HR: 1330h
AN: PP42A-0866    [PDF]
TI: Dynamical Mechanisms for Monsoon Changes During the Mid-Holocene
AU: * Su, H
EM: hui@atmos.ucla.edu
AF: Dept. of Atmospheric Sciences,University of California, Los Angeles, 405 Hilgard Ave., Los Angeles, CA 90095-1565 United States
AU: Neelin, J
EM: neelin@atmos.ucla.edu
AF: Dept. of Atmospheric Sciences,University of California, Los Angeles, 405 Hilgard Ave., Los Angeles, CA 90095-1565 United States
AU: Neelin, J
EM: neelin@atmos.ucla.edu
AF: Institute of Geophysics and Planetary Physics, University of California, Los Angeles, 405 Hilgard Ave., Los Angeles, CA 90095-1565 United States
AU: Meyerson, J E
EM: hobo@atmos.ucla.edu
AF: Dept. of Atmospheric Sciences,University of California, Los Angeles, 405 Hilgard Ave., Los Angeles, CA 90095-1565 United States
AB: One of the most prominent climate changes during the mid-Holocene is the northward expansion of the African monsoon. A number of studies have explored the impacts of orbital forcing on the monsoon changes and feedbacks associated with land-surface characteristics. The impacts of solar forcing changes upon precipitation and land-surface are mediated by complex atmosphere-ocean dynamical mechanisms and we analyze this aspect of the Holocene monsoon variations. We use an intermediate complexity climate model, the quasi-equilibrium tropical circulation model (QTCM), combined with a slab mixed-layer ocean model. In addition to standard PMIP-type experiments where SST is fixed at present day values, we conduct simulations with different land-surface-vegetation configurations and with mixed-layer ocean coupling. Moist static energy budget analysis is performed to examine to the relative importance of each dynamical process in various model settings. The QTCM PMIP-type simulation produces precipitation and temperature changes during the mid-Holocene comparable to other general circulation models. In such simulations, the advancement of the African monsoon is not as north as paleo-data suggests. When surface albedo of the north Africa is reduced to 0.25, a typical value for grassland, precipitation increases over a broad area in the equatorial Africa south of 20N. This provides a case akin to interactive vegetation runs that can be used to understand the role of dynamical effects. Analysis of moist static energy budget shows changes in advection of temperature and moisture, cloud-radiative feedback and surface heat fluxes interact strongly to regulate the intensity of the African monsoon during the mid-Holocene.
DE: 3344 Paleoclimatology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting