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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

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.

Tropical precipitation and cross-equatorial ocean heat transport during the mid-Holocene

Liu, X., D.S. Battisti, A. Donohoe, "Tropical precipitation and cross-equatorial ocean heat transport during the mid-Holocene," J. Clim., 30, 3529-3547, doi:10.1175/JCLI-D-16-0502.1, 2017.

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1 May 2017

Summertime insolation intensified in the Northern Hemisphere during the mid-Holocene, resulting in enhanced monsoonal precipitation. In this study, the authors examine the changes in the annual-mean tropical precipitation as well as changes in atmospheric circulation and upper-ocean circulation in the mid-Holocene compared to the preindustrial climate, as simulated by 12 coupled climate models from PMIP3. In addition to the predominant zonally asymmetric changes in tropical precipitation, there is a small northward shift in the location of intense zonal-mean precipitation (mean ITCZ) in the mid-Holocene in the majority (9 out of 12) of the coupled climate models. In contrast, the shift is southward in simulations using an atmospheric model coupled to a slab ocean. The northward mean ITCZ shift in the coupled simulations is due to enhanced northward ocean heat transport across the equator [OHT(EQ)], which demands a compensating southward atmospheric energy transport across the equator, accomplished by shifting the Hadley cell and hence the mean ITCZ northward. The increased northward OHT(EQ) is primarily accomplished by changes in the upper-ocean gyre circulation in the tropical Pacific acting on the zonally asymmetric climatological temperature distribution. The gyre intensification results from the intensification of the monsoonal winds in the Northern Hemisphere and the weakening of the winds in the Southern Hemisphere, both of which are forced directly by the insolation changes.

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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