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

• Climatology
• Geology
• Environmental science
• Oceanography
• Physics
• Geomorphology

Selected publications

• An Energetic Perspective on Heat Waves Using a Fixed Atmospheric Mass Calculation of Instantaneous Atmospheric Heat Flux Convergence

  Journal of Climate · 2026-01-15

  article

  Abstract The atmospheric energy budget associated with the heating and cooling of the atmosphere on daily time scales across the globe is analyzed using a fixed atmospheric mass calculation of the instantaneous atmospheric heat flux convergence. The heating and moistening of the atmospheric column during a typical heating event requires of order 1000 W m −2 of energy input to the atmosphere. The required energy input is predominantly provided by the atmospheric heat transport convergence. In contrast, the temporal variability of energy inputs by surface turbulent fluxes and radiation are an order of magnitude smaller. This result suggests that the atmospheric temperature variability is set by the magnitude of variability in lateral energy fluxes in the atmosphere, limited by the heat capacity of the atmosphere, and provides a framework for understanding the controls on heat wave intensity. To relate the magnitude of atmospheric heating to the intensity of heat waves—measured by the variance of surface temperature—additional considerations are made for (i) the temporal duration of heating events, (ii) the fraction of atmospheric energy input that goes into moistening versus warming the atmosphere, and (iii) the vertical structure of temperature changes during heating events. Of these factors, surface heat wave intensity is damped by the moisture storage contribution by a factor of four in the tropics and amplified by the vertical structure of temperature by almost an order of magnitude over extratropical landmasses as compared to the ocean.

  PublisherDOI

• Why April Stands Out: Monthly Impacts of Internal Variability on Arctic Amplification

  2026-05-06

  article
  PublisherDOI

• The Key Role of the Southern Annular Mode During the Seasonal Sea Ice Maximum in Recent Antarctic Sea Ice Loss

  2025-03-15

  preprintOpen accessSenior author

  Southern Hemisphere sea ice area (SH SIA) exhibited weak increases from the early 1980s until 2015 when it abruptly dropped, setting record low values in 2017, 2022, and 2023. The reasons for the rapid declines in SH SIA remain open to debate, with potential explanations ranging from changes in tropical Pacific climate, warming of the high latitude subsurface ocean, and contemporaneous variations in the extratropical atmospheric circulation. Here we provide novel insights into the role of the extratropical atmospheric circulation in driving year-to-year and long-term changes in Antarctic sea ice, with a focus on the influence of the Southern annular mode (SAM) on recent trends in SH sea ice area. The influence of the SAM on SH SIA exhibits a more pronounced seasonal variation than that indicated in previous work: during the annual sea ice minimum, anomalous circumpolar westerlies associated with the positive polarity of the SAM lead to increases in SH SIA that persistent for several months. In contrast, during the annual sea ice maximum, anomalous circumpolar westerlies associated with the positive polarity of the SAM lead to pronounced decreases in Antarctic sea ice that persist for up to a year. In terms of annual-mean SH SIA, by far the largest impacts arise from variations in the atmospheric circulation during the sea ice maximum. As a result, changes in the SAM during the sea ice maximum have had a marked impact on long-term changes in SH SIA. These linkages are robust in both observationally constrained data products and modeled data, with additional results exploring how this relationship changes as the mean state of the climate changes under global warming.

  PublisherDOI

• Increasing boreal fires reduce future global warming and sea ice loss

  Proceedings of the National Academy of Sciences · 2025-06-03 · 10 citations

  articleOpen access1st authorCorresponding

  Biomass burning can affect climate via the emission of aerosols and their subsequent impact on radiation, cloud microphysics, and surface and atmospheric albedo. Biomass burning emissions (BBEs) over the boreal region have strongly increased during the last decade and are expected to continue increasing as the climate warms. Climate models simulate aerosol processes, yet historical and future Coupled Model Intercomparison Project (CMIP) simulations have no active fire component, and BBEs are prescribed as external forcings. Here, we show that CMIP6 used future boreal BBEs scenarios with unrealistic near-zero trends that have a large impact on climate trends. By running sensitivity experiments with ramped up boreal emissions based on observed trends, we find that increasing boreal BBEs reduces global warming by 12% and Arctic warming by 38%, reducing the loss of sea ice. Tropical precipitation shifts southward as a result of the hemispheric difference in boreal aerosol forcing and subsequent temperature response. These changes stem from the impact of aerosols on clouds, increasing cloud droplet number concentration, cloud optical depth, and low cloud cover, ultimately reducing surface shortwave flux over northern latitudes. Our results highlight the importance of realistic boreal BBEs in climate model simulations and the need for improved understanding of boreal emission trends and aerosol-climate interactions.

