Tag: weather

Bless the weather

bob-150x144.gif As if to demonstrate to its peers what the art of good science communication is all about, MetService has just launched a blog. Bob McDavitt (left – great pic!) has posted an excellent article about autumn colour, describing the process that creates the yellows and reds that make our countryside reliably spectacular at this time of year. Erick Brenstrum has a post about a landslide on Stewart Island in 1810, and Ross Marsden has a note on regional cloudscapes. With a team of seven bloggers and a mandate to generate regular material, it promises to be a must visit site for anyone with weather watching tendencies. I hope they can also match some the excellent blog coverage The Weather Channel provides for big US weather events.

[John Martyn, RIP]

Fires (which burn brightly)

Vicfires090210.jpg

The sheer scale of the Victorian bushfire tragedy (over 170 dead at the time of writing: BBC coverage here) is apparent in this false colour satellite image from NASA’s Earth Observatory, captured on Feb 9th. Melbourne is at the top of the bay bottom left, and two large brown areas are the extensive burnt areas centred round Kinglake (left) and Marysville (right) in the Barry Mountains. Red boxes mark active fires, and in some of those boxes bright orange colours show intense heat, probably flames. To be visible from satellite, those fires must be enormous.

The Australian Bureau of Meteorology has updated its statement on the heatwave [PDF], prompting further commentary by Barry Brooks. For me, the money quote is this:

[…] a colleague at BOM pointed out just how exceptional this event was:

“Given that this was the hottest day on record on top of the driest start to a year on record on top of the longest driest drought on record on top of the hottest drought on record the implications are clear… It is clear to me that climate change is now becoming such a strong contributor to these hitherto unimaginable events that the language starts to change from one of “climate change increased the chances of an event” to “without climate change this event could not have occured”.

Jeff Masters at Weather Underground also adds his thoughts. The Herald has details on how to make donations to support fire victims.

[Procol Harum]

Fractured air

The roots of the recent cold weather in Britain and eastern North America lie in unusual goings on high in the atmosphere above the North Pole, as this animation from NASA’s Earth Observatory demonstrates (full video here: 6MB .mov file). The left hand image shows vorticity (rotation, roughly) and the right the temperature at 20km. As the animation moves through January into February, we see the polar vortex (the red bit in the middle) split into two, and stratosphere temperatures over the Arctic jump by as much as 50C. The Earth Observatory explains:

The big change in the Arctic came when the polar vortex ripped apart. A developing weather system in the lower atmosphere traveled upward into the stratosphere. The disturbance nudged into the center of the Arctic air mass, elongating it and eventually splitting it like a cell in mitosis. By February 2, two air masses existed, each with a jet of wind circling it counterclockwise […]. Warm air filled the gap between the two colder air masses, and temperatures high over the North Pole climbed […]. Now the colder air had shifted farther south over Canada and Siberia. Over North America, this piece of the stratospheric polar vortex had a deep reach into the lower atmosphere (troposphere), which created strong winds from the north that carried cold Arctic air far south into the United States.

In Europe, the split in the air mass actually changed the direction of winds in the lower atmosphere. The second piece of the polar vortex was centered east of Western Europe […], and it too was surrounded by a jet of strong wind moving counterclockwise. Like the segment of the polar vortex over North America, this piece of the polar vortex also had a deep reach into the lower atmosphere. It caused cold continental air to blow in from the east, replacing the warmer air that typically blows in from the west. As the frigid air moved over the North Sea, it picked up moisture, which fell over the United Kingdom and parts of France as heavy snow.

There’s a full explanation of the polar circulation at the Earth Observatory page. Well worth a read. Any meteorologists care to comment on just how unusual a feature this is? Are the large blocking highs that bring cold easterlies to Western Europe often associated with polar vortex splits? This is weather, not climate, but the Arctic is experiencing rapid climate change, and this will be expressed as changing weather patterns. A new paper in Climate Dynamics examines this and found “large increases in the potential for extreme weather events […] along the entire southern rim of the Arctic Ocean, including the Barents, Bering and Beaufort Seas.”

[Calexico]

Long hot summer

kanga.jpgThere’s record heat in Australia and deep snow in England (with more to come, say Met men), and it’s all consistent with continuing global warming. Over at Wellington’s leading public transport blog, this is enough to inspire a remarkably ill-informed diatribe:

Following the news as I do, it was delicious today to see the global warmers claiming Melbourne’s summer heatwave was proof of Pope Gore’s alarmism, while ignoring the inconvenient truth that the heaviest snowfalls in decades are falling in London, Paris and much of the north-east of North America.

The really inconvenient truth, of course, is that both weather events neatly demonstrate some of the impