How ice loss influences the jet stream

I’ve spent a fair bit of time discussing the record warm weather we experienced in March over the last few weeks. We’ve looked at just what led to this remarkable weather and we discussed just how intense it really was. The fact that we saw temperatures that were between three and four standard deviations above the long-term average is truly remarkable, and for some of us this might be a once-in-a-lifetime event.

To try and put this into a different perspective, I bumped into my good friend Danny Blair, climatologist and associate dean of science over at the University of Winnipeg just last week, and we briefly discussed the scope of the March heat wave. While I don’t have the exact numbers right now, Dr. Blair informed me he had crunched some of the numbers and discovered this was the most intense above-average period of warm weather our region has experienced since records began in 1872. That is, the eight days of record- or near-record-breaking weather had the most above-average temperatures of any other similar period in Winnipeg’s history, no matter what time of year. If this had occurred in July we would have seen daily high temperatures in the 40 to 45 C range, with overnight lows around 30 C! This truly could be a once-in-a-lifetime event — or could it?

New research is coming out that has looked at what effects the loss of ice cover in the Arctic is having on the world’s weather. What the early results seem to show is that the increase in available heat in the Arctic seems to be contributing to a much more amplified long wave pattern in the Northern Hemisphere.

In the past we have had discussions about the jet stream and how it meanders around the Earth, creating large ridges and troughs. These curves in the jet stream control much of our mid-latitude weather. When there is a ridge over us, we have relatively clear and warm weather; when there is a trough, our weather is unsettled and cool. These ridges and troughs are generally fairly broad and will slowly move around the Earth, bringing periods of warm and cool weather. Occasionally these ridges and troughs can become amplified — that is, they become much larger in a north-south direction. When this happens the ridges and troughs can get “stuck” in position. This will then lead not only to longer periods of either cold or warm weather, but more intense temperatures as well. This is exactly what we saw happen in March. The interesting part is that the warm sector was much more extremely warm than the cold sector was extremely cold. While there were hundreds of heat records broken, with several all-time heat records, there were only a handful of cold records broken on the cold side of this pattern.

Normally this type of amplification of the pattern doesn’t happen very often. This new research is starting to indicate this type of pattern may become much more prevalent, meaning we may see more frequent periods of extreme record-breaking warmth, but we may also see periods of cold as well. So this once-in-a-lifetime warm spell may not be a once-in-a-lifetime event after all — we may see more of this type of weather in the not-so-distant future.

Another interesting study came out recently looking at ice cover over the Great Lakes since 1973. What the study found was that ice cover during this period has declined by as much as 71 per cent and winter air temperatures over the southern Great Lakes have warmed around 2 C, while over the northern lakes the increase has been as much as 3 C. This results in increased winter evaporation from the lakes, which results in lower lake levels, but also results in increased lake effect snows.

Now to end off this week’s article I came across a really cool weather-related web page. This page shows the wind pattern and speed across the United States in a rather unique and interesting way. It is updated every hour using data from the U.S. National Digital Forecast Database and was done as part of an art project. It can really help you see how air spirals out of areas of high pressure, and how wind can converge in one area, resulting in lift. You can check it out at http://hint.fm/wind/index.html.

About the author

Co-operator contributor

Daniel Bezte

Daniel Bezte is a teacher by profession with a BA (Hon.) in geography, specializing in climatology, from the U of W. He operates a computerized weather station near Birds Hill Park.

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