PhD Dissertation DefenseJuly 17, 3:00pm - 4:00pm
Mānoa Campus, Marine Science Building, Room 100 (MSB100)
***PHD DISSERTATION DEFENSE*** 7/17/12
Title: Dynamics and Uuncertainties of Global Warming Patterns: Sea Surface Temperature, Precipitation and Atmospheric Circulation.
By: Mr. (Tony) Jian Ma
Department of Meteorology
University of Hawaii at Manoa
Date: Tuesday, July 17, 2012
Location: Marine Science Building, Room 100 (MSB100)
Precipitation and atmospheric circulation changes in response to global warming have profound impacts on the environment for life but are highly uncertain. This study investigates fundamental mechanisms controlling these changes and relates them to the effects of sea surface temperature (SST) change, using Coupled Model Intercomparison Project simulations. The SST warming is decomposed into a spatially uniform SST increase (SUSI) and deviations from it.
The SST pattern effect is found important in explaining both the multi-model ensemble mean distribution and inter-model variability of rainfall change over tropical oceans. In ensemble mean, the annual rainfall change follows a “warmer-get-wetter” pattern, increasing where the SST warming exceeds the tropical mean, and vice versa. Two SST patterns stand out both in the ensemble mean and inter-model variability: an equatorial peak that anchors a local precipitation increase, and a meridional dipole mode with increased rainfall and weakened trade winds over the warmer hemisphere. These two modes of inter-model variability in SST account for up to one third of inter-model spread in rainfall projection.
Tropospheric warming follows the moist adiabat in the tropics, and static stability increases globally in response to SST warming. A diagnostic framework is developed based on a linear baroclinic model (LBM) of the atmosphere. The mean advection of stratification change (MASC) by climatological vertical motion, often neglected in interannual variability, is an important thermodynamic term for global warming. MASC and SST-pattern effects are on the same order of magnitude in LBM simulations. Once MASC effect is included, LBM shows skills in reproducing general circulation model (GCM) results by prescribing latent heating diagnosed from the GCMs.
Common to all GCMs, MASC causes both the Hadley and Walker circulation to slow down as articulated by previous studies. The weakening of the Walker circulation is robust across models as the SST pattern effect is weak. The Hadley circulation change, by contrast, is significantly affected by SST warming patterns. As a result, near and south of the equator, the Hadley circulation change is weak in the multi-model ensemble mean and subject to large inter-model variability due to the differences in SST warming patterns, explaining up to four fifth of the inter-model variability in changes of the overturning circulation.
Meteorology Department, Mānoa Campus
Tuesday, July 17
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