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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

Controls on the width of tropical precipitation and its contraction under global warming

Donohoe, A., A.R. Atwood, and M.P. Byrne, "Controls on the width of tropical precipitation and its contraction under global warming," Geophys. Res. Lett., 46, 9958-9967, doi:10.1029/2019GL082969, 2019.

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28 Aug 2019

Climate models robustly and unanimously simulate narrowing of the intense tropical precipitation under greenhouse gas forcing. We argue that the meridional width of tropical precipitation is controlled by the seasonal meridional range of the Intertropical Convergence Zone (ITCZ). The contraction of tropical precipitation under greenhouse forcing results from a reduced seasonal range of ITCZ migration. An energetic theory — similar to the energetic theory for ITCZ shifts based on the hemispheric contrast of energy input to the atmosphere — is developed. The meridional width of tropical precipitation is proportional to the seasonal range of the interhemispheric contrast in atmospheric heating divided by the efficiency of atmospheric cross‐equatorial heat transport. Climate models are biased toward overly expansive tropical precipitation resulting from an exaggerated seasonal atmospheric heating. The robust contraction of tropical precipitation under global warming results from increased efficiency of interhemispheric energy transport consistent with enhanced gross moist stability of the tropical atmosphere.

Meridional atmospheric heat transport constrained by energetics and mediated by large-scale diffusion

Armour, K.C., N. Siler, A. Donohoe, and G.H. Roe, "Meridional atmospheric heat transport constrained by energetics and mediated by large-scale diffusion," J. Clim., 32, 3655-3680, doi:10.1175/JCLI-D-18-0563.1, 2019.

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1 Jun 2019

Meridional atmospheric heat transport (AHT) has been investigated through three broad perspectives: a dynamic perspective, linking AHT to the poleward flux of moist static energy (MSE) by atmospheric motions; an energetic perspective, linking AHT to energy input to the atmosphere by top-of-atmosphere radiation and surface heat fluxes; and a diffusive perspective, representing AHT in terms downgradient energy transport. It is shown here that the three perspectives provide complementary diagnostics of meridional AHT and its changes under greenhouse gas forcing. When combined, the energetic and diffusive perspectives offer prognostic insights: anomalous AHT is constrained to satisfy the net energetic demands of radiative forcing, radiative feedbacks, and ocean heat uptake; in turn, the meridional pattern of warming must adjust to produce those AHT changes, and does so approximately according to diffusion of anomalous MSE. The relationship between temperature and MSE exerts strong constraints on the warming pattern, favoring polar amplification. These conclusions are supported by use of a diffusive moist energy balance model (EBM) that accurately predicts zonal-mean warming and AHT changes within comprehensive general circulation models (GCMs). A dry diffusive EBM predicts similar AHT changes in order to satisfy the same energetic constraints, but does so through tropically amplified warming — at odds with the GCMs' polar-amplified warming pattern. The results suggest that polar-amplified warming is a near-inevitable consequence of a moist, diffusive atmosphere's response to greenhouse gas forcing. In this view, atmospheric circulations must act to satisfy net AHT as constrained by energetics.

Does surface temperature respond to or determine downwelling logwave radiation?

Vargas Zeppetello, L.R., A. Donohoe, and D.S. Battisti, "Does surface temperature respond to or determine downwelling logwave radiation?" Geophys. Res. Lett., 46, 2781-2789, doi:10.1029/2019GL082220, 2019.

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16 Mar 2019

Downward longwave radiation (DLR) is often assumed to be an independent forcing on the surface energy budget in analyses of Arctic warming and land‐atmosphere interaction. We use radiative kernels to show that the DLR response to forcing is largely determined by surface temperature perturbations. We develop a method by which vertically integrated versions of the radiative kernels are combined with surface temperature and specific humidity to estimate the surface DLR response to greenhouse forcing. Through a decomposition of the DLR response, we estimate that changes in surface temperature produce at least 63% of the clear‐sky DLR response in greenhouse forcing, while the changes associated with clouds account for only 11% of the full‐sky DLR response. Our results suggest that surface DLR is tightly coupled to surface temperature; therefore, it cannot be considered an independent component of the surface energy budget.

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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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