Understanding the Role of the Ocean in a Changing Climate through Model Hierarchies
Due to the growing complexity of climate models, model hierarchies are becoming important in understanding climate dynamics. In this dissertation, I build two hierarchies of ocean models to study the ocean's role in a changing climate. In chapter 2, I develop a hierarchy of simplified ocean mod...
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| Other Authors: | , |
| Format: | Thesis |
| Language: | English |
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eScholarship, University of California
2022
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| Online Access: | https://escholarship.org/uc/item/8zh5d870 https://escholarship.org/content/qt8zh5d870/qt8zh5d870.pdf |
| Summary: | Due to the growing complexity of climate models, model hierarchies are becoming important in understanding climate dynamics. In this dissertation, I build two hierarchies of ocean models to study the ocean's role in a changing climate. In chapter 2, I develop a hierarchy of simplified ocean models for the coupled ocean, atmosphere, and sea ice climate simulations using the Community Earth System Model version 1 (CESM1). The hierarchy has four members: a slab ocean model (SOM), a mixed-layer model (MLM) with entrainment and detrainment, an Ekman mixed-layer model (EMOM), and an ocean general circulation model (OGCM). Flux corrections of heat and salt are applied to the simplified models ensuring that all hierarchy members have the same climatology. I diagnose the needed flux corrections from auxiliary simulations in which I restore the temperature and salinity to the daily climatology obtained from a target CESM1 simulation. The resulting three-dimensional corrections contain the interannual variability fluxes that maintain the correct vertical gradients of temperature and salinity in the tropics. I find that the inclusion of mixed-layer entrainment and Ekman flow produces sea surface temperature and surface air temperature fields whose means and variances are progressively more similar to those produced by the target CESM1 simulation.To illustrate the usefulness of the hierarchy, I revisit the ITCZ problem. The position of ITCZ is controlled by the interhemispheric energy imbalance. The ITCZ problem involves determining mechanisms responsible for reducing the shift of ITCZ in fully coupled climate models compared to those that couple the atmosphere to a simple SOM. In this dissertation, I tackle this problem in the context of the loss of Arctic sea ice. In the absence of dynamic ocean circulation, energy-balance considerations require the ITCZ to shift northward so that the expansion of the southern Hadley cell produces a southward energy transport. This transport eliminates the interhemispheric energy imbalance ... |
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