains the biggest source of uncertainty in anthropogenic radiative forcing on the climate. Correct characterization of intensive aerosol optical properties, particularly in conditions where absorbing aerosol is present, is a crucial factor in quantifying these effects. The south...

Determining the direct aerosol radiative effect (DARE) of absorbing aerosols above clouds from satellite observations alone is a challenging task, in part because the radiative signal of the aerosol layer is not easily untangled from that of the clouds below. In this study, we use aircraft measurements from the NASA ObseRvations of CLouds above Aer...

Vertical profiles of black carbon (BC) and other light-absorbing impurities were measured in seasonal snow and permanent snowfields in the Chilean Andes during Austral winters 2015 and 2016, at 22 sites between latitudes 18°S and 41°S. The samples were analyzed for spectrally-resolved visible light absorption. For surface snow, the average mass mix...

The total effect of aerosols, both directly and on cloud properties, remains the biggest source of uncertainty in anthropogenic radiative forcing on the climate. Correct characterization of intensive aerosol optical properties, particularly in conditions where absorbing aerosol is present, is a crucial factor in quantifying these effects. The South...

Using field observation, we perform radiative transfer calculations on snowpacks in the Arctic, China, and North America to quantify the impact of light-absorbing particles (LAPs) on snow albedo and its sensitivity to different factors. For new snow, the regional-averaged albedo reductions caused by all LAPs in the Arctic, North America, and China...

1. Human activities continue to significantly affect Earth’s climate by altering factors that change its radiative balance. These factors, known as radiative forcings, include changes in greenhouse gases, small airborne particles (aerosols), and the reflectivity of the Earth’s surface. In the industrial era, human activities have been, and are incr...

A characterization of black carbon (BC) and other light-absorbing particles in snow is presented for three mountain valley sites in Idaho in early 2014 and for one site near Vernal, Utah, in early 2013 and 2014. The focus of the study was on constraining the magnitude and drivers of variations in particulate absorbers in midlatitude U.S. seasonal s...

The Community Atmosphere Model (CAM5), equipped with a technique to tag black carbon (BC) emissions by source regions and types, has been employed to establish source–receptor relationships for atmospheric BC and its deposition to snow over western North America. The CAM5 simulation was conducted with meteorological fields constrained by reanalysis...

The surface energy balance and meltwater production of the Greenland ice sheet (GrIS) are modulated by snow and ice albedo through the amount of absorbed solar radiation. Here we show, using spaceborne multispectral data collected during the three decades from 1981 to 2012, that summertime surface albedo over the GrIS decreased at a statistically s...

Samples of snow on sea ice were collected in springtime of the six years 2008–2013 in the region between Greenland, Ellesmere Island, and the North Pole (82-89°N, 0-100°W). The meltwater was passed through filters, whose spectral absorption was then measured to determine the separate contributions by black carbon (BC) and other light-absorbing impu...

Limited observational data sets and incomplete surface energy balance models constrain understanding of the driving processes for Greenland's ice sheet.

The Community Atmosphere Model (CAM5), equipped with a technique to tag black carbon (BC) emissions by source regions and types, has been employed to establish source-receptor relationships for atmospheric BC and its deposition to snow over Western North America. The CAM5 simulation was conducted with meteorological fields constrained by reanalysis...

Light absorbing particles (LAP, e.g., black carbon, brown carbon, and dust) influence water and energy budgets of the atmosphere and snowpack in multiple ways. In addition to their effects associated with atmospheric heating by absorption of solar radiation and interactions with clouds, LAP in snow on land and ice can reduce the surface reflectance...

Vertical profiles of light-absorbing particles in seasonal snow were sampled from 67 North American sites. Over 500 snow samples and 55 soil samples from these sites were optically analyzed for spectrally-resolved visible light absorption. The optical measurements were used to estimate black carbon (BC) mixing ratios in snow (),contributions to abs...

Black carbon (BC) in snow lowers its albedo, increasing the absorption of sunlight, leading to positive radiative forcing, climate warming and earlier snowmelt. A series of recent studies have used prescribed-aerosol deposition flux fields in climate model runs to assess the forcing by black carbon in snow. In these studies, the prescribed mass dep...

Black carbon (BC) in snow lowers its albedo, increasing the absorption of sunlight, leading to positive radiative forcing, climate warming and earlier snowmelt. A series of recent studies have used prescribed-aerosol deposition flux fields in climate model runs to assess the forcing by black carbon in snow. In these studies, the prescribed mass dep...

We examine the impacts of atmospheric aerosols on Arctic and global climate using a series of 20th century transient simulations from Community Climate System Model version 4 (CCSM4). We focus on the response of surface air temperature to the direct radiative forcing driven by changes in sulfate and black carbon (BC) concentrations from 1975 to 200...

We examine the impacts of atmospheric aerosols on Arctic and global climate using a series of 20th century transient simulations from Community Climate System Model version 4 (CCSM4). We focus on the response of surface air temperature to the direct radiative forcing driven by changes in sulfate and black carbon (BC) concentrations from 1975 to 200...

Light-absorbing impurities in snow reduce snow albedo, producing a positive radiative forcing, warming the surface air and snowpack, and accelerating snow melt. As the snow melts, black carbon (BC) and other insoluble light-absorbing particulate impurities (ILAP) are retained at the snow surface because their scavenging efficiency with meltwater is...

