Welcome

I’m a climate scientist at the Bjerknes Centre for Climate Research in Bergen, Norway. More info about me and a detailed list of my publications can be found in the menu to the right. The picture in the banner above was taken during a thunderstorm in Denmark this summer. For my Norwegian site, click here. For a short CV, go here.

Nice forecast

This was the forecast for 19–20 November 2009. The numbers are in millimeters.

Forecasting of polar storms

My role in the research project that I work at is to explore the links between cold air outbreaks over the ocean and large weather patterns. Here’s a popular science piece I wrote on a recently published article:

A new study represents a step towards better forecasting of severe weather in polar regions. Cold air outbreaks over the ocean can be linked to large-scale weather patterns, and this leads the way to using new tools to forecast such events.

Marine cold air outbreaks are the breeding grounds of severe weather in the maritime polar regions. An MCAO is a large-scale departure of cold air, typically from regions covered with sea ice, into regions with open ocean. The temperature contrast between the (relatively) warm ocean and the air can be more than 20 degrees Celsius, and this leads to rising air and the development of low-pressure systems. The best-known weather phenomenon associated with MCAOs is the polar low. Sometimes compared to hurricanes, although smaller in scale, these cyclones can produce hurricane-force winds and large amounts of snow. MCAOs therefore form a significant part of the marine hazard in populated coastal regions of Norway, Russia, Iceland, Japan and even the British isles. MCAOs are also important factors in determining the amount of heat that is lost from the ocean to the air during winter. Such heat loss is associated with deep-water formation and the strength of the oceanic thermohaline circulation, the Great Ocean Conveyor. In a new study, published in Climate Dynamics and led by Bjerknes researcher Erik Kolstad, the correspondence between large-scale weather patterns and MCAOs is explored. Over the Nordic Seas region, a pronounced high-pressure anomaly over Greenland, either acting alone or in concert with a strong low-pressure anomaly over northeastern Europe, were shown to be favourable for MCAOs to form. This is potentially important because such conditions are linked to negative phases of the North Atlantic Oscillation, the primary weather pattern in the North Atlantic region. This means that any progress in medium and long range forecasting of the NAO – a large research field – may also be translated to enhanced forecasting of MCAOs.

Complete reference: Kolstad, E. W., Bracegirdle, T. J. & Seierstad, I. A. (2009), Marine cold-air outbreaks in the North Atlantic: temporal distribution and associations with large-scale atmospheric circulation, Climate Dynamics, 33(2), 187-197.

A pre-print of the article can be downloaded here.

New paper submitted

I just submitted a paper that I co-authored with T. Breiteig and A. A. Scaife to the Quarterly Journal of the Royal Meteorological Society. The title of the paper is: The association between stratospheric weak polar vortex events and cold air outbreaks and here is the abstract:

Previous studies have identified an association between near-surface temperature anomalies in the Northern Hemisphere and weak stratospheric polar westerlies. Large regions in northern Asia, Europe and North America have been found to cool in the mature and late stages of stratospheric weak vortex events. A substantial part of the temperature changes are associated with changes to the tropospheric Northern Annular Mode and North Atlantic Oscillation pressure patterns. The apparent coupling between the stratosphere and the troposphere may be of relevance for weather forecasting, but only if the temporal and spatial nature of the coupling is known. Here we show, using 51 winters of re-analysis data, that the tropospheric temperature development relative to stratospheric weak polar vortex events goes through a series of well-defined stages, including geographically distinct cold air outbreaks. At the inception of weak vortex events, a precursor signal in the form of a strong high-pressure anomaly is found over Northwest Europe. At the same time, long-lived and robust cold anomalies appear over Asia and Western Europe. A few weeks later, near the mature stage of weak vortex events, a shorter-lived cold anomaly emerges off the east coast of North America.The probability of cold air outbreaks in different phases of the weak vortex life cycle increases by 40–70 % in four key regions. This shows that the stratospheric polar vortex contains information that can be used to enhance forecasts of cold air outbreaks. 300-year pre-industrial control runs of 11 state-of-the-art coupled climate models corroborate our results.

The curret version is available for PDF download at arxiv. All manner of comments are welcome.

Reuters article

A paper that I published last year with Tom Bracegirdle of British Antarctic Survey was picked up by Reuters today. First the press release was put on the front page of the International Polar Year web site, then I was called up by Reuters. The article can be found here.

