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The Azores High is a subtropical high-pressure ridge in the North Atlantic surrounded by anticyclonic winds that steer rain-bearing weather systems. The size and intensity of the Azores High modulate the oceanic moisture transport to Europe thereby affecting hydroclimate across western Europe, especially during wintertime. While changes in the North Atlantic storm track have been linked to the variability of the North Atlantic Oscillation (NAO), we focus on North Atlantic variability with a subtropical perspective by focusing on the Azores High independently of the Icelandic Low. The subtropical perspective provides a direct understanding of regional climate variability in the western Mediterranean and reveals dramatic changes to North Atlantic climate throughout the past century and can provide insight into the impact of future warming on the dynamics of the Azores High and associated hydroclimate. Here we show that winters with an extremely large Azores High are significantly more common in the industrial era (since 1850 CE) than in preindustrial times, resulting in anomalously dry conditions across the western Mediterranean, including the Iberian Peninsula. Climate model simulations of the past millennium indicate that the industrial-era expansion of the Azores High is unprecedented throughout the last millennium (since 850 CE), consistent with proxy evidence from Portugal. Azores High expansion emerges after the end of the Little Ice Age and strengthens into the 20th century consistent with anthropogenically-driven warming.
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On the Drivers of Decadal Variability of the Gulf Stream North Wall
The Gulf Stream is bounded to the north by a strong temperature front known as the North Wall. The North Wall is subject to variability on a wide range of temporal and spatial scales—on interannual time scales, the dominant mode of variability is a longitudinally coherent north–south migration. North Wall variability since 1970 has been characterized by regular oscillations with a period of approximately nine years. This periodic variability, and its relationship to major modes of Atlantic climate variability, is examined in the frequency domain. The North Atlantic Oscillation (NAO) and the Atlantic meridional mode (AMM) both covary with the North Wall on decadal time scales. The NAO leads the North Wall by about one year, whereas the covariability between the North Wall and the AMM is synchronous (no lag). Covariability between the North Wall and the NAO is further examined in terms of the centers of action comprising the NAO: the Icelandic low and Azores high. It is found that the strength of the Icelandic low and its latitude as well as the strength of the Azores high play a role in decadal North Wall variability.
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- Award ID(s):
- 1634829
- PAR ID:
- 10084186
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of Climate
- Volume:
- 32
- Issue:
- 4
- ISSN:
- 0894-8755
- Page Range / eLocation ID:
- p. 1235-1249
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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