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© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 16 Nov 2018

Research article | 16 Nov 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Ocean Science (OS).

Synoptic scale variability of surface winds and expected changes in the ocean–atmosphere dynamics of the eastern Austral Pacific Ocean

Iván Pérez-Santos1,2, Romanet Seguel2,3,4, and Wolfgang Schneider5,6 Iván Pérez-Santos et al.
  • 1Centro i-mar de la Universidad de los Lagos, Puerto Montt, Chile
  • 2Centro de Investigación Oceanográfica COPAS Sur-Austral, Universidad de Concepción, Chile
  • 3Programa de Postgrado en Oceanografía, Departamento de Oceanografía, Universidad de Concepción, Chile
  • 4Instituto de Fomento Pesquero, Aysén, Chile
  • 5Departamento de Oceanografía, Campus Concepción, Universidad de Concepción, Chile
  • 6Millennium Institute of Oceanography (IMO), University of Concepción, Chile

Abstract. In the southern hemisphere, macroscale atmospheric systems such as the westerly winds and the Southeast Pacific Subtropical anti-cyclone (SPSA) influence the wind regime of the eastern Austral Pacific Ocean. The average and seasonal behaviors of these systems are well known, although wind variability at different time and distance scales was previously unexamined. The main goal of this study was, therefore, to determine the space and time scale variabilities of surface winds from 40° to 56° S, using QuikSCAT, ASCAT, and ERA-Interim surface wind information, complemented by in situ meteorological data. In addition, interactions between atmospheric systems, together with the ocean–atmosphere dynamics, were evaluated, from 1999 to 2015. The empirical orthogonal function detected dominance at the synoptic scale in mode 1, representing approximately 30 % of the total variance. In this mode, low and high atmospheric pressure systems characterized wind variability, with a cycle length of 16.5 days. Initially, mode 2, representing approximately 22 % of the variance, was represented by westerly winds (43° to 56° S), which occurred mostly during spring and summer, with an annual time scale (1999–2008), until they were replaced by systems cycling at 27.5 days (2008–2015), reflecting the influence of the Southern Hemisphere's baroclinic annular mode. Mode 3, representing approximately 15 % of the variance, involved passage of small scale, low and high atmospheric pressure (LAP, HAP) systems throughout Patagonia. Persistent Ekman suction south of the Gulf of Penas, and up to and beyond the Pacific mouth of the Magellan Strait, occurred throughout the year. Easterly Ekman transport (ET) piled these upwelled waters onto the western shore of South America, when the winds blew southward. These physical mechanisms were essential in bringing nutrients to the surface, and then transporting planktonic organisms from the oceanic zone into Patagonian fjords and channels. In a variation, between 41° and 43° S, surface wind from the SPSA produced offshore ET during spring and summer, causing reduced sea surface temperature, and increased chlorophyll-a; this is the first time that such upwelling conditions have been reported so far south, in the eastern Pacific Ocean. The influence of northward migrating LAP systems on the ocean–atmosphere interphase allowed us to understand, for the first time, their direct relationship with recorded night time air temperature maxima (locally referred to as Nighttime heat wave events). In the context of global climate change, greater attention should be paid to these processes, based on their possible impact on the rate of glacier melting, and on the austral climate.

Iván Pérez-Santos et al.
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Iván Pérez-Santos et al.
Iván Pérez-Santos et al.
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Short summary
Satellite wind data were used to understand surface wind variability in the eastern Austral Pacific Ocean, a region dominated generally by strong westerlies but, the empirical orthogonal function demonstrated that wind variability was dominated by synoptic scale. Nighttime heat waves events were detected producing air temperature maxima which exceeded the normal midday maxima caused by solar radiation. Downwelling conditions prevailed in the study region, owing to onshore Ekman transport.
Satellite wind data were used to understand surface wind variability in the eastern Austral...