Date of Award

5-1-2021

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 (iv, 53 pages) : color illustrations, color maps.

Dissertation/Thesis Chair

Aiguo Dai

Committee Members

Mathias Vuille

Keywords

Precipitation (Meteorology), Atmospheric temperature, Ocean-atmosphere interaction, Temperature, Southern oscillation

Subject Categories

Atmospheric Sciences

Abstract

The Atlantic Multidecadal Oscillation (AMO) and Interdecadal Pacific Oscillation (IPO) have been shown to impact temperature and precipitation across the globe. However, the seasonal differences in their impacts are not well studied. This study analyzes the seasonal differences in the impacts of the AMO and IPO on South American temperature and precipitation. Observational and reanalysis data with enough temporal coverage to isolate the multidecadal modes were used first to identify the regions impacted by the AMO and IPO through a correlation analysis. Then Empirical Orthogonal Functions (EOF) and a Maximum Covariance Analysis (MCA) were used to determine the seasonal spatial anomaly patterns of the surface air temperature (SAT) and precipitation (P) associated with the AMO and IPO. To determine the magnitude of the SAT and P anomalies and associated atmospheric anomaly circulation, a composite analysis was done. It was found that during a positive AMO phase the wet season (DJF and MAM) has the largest anomalies across South America. Due to an anomalous clockwise circulation only present in austral summer (DJF), drier conditions are present in southeastern South America. A weakening in the South American Low-Level Jet (SALLJ) occurs from interacting with this anomalous circulation, causing it to slow down and therefore decrease the precipitation in the region. The results indicate that the AMO influences South American climate mainly during DJF. During a warm IPO phase there is enhancement of the SALLJ due to anomalous circulation patterns in DJF. This would increase precipitation for eastern-central South America as more warm and moist air moves from the north to the southeast. An anomalous low-pressure system is present on the tip of Argentina during DJF, MAM and SON but not in JJA. Under positive-phase IPO conditions, there are dry to neutral conditions in JJA while for the other seasons there is about a 0.5 mm/day anomalous precipitation.

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