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作者 Williams, Ian Nobuo
書名 Tropical convection and climate sensitivity
國際標準書號 9781267247940
book jacket
說明 121 p
附註 Source: Dissertation Abstracts International, Volume: 73-07, Section: B, page:
Adviser: Raymond T. Pierrehumbert
Thesis (Ph.D.)--The University of Chicago, 2012
Surface temperature has become a popular measure of climate change, but it does not provide the most critical test of climate models. This thesis presents new methods to evaluate climate models based on processes determining the climate sensitivity to radiative forcing from atmospheric greenhouse gases. Cloud radiative feedbacks depend on temperature and relative humidity profiles in addition to surface temperature, through the dependence of cloud type on boundary layer buoyancy. Buoyancy provides a reference to which the onset of deep convection is invariant, and gives a compact description of sea surface temperature changes and cloud feedbacks suitable for diagnostics and as a basis for simplified climate models. This thesis also addresses uncertainties in climate sensitivity involving terrestrial ecosystem responses to global warming. Different diagnostics support different conclusions about atmospheric transport model errors that could imply either stronger or weaker northern terrestrial carbon sinks. Equilibrium boundary layer concepts were previously used in idealized tropical climate models, and are extended here to develop a diagnostic of boundary layer trace gas transport and mixing
Hypotheses linking surface temperature to climate and precipitation sensitivity were tested in this thesis using comprehensive and idealized climate model simulations, and observational datasets. The results do not support the thermostat hypothesis that predicts deep cloud cover will increase with radiative forcing and limit sea surface temperatures to the maximum present-day warm pool temperature. Warm pool temperatures increased along with or even faster than the tropical average over the past several decades, while diagnosed deep cloud cover has not significantly increased, in agreement with global warming simulations. Precipitation sensitivity also depends on more than surface temperature alone, including thermodynamic profiles and air-sea temperature differences. The atmosphere remains sufficiently optically thin for the surface and lower troposphere to cool by radiation in some parts of the infrared spectrum, even as absorber amounts increase. Processes affecting the surface energy balance can therefore force changes in infrared radiative cooling by changing the surface-to-air temperature difference and lifted condensation level. These results reject previous hypotheses for climate and precipitation sensitivities that assumed deterministic relationships between surface temperature and the atmospheric radiation budget
School code: 0330
Host Item Dissertation Abstracts International 73-07B
主題 Climate Change
Atmospheric Sciences
0404
0725
Alt Author The University of Chicago. Geophysical Sciences
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