About

The faculty, staff and students in the Department of Atmospheric and Climate Science at the University of Washington are engaged in the study of a broad range of atmospheric phenomena and processes, using methods ranging from mathematical analysis to field experimentation. Research projects range in size from small studies involving individual scientists to large national and international programs involving teams of scientists. Research groups in the department are concerned with Atmospheric Chemistry, Atmospheric Dynamics, Boundary Layer Processes, Cloud and Aerosol Research, Glaciology and Planetary Atmospheres, Cloud Dynamics, Precipitation Processes, Storms, Weather Analysis and Forecasting, Climate, Global change, Airflow over mountains, and other topics. Some groups maintain special research facilities for the use of their students. In some of these activities, there is close cooperation with the University of Alaska Fairbanks, Oregon State University and the National Oceanic and Atmospheric Administration (NOAA) Regional Center through the Cooperative Institute for Climate, Ocean and Ecosystem Studies. Faculty members often have interests in more than one area, and research projects frequently involve questions of broad scope which do not fall neatly into a single category. This is particularly true of research projects directed toward understanding the chemical and physical modification of the environment by human activities.

Research topics

• Environmental science
• Atmospheric sciences
• Climatology
• Geology
• Meteorology
• Geography
• Oceanography
• Physics
• Chemistry
• Agronomy
• Biotechnology
• Environmental protection
• Remote sensing
• Engineering
• Medicine
• Natural resource economics
• Environmental health
• Ecology
• Business
• Biology

Selected publications

• Impact on the stratocumulus-to-cumulus transition of the interaction of cloud microphysics and macrophysics with large-scale circulation

  Atmospheric chemistry and physics · 2025-05-26 · 4 citations

  articleOpen access

  Abstract. This study examines the impact of the interaction of cloud microphysics and macrophysics with the large-scale circulation on the stratocumulus-to-cumulus transition (SCT) using a large-eddy simulation (LES) combined with weak-temperature-gradient (WTG) parameterization. The WTG approximates large-scale circulation by inducing domain-mean subsidence to counter buoyancy perturbations relative to a reference thermodynamic profile. A stationary sea-salt sprayer perturbs transitioning clouds over a Lagrangian domain. Results show that the cloud response to aerosol injection differs significantly depending on whether stratified adjustments in the large-scale circulation in response to buoyancy perturbations are considered. Aerosol injection suppresses precipitation and enhances entrainment in both cases. Additionally, reduced surface sensible heat flux by precipitation suppression weakens boundary layer turbulence. Without the WTG, cloud-top height rises without a compensating adjustment in subsidence, delaying drizzle-induced stratocumulus thinning (“drizzle-depletion” feedback) by several days. With the WTG, intensified subsidence restrains cloud-top growth and accelerates stratocumulus thinning, leading to reduced boundary layer turbulence by weakened longwave cloud-top cooling and increased susceptibility to cloud breakup. For lightly precipitating clouds, aerosol injection accelerates the SCT by enhancing cloud thinning through warming driven by increased entrainment (“deepening–warming” mechanism). For heavily precipitating clouds, where the SCT is dominated by drizzle-depletion feedback, aerosol injection delays the SCT marginally as intensified subsidence amplifies the deepening–warming mechanism. These findings suggest that ignoring large-scale circulation adjustments in limited-domain models may overestimate aerosol cooling effects by ∼15–30 W m−2.

  PublisherOA PDFDOI

• Investigation of Ship‐Induced Mesoscale Circulation Mechanics and Aerosol Plume Spreading Rates

  Geophysical Research Letters · 2025-10-15 · 2 citations

  articleOpen access

  Abstract Aerosol plumes emitted from ships can cause brightening of low clouds. The aerosol plume spreading rate controls what fraction of the cloud may experience brightening. Developing a deeper physical understanding of the mechanisms driving variations in spreading rate could inform the development of plume‐spreading parameterizations in global climate models, which may be relevant for assessing the feasibility of Marine Cloud Brightening. In this study, we employ large‐eddy simulations of two idealized precipitating stratocumulus cases to investigate the roles of collision‐coalescence, cloud droplet sedimentation, and droplet effective radius in the ship track and quantify their individual and combined effects on plume buoyancy anomalies and spreading rates. Our results indicate that cloud droplet sedimentation and collision‐coalescence are the primary mechanisms controlling buoyancy and horizontal spreading, whereas the influence of effective radius is negligible. Sensitivity tests indicate that mesoscale circulations can develop within the ship track even in the absence of precipitation suppression.

