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</o:shapelayout></xml><![endif]--></head><body lang=ES link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span lang=EN-US style='font-size:12.0pt;font-family:"Arial","sans-serif";mso-fareast-language:ES'>PNAS <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:12.0pt;font-family:"Arial","sans-serif";mso-fareast-language:ES'>January 27, 2020 <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Arial","sans-serif";mso-fareast-language:ES'><a href="https://doi.org/10.1073/pnas.1717707117"><span lang=EN-US style='color:windowtext'>https://doi.org/10.1073/pnas.1717707117</span></a></span><span style='font-size:12.0pt;font-family:"Arial","sans-serif";mso-fareast-language:ES'> <span lang=EN-US><o:p></o:p></span></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><span lang=EN-US style='font-size:24.0pt;font-family:"Arial","sans-serif";mso-fareast-language:ES'>Influence of Arctic sea-ice variability on Pacific trade winds<o:p></o:p></span></b></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-US style='font-size:12.0pt;font-family:"Arial","sans-serif";mso-fareast-language:ES'>Charles F. Kennel and Elena Yulaeva</span><b><span lang=EN-US style='font-size:24.0pt;font-family:"Arial","sans-serif";mso-fareast-language:ES'><o:p></o:p></span></b></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><span style='font-size:18.0pt;font-family:"Arial","sans-serif";mso-fareast-language:ES'>Significance<o:p></o:p></span></b></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-US style='font-size:12.0pt;font-family:"Arial","sans-serif";mso-fareast-language:ES'>By 20th-century standards, the Central Pacific trade winds that drive the El Nino–Southern Oscillation feedback system to instability have been unusually strong in the 21st century. The annual summer melts of Arctic sea ice are up to twice as large in area as in the 20th century. Arctic sea ice, upper atmospheric circulation, surface wind, and sea-surface temperature data provide evidence that upper troposphere transport processes connect the increased summer losses of Arctic sea ice to the trade-wind and Central Pacific El Nino events characteristic of the present climate state. These results add to the evidence that loss of Arctic sea ice is having a major impact on climatic variability around the world.<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><span lang=EN-US style='font-size:18.0pt;font-family:"Arial","sans-serif";mso-fareast-language:ES'>Abstract<o:p></o:p></span></b></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-US style='font-size:12.0pt;font-family:"Arial","sans-serif";mso-fareast-language:ES'>A conceptual model connecting seasonal loss of Arctic sea ice to midlatitude extreme weather events is applied to the 21st-century intensification of Central Pacific trade winds, emergence of Central Pacific El Nino events, and weakening of the North Pacific Aleutian Low Circulation. According to the model, Arctic Ocean warming following the summer sea-ice melt drives vertical convection that perturbs the upper troposphere. Static stability calculations show that upward convection occurs in annual 40- to 45-d episodes over the seasonally ice-free areas of the Beaufort-to-Kara Sea arc. The episodes generate planetary waves and higher-frequency wave trains that transport momentum and heat southward in the upper troposphere. Regression of upper tropospheric circulation data on September sea-ice area indicates that convection episodes produce wave-mediated teleconnections between the maximum ice-loss region north of the Siberian Arctic coast and the Intertropical Convergence Zone (ITCZ). These teleconnections generate oppositely directed trade-wind anomalies in the Central and Eastern Pacific during boreal winter. The interaction of upper troposphere waves with the ITCZ air–sea column may also trigger Central Pacific El Nino events. Finally, waves reflected northward from the ITCZ air column and/or generated by triggered El Nino events may be responsible for the late winter weakening of the Aleutian Low Circulation in recent years.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p></div></body></html>