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Aaron Donohoe

Principal Research Scientist

Email

adonohoe@apl.washington.edu

Phone

206-616-2314

Department Affiliation

Polar Science Center

Education

B.A. Physics, Bowdoin College, 2003

Ph.D. Atmospheric Sciences, University of Washington, 2011

Publications

2000-present and while at APL-UW

Trends in atmospheric heat transport since 1980

Cox, T., A. Donohoe, K.C. Armour, D.M.W.Frierson, and G.H. Roe, "Trends in atmospheric heat transport since 1980," J. Clim., 37, 1539-1550, doi:10.1175/JCLI-D-23-0385.1, 2024.

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1 Mar 2024

We investigate the linear trends in meridional atmospheric heat transport (AHT) since 1980 in atmospheric reanalysis datasets, coupled climate models, and atmosphere-only climate models forced with historical sea surface temperatures. Trends in AHT are decomposed into contributions from three components of circulation: (i) transient eddies, (ii) stationary eddies, and (iii) the mean meridional circulation. All reanalyses and models agree on the pattern of AHT trends in the Southern Ocean, providing confidence in the trends in this region. There are robust increases in transient-eddy AHT magnitude in the Southern Ocean in the reanalyses, which are well replicated by the atmosphere-only models, while coupled models show smaller magnitude trends. This suggests that the pattern of sea surface temperature trends contributes to the transient-eddy AHT trends in this region. In the tropics, we find large differences between mean-meridional circulation AHT trends in models and the reanalyses, which we connect to discrepancies in tropical precipitation trends. In the Northern Hemisphere, we find less evidence of large-scale trends and more uncertainty, but note several regions with mismatches between models and the reanalyses that have dynamical explanations. Throughout this work we find strong compensation between the different components of AHT, most notably in the Southern Ocean where transient-eddy AHT trends are well compensated by trends in the mean-meridional circulation AHT, resulting in relatively small total AHT trends. This highlights the importance of considering AHT changes holistically, rather than each AHT component individually.

The sensitivity of climate and climate change to the efficiency of atmospheric heat transport

Ge, Q., Z. Zheng, L.T. Kang, A. Donohoe, K. Armour, and G. Roe, "The sensitivity of climate and climate change to the efficiency of atmospheric heat transport," Clim. Dyn., EOR, doi:10.1007/s00382-023-07010-3, 2023.

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7 Dec 2023

Atmospheric heat transport (AHT) moderates spatial gradients in surface temperature, and its efficiency (hereinafter referred to as diffusivity) shapes the distribution of moist static energy and the hydrological cycle. Using a linear downgradient rule for AHT, we diagnose zonal-mean diffusivity using observational and model data. We find it varies two- to threefold with season and latitude, but is nearly invariant across different climate states. We then employ a moist energy balance model (MEBM) to explore the impacts of changing the magnitude and spatial pattern of diffusivity on the climatology and climate response to forcing. Spatial anomalies in diffusivity in the extra-tropics have a larger impact on temperature and hydrology than diffusivity anomalies in the tropics. We demonstrate that compensating dynamical adjustments in the MEBM act to mute the impact of changing diffusivity patterns on the resulting climate. We isolate the impacts of spatial patterns of forcing, ocean heat uptake, radiative feedbacks, and diffusivity on the spatial pattern of climate change; and find that the pattern of climate change is least sensitive to the detailed pattern of diffusivity. Overall, these results suggest that although diffusivity is far from spatially invariant, understanding the climatology and spatial patterns of climate change does not depend on a detailed characterization of the spatial pattern of diffusivity.

Diagnosing mechanisms of hydrologic change under global warming in the CESM1 Large Ensemble

Siler, N., D.B. Bonan, and A. Donohoe, "Diagnosing mechanisms of hydrologic change under global warming in the CESM1 Large Ensemble," J. Clim., 36, 8243-8257, doi:10.1175/JCLI-D-23-0086.1, 2023.

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1 Dec 2023

Global warming is expected to cause significant changes in the pattern of precipitation minus evaporation (P – E), which represents the net flux of water from the atmosphere to the surface or, equivalently, the convergence of moisture transport within the atmosphere. In most global climate model simulations, the pattern of P – E change resembles an amplification of the historical pattern — a tendency known as "wet gets wetter, dry gets drier." However, models also predict significant departures from this approximation that are not well understood. Here, we introduce a new method of decomposing the pattern of P – E change into contributions from various dynamic and thermodynamic mechanisms and use it to investigate the response of P – E to global warming within the CESM1 Large Ensemble. In contrast to previous decompositions of P – E change, ours incorporates changes not only in the monthly means of atmospheric winds and moisture, but also in their temporal variability, allowing us to isolate the hydrologic impacts of changes in the mean circulation, transient eddies, relative humidity, and the spatial and temporal distributions of temperature. In general, we find that changes in the mean circulation primarily control the P – E response in the tropics, while temperature changes dominate at higher latitudes. Although the relative importance of specific mechanisms varies by region, at the global scale departures from the wet-gets-wetter approximation over land are primarily due to changes in the temperature lapse rate, while changes in the mean circulation, relative humidity, and horizontal temperature gradients play a secondary role.

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In The News

Scientists found the most intense heat wave ever recorded — in Antarctica

Washington Post, Kasha Patel

In March 2022, temperatures near the eastern coast of Antarctica spiked 70 degrees Fahrenheit (39 degrees Celsius) above normal — making it the most intense recorded heat wave to occur anywhere on Earth, according to a recent study.

24 Sep 2023

New perspectives on the enigma of expanding Antarctic sea ice

Eos — Science News by AGU, Blanchard-Wrigglesworth, Eisenman, Zhang, Sun, and Donohoe

Recent research offers new insights on Antarctic sea ice, which, despite global warming, has increased in overall extent over the past 40 years. Most climate models indicate that Antarctic sea ice extent should have decreased over the past several decades. Here the authors discuss results from three recent independent studies that all applied a "nudging" technique to the same climate model to study the influences of different processes on Antarctic sea ice extent.

11 Feb 2022

Deep, old water explains why Antarctic Ocean hasn't warmed

UW News and Information, Hannah Hickey

Observations and climate models show that the unique currents around Antarctica continually pull deep, centuries-old water up to the surface — seawater that last touched Earth’s atmosphere before the machine age, and has never experienced fossil fuel-related climate change.

30 May 2016

More News Items

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