  PublisherOA PDFDOI

• Quantification of aerosol influence on day-to-day mesoscale variability of shallow convection

  2025-03-15

  preprintOpen accessCorresponding

  A major uncertainty in the cloud-feedback to a warming climate can be attributed to shallow convection in the trades. With recent advances in observational and computational resources, the potential impact of the mesoscale organization of these clouds became apparent. While the processes leading to the mesoscale organization are not resolved in current climate models, observations of these features and more importantly their interaction with different scales became available through field campaigns like EUREC4A.This study quantifies the ability of large-domain large-eddy simulations to represent the observed mesoscale variability in cloudiness. By using forward operators to mimic the observations, we show that the stratiform cloud amount and precipitation frequency remain challenging to simulate at hectometre resolutions. Despite these challenges, the simulations show a similar sensitivity in cloud distribution to environmental conditions.By perturbing the 41 days simulation with a 13-fold increase in CCN concentration we quantify the sensitivity of the mesoscale cloud organisation to changes in precipitation and show the strong influence on the cold-pool driven cloud formations. We further emphasise the importance to correctly represent the mesoscale processes in climate simulations by showing that changes in cloud-radiative effects due to aerosol changes vary day-by-day with varying contributions from changes in cloud albedo and cloud fraction.

  PublisherDOI

• Forcing Susceptibility and Climate Sensitivity to Midlatitude Marine Cloud Brightening

  Journal of Climate · 2025-12-12 · 1 citations

  article

  Abstract The climate intervention approach marine cloud brightening (MCB) would aim to reduce climate warming by injecting sea salt aerosol (iSSA) into the lower troposphere to increase cloud albedo, reflect more sunlight, and cool the surface. Due to the short atmospheric lifetime of tropospheric aerosol, MCB iSSA emissions and their resulting radiative forcing are regional by nature. This presents a significant challenge and opportunity, as there are many potential MCB implementation patterns that could produce widely varying climate responses. Previous modeling studies suggest that MCB implementation in the subtropical oceans can cause global cooling but often result in remote regional temperature and precipitation responses that may be considered undesirable. Here, we use three Earth system models (ESMs) to estimate the impact of MCB implementation in 14 different ocean regions, assessing MCB forcing and cooling efficiency in each region and examining the patterns of temperature response from each case. We find that iSSA emissions in the midlatitude oceans produce stronger cloud forcing, greater cooling efficiency, and more spatially uniform cooling. With this information, we evaluate a novel MCB emission strategy that emits iSSA in the midlatitude oceans. The ESMs show this iSSA emission pattern produces temperature and precipitation responses across all three ESMs that are quite similar in pattern (but of opposite sign) to the greenhouse gas (GHG) response. Thus, compared to previously tested iSSA injection patterns, midlatitude MCB implementations may be more suitable when intending to maintain climates close to present-day conditions. Significance Statement Global climate models (GCMs) suggest sunlight reflection by marine cloud brightening (MCB) via injecting sea salt aerosol (iSSA) could produce substantial cooling to offset the impacts of greenhouse gas warming. They also show that the impacts of MCB depend strongly on the location it is applied. Using a dataset of 14 MCB simulations in three GCMs, we identify a novel MCB strategy that more effectively offsets climate warming by emitting iSSA in the midlatitude oceans in all three models. This reduces certain unintended negative climate impacts that have been found in other MCB modeling studies and enables the development of more plausible cooperative MCB scenarios.

  PublisherDOI

• Understanding Aitken Mode Aerosol Variability Over the Southern Ocean and Antarctica: Insights From Cloud Condensation Nuclei Data

