Date of Award

1-1-2017

Language

English

Document Type

Master's Thesis

Degree Name

Master of Science (MS)

College/School/Department

Department of Atmospheric and Environmental Sciences

Content Description

1 online resource (ix, 62 pages) : color illustrations.

Dissertation/Thesis Chair

Brian Rose

Keywords

Atmospheric Radiation, Climate Dynamics, General Circulation, Hadley Cell, Meridional Energy Transport, Ocean Heat Transport, Climatic changes, Ocean-atmosphere interaction, Ocean circulation, Ocean temperature, Heat

Subject Categories

Atmospheric Sciences | Climate

Abstract

One of the outstanding problems within the climate community has been how to reconcile the geological proxy records of past warm, equable climates, characterized by both an increase in the global mean surface temperature and a decrease in the equator-to-pole temperature gradient, with numerical simulations of the same period. Recent work has shown that tectonic driven changes in the meridional ocean heat transport (OHT) may have played a signicant role in the warming. Here, we study the adjustment of the climate to variations in OHT using a suite of slab-ocean aquaplanet GCM simulations spanning 24 different imposed variations in OHT and two dierent initial states. We find that increasing the OHT out of the tropics works to warm the global mean climate at a linear rate of 2 K/PW, insensitive to the structure of the transport. However, because of the localized nature of the warming and the compensating changes in the atmospheric heat transport (AHT), the mechanisms driving the climate change are highly dependent on the spatial pattern of the OHT. We find substantial but incomplete atmospheric compensation in which the adjustment of the Hadley circulation (HC) plays a key role, driving asymmetries in radiative feedback processes that work to offset the prescribed tropical energy sink. We decompose the HC adjustment into dynamical and thermodynamical components, analyzing causal relationships between radiation imbalance, circulation slowdown, and changes in Gross Moist Stability (GMS). In the subtropics/midlatitudes, we find that the warming is primarily driven by enhanced greenhouse trapping associated with the convective moistening of the upper troposphere in the outer flanks of the HC and in the midlatitude storm tracks. We also show that these adjustments are not dependent on the initial climate states of the model.

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