[pccgrads] Special PO Lunch Seminar, Weds 7/20 at 12:30 in 425 OSB

[UW Program On Climate Change]

Special Phys Ocean Seminar, 20 Jul 2022
Wednesday, July 20, 12:30 PM to 01:30 PM PDT

Special Physical Oceanography Lunch Seminar
Causal attribution of North Atlantic sector variability using ocean adjoint
models

Dafydd Stephenson
NCAR

12:30 P.M., 425 Ocean Sciences Bldg

ABSTRACT: The unique role of the large-scale ocean circulation in the North
Atlantic may offer predictability of climatically important quantities
years to decades ahead. Modern observations and models reveal a complex
picture of variability in these quantities, however. A particularly useful
tool for tracing variability to its origins is the adjoint model, which
takes as input a definition of an ocean dynamical quantity (e.g., volume
transport, heat content, etc.) and returns as output the sensitivity of
that quantity to earlier changes, based on model physics. Here, we present
a range of recent work demonstrating the use of these models to address
fundamental questions about the ocean’s role in North Atlantic climate
variability. Firstly, we ask whether heat content variability is a purely
passive response to atmospheric forcing, or whether dynamical changes in
ocean heat transport have a significant role. We show that surface
temperature variations are primarily passive, but that full-depth heat
content fluctuations in the North Atlantic reflect large-scale ocean
dynamics, in particular the Atlantic Meridional Overturning Circulation
(AMOC). We then estimate the proportion of large-scale ocean variability
which is forced by chaotic fluctuations at the oceanic mesoscale, using a
stochastic representation of eddy buoyancy fluxes. This suggests that
year-to-year subtropical AMOC variability is primarily attributable to
ocean eddies, but that subpolar variability is predominantly surface forced
at all considered timescales. We conclude with an overview of recent work
aiming to attribute this subpolar variability to dominant patterns of
surface forcing.


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