Cold winters from warm oceans

摘要

Barcelona and London both lie north of New York, yet winters in these two European cities are warmer than winters in the northeastern United States (Fig. 1). It would seem easy to attribute this difference simply to the fact that Europe lies downwind of the warm North Atlantic Ocean. But Kaspi and Schneider (page 621 of this issue)~1 put forward the counter-intuitive argument that the northeastern parts of North America, and also of Asia, are instead cooled in winter by heat released from oceans just off their coasts. No exotic thermodynamics is needed to create continental cold from oceanic warmth. Instead, Kaspi and Schneider show that heat emitted by a warm swathe of mid-latitude ocean can set up a pattern of north-south flow that draws cold Arctic air into regions immediately upstream of the heat source. Waters just east of Asia and North America do indeed emit large amounts of heat into the atmosphere during winter, when prevailing eastward winds draw cold continental air over the warm waters of the Gulf Stream and the Kuroshio, Asia's analogous continental boundary current.