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

• Physics
• Environmental science
• Atmospheric sciences
• Meteorology
• Geology
• Climatology
• Oceanography
• Geography

Selected publications

• Dominant Modes of Terrain-Tied Vertical Motion Variability over the Payette River Basin of Idaho: Results from SNOWIE

  Journal of Applied Meteorology and Climatology · 2026-01-27

  article

  Abstract Precipitation enhancement over complex terrain is predominantly driven by quasi-stationary, terrain-tied vertical motions, making their variability a critical factor in shaping precipitation distributions and accumulation. This study quantifies the dominant modes of terrain-tied vertical motion variability over the Payette River basin of Idaho. Principal component analysis is applied to a seasonal simulation spanning November 2016–April 2017, which encompassed the Seeded and Natural Orographic Wintertime Clouds: the Idaho Experiment (SNOWIE) field campaign (January–March 2017). The first mode, accounting for more than 20% of the variance in vertical motion, captures ridge-tied updrafts and represents the primary pattern of terrain-induced ascent. The second mode (8%) reflects how synoptic-scale variations modulate updraft orientation, distinguishing between north–south and east–west ridgelines. The third mode (6%) isolates variability in updraft width and magnitude. These three dominant modes of variability, which explain over one-third of the vertical velocity variance in the seasonal simulation, strongly influence the distribution of supercooled liquid water (SLW) and precipitation over the terrain. Results show that the dominant modes of vertical motion variability were consistent with patterns commonly observed during SNOWIE research flights. Additionally, we quantified vertical motion, SLW, and precipitation means as a function of phase space between the modes, demonstrating that enhanced SLW and precipitation occurred when quasi-stationary waves were present over the terrain.

  PublisherDOI

• Morphological Characteristics of Tropical Precipitation Features Producing Extreme Instantaneous Rain Rates in Observations and a Global Storm-Resolving Model

  2026-02-06

  articleOpen access

  As global warming may influence convective organization, it is important to observationally constrain the effects of convective organization on the production of extreme instantaneous tropical rain rates. It is also important to evaluate the ability of global storm-resolving models in capturing this coupling. We quantify the spatial morphology of tropical precipitation features that contain extreme tropical rain rates. We compare these morphological measures to the morphology of extreme precipitation features as simulated by a global storm-resolving model. We find that in both observations and the model simulation, precipitation features with extreme rain rates are on average larger and have higher convective area fraction than the average precipitation feature. Further, among precipitation features with a similar amount of total convection, those with spatially concentrated convective cores generated on average more intense maximum precipitation rates. Our evaluated model underestimates the influence of the spatial concentration of convection on maximum rain rate.

  PublisherOA PDFDOI

• Climate warming could weaken aerosol-cloud interactions in subtropical marine stratocumulus

  npj Climate and Atmospheric Science · 2026-02-25 · 1 citations

  articleOpen access

  Abstract Radiative effects of aerosol-cloud interactions constitute the most uncertain climate forcing of the Earth system. To understand how these interactions may change with climate, we conduct 3-day-long large-eddy simulations of a stratocumulus-to-cumulus transition along an airmass-following trajectory over the Northeast Pacific Ocean. By perturbing boundary-layer aerosol concentrations, aerosol-cloud interactions are simulated in present-day and warmed climate with increased CO 2 . Aerosol-induced cloud changes, including the Twomey effect and adjustments of cloud fraction and liquid water path, are inhibited in a doubled-CO 2 climate. Decomposing the aerosol-induced cloud radiative effect change (ΔCRE) reveals that aerosol-induced cloud fraction changes dominate ΔCRE. Doubling CO 2 attenuates the aerosol-induced ΔCRE (i.e., cooling) by >30% in our simulations. Our results also show that low cloud feedbacks are sensitive to the background aerosol concentration, highlighting the interplay between climate forcings and feedbacks. These results may aid in predicting the cooling potential of marine cloud brightening in a changing climate.

  PublisherOA PDFDOI

• A New Theoretical Framework for Parameterizing Nonequilibrium Fractionation During Evaporation From the Ocean

  Journal of Advances in Modeling Earth Systems · 2026-03-01

  articleOpen access

  Abstract The evaporation model for water isotopes proposed by Craig and Gordon (1965, https://books.google.co.in/books?id=6wIKAQAAIAAJ ) is used in most isotope‐enabled atmospheric models for the parameterization of nonequilibrium fractionation during evaporation from the ocean. In this model, one of the most uncertain parameters is the nonequilibrium fractionation factor . Many isotope models use the formulation of Merlivat and Jouzel (1979, https://doi.org/10.1029/jc084ic08p05029 ), which parameterizes as a function of wind speed and distinguishes between a smooth and a rough regime to account for the effect of ocean waves. The resulting discontinuity in between smooth and rough regimes has been disputed by several empirical studies. Here, we present a new approach to parameterizing by explicitly accounting for the influence of wave drag on the momentum flux near the surface. Following Cifuentes‐Lorenzen et al. (2018, https://doi.org/10.1007/s10546‐018‐0376‐0 ), we add a third wave‐induced component to the total momentum flux, in addition to the viscous and turbulent components, and extend the definition of the eddy viscosity to account for the momentum flux due to waves and turbulent dissipation near the surface. The new scheme predicts a slight decrease of with wind speed, similar to the smooth‐regime parameterization of Merlivat and Jouzel (1979, https://doi.org/10.1029/jc084ic08p05029 ). This new parameterization is incorporated into the isotope‐enabled Community Atmosphere Model, where it improves the correlation of simulated and measured vapor deuterium excess relative to the default version and a version with constant , suggesting that it may be used as a valid representation of fractionation during evaporation from the ocean in future isotope models.

  PublisherDOI

• Understanding tropical cyclone frequency biases in a global storm resolving model

  2026-02-07

  article

  Global storm resolving models (GSRMs) provide an excellent testbed for understanding the role of small-scale processes in tropical cyclogenesis. In this study, we assess tropical cyclone (TC) genesis and frequency in the Geophysical Fluid Dynamics Laboratory’s eXperimental System for High‐resolution prediction on Earth‐to‐Local Domains version 2021 (X-SHiELD v2021). Compared to observations, X-SHiELD produces significantly fewer TCs, albeit with realistic representations of both the number of pre-TC disturbances (TC seeds) and the mean state relative to ERA5. We find that the TC seed-to-TC transition rate is underestimated in X-SHiELD because the spin-up of TC seed vortex is inefficient. The inefficient TC seed spin-up in X-SHiELD is associated with a weaker-than-observed low-level inflow, which is coupled to mesoscale ascent near the center that is too weak and too top-heavy. The biases in vertical velocity are associated with a dry bias at low levels, which is caused by the overly active shallow convection scheme. Our results underscore the importance of subgrid scale processes, particularly low level mixing through shallow convection, in the representation of TC genesis process even in kilometer scale models.

  PublisherDOI

• Resolving Low Cloud Feedbacks Globally With E3SM High‐Res MMF: Agreement With LES but Stronger Shortwave Effects

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

  articleOpen accessCorresponding

  Abstract This study investigates low cloud feedback in a warmer climate using global simulations from the High‐Resolution Multi‐scale Modeling Framework (HR‐MMF), which explicitly simulates small‐scale eddies globally. Two 5‐year simulations—one with present‐day sea surface temperatures (SSTs) and a second with SSTs warmed uniformly by 4 K—reveal a positive global shortwave cloud radiative effect (SWCRE = 0.3 W//K), comparable to estimates from CMIP models. As the climate warms, significant reductions in low cloud cover occur over stratocumulus regions. This study is the first attempt to compare HR‐MMF results with predictions from idealized large‐eddy simulations from the CGILS intercomparison. Despite different underlying assumptions, we find qualitative agreement in SWCRE and inversion height changes between HR‐MMF and CGILS predictions. This suggests reasonable credibility for the CGILS framework in predicting cloud responses under the out‐of‐sample conditions found in HR‐MMF. However, the HR‐MMF exhibits stronger SWCRE changes than predicted by CGILS. We explore potential causes for this discrepancy, examining variations in cloud‐controlling factors (CCFs) and cloud conditions. Our results show a fairly homogeneous SWCRE response, with little systematic variation tied to the variations in CCFs. This reveals a dominant role for SST forcing in modulating SWCRE.

  PublisherOA PDFDOI

• Multiscale Convective Circulations and Scale Interactions in a Global Storm-Resolving Model

  2025-04-22

  preprintOpen access

  Understanding the relation between large-scale ($>$ O(100km)) tropical atmospheric circulations and small-scale convective circulations remains a challenge despite its crucial role in developing Earth System models. In this study, a 40-day simulation made with a global storm-resolving model at 4 km horizontal resolution is used to simultaneously characterize large- and small-scale convective circulations and examine their relationships. The large-scale motions are characterized with the area-averaged vertical mass flux profile over tropical domains; small-scale motions are computed as deviations of vertical mass flux from the large-scale mean. We find that the simulated large-scale circulations tend to evolve in a systematic way that bears qualitative resemblance to the canonical evolution of tropical convective systems, with large-scale regimes that progress from weak but widespread subsidence, to shallow/congestus clouds, to deep convection, to stratiform anvils, and finally returning to a dissipated state. We utilize the moisture-space framework to compare the structure of the small-scale circulations in different large-scale regimes. We find that the evolution of the large-scale vertical motions is tied to the changes in the small-scale circulation. We examine these small-scale circulations, as well as their connections to the evolution of buoyancy and clouds. We find that large-scale circulations evolve faster when associated small-scale circulations are stronger, suggesting upscale feedback. These findings support the notion of mutual scale interaction in the tropics as being an essential part of the evolution of large-scale vertical motions in models and observations.

  PublisherOA PDFDOI

• Flower‐Type Organized Trade‐Wind Cumulus: A Multi‐Day Lagrangian Large Eddy Simulation Intercomparison Study

  Journal of Advances in Modeling Earth Systems · 2025-10-01

  articleOpen access

  Abstract Shallow cumulus cloud fields in subtropical marine trade wind environments, particularly over the tropical Atlantic Ocean, show distinct organizational patterns. Among these, Flower‐type clouds are characterized by expansive stratiform cloud patches surrounded by regions of scattered convection. The objectives of this study were (a) to construct a case study of a time period during the A/ATOMIC field campaign when Flower‐type organization was observed, (b) to evaluate the fidelity of a multi‐model ensemble of large eddy simulations of that case, and (c) to analyze the interaction between cloud and precipitation processes and mesoscale organization in the simulations. The simulations follow a quasi‐Lagrangian trajectory, allowing mesoscale features to develop over time in a domain that follows the boundary‐layer airmass. The results show a broad agreement in simulated thermodynamic properties across different LES codes, with Flower‐type cloud patches appearing within hours of each other. The consensus among models is consistent with observations made during the A/ATOMIC field campaign on the specific day of interest. The cloud structure reveals three distinct peaks in the joint probability densities of cloud base and cloud top height, with the dominant peak at any given time influenced by the stage of cloud organization. The simulated cloud system evolution reveals consistent occurrence of maxima in liquid water path and rain rate before Flower reaches its maximum length scale. Targeted sensitivity tests reveal a weak relationship between Cloud Droplet Number concentration and the extent/degree/type of organization.

  PublisherOA PDFDOI

• 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

• 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

Recent grants

• Collaborative Research: Advancing Understanding of Aerosol-Cloud Feedback Using the World's First Global Climate Model with Explicit Boundary Layer Turbulence

  NSF · $419k · 2019–2024

• Collaborative Research: EUREC4A-iso--Constraining the Interplay between Clouds, Convection, and Circulation with Stable Isotopologues of Water Vapor

  NSF · $389k · 2019–2024

• Collaborative Research: Isotopic Fractionation in Snow (IFRACS)

  NSF · $216k · 2013–2017

Frequent coauthors

• Christopher S. Bretherton

  Allen Institute for Artificial Intelligence

  130 shared

• Robert Wood

  University of Washington

  32 shared

• S. J. Doherty

  Seattle University

  29 shared

• Grégoire Védeau

  Commissariat à l'Énergie Atomique et aux Énergies Alternatives

  28 shared

• Caroline Muller

  Institute of Science and Technology Austria

  28 shared

• Camille Risi

  25 shared

• Françoise Vimeux

  Université Paris-Saclay

  24 shared

• Jacqueline M Nugent

  Allen Institute for Artificial Intelligence

  22 shared

Awards & honors

• 2018 AGU Editors’ Citation for Excellence in Refereeing from…
• 2016 AGU Editors’ Citation for Excellence in Refereeing from…