Interannual variability of the boreal winter subtropical jet stream and teleconnections over the CORDEX-CAM domain durin
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Interannual variability of the boreal winter subtropical jet stream and teleconnections over the CORDEX‑CAM domain during 1980–2010 Rosa Luna‑Niño1 · Tereza Cavazos1 · Jose Abraham Torres‑Alavez2 · Filippo Giorgi2 · Erika Coppola2 Received: 11 March 2020 / Accepted: 15 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The interannual variability of the boreal winter (DJF) subtropical jet stream (STJ) is analyzed over the Coordinated Regional Downscaling Experiment—Central America, Mexico, and Caribbean domain (CORDEX-CAM) during 1980–2010. We use simulations with the regional climate model RegCM4 (version 7) at 25 km resolution driven by ERA-Interim (RegERA) and three global models (RegGCMs). The simulations are evaluated using zonal winds at 200 hPa level from ERA-Interim and MERRA2, which show similar results, and no significant trends in the STJ. Despite some biases, RegERA captures the STJ variability and its relationship with several teleconnections. The polarities of the principal mode of variability of the Pacific and Atlantic jets are significantly anti-correlated; they represent the longitudinal extension/retraction and the poleward/equatorward migration of the jet cores, respectively. During El Niño and the + PNA (Pacific North America), the North Pacific jet exit region and the North Atlantic jet show maximum speeds equatorward of their climatological positions. During these conditions, there is an extended and strong STJ over the domain; this pattern also tends to occur during the negative phases of the Arctic and North Atlantic oscillations. The RegGCMs simulate better the principal modes of the Atlantic jet variability than those of the Pacific jet exit region; nevertheless, they reproduce the observed sign of the variations of the jet speeds and their latitudinal changes in the two basins. They also partially capture the sign of the temperature and precipitation anomalies in the domain, which respond to the STJ polarities and their interaction with the teleconnections. Keywords Subtropical jet stream · Boreal winter · Teleconnections · North america · RegCM4 · CORDEX-CAM
1 Introduction The jet streams are narrow speed bands similar to atmospheric rivers near the top of the troposphere at heights of about 10–15 km (Ahrens 2012). They have their origin in the differential heating between low and high latitudes that causes a horizontal meridional temperature gradient, which is more intense during winter (Holton 1992). These upper winds are relevant for the daily weather because they transport heat, and their position is related to other weather systems such as storm tracks and fronts. In particular, the subtropical westerly jet stream (STJ) is usually strongest * Tereza Cavazos [email protected] 1
Department of Physical Oceanography, Ensenada Center for Scientific Research and Higher Education, CICESE, Ensenada, Mexico
Earth System Physics, EPS, The Abdus Salam International Centre for Theoretical Physics, Trieste, Italy
2
slightly above the 200 h
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