Trapping of giant waves in atmosphere behind extreme weather events
28.02.2013 - Atmosphere & Space, Arctic
Researchers at the Potsdam Institute for Climate Impact Research (PIK) have recently released a study in the US Proceedings of the National Academy of Sciences detailing how anthropogenic climate change can repeatedly disturb atmospheric flow patters throughout the Northern Hemisphere, creating weather extremes in the Northern Hemisphere.
Atmospheric motion normally takes the form of waves in the mid-latitudes that oscillate between the tropics and the Arctic. Sometimes they bring warm air from the tropics northwards, and sometimes they bring cold air from the Arctic southward.
However when these waves “freeze” for long periods of several weeks you get extreme weather events in the mid-latitudes such as droughts, floods and massive storms that can put stress on human infrastructure and ecosystems. According to lead author of the study Dr. Vladimir Petuokhov, there is a “strong amplification of the usually weak, slowly moving component of these waves.”
Temperature difference between the Arctic and the mid and lower latitudes is the main driver of the atmospheric wave flow in the atmosphere. Yet as the Arctic has warmed, and sea ice has melted, creating a positive feedback loop of warming, the temperature difference between the upper and lower two parts of the Northern Hemisphere has decreased, disturbing the normal flow of air in the atmosphere, resulting in the “freezing” of the undulations of the atmospheric flow.
The research team devised equations to describe the wave motions of the atmosphere in the Northern Hemisphere north of the tropics and show how atmospheric wave patterns can become locked. Using weather data overt 32 years, they tested their hypotheses and were able to determine the mechanism behind the changes.
They discovered that at the time of several extreme weather events over the past few years, there was a block and amplification of particular waves – especially a wave called “wave seven” due to the fact it has seven undulations as it makes its way around the planet. The data from the research show with 90% confidence that there has been an increase of these blocking patterns over the past few years.
The study makes a significant advance in linking recent weather extremes human-driven climate change, and shows that extreme weather is a non-linear response to the overall warming trend. Researchers involved in the study were surprised to find out how far outside the norm of past weather patterns recent extreme events have been.