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Farrell, Brian

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Farrell

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Farrell, Brian

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2009 - 20102

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Author's Publications: search.filters.isAuthorOfPublication.9a00a086-b102-49a2-8390-dbbcdf453480

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    Nonnormal Frontal Dynamics
    (American Meteorological Society, 2010) Feliks, Yizhak; Tziperman, Eli; Farrell, Brian
    The generalized stability of the secondary atmospheric circulation over strong SST fronts is studied using a hydrostatic, Boussinesq, two-dimensional f-plane model. It is shown that even in a parameter regime in which these circulations are stable to small perturbations, significant nonnormal growth of optimal initial perturbations occurs. The maximum growth factor in perturbation total energy is 250 and is dominated by the potential energy, which obtains a growth factor of 219 two to five hours after the beginning of the integration. This domination of potential energy growth is consistent with the observation that the available potential energy (APE) of the secondary circulation is larger by two orders of magnitude than the kinetic energy as well as with the transfer of kinetic to potential perturbation energy at the beginning of the growth of the perturbations. The norm kernel is found to significantly influence the structure of the optimal initial perturbation as well as the energy obtained by the mature perturbations, but the physical mechanism of growth and the structure of the mature perturbations are robust.
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    Pliocene equatorial temperature: Lessons from atmospheric superrotation
    (American Geophysical Union, 2009) Tziperman, Eli; Farrell, Brian
    There is proxy evidence that the pronounced east-west temperature difference observed today across the equatorial Pacific Ocean may not have existed in the early Pliocene (4–5 Ma BP) and that the east Pacific cold tongue developed gradually toward the end of the Pliocene (2 Ma BP). The east Pacific temperature influences weather and climate worldwide, and the Pliocene climate may be an instructive analogue to a future warm climate arising from anthropogenic elevation of CO2, making understanding the Pliocene equatorial SST gradient especially relevant. A mechanism for maintaining a weaker Pliocene equatorial temperature gradient is proposed that borrows from theories of atmospheric superrotation. The mechanism is based on enhanced or rearranged tropical convective activity during the warmer Pliocene climate exciting atmospheric Rossby waves that propagated poleward from the equator. These waves produced an equatorward flux of westerly momentum that weakened the surface easterlies and therefore the east-west thermocline slope and SST gradient.