Thursday, 28 January 2016

Is the Pacific Storm Track Being Shoved North by Arctic Warming?

Polar Amplification vs a Godzilla El Nino — Is the Pacific Storm Track Being Shoved North by Arctic Warming?

27 January, 2016

It’s an El Nino year. One of the top three strongest El Ninos on record. The strongest by some NOAA measures. And we are certainly feeling its effects all over the world. From severe droughts in Southeast Asia, Africa, and South America, to Flooding in the Central and Eastern US, Southern Brazil, and India, these impacts, this year and last, have been extreme and wide-ranging. During recent days, Peru and Chile saw enormous ocean waves and high tides swamping coastlines. Record flooding and wave height events for some regions. All impacts related to both this powerful El Nino and the overall influence of human-forced warming by more than 1 C above 1880s temperatures on the whole of the hydrological cycle.

Amped up by a global warming related 7 percent increase in atmospheric water vapor (and a related increase in evaporation and precipitation over the Earth’s surface), many of these El Nino related impacts have followed a roughly expected pattern (you can learn more about typical El Nino patterns and links to climate change related forcings in this excellent video by Dr Kevin Trenberth here). However, so far, some of the predicted kinds of events you’d typically see during a strong El Nino have not yet emerged. A circumstance that may also be related to the ongoing human-forced warming of the globe.

Storm Track Not Making it Far Enough South

Particularly, there has been an absence of powerful storms running in over Southern California then surging on into Arizona, New Mexico and West Texas. During strong El Nino events, heat and moisture bleeding off the super-warmed Equator have typically fed powerful storms racing across the Pacific. These storms have tended to engulf the entire US Pacific Coast from San Diego through to Seattle. However, much of the storm energy is often directed further south toward Central and Southern California.
Ridiculously Resilient Ridge Returns
(A massive Pacific storm being warded off by high pressure systems over the US West Coast on Tuesday, January 26th. Image source: Earth Nullschool.)

These storms tend to run over regions that are typically much drier. So strong El Ninos of the past have often generated abnormal and memorable storms and rains. But this year there has been, mostly, an abscense of such events. Storms have slammed into Northern California, Oregon, been deflected back into the coasts of Canada and Alaska, or even been bottled up near the Aleutian Island Chain.
But today, a high pressure cell dominates the western US, warding off a powerful storm system. The storm, howling just south of Alaska and pushing out average 60 foot wave heights and hurricane force winds across the Pacific, is predicted to rebound toward Alaska where it will become bottled up in the Bering sea and push above freezing temperatures into the Arctic Beaufort Sea during Winter. The storms and rains will steer far away from Southern California and even much of California altogether.
Rainfall Patterns Have Tended Toward the North, Contrary to NOAA’s Seasonal Predictions
NOAA Precipitation
(NOAA precipitation quantities prediction for the coming week is indicative a continued northward shift of the Pacific Storm track. Image source: NOAA.)

It’s a pattern more reminiscent of some strange ridiculously resilient ridge (RRR) than that of a strong El Nino. And though storms later this week are again predicted to slam into the Northwest and weekly rainfall totals are expected to rise to near 1 inch for parts of Southern California, the path of these storms and related moisture flows are quite a bit further north than one would expect for a year in which strong El Nino was the dominant feature.
The moisture flow, instead, so far has tended northward across the upper and central tiers of the US even as the El Nino related moisture bleed toward the Gulf and East Coasts has remained quite intense. Such observed weather is both contrary to what we’ve tended to know about Strong El Nino and to NOAA’s seasonal forecasts which had predicted much more rain for the southwest than what we’ve seen so far.
Seasonal Outlook NOAA
(NOAA three month outlook is more in line with traditional strong El Nino forecasts bringing strong storms in through the southwestern US. We currently do not see a prevalence of that particular pattern. Image source: NOAA’s Climate Prediction Center.)

Polar Warming + Hot Blob Tugging the Storm Track Northward?

Since weather patterns related to El Nino are an aspect of global atmospheric dynamics — teleconnections between the influence of an excess of hot air and heavy rainfall at the Equator and of large scale atmospheric wave patterns downstream, you have to wonder if there isn’t some kind of influence competing with El Nino on a global scale. One with enough oomph to nudge the Pacific Storm Track northward.
Hot Blob Pacific Northwest
(The Hot Blob is still a dominant feature of ocean waters in the Pacific Northwest. Is its influence helping to pull the Pacific Storm Track northward during a strong El Nino year? Image source: Earth Nullschool.)

The first likely suspect is the pool of still much warmer than normal sea surface temperatures lurking off the US West Coast. Though somewhat diminished from their peak during 2014 and 2015, the waters in the hot blob off California, Oregon, Washington, Canada and Alaska are still in the range of 1 to 3 C above average. A very large region of significantly warmer than normal ocean surfaces that wasn’t present during the 1982-83 and 1997-1998 super El Ninos. And much of the warmest anomalies are now centered much further to the north along the coast of Alaska.
But the second potential player is likely even more significant. And that would be an ongoing and extreme warming of the northern polar region. Heating at the Pole generates less thermal gradient between the higher Latitudes and the Equator. And such a lessened gradient would tend to impact the strength of the circumpolar winds that drive weather systems and storm tracks. In particular, the overall warming of the globe would tend to pull these storm tracks northward even as the loss of thermal gradient would tend to enhance wave patterns in the Jet Stream.
Polar Amplification January 26
(Polar Amplification shown as very intense in the January 26 Climate Reanalyzer graphic. Is Polar Amplification helping to shove the Pacific Storm Track northward even during a record strong El Nino year? If so, it’s bad news for long term moisture levels in the US Southwest. Image source: Climate Reanalyzer.)

Perhaps also specifically related to this ongoing polar amplification, we find that two warm slots — one over the Barents and far North Atlantic east of Greenland and another over the Bering — have tended to develop during recent Winter years. These slots have often served as staging areas for warm air invasions of the Arctic. But what they also represent are regions of water that have been freshly liberated from their sea ice coverings. As such, these vast regions of water serve as heat transport and ventilation zones. And all this extra heat energy may be sucking the related North Atlantic and North Pacific Storm tracks into what may well be described as an oceanic and atmospheric trap.
If such a situation where the case, we’d tend to see a dipole of warm east, cold west in the storm trap regions. And that’s exactly what we’ve seen more and more of with Greenland and Siberia serving as the backdrops to reinforce this tendency. Thus setting up the stage for cold air slots cutting through Northeast Siberia and Northeast Canada and warm, wet air slots over Alaska and the UK.
The question to be asked is, then, are these new influences related to human-forced warming also now doing battle with El Nino for control over the Pacific Storm Track? And has that influence increased enough to dramatically nudge that track northward? We may find the answer to that question in what happens to the direction of powerful Pacific Storms over the next few months. But early indications seem to be that polar warming and the related hot blob may have thrown a wrench in the kinds of El Nino storms that we’ve been used to.
Hat Tip to Colorado Bob
Hat Tip to DT Lange
Hat Tip to Andy in San Diego

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