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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

Radiative feedbacks from stochastic variability in surface temperature and radiative imbalance

Proistosescu, C., A. Donohoe, K.C. Armor, G.H. Roe, M.F. Sticker, and C.M. Bitz, "Radiative feedbacks from stochastic variability in surface temperature and radiative imbalance," Geophys. Res. Lett., 45, 5082-5094, doi:10.1029/2018GL077678, 2018.

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28 May 2018

Estimates of radiative feedbacks obtained by regressing fluctuations in top‐of‐atmosphere (TOA) energy imbalance and surface temperature depend critically on the sampling interval and on assumptions about the nature of the stochastic forcing driving internal variability. Here we develop an energy balance framework that allows us to model the different impacts of stochastic atmospheric and oceanic forcing on feedback estimates. The contribution of different forcing components is parsed based on their impacts on the covariance structure of near‐surface air temperature and TOA energy fluxes, and the framework is validated in a hierarchy of climate model simulations that span a range of oceanic configurations and reproduce the key features seen in observations. We find that at least three distinct forcing sources, feedbacks, and time scales are needed to explain the full covariance structure. Atmospheric and oceanic forcings drive modes of variability with distinct relationships between temperature and TOA radiation, leading to an effect akin to regression dilution. The net regression‐based feedback estimate is found to be a weighted average of the distinct feedbacks associated with each mode. Moreover, the estimated feedback depends on whether surface temperature and TOA energy fluxes are sampled at monthly or annual time scales. The results suggest that regression‐based feedback estimates reflect contributions from a combination of stochastic forcings and should not be interpreted as providing an estimate of the radiative feedback governing the climate response to greenhouse gas forcing.

A source–receptor perspective on the polar hydrologic cycle: Sources, seasonality, and Arctic–Antarctic parity in the hydrologic cycle response to CO2 doubling

Singh, H.K.A., C.M. Bitz, A. Donohoe, and P.J. Rasch, "A source–receptor perspective on the polar hydrologic cycle: Sources, seasonality, and Arctic–Antarctic parity in the hydrologic cycle response to CO2 doubling," J. Climate, 30, 9999-10017, doi:10.1175/JCLI-D-16-0917.1, 2017.

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1 Dec 2017

Numerical water tracers implemented in a global climate model are used to study how polar hydroclimate responds to CO2-induced warming from a source–receptor perspective. Although remote moisture sources contribute substantially more to polar precipitation year-round in the mean state, an increase in locally sourced moisture is crucial to the winter season polar precipitation response to greenhouse gas forcing. In general, the polar hydroclimate response to CO2-induced warming is strongly seasonal: over both the Arctic and Antarctic, locally sourced moisture constitutes a larger fraction of the precipitation in winter, while remote sources become even more dominant in summer. Increased local evaporation in fall and winter is coincident with sea ice retreat, which greatly augments local moisture sources in these seasons. In summer, however, larger contributions from more remote moisture source regions are consistent with an increase in moisture residence times and a longer moisture transport length scale, which produces a robust hydrologic cycle response to CO2-induced warming globally. The critical role of locally sourced moisture in the hydrologic cycle response of both the Arctic and Antarctic is distinct from controlling factors elsewhere on the globe; for this reason, great care should be taken in interpreting polar isotopic proxy records from climate states unlike the present.

Twentieth century correlations between extratropical SST variability and ITCZ shifts

Green, B., J. Marshall, and A. Donohoe, "Twentieth century correlations between extratropical SST variability and ITCZ shifts," Geophys. Res. Letts., 44, 9039-9047, doi:10.1002/2017GL075044, 2017.

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16 Sep 2017

The Intertropical Convergence Zone (ITCZ) is a global-scale band of tropical precipitation lying, in the annual mean, just north of the equator. Its position can be tied to the atmosphere's energy balance: the Northern Hemisphere is heated more strongly than the Southern Hemisphere, biasing the atmosphere's circulation and ITCZ north of the equator. In the context of this energy balance framework, we examine multidecadal connections between variations in the position of the global ITCZ and indices of extratropical sea surface temperature (SST) variability over the twentieth century. We find that the ITCZ and atmospheric circulation are shifted farther to the north during periods when North Atlantic and North Pacific SSTs are anomalously warm. Additionally, a warmer North Atlantic is correlated with a relatively warm Northern Hemisphere atmosphere. Our results suggest an important role for the ocean circulation in modulating ITCZ migrations on decade-and-longer timescales.

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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