Date of Award

1-1-2022

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 (v, 45 pages) : illustrations (some color)

Dissertation/Thesis Chair

Liming Zhou

Keywords

Climate, Hadley Circulation, Sahara Desert, Atmospheric circulation, Climatic changes, Global warming

Subject Categories

Atmospheric Sciences

Abstract

Changes in temperature due to climate change are not spatially uniform, and deserts and other drylands, which are greatly underrepresented in climate studies, are warming at a much faster rate than much of the globe with increasing concentrations of greenhouse gases. This strong warming amplification over deserts, termed Desert Amplification (DA), is most pronounced over the world’s largest and driest Sahara Desert and the Arabian Peninsula. The Sahara and Arabian deserts are formed in the subtropical subsiding branch of the Hadley Circulation (HC) and so the changes in large-scale subsidence associated with adiabatic heating could impact the DA dynamically. While there is evidence to suggest that thermodynamic impacts such as stronger warming-enhanced large-scale water vapor feedback over drier ecoregions may play a major role in this warming, the dynamic impacts of HC change have yet to be examined with respect to DA. Using two widely used reanalysis datasets, MERRA2 and ERA5, Zonal Mean Meridional Stream Function (ZMMSF) is examined in conjunction with vertical velocity (omega) to assess the strength and location changes of the boundaries of HC and subsidence over the Sahara and compare these changes with the corresponding global values. Results show that changes in HC are not uniform across seasons or when averaged globally versus regionally. There is a strong agreement between the two datasets for weak intensification of both ZMMSF and omega globally during DJF, while both are weakening during JJA. For the Sahara however, there is weaker certainty in weakening of ZMMSF and omega during DJF, but strong certainty of weakening during JJA. These results suggest that changes in HC cannot account for DA over the Sahara as the changes in HC between 1980 and 2019 are either negligible or act in a way that would weaken DA, not strengthen or result in it.

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