BASKING IN THE ‘RIDICULOUSLY RESILIENT RIDGE’
Jet stream orientation warms the West, freezes the East
CALGARY The past two winters have been marked by a strange trend in weather patterns: the eastern half of the continent has been swamped by insane snowstorms and frigid temperatures, while the West has luxuriated in springlike temperatures.
The bizarre trend has sparked a flurry of research, including a new theory that may soon become as familiar as El Niño.
One scientist is suggesting longterm shifts in temperature in the Pacific Ocean may be creating a ripple effect that draws warm weather West and cold weather East.
“We’ve been following the weather for 40 years and we sometimes see a difference between the West and the East, but my gosh, it hasn’t been as dramatic as what we saw this year,” said Environment Canada senior climatologist David Phillips.
“In the East, we’ve had the second coldest back-to-back winters we’ve witnessed in 68 years. Only in the late 1970s, when people thought the Ice Age was coming, have we ever had colder back-toback winters.”
Meanwhile, Western Canada and western states have barely recorded winter at all, sparking fears of drought and early grass fires.
These trends can be traced to what’s happening offshore. Ocean temperatures and currents play huge roles in climate and weather on land. Notably, they direct and corral the atmospheric jet stream, which generally pulls air from west to east across Canada.
In the past two winters, the jet stream has taken on a jagged, north-south orientation, with warm southerly air being pulled into the West, and cold Arctic air into the East. This shift is responsible for the polar vortex that made winters east of Manitoba so hellish over the past 18 months.
It has also created a pattern dubbed the “Ridiculously Resilient Ridge” by meteorologists, a ridge of high pressure that has blanketed the West Coast. This year, that ridge would not dissipate, keeping the East cold and the West warm for months on end.
“You were hoarding all of the good weather out West because this Pacific dominance was preventing any of this weather from across to the East,” Phillips said.
“Cold air is like molasses. It fills every nook and cranny, and nothing was kicking it away.”
These trends appear to be connected to a broader shift in hemispheric climate patterns that can be traced to variations in sea surface temperature. There has been an enormous blob of warm water washing up against the B.C. coast for almost two years.
Dennis Hartmann, a professor of atmospheric sciences at the University of Washington, recently published a paper suggesting the blob is the result of a lesser-known and longer-term phenomenon he’s termed North Pacific Mode and which may be a factor in the wildly varying winter weather. “There’s a particular structure that explains a lot of the variability,” he said.
“(We see) warm sea surface temperatures in the North Pacific — Canada and westward, basically — and cooler temperatures in the lower latitudes off toward Japan, and then warm temperatures again as you go into the lower latitudes.”
There was very little El Niño effect this year, Hartmann adds, so different patterns must be accounting for the unseasonably warm winter in the West.
“We have seen this pattern before,” he said. “It’s not like something we’ve never seen before. But … this pattern has become more prominent since about 1980. We don’t yet know if that’s an expression of some longer-term natural variability, or differences of observing systems, or whether some of it is contributed by the earth warming up.”
Winters typically vary from year to year. But if North America experiences another winter like the last two, Hartmann said he would be more inclined to think global warming was responsible for a more permanent shift in weather.
Jennifer Francis, research professor in the department of marine and coastal sciences at Rutgers University, is not so sure.
Her 2012 paper argued the reduction in ice in the Arctic, which is warming at a much faster rate than other latitudes, would intensify pressure ridges, making them more extreme and persistent.
“Last winter and this winter we saw this huge ridge parked over the West Coast of North America the whole time. This is exactly the kind of situation we hypothesized,” she said.
Phillips says this theory is controversial, but could explain why the ridge caused by the change in sea surface temperature became so intractable.
“What we’ve known is that the jet stream has slowed down. It’s 15 per cent (slower) than it was in the 1990s,” he said. That means extreme weather of all kinds tends to stick around a lot longer.
We have seen this pattern before. It’s not like something we’ve never seen before. But … this pattern has become more prominent since about 1980.