学术报告题目: The role of oceanic feedback in the climate response to doubling CO2
报告人: Jian Lu教授 (COLA and George Mason University)
Two suites of partial coupling experiments are devised with the upper ocean dynamics
version (UOM) of the CCSM3 to isolate the effects of the feedbacks from the changed
wind-driven ocean circuation and the air-sea interaction in the global climate response to
doubling CO2 forcing. Since the deep ocean in the UOM is prescribed as repeating
climatotolgy and hence not allowed to respond to external climate forcing, the UOM can
be equilibriated within a few decades, a unique feature of the UOM facilitating the
current investigation of the equilibrium climate response to greenhouse gas forcing.
The partial coupling is achieved by implementing a so-called overriding technique, which
helps quantitatively partition the total response in the fully coupled model to the feedback
component in question and the response to external forcing in the absence of the former.
By overriding the wind stress that is the momentum driving for the ocean and the wind
speed used in the bulk formula for evaportaion, the experiments help to reveal (i) the
weakened tropical Pacific wind may not be responsible for the El Ni？o-like SST warming
as previously speculated from the thermocline feedback; (ii) the wind-evaporation-SST
feedback is the main formation mechanism for the tropical SST formation under the CO2
forcing, verifying the hypothesis proposed by Xie et al. (2010); (iii) WES is also the
leading mechanism for shaping the tropical precipitation response in the ocean; (iv) Both
the wind-driven ocean dynamical feedback and the WES feedback act to increase the
persistence of the Southern Annular mode (SAM), and the increased time scale of the
SAM due to these feedbacks manifests itself in the response of the jet shift to an identical
CO2 forcing, in a manner conforming to the fluctuation-dissipation theorem.
Overriding can lead to conspicuous climate drift, which could be mistakenly interpreted
as climate response signal. The procedures to carefully address the drift due to the
application of the overriding is also articulated.