Multi-model changes in El Ni?o teleconnections over North America in a future warmer climate

详细信息    查看全文

• 作者：Gerald A. Meehl and Haiyan Teng
• 刊名：Climate Dynamics
• 出版年：2007
• 出版时间：December, 2007
• 年：2007
• 卷：29
• 期：7-8
• 页码：779-790
• 全文大小：1,296 KB

文摘

Previous studies with single models have suggested that El Ni?o teleconnections over North America could be different in a future warmer climate due to factors involving changes of El Ni?o event amplitude and/or changes in the midlatitude base state circulation. Here we analyze a six-member multi-model ensemble, three models with increasing future El Ni?o amplitude, and three models with decreasing future El Ni?o amplitude, to determine characteristics and possible changes to El Ni?o teleconnections during northern winter over the North Pacific and North America in a future warmer climate. Compared to observed El Ni?o events, all the models qualitatively produce general features of the observed teleconnection pattern over the North Pacific and North America, with an anomalously deepened Aleutian Low, a ridge over western North America, and anomalous low pressure over the southeastern United States. However, associated with systematic errors in the location of sea surface temperature and convective heating anomalies in the central and western equatorial Pacific (the models’ anomaly patterns are shifted to the west), the anomalous low pressure center in the North Pacific is weaker and shifted somewhat south compared to the observations. For future El Ni?o events, two different stabilization experiments are analyzed, one with CO₂ held constant at year 2100 concentrations in the SRES A1B scenario (roughly doubled present-day CO₂), and another with CO₂ concentrations held constant at 4XCO₂. Consistent with the earlier single model results, the future El Ni?o teleconnections are changed in the models, with a weakened as well as an eastward- and northward-shifted anomalous low in the North Pacific. This is associated with weakened anomalous warming over northern North America, strengthened cooling over southern North America, and precipitation increases in the Pacific Northwest in future events compared to present-day El Ni?o event teleconnections. These changes are consistent with the altered base state upper tropospheric circulation with a wave-5 pattern noted in previous studies that is shown here to be consistent across all the models whether there are projected future increases or decreases in El Ni?o amplitude. The future teleconnection changes are most consistent with this anomalous wave-5 pattern in the models with future increases of El Ni?o amplitude, but less so for the models with future decreases of El Ni?o amplitude.