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Aaron Donohoe

Senior Research Scientist

Email

adonohoe@apl.washington.edu

Phone

206-616-3471

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

Stratospheric and tropospheric flux contributions to the polar cap energy budgets

Cardinale, C.J., B.E.J. Rose, A.L. Lang, and A. Donohoe, "Stratospheric and tropospheric flux contributions to the polar cap energy budgets," J. Clim., 34, 4261–4278, doi:10.1175/JCLI-D-20-0722.1, 2021.

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1 Jun 2021

The flux of moist static energy into the polar regions plays a key role in the energy budget and climate of the polar regions. While usually studied from a vertically integrated perspective (Fwall), this analysis examines its vertical structure, using the NASA-MERRA-2 reanalysis to compute climatological and anomalous fluxes of sensible, latent, and potential energy across 70°N and 65°S for the period 1980–2016. The vertical structure of the climatological flux is bimodal, with peaks in the mid- to lower-troposphere and mid- to upper-stratosphere. The near zero flux at the tropopause defines the boundary between stratospheric (Fstrat) and tropospheric (Ftrop) contributions to Fwall. Especially at 70°N, Fstrat is found to be important to the climatology and variability of Fwall, contributing 20.9 Wm-2 to Fwall (19% of Fwall) during the winter and explaining 23% of the variance of Fwall. During winter, an anomalous poleward increase in Fstrat preceding a sudden stratospheric warming is followed by an increase in outgoing longwave radiation anomalies, with little influence on the surface energy budget of the Arctic. Conversely, a majority of the energy input by an anomalous poleward increase in Ftrop goes toward warming the Arctic surface. Ftrop is found to be a better metric than Fwall for evaluating the influence of atmospheric circulations on the Arctic surface climate.

Radiative and dynamic controls on atmospheric heat transport over different planetary rotation rates

Cox, T., K.C. Armour, G.H. Roe, A. Donohoe, and D.M.W. Frierson, "Radiative and dynamic controls on atmospheric heat transport over different planetary rotation rates," J. Clim., 34, 3543-3554, doi:10.1175/JCLI-D-20-0533.1, 2021.

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8 Feb 2021

Atmospheric heat transport is an important piece of our climate system, yet we lack a complete theory for its magnitude or changes. Atmospheric dynamics and radiation play different roles in controlling the total atmospheric heat transport (AHT) and its partitioning into components associated with eddies and mean meridional circulations. This work focuses on two specific controls: a radiative one, atmospheric radiative temperature tendencies; and a dynamic one, planetary rotation rate. We use an idealized grey radiation model to employ a novel framework to lock the radiative temperature tendency and total AHT to climatological values, even while the rotation rate is varied. This setup allows for a systematic study of the effects of radiative tendency and rotation rate on AHT. We find that rotation rate controls the latitudinal extent of the Hadley cell and the heat transport efficiency of eddies. Both rotation rate and radiative tendency influence the strength of the Hadley cell and the strength of equator-pole energy differences that are important for AHT by eddies. These two controls do not always operate independently and can reinforce or dampen each other. In addition, we examine how individual AHT components, which vary with latitude, sum to a total AHT that varies smoothly with latitude. At slow rotation rates the mean meridional circulation is most important in ensuring total AHT varies smoothly with latitude, while eddies are most important at rotation rates similar to, and faster than, the Earth's.

Impact of winds and Southern Ocean SSTs on Antarctic sea ice trends and variability

Blanchard-Wigglesworth, E., L.A. Roach, A. Donohoe, and Q. Ding, "Impact of winds and Southern Ocean SSTs on Antarctic sea ice trends and variability," J. Clim., 34, 949-965, doi:10.1175/JCLI-D-20-0386.1, 2021.

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1 Feb 2021

Antarctic sea ice extent (SIE) has slightly increased over the satellite observational period (1979 to the present) despite global warming. Several mechanisms have been invoked to explain this trend, such as changes in winds, precipitation, or ocean stratification, yet there is no widespread consensus. Additionally, fully coupled Earth system models run under historic and anthropogenic forcing generally fail to simulate positive SIE trends over this time period. In this work, we quantify the role of winds and Southern Ocean SSTs on sea ice trends and variability with an Earth system model run under historic and anthropogenic forcing that nudges winds over the polar regions and Southern Ocean SSTs north of the sea ice to observations from 1979 to 2018. Simulations with nudged winds alone capture the observed interannual variability in SIE and the observed long-term trends from the early 1990s onward, yet for the longer 1979–2018 period they simulate a negative SIE trend, in part due to faster-than-observed warming at the global and hemispheric scale in the model. Simulations with both nudged winds and SSTs show no significant SIE trends over 1979–2018, in agreement with observations. At the regional scale, simulated sea ice shows higher skill compared to the pan-Antarctic scale both in capturing trends and interannual variability in all nudged simulations. We additionally find negligible impact of the initial conditions in 1979 on long-term trends.

More Publications

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center
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