Here’s a list of sites to run the story:

Scientific American | USA Today | Yahoo! Finance | CNBC | Forbes

The original press release (that I wrote) was printed more or less verbatim elsewhere:

Science Daily | Science Centric

The Canadian new service Canwest also wrote about this after interviewing my by e-mail:

Edmonton Journal | The Province | dose.ca

Pictures from a field trip

I have just uploaded a new photo album from a scientific cruise near Svalbard in the Arctic in March, 2008. We spent a week on a Norwegian coast guard icebreaker, deploying instruments for measuring radiation over the sea-ice and, more importantly, testing a tiny remote-controlled aircraft. This little thing can record vertical profiles of wind, temperature and humidity in the lower atmosphere. See more pictures here

Weather poetry

Anyone familiar with the work of Cormac McCarthy knows that he loves weather. His dark, disturbing and poetic desciptions of the desert landscape are filled with references to thunderstorms, shifting ambient lighting and even frost and snow. Here’s one of my favourite paragraphs:

That night they rode through a region electric and wild where strange shapes of soft blue fire ran over the metal of the horses’ strappings and the wagonwheels rolled in hoops of fire and little shapes of pale blue light came to perch in the ears of the horses and in the beards of men. All night sheetlightning quaked sourceless to the west beyond the midnight thunderheads, making a bluish day of the distant desert, the mountains on the sudden skyline stark and black and livid like a land of some other order out there whose true geology was not stone but fear. The thunder moved up from the southwest and lightning lit the desert all about them, blue and barren, great clanging reaches ordered out of the absolute night like some demon kingdom summoned up or changeling land that come the day would leave them neither trace nor smoke nor ruin more than any troubling dream.

– Blood meridian

Polar low

The polar low season started early this year. In this picture, which was taken on Tuesday 28 October, 2008, we see a pretty specimen centered roughly over Shetland. This polar low is part of the first proper cold-air outbreak this winter, yielding October snow in London for the first time since the 1930s.

The polar lows season in the North Atlantic usually starts in October/November and ends in March/April. The season that ended earlier this year was characterized by weak activity and few cold-air outbreaks.

Cold-air outbreaks

My research is pretty much focussed on high-latitude weather, and things like polar lows [?] in particular. I’m currently writing a paper about marine cold-air outbreaks, i.e. large-scale departures of cold, polar air from over the sea ice into regions of relatively warm, open ocean. In these situations, the cold air sucks huge amounts of energy out of the water, much like what happens during tropical cyclones (hurricanes and typhoons).

My colleague Tom Bracegirdle and I have devised a fairly simple cold-air outbreak index. If you know the temperature of the sea surface and the air temperature at an altitude of some 2,000 metres, this index can be calculated at any time and place. I’ve done just that and picked out the most extreme cases in the last few years. This satellite image was taken over the North-East Atlantic around noon on 23 January, 2003 (click for a larger version):

The wind is coming from the north-west, down through the Fram Strait between Spitsbergen and Greenland and off the sea ice along the east coast of Greenland. After travelling a few hundred kilometres over the open ocean, it is heated enough for some no-nonsense clouds to develop. The white areas with the spirally shape are polar lows. The surface winds in this region were around 50 knots at the most intense. That’s not so far from hurricane force winds.

Another very cool feature is the von Kármán vortices [?] downstream of Jan Mayen near the middle left edge of the picture.

This kind of weather is important in many ways. The potential for accidents is only the most obvious issue. The worst accident in later years was when the British trawler FV Gaul went down in 1974, killing all 36 men on board [?]. Colleagues of mine here in Bergen have simulated the weather on this day using numerical weather prediction models, and they found that there was an “arctic front” (a phenomenon that is highly related to polar lows) in the region when the ship sank.

In Norwegian waters, there are numerous examples of ugly accidents at sea, especially in earlier times, when the forecasts were erratic or even non-existent.

Cold-air outbreaks are also important for the ocean. Alan Condron of Woods Hole, MIT is the lead author a new, important paper in the Journal of Geophysical Research. His group found that if the weather typically associated with cold-air outbreaks had been better represented in the widely used re-analysis data sets such as ERA-40 [?], it would have led to (in models)

enhanced surface latent and sensible heat fluxes and a dramatic increase in the cyclonic rotation of the Nordic Seas gyre by four times the average interannual variability. In response to these changes, Greenland Sea deep water formation generally increases by up to 20% in 1 month, indicating more active open ocean convection.

Condron’s study is a welcome addition to the literature, in that it couples the atmosphere and the ocean in an elegant manner. The disciplines of meteorology and oceanography, for all their similarities, are too often treated as separate entities. For instance, it was not until 1957 that one realized that the ocean phenomenon El Niño was intimately coupled with the atmospheric Southern Oscillation. Although one sometimes still refers to this system as simply El Niño, it is now known as the combination of the two: El Niño-Southern Oscillation, or ENSO [?].

Poles apart

I recently submitted four images to an International Polar Year (IPY) photo exhibit. Note that they are all copyrighted. If you wish to use any of them, you must contact me first.

1. The intense energy fluxes from the ocean to the atmosphere are made visible by the clouds at the outskirts of a polar low. This aerial photograph was taken during the IPY-THORPEX field campaign near Tromsø, Norway in March, 2008.

2. These footprints were left by scientists and the crew at a coast guard icebreaker in the sea ice near Svalbard. The photograph was taken during the IPY-THORPEX field campaign in March, 2008.

3. A helicopter leaves a coast guard icebreaker in the sea ice near Svalbard. The photograph was taken during the IPY-THORPEX field campaign in March, 2008.

4. The intense heat fluxes from the open ocean to the atmosphere can be seen as “Arctic Smoke”. The photograph was taken from a coast guard icebreaker in the sea ice near Svalbard during the IPY-THORPEX field campaign in March, 2008.