Variations in North American Summer Precipitation Driven by the Atlantic Multidecadal Oscillation

• Main Authors: Hu, Qi, Feng, Song, Oglesby, Robert J.
• Format: Text
• Language: unknown
• Published: DigitalCommons@University of Nebraska - Lincoln 2011
• Subjects: Environmental Sciences; Natural Resources and Conservation; Natural Resources Management and Policy; Other Environmental Sciences; Arctic; Pacific; Nash; North Atlantic
• Online Access: https://digitalcommons.unl.edu/natrespapers/394; https://digitalcommons.unl.edu/context/natrespapers/article/1398/viewcontent/Hu_JC_2011_Variations_in_North_American_Summer.pdf

Understanding the development and variation of the atmospheric circulation regimes driven by the Atlantic multidecadal oscillation (AMO) is essential because these circulations interactwith other forcings on decadal and interannual time scales. Collectively, they determine the summer (June, July, and August) precipitation variations for NorthAmerica. In this study, a general circulation model (GCM) is used to obtain such understanding, with a focus on physical processes connecting the AMO and the summertime precipitation regime change in NorthAmerica. Two experimental runs are conducted with sea surface temperature (SST) anomalies imposed in the North Atlantic Ocean that represent the warm and cold phases of the AMO. Climatological SSTs are used elsewhere in the oceans. Model results yield summertime precipitation anomalies in North America closely matching the observed anomaly patterns in North America, suggesting that the AMO provides a fundamental control on summertime precipitation in North America at decadal time scales. The impacts of the AMO are achieved by a chain of events arising from different circulation anomalies during warm and cold phases of the AMO. During the warm phase, the North Atlantic subtropical high pressure system (NASH) weakens, and the North American continent is much less influenced by it. A massive body of warm air develops over the heated land in North America from June–August, associated with high temperature and low pressure anomalies in the lower troposphere and high pressure anomalies in the upper troposphere. In contrast, during the cold phase of the AMO, the NorthAmerican continent, particularly to the west, is much more influenced by an enhanced NASH. Cooler temperatures and high pressure anomalies prevail in the lower troposphere, and a frontal zone forms in the upper troposphere. These different circulation anomalies further induce a three-cell circulation anomaly pattern over North America in the warm and cold phases of the AMO. In particular, during the cold phase, the ...