  PublisherOA PDFDOI

• Artificial Flooding Leads to Thicker and Brighter Arctic Sea Ice

  Earth s Future · 2025-12-12

  articleOpen access1st authorCorresponding

  Abstract We describe and present results from a 2024/2025 field campaign that is the first to test and observe the impact of flooding and meltwater draining on Arctic sea ice over the winter growth and spring melt seasons. The campaign was conducted in Cambridge Bay, Nunavut, Canada. A 1 by 1 km fieldwork site was used, comprising three control areas, which were never flooded, and eight test areas. In these, flooding treatments were carried out by pumping seawater onto the sea ice. Some test areas were flooded once (in December or January), while others were flooded twice (in December and February, or January and February). The total area flooded was 0.25 . Additionally, one control area was used for a melt pond drainage experiment during spring. By mid May, prior to melt, flooded test areas were up to 32 cm thicker than control areas, with snow cover that was 1–13 cm thinner. Areas flooded twice exhibited greater thickening than those flooded once. During the melt period, sea ice in the flooded areas appeared brighter and showed slower melt rates, remaining thicker than that in the control areas. The drained melt pond site also brightened markedly within 1 week of borehole drilling. Comparison with a historical sea ice thickness record from Cambridge Bay indicates that a 30 cm increase corresponds to roughly the magnitude of long‐term thinning observed over the past 50 years.

  PublisherDOI

• Record Warmth of 2023 and 2024 was Highly Predictable and Resulted From ENSO Transition and Northern Hemisphere Absorbed Shortwave Anomalies

  Geophysical Research Letters · 2025-05-13 · 6 citations

  articleOpen access1st authorCorresponding

  Abstract Global mean temperature rapidly warmed during 2023, making 2023 the second warmest year on record at 1.45°C above pre‐industrial climate, and 2024 became the first year on record to surpass 1.5°C. Here we explore the likelihood, mechanisms, and predictability of the rapid warming during 2023 with CMIP simulations and a fully‐coupled forecast ensemble initialized on 1 November 2022. The year‐to‐year (Y2Y) warming for the second half of 2023 of 0.49°C equaled the largest on record since 1850, and is simulated as a 1 in 6,000 years event. The forecast ensemble‐mean predicts about 75% of the observed warming during 2023. The remaining 25% of the warming lies within the forecast spread, with members that forecast a strong 2023 El Niño and positive absorbed shortwave anomalies more likely to forecast the entirety of the observed warming. The forecast ensemble succesfully predicts 2024 to be the first year on record above 1.5°C.

  PublisherOA PDFDOI

• Observed winds alone cannot explain recent Arctic warming and sea ice loss

  Environmental Research Climate · 2025-10-10

  articleOpen accessCorresponding

  Abstract Since the 1980s, observations show the Arctic surface has warmed four times more than the global mean. Over the Arctic Ocean, this recent large warming is connected to sea ice loss. While earth system models are useful tools for prediction, exact replication of observed Arctic warming and sea ice loss is not expected in freely-evolving models because of internal climate variability. Previous studies have shown that historical hindcasts with model winds nudged to reanalysis can reproduce recent Arctic warming and sea ice loss. However, the influence of observed winds on these recent Arctic changes in absence of anthropogenic forcing has not been assessed. Here, we show that nudging to recent (1980–2023) observed winds alone in a pre-industrial model experiment does not reproduce the magnitude of observed warming and sea ice extent loss. This means that the large-scale winds are not the primary driver of recently observed large Arctic trends. Yet, the winds do partially reproduce the interannual, seasonal, and spatial variability, especially in spring. We also show that in a pre-industrial climate simulation, these results are largely independent of mean state sea ice thickness. In short, the observed winds drive part of the Arctic temperature and sea ice variability but not long-term trends.

  PublisherDOI

• Record warmth of 2023 and 2024 resulted from ENSO transition and Northern Hemisphere absorbed shortwave anomalies

  2025-03-01 · 1 citations

  preprintOpen access1st authorCorresponding

  Global mean temperature rapidly warmed during 2023, making 2023 the second warmest year on record at 1.45°C above pre-industrial climate, and 2024 became the first year on record to surpass 1.5°C. Here we explore the likelihood, mechanisms, and predictability of the rapid warming since 2023 with CMIP simulations and a fully-coupled forecast ensemble initialized on November 1 2022. The year-to-year (Y2Y) warming for the second half of 2023 of 0.49°C equaled the largest on record since 1850, and is simulated as a 1 in 6000 year event. The forecast ensemble-mean predicts about 70% of the observed warming during 2023. The remaining 30% of the warming lies within the forecast spread, with members that forecast a strong 2023 El Niño and positive absorbed shortwave anomalies more likely to forecast the entirety of the observed warming. The forecast ensemble succesfully predicts 2024 to be the first year on record above 1.5°C