Black carbon aerosol plays a unique and important role in Earth's climate system. Black carbon is a type of carbonaceous material with a unique combination of physical properties. This assessment provides an evaluation of black-carbon climate forcing that is comprehensive in its inclusion of all known and relevant processes and that is quantitative...

Black carbon aerosol plays a unique and important role in Earth's climate system. Black carbon is a type of carbonaceous material with a unique combination of physical properties. This assessment provides an evaluation of black-carbon climate forcing that is comprehensive in its inclusion of all known and relevant processes and that is quantitative...

[1] Black carbon (BC), organic carbon (OC), and mineral dust (MD) are the most important light-absorbing particulate impurities in snow. A field campaign was conducted in January and February 2010 to measure light-absorbing particles in snow across northern China. About 400 snow samples were collected at 46 sites in six provinces. A spectrophotomet...

We evaluate the performance of the Single Particle Soot Photometer (SP2) and the Integrating Sphere/Integrating Sandwich Spectrophotometer (ISSW) in quantifying the concentration of refractory black carbon (BC) in snow samples. We find that the SP2 can be used to measure BC mass concentration in snow with substantially larger uncertainty (60%) than...

The presence of light-absorbing aerosol particles deposited on arctic snow and sea ice influences the surface albedo, causing greater shortwave absorption, warming, and loss of snow and sea ice, lowering the albedo further. The Community Earth System Model version 1 (CESM1) now includes the radiative effects of light-absorbing particles in snow on...

We use observations of the absorption properties of black carbon and non-black-carbon impurities in near-surface snow collected near the research stations at South Pole and Dome C, Antarctica and Summit, Greenland combined with a snowpack actinic flux parameterization to estimate the vertical profile and e-folding depth of ultraviolet/near-visible...

We evaluate the performance of the Single Particle Soot Photometer (SP2) and the Integrating Sphere/Integrating Sandwich Spectrophotometer (ISSW) in quantifying the concentration of refractory black carbon (BC) in snow samples. We find that the SP2 can be used to measure BC mass concentration in snow with substantially larger uncertainty (60%) than...

The presence of light-absorbing aerosol particles deposited on arctic snow and sea ice influences the surface albedo, causing greater shortwave absorption, warming, and loss of snow and sea ice, lowering the albedo further. The Community Earth System Model version 1 (CESM1) now includes the radiative effects of light-absorbing particles in snow on...

We use a global chemical transport model (GEOS-Chem CTM) to interpret observations of black carbon (BC) and organic aerosol (OA) from the NASA ARCTAS aircraft campaign over the North American Arctic in April 2008, together with longer-term records in surface air and in snow. We find that Russian open fires were the dominant source of OA in the trop...

Correctly attributing light absorption in snow to its proper source is important for assessing the relative impact of absorbing constituents on snow and ice melt and its associated positive climate feedback. Here we evaluate the ability of a Single Particle Soot Photometer (SP2) to quantify black carbon (BC) concentrations in melted snow. We compar...

Model estimates indicate that black carbon (BC) transport to the Arctic and deposition to the surface contributes to the warming of the Arctic through darkening of the surface, enhanced absorption of solar radiation, and melting of snow and ice. The Soot Transport and Deposition Study (STADS) was conducted in Svalbard, Norway in April 2011 as part...

Black carbon (BC), organic carbon (OC), and mineral dust are the most important light-absorbing aerosols (LAA) in snow. The physical, chemical and optical properties of these aerosols differ greatly; the different spectral dependences of their light-absorption can be used to quantify their concentrations in snow. A field campaign was conducted in J...

We use a global chemical transport model (GEOS-Chem CTM) to interpret observations of black carbon (BC) and organic aerosol (OA) from the NASA ARCTAS aircraft campaign over the North American Arctic in April 2008, as well as longer-term records in surface air and in snow (2007–2009). BC emission inventories for North America, Europe, and Asia in th...

Simultaneous measurements of aerosol black carbon (BC) in both fresh snow and in air on Svalbard are presented. From these, washout ratios for BC are calculated and compared to sparse previous measurements of this metric in the arctic. The current ratios are significantly higher than previously found measured values. We argue that the degree of sno...

Light absorption by particulate impurities in snow and ice can affect the surface albedo and is important for the climate. The absorption properties of these particles can be determined by collecting and melting snow samples and extracting the particulate material by filtration of the meltwater. This paper describes the optical design and testing o...

The influence of aerosols, such as black carbon, on snow and ice albedo may be responsible for a significant portion of the high northern latitude climate change in the past century. To investigate their role, aerosol cycling and optics have been incorporated into CESM for black carbon, organic carbon, and dust on terrestrial snow and sea ice. The...

Abstract Light-absorbing aerosols (LAA) deposited on the arctic snow pack, in particular black carbon (BC), contribute appreciably to the arctic radiation budget and their reduction has been suggested as a means to attenuate warming in the arctic. Effective prediction and mitigation of Arctic snow LAA requires that the sources of the LAA be elucida...

The possibility of controlling emissions with high black carbon (BC) fractions is being discussed as a partial, immediate response to climate change. Reductions in absorbing aerosol could rapidly reduce warming in both the atmosphere and on snow surfaces in sensitive regions such as the Arctic and the Himalayas. We review a recent community effort,...

Absorption of radiation by ice is extremely weak at visible and near-ultraviolet wavelengths, so small amounts of light-absorbing impurities in snow can dominate the absorption of solar radiation at these wavelengths, reducing the albedo relative to that of pure snow, contributing to the surface energy budget and leading to earlier snowmelt. In thi...