Dissertation/Thesis Abstract

Investigating the variability of subtropical marine boundary layer clouds in observations and climate models
by Myers, Timothy Albert, Ph.D., University of California, San Diego, 2015, 131; 3714206
Abstract (Summary)

Low-level clouds found over the eastern subtropical oceans have a substantial cooling effect on Earth’s climate since they strongly reflect solar radiation back to space, and their simulation in climate models contributes to large uncertainty in global warming projections. This thesis aims to increase understanding of these marine boundary layer clouds through observational analysis, theoretical considerations, and an evaluation of their simulation in climate models. Examination of statistical relationships between cloud properties and large-scale meteorological variables is a key method employed throughout the thesis. The meteorological environment of marine boundary layer clouds shapes their properties by affecting the boundary layer’s depth and structure.

It is found that enhanced subsidence, typically thought to promote boundary layer cloudiness, actually reduces cloudiness when the confounding effect of the strength of the temperature inversion capping the boundary layer is taken into account. A conceptual model is able to explain this result. Next, fundamental deficiencies in the simulation of subtropical clouds in two generations of climate models are identified. Remarkably, the newer generation of climate models is in some ways inferior to the older generation in terms of capturing key low-level cloud processes. Subtropical mid- and high-level clouds are also found to contribute more to variability in the radiation budget at the top of the atmosphere than previously thought. In the last portion of the thesis, large inter-model spread in subtropical cloud feedbacks is shown to arise primarily from differences in the simulation of the interannual relationship between shortwave cloud radiative effect and sea surface temperature. An observational constraint on this feedback suggests that subtropical marine boundary layer clouds will act as a positive feedback to global warming.

Indexing (document details)
Advisor: Norris, Joel R.
Commitee: Eisenman, Ian, Hendershott, Myrl, Kleissl, Jan, Xie, Shang-Ping
School: University of California, San Diego
Department: Earth Sciences
School Location: United States -- California
Source: DAI-B 76/11(E), Dissertation Abstracts International
Subjects: Climate Change, Atmospheric sciences
Keywords: Climate change, Cloud feedbacks, Low-level clouds, Marine boundary layer
Publication Number: 3714206
ISBN: 978-1-321-91334-7
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