  Journal of Geophysical Research Atmospheres · 2025-10-02

  articleOpen access

  Abstract Aitken mode aerosol particles can influence cloud properties and lifetime by acting as a reservoir of potential cloud condensation nuclei (CCN) that can replenish the CCN population against precipitation scavenging. However, data on Aitken‐mode aerosols in remote regions are limited. In this study, we developed a method to estimate Aitken mode aerosol concentrations and size distribution using CCN measurements and κ ‐Köhler theory. The performance of this method was evaluated using scanning mobility particle sizer data from recent field campaigns to demonstrate its skills and applicability. The method reasonably estimates Aitken‐ and accumulation‐mode aerosol concentrations, achieving correlations of 0.7–0.9 with only modest biases (mean fractional bias within ±23% for Aitken mode and ±37% for accumulation‐mode). This method is further applied to measurements collected over the Southern Ocean and Antarctica in recent years from multiple platforms, including ground sites, aircraft, and ships, to derive Aitken and accumulation‐mode aerosol concentrations. Using the derived data, we examine the seasonal cycle, latitudinal variations, and vertical distribution of aerosols. Aitken mode aerosol concentrations are elevated over the Southern Ocean and Antarctica during the austral summer, similar to the accumulation mode. In the austral summer, the free troposphere has more Aitken mode aerosols and fewer accumulation mode aerosols than the boundary layer, and thus likely serves as an important source of cloud‐forming aerosol while also diluting the accumulation mode.

  PublisherDOI

• Building a comprehensive library of observed Lagrangian trajectories for testing modeled cloud evolution, aerosol–cloud interactions, and marine cloud brightening

  Atmospheric chemistry and physics · 2025-08-12 · 3 citations

  articleOpen access

  Abstract. As the evolution of marine low clouds 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 creating a comprehensive library of observed environmental conditions. Using reanalysis and satellite data, over 2200 Lagrangian trajectories are generated within the stratocumulus deck region of the Northeast Pacific during summer 2018–2021. By using eight important cloud-controlling factors (CCFs), we employ principal component analysis (PCA) to reduce the dimensionality of data. This technique demonstrates that two principal components capture 43 % of the variability among CCFs. Notably, PCA facilitates the selection of a reduced number of trajectories (e.g., 54) that represent a diverse array of the observed CCF, aerosol, and cloud variability and co-variability. These trajectories can then be used for process model studies, e.g., with large-eddy simulations (LES), to evaluate the efficacy of marine cloud brightening. Two distinct cases are selected to initiate 2 d long, high-resolution, large-domain LES experiments. The results highlight the ability of our LES to simulate observed conditions. Although perturbed aerosols delay cloud breakup and enhance the cloud radiative effect, the strength of such effects is sensitive to “precipitation-aerosol feedback”. The first case is precipitating and shows the potential for “precipitation-driven” cloud breakup due to positive precipitation-aerosol feedback. The second case is non-precipitating with classic cloud breakup of the “deepening-warming” type, highlighting the impact of entrainment.

  PublisherDOI

• Analyses of Virtual Ship‐Tracks Systematically Underestimate Aerosol‐Cloud Interactions Signals

  Geophysical Research Letters · 2025-04-02 · 3 citations

  articleOpen access

  Abstract Ship‐tracks are important natural/opportunistic experiments to study aerosol‐cloud interactions (ACIs). However, detectable ship‐tracks are not produced in many instances. Virtual ship‐tracks have been conceived to expand the scale of ACIs analyses. Cloud responses in virtual ship‐tracks differ strongly from those of detected ones. Here we show that the current approach of virtual ship‐tracks can lead to systematic biases and errors and suggest necessary improvements. Errors in trajectory modeling introduce mismatches between areas actually affected by ship‐emissions and virtual ship‐track locations, that is, positional errors. Positional errors systematically underestimate ACI signals and the underestimate is severe as indicated by analysis of cloud droplet number concentration changes. The assumption of fixed ship‐track width also systematically diminishes resulting aerosol effects by more than 10%, which leads to a forcing difference of around 0.1 . We make suggestions to improve the simulation of virtual ship‐tracks so that their full potential for studying ACIs can be unleashed.

  PublisherOA PDFDOI

• Cloud Susceptibility and Climate Sensitivity to Midlatitude Marine Cloud Brightening

  2025-06-30

  preprintOpen access
  PublisherOA PDFDOI

• Impacts of DMS Emissions and Chemistry on E3SMv2 Simulated Cloud Droplet Numbers and Aerosol Concentrations Over the Southern Ocean