  PublisherOA PDFDOI

• Clouds Are Crucial to Capture Antarctic Sea Ice Variability

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

  articleOpen accessSenior author

  Abstract Models from the Coupled Model Intercomparison Project phase 6 (CMIP6) typically struggle to reproduce observed Antarctic sea ice trends, a bias that is substantially alleviated when constraining winds. We use wind‐nudged simulations from two CMIP models to investigate the influence of clouds on sea ice area (SIA). We find that nudging model winds in coupled simulations toward reanalysis, in addition to improving SIA variability, is crucial to reproduce realistic anomalies in cloud radiative effect (CRE) and cloud cover. Biases in the variability of cloud properties at sea ice edge—characterized by CRE anomalies—help explain the remaining discrepancies between simulated and observed SIA; a bias of 1 in the CRE anomaly corresponds to a negative bias of 0.43 in SIA anomaly. Finally, we find that most CMIP6 models show positive trends in CRE anomaly biases, which should contribute to enhanced SIA decline, a long‐standing bias in CMIP models.

  PublisherOA PDFDOI

• Decoded Antarctic snow accumulation history reconciles observed and modeled trends in accumulation and large-scale warming patterns

  2025-09-16

  preprintOpen accessCorresponding

  Abstract. Ice-core reconstructions indicate that increased snow accumulation on the Antarctic Ice Sheet mitigated global sea level rise by ~11 mm during 1901–2000. However, in the most recent 40 years of more intense observation and warming, the trend in the Antarctic-wide accumulation rate has been negligible. We attribute these trends by evaluating Earth system model experiments in comparison with dynamically consistent reconstructions of surface climate. Single-forcing experiments reveal that rising concentrations of greenhouse gases (GHGs) have been the underlying driver of increased accumulation, yet acting alone would have caused twice the observed accumulation-related sea level mitigation during 1901–2000. Aerosol-driven cooling partially compensates this overprediction, but there is strong evidence for other processes at work. We hypothesize that high-latitude winds have been working together with ice-shelf meltwater fluxes to dampen Southern Ocean surface warming and suppress the GHG-driven accumulation increase since the initiation of West Antarctic ice shelf thinning in the mid-twentieth century. The wind pattern associated with strengthening of the Southern Hemisphere westerlies and deepening of the Amundsen Sea Low distributes accumulation unevenly across the continent in an orographic pattern that is consistent across models and the reconstructions. In reconstructions, these same wind and accumulation patterns are associated with muted surface warming across the eastern Pacific and Southern Ocean, a pattern not captured in climate projections including the all-forcings large ensemble studied here. However, the westerly wind history constrained by paleoclimate data assimilation largely reconciles differences between the model's ensemble-mean response and the observed world for both Antarctic-wide accumulation and large-scale warming patterns. Although the large ensemble simulates similar wind histories to the real one, its corresponding responses in SSTs and Antarctic-wide accumulation are decoupled from the wind. We discuss how this significant observation-model discrepancy, which has widespread implications for projecting regional climate change, likely arises from omitted meltwater forcing and/or resolution limitations. As a component of the sea level budget and a gauge of the magnitude and spatial pattern of climate change, Antarctic snow accumulation is a critical target for models to replicate.

  PublisherOA PDFDOI

Frequent coauthors

• Cecilia M. Bitz

  University of Washington

  61 shared

• Lettie A. Roach

  Columbia University

  25 shared

• Martin Vancoppenolle

  Sorbonne University Abu Dhabi

  25 shared

• Kenza Himmich

  Sorbonne Université

  20 shared

• François Massonnet

  UCLouvain

  19 shared

• Mitchell Bushuk

  NOAA Geophysical Fluid Dynamics Laboratory

  14 shared

• Melinda Webster

  Johns Hopkins University Applied Physics Laboratory

  14 shared

• Steffen Tietsche

  European Centre for Medium-Range Weather Forecasts

  13 shared

Education

• PhD, Atmospheric Sciences

  University of Washington

Awards & honors

• WCRP Open Science Conference poster award, Oct 2011
• Top Scholar award, The Graduate School, 2007 (University of…
• Girton College Emily Davies Scholarship, 2003 (University of…
• Girton College Janet Chamberlain Dissertation Prize, 2003 (U…
• Cambridge University William Vaughan Lewis Dissertation Priz…