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Aaron Donohoe

Post-Doctoral Research Associate

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 mathematical framework for analysis of water tracers. Part II: Understanding large-scale perturbations in the hydrological cycle due to CO2 doubling

Singh, H.K.A., C. Bitz, A. Donohoe, J. Nussbaumer, and D.C. Noone "A mathematical framework for analysis of water tracers. Part II: Understanding large-scale perturbations in the hydrological cycle due to CO2 doubling," J. Climate, 29, 6765-6782, doi:10.1175/JCLI-D-16-0293.1, 2016.

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1 Sep 2016

The aerial hydrological cycle response to CO2 doubling from a Lagrangian, rather than Eulerian, perspective is evaluated using information from numerical water tracers implemented in a global climate model. While increased surface evaporation (both local and remote) increases precipitation globally, changes in transport are necessary to create a spatial pattern where precipitation decreases in the subtropics and increases substantially at the equator. Overall, changes in the convergence of remotely evaporated moisture are more important to the overall precipitation change than changes in the amount of locally evaporated moisture that precipitates in situ. It is found that CO2 doubling increases the fraction of locally evaporated moisture that is exported, enhances moisture exchange between ocean basins, and shifts moisture convergence within a given basin toward greater distances between moisture source (evaporation) and sink (precipitation) regions. These changes can be understood in terms of the increased residence time of water in the atmosphere with CO2 doubling, which corresponds to an increase in the advective length scale of moisture transport. As a result, the distance between where moisture evaporates and where it precipitates increases. Analyses of several heuristic models further support this finding.

Greater aerial moisture transport distances with warming amplify interbasin salinity contrasts

Singh, H.K.A., A. Donohoe, C.M. Bitz, J. Nusbaumer, and D.C. Noone, "Greater aerial moisture transport distances with warming amplify interbasin salinity contrasts," Geophys. Res. Lett., 43, 8677-8684, doi:10.1002/2016GL069796, 2016.

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28 Aug 2016

The distance atmospheric moisture travels is fundamental to Earth's hydrologic cycle, governing how much evaporation is exported versus precipitated locally. The present-day tropical Atlantic is one region that exports much locally evaporated moisture away, leading to more saline surface waters in the Atlantic compared to the Indo-Pacific at similar latitudes. Here we use a state-of-the-art global climate model equipped with numerical water tracers to show that over half of the atmospheric freshwater exported from the Atlantic originates as evaporation in the northern Atlantic subtropics, primarily between 10°N and 20°N, and is transported across Central America via prevailing easterlies into the equatorial Pacific. We find enhanced moisture export from the Atlantic to Pacific with warming is due to greater distances between moisture source and sink regions, which increases moisture export from the Atlantic at the expense of local precipitation. Distance traveled increases due to longer moisture residence times, not simply Clausius–Clapeyron scaling.

Southern Ocean warming delayed by circumpolar upwelling and equatorward transport

Armor, K.C., J. Marshall, J.R. Scott, A. Donohoe, and E.R. Newsroom, "Southern Ocean warming delayed by circumpolar upwelling and equatorward transport," Nature Geosci., 9, 549–554, doi:10.1038/ngeo2731, 2016.

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30 May 2016

The Southern Ocean has shown little warming over recent decades, in stark contrast to the rapid warming observed in the Arctic. Along the northern flank of the Antarctic Circumpolar Current, however, the upper ocean has warmed substantially. Here we present analyses of oceanographic observations and general circulation model simulations showing that these patterns—of delayed warming south of the Antarctic Circumpolar Current and enhanced warming to the north—are fundamentally shaped by the Southern Ocean’s meridional overturning circulation: wind-driven upwelling of unmodified water from depth damps warming around Antarctica; greenhouse gas-induced surface heat uptake is largely balanced by anomalous northward heat transport associated with the equatorward flow of surface waters; and heat is preferentially stored where surface waters are subducted to the north. Further, these processes are primarily due to passive advection of the anomalous warming signal by climatological ocean currents; changes in ocean circulation are secondary. These findings suggest the Southern Ocean responds to greenhouse gas forcing on the centennial, or longer, timescale over which the deep ocean waters that are upwelled to the surface are warmed themselves. It is against this background of gradual warming that multidecadal Southern Ocean temperature trends must be understood.

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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