  Journal of Advances in Modeling Earth Systems · 2025-05-01 · 3 citations

  articleOpen access

  Abstract The accurate representation of cloud droplet number concentration (N d ) is crucial for predicting future climate. However, models often underestimate N d over the Southern Ocean (SO), where natural sources dominate, and aerosols are composed primarily of marine biogenic sulfate and sea spray. This study uses a range of diverse data sets to evaluate and untangle biases in Energy Exascale Earth System Model version 2 (E3SMv2) simulated clouds, aerosols, and sulfur species. The default E3SMv2 underestimates N d over SO by a factor of 2 when compared with observations in 3 km‐resolution simulations. Updating the dimethyl sulfide (DMS) emission and chemistry leads to a better agreement between the model and the observations in N d and boundary layer aerosols, but low biases persist in the free tropospheric aerosol concentrations larger than 70 nm, possibly attributable to insufficient particle growth. Furthermore, updates to DMS emissions and chemistry resulted in reduced vertical DMS concentrations and improved the overall agreement between simulated and observed DMS vertical profiles. Preliminary evaluation also reveals remaining biases in simulated sulfur species, including overestimation in DMS at high latitudes, and in simulated sulfate mass concentration, highlighting the necessity for further efforts to improve the model treatment of relevant processes.

  PublisherOA PDFDOI

• Key Gaps in Models' Physical Representation of Climate Intervention and Its Impacts

  Journal of Advances in Modeling Earth Systems · 2025-06-01 · 4 citations

  articleOpen access

  Abstract Solar radiation modification (SRM) is increasingly discussed as a potential method to ameliorate some negative effects of climate change. However, unquantified uncertainties in physical and environmental impacts of SRM impede informed debate and decision making. Some uncertainties are due to lack of understanding of processes determining atmospheric effects of SRM and/or a lag in development of their representation in models, meaning even high‐quality model intercomparisons will not necessarily reveal or address them. Although climate models at multiple scales are advancing in complexity, there are specific areas of uncertainty where additional model development (often requiring new observations) could significantly advance understanding of SRM's effects, and improve our ability to assess and weigh potential risks against those of choosing to not use SRM. We convene expert panels in the areas of atmospheric science most critical to understanding the three most widely discussed forms of SRM. Each identifies three key modeling gaps relevant to either stratospheric aerosols, cirrus, or low‐altitude marine clouds. Within each area, key challenges remain in capturing impacts due to complex interactions in aerosol physics, atmospheric chemistry/dynamics, and aerosol‐cloud interactions. Across all three, in addition to arguing for more observations, the panels argue that model development work to either leverage different capabilities of existing models, bridge scales across which relevant processes operate, or address known modeling gaps could advance understanding. By focusing on these knowledge gaps we believe the modeling community could advance understanding of SRM's physical risks and potential benefits, allowing better‐informed decision‐making about whether and how to use SRM.

  PublisherOA PDFDOI

Recent grants

• VOCALS: C-130 Observations and Numerical Modeling of Marine Boundary Layer Clouds during the VOCALS Regional Experiment (REx)

  NSF · $841k · 2008–2012

• Analysis of G-V Aircraft and Complementary SOCRATES Observations to Understand Clouds, Aerosols and their Interactions Over the Southern Ocean

  NSF · $1.1M · 2017–2021

• Collaborative Research: Cloud Macrophysical Parameterization and Its Application to Aerosol Indirect Effects

  NSF · $578k · 2010–2015

• Collaborative Research: Cloud System Evolution in the Trades

  NSF · $482k · 2014–2018

• Simulation of Microphysical Properties, Mesoscale Organization and Variability of Stratocumulus Clouds During the VOCALS Regional Experiment (REx)

  NSF · $400k · 2011–2015

Frequent coauthors

• Paquita Zuidema

  148 shared

• Christopher S. Bretherton

  Allen Institute for Artificial Intelligence

  135 shared

• Isabel L. McCoy

  130 shared

• J. Redemann

  University of Oklahoma

  103 shared

• Paola Formenti

  Université Paris Cité

  82 shared

• Craig Gralley

  Defense Intelligence Agency

  81 shared

• Marion Priest

  University of Arkansas for Medical Sciences

  81 shared

• Isabelle Thabault

  Ministry of Security and Justice

  81 shared

Labs

• Department of Atmospheric and Climate SciencePI

Awards & honors

• The 2001 L. F. Richardson Prize, Royal Meteorological Societ…
• Editors’ Citation for Excellence in Refereeing for Journal o…
• University of Washington Department of Atmospheric Sciences…
• The 2011 Henry G Houghton Award, American Meteorological Soc…