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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

The partitioning of meridional heat transport from the last glacial maximum to CO2 quadrupling in coupled climate models

Donohoe, A., "The partitioning of meridional heat transport from the last glacial maximum to CO2 quadrupling in coupled climate models," J. Clim., 33, 4141-4165, doi:10.1175/JCLI-D-19-0797.1, 2020.

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1 May 2020

Meridional heat transport (MHT) is analyzed in ensembles of coupled climate models simulating climate states ranging from the Last Glacial Maximum (LGM) to quadrupled CO2. MHT is partitioned here into atmospheric (AHT) and implied oceanic (OHT) heat transports. In turn, AHT is partitioned into dry and moist energy transport by the meridional overturning circulation (MOC), transient eddy energy transport (TE), and stationary eddy energy transport (SE) using only monthly averaged model output that is typically archived. In all climate models examined, the maximum total MHT (AHT + OHT) is nearly climate-state invariant, except for a modest (4%, 0.3 PW) enhancement of MHT in the Northern Hemisphere (NH) during the LGM. However, the partitioning of MHT depends markedly on the climate state, and the changes in partitioning differ considerably among different climate models. In response to CO2 quadrupling, poleward implied OHT decreases, while AHT increases by a nearly compensating amount. The increase in annual-mean AHT is a smooth function of latitude but is due to a spatially inhomogeneous blend of changes in SE and TE that vary by season. During the LGM, the increase in wintertime SE transport in the NH midlatitudes exceeds the decrease in TE resulting in enhanced total AHT. Total AHT changes in the Southern Hemisphere (SH) are not significant. These results suggest that the net top-of-atmosphere radiative constraints on total MHT are relatively invariant to climate forcing due to nearly compensating changes in absorbed solar radiation and outgoing longwave radiation. However, the partitioning of MHT depends on detailed regional and seasonal factors.

Seasonal asymmetries in the lag between insolation and surface temperature

Donohoe, A., E. Dawson, L. McMurdie, D.S. Battisti, and A. Rhines, "Seasonal asymmetries in the lag between insolation and surface temperature," J. Clim., 33, 3921–3945, doi:10.1175/JCLI-D-19-0329.1, 2020.

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7 Apr 2020

We analyze the temporal structure of the climatological seasonal cycle in surface air temperature across the globe. We find that, over large regions of Earth, the seasonal cycle of surface temperature departs from an annual harmonic: the duration of fall and spring differ by as much as 2 months. We characterize this asymmetry by the metric ASYM, defined as the phase lag of the seasonal maximum temperature relative to the summer solstice minus the phase lag of the seasonal minimum temperature relative to winter solstice. We present a global analysis of ASYM from weather station data and atmospheric reanalysis and find that ASYM is well represented in the reanalysis. ASYM generally features positive values over land and negative values over the ocean, indicating that spring has a longer duration over the land domain whereas fall has a longer duration over the ocean. However, ASYM also features more positive values over North America compared to Europe and negative values in the polar regions over ice sheets and sea ice. Understanding the root cause of the climatological ASYM will potentially further our understanding of controls on the seasonal cycle of temperature and its future/past changes. We explore several candidate mechanisms to explain the spatial structure of ASYM including 1) modification of the seasonal cycle of surface solar radiation by the seasonal evolution of cloud thickness, 2) differences in the seasonal cycle of the atmospheric boundary layer depth over ocean and over land, and 3) temperature advection by the seasonally evolving atmospheric circulation.

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.

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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