Atmospheric equilibrium,instability and energy transport at the last glacial maximum |
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Authors: | Nicholas M J Hall Buwen Doug Paul J Valdes |
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Institution: | (1) Department of Meteorology, University of Reading, RG6 2AU Reading, UK;(2) Present address: CIRES, University of Colorado, 80309-0449 Boulder, CO, USA |
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Abstract: | A range of diagnostics from two GCM simulations, one of the present-day climate and one of the last glacial maximum (LGM)
is used to gain insight into their different temperature structures and eddy dynamics. There are large local increases in
baroclinicity at the LGM, especially in the Atlantic storm track, with large accompanying increases in the low level transient
eddy heat flux. However, the differences in the zonal mean are much smaller, and the increases in both baroclinicity and heat
flux are confined to low levels. Supplementary experiments with baroclinic wave lifecycles confirm the marked contrast between
local and zonal mean behaviour, but do not adequately explain the differences between the zonal mean climates. The total flux
of energy across latitude circles in the Northern Hemisphere does not change much during DJF, although its transient component
is actually reduced at the LGM (during JJA the transient component is increased). Calculations of total linear eddy diffusivity
reveal that changes in the time mean stationary waves are chiefly responsible for the seasonal range of this quantity at the
LGM, while they only account for half the seasonal range at the present-day. |
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