Sea level has jumped off the east coast of north America since March 2013. The warmest and saltiest water ever seen in the northwest Atlantic is mixing with icy water drained from the Arctic ocean and sinking to the bottom of the Labrador Sea.
AVISO's global map of sea-surface height departure from normal for March 14, 2015, shows a huge rise in sea level off the east coast of north America. This water has the highest levels of heat and salt ever measured in this region.
Sea-surface heights were relatively low off the east coast on March 14, 2013, when the polar vortex split and deep water formation in the Labrador Sea collapsed. Arctic sea ice staged a major recovery because cold fresh water stayed in the Arctic and the Gulf Steam and Norwegian currents weakened.
March 1995 had the most similar sea-surface-height pattern to 2015 in AVISO's 22-year, on-line record. March 1995 was when deep water formation in the Labrador sea was at a 50-year maximum
The sudden return to active deep-water formation in the Labrador Sea has profound implications for Northern Hemispheric weather and Arctic sea ice. The strong deep convection in the 1990s led to the rapid North Atlantic and Arctic Ocean warming that occurred in the following decade. Moreover, strong Labrador Sea deep convection brings cold air down from the Arctic into eastern North America and brings warm Atlantic Ocean air to the coastal areas of Europe. And it brings very intense storms to the east coasts of North America and Greenland. This pattern explains the very severe weather the U.S. east coast went through in February 2015. The east coast of North America was the only continental area on earth colder than normal in February. Western Europe and western North America were very warm.
After the very weak polar vortex year of 2013, when a sudden stratospheric warming split the polar vortex in two and deep convection failed to start in the Labrador Sea, the polar vortex strengthened and storminess in the western North Atlantic intensified. Cooling began in 2014 in the Labrador Sea, while water temperatures rose to record levels in the Gulf of Maine and adjacent North American waters. The polar vortex and Labrador Sea deep convection grew stronger in late winter 2015 after an incipient stratospheric warming formed an anticyclone high over the subtropical North Atlantic. This anticyclone in the stratosphere disrupted the westward movement of atmospheric waves across the Atlantic, directing them northeastwards towards Norway and the Arctic Ocean. This block in the flow intensified the polar vortex and strengthened storms over the North Atlantic.
Strong polar vortex and Labrador Sea deep convection pattern. This strong polar vortex, strong deep convection pattern described by Reichler and others in Nature Geoscience fits this March's sea-surface height pattern exactly. "Shown are composite anomalies averaged from day 0 to 60 following the strong vortex events of Fig. 2. Sea-level pressure anomalies are contoured at positive and negative 0.5, 1, 2, 3, 4 hPa; red and blue lines indicate positive and negative values, respectively. Shading shows the sum of latent and sensible heat flux anomalies (in Wm^-2), with positive and negative anomalies indicating oceanic heat gain and loss, respectively. Vectors represent the magnitude and direction of surface wind stress anomalies."
Preliminary NSIDC figures show that a record minimum winter sea ice maximum extent was reached on February 25, 2015. "Figure 1. Arctic sea ice extent for February 25, 2015, was 14.54 million square kilometers (5.61 million square miles). The orange line shows the 1981 to 2010 median extent for that day."
On February 25, 2015, Arctic sea ice likely reached its maximum extent for the year, at 14.54 million square kilometers (5.61 million square miles). This year’s maximum ice extent was the lowest in the satellite record, with below-average ice conditions everywhere except in the Labrador Sea and Davis Strait. The maximum extent is 1.10 million square kilometers (425,000 square miles) below the 1981 to 2010 average of 15.64 million square kilometers (6.04 million square miles) and 130,000 square kilometers (50,200 square miles) below the previous lowest maximum that occurred in 2011. This year’s maximum occurred 15 days earlier than the 1981 to 2010 average date of March 12. The date of the maximum has varied considerably over the years, occurring as early as February 24 in 1996 and as late as April 2 in 2010.The outlook for Arctic sea ice this summer is poor because warmer than normal water is surging up the coast of Norway into the Arctic, while cold water which has been stored for years in the Arctic ocean is draining through the Canadian passages into the Labrador sea. Moreover, stratospheric and Arctic patterns can reverse with the seasons, so a strong winter polar vortex may be followed by high pressure and warm sunny weather in the late spring. The Arctic sea ice recovery of 2013 is very likely over. Summer sea ice appears to be back on the long downward trend towards zero.
NOAA's Ocean Prediction Center made a short silent movie of two hurricane-force storms in early March this year. These storms were two of the most intense lows to develop in this extremely stormy winter in the North Atlantic. The extraordinarily stormy weather in February and March has spun up the thermohaline circulation, draining icy, relatively fresh water from the Canadian side of the Arctic Ocean and driving warm salty water that originated in the Gulf Stream up the coast of Norway, into the European side of the Arctic Ocean. The influx of warm air and water from these storms caused Arctic sea ice to retreat and set a provisional record-low maximum on February 25, 2015.
Supplementary figure showing the intense polar vortex event associated with the extreme winter storms and Labrador sea deep convection in February and March, 2015
The polar vortex was stronger than normal in February and the first half of March 2015. Blue from the surface to the stratosphere shows a strong polar vortex. The polar vortex strength for winter 2014-2015 is displayed as the geopotential height anomaly versus time for 65-90 degrees N.
Warmer than normal water is flowing up the coast of Norway into the Arctic.
Warmer than normal water is flowing up the coast of Norway into the Arctic.
Water temperatures at a depth of 1,000 feet (318 m) March 20, 2014, Mercator Ocean analysis, in and around the Arctic.
attribution: Mercator Ocean
Map of water temperature at a depth of 1,000 feet for March 20, 2015. Warm Atlantic water has surged into the Arctic and cold Arctic water has drained into the Labrador sea since the same date a year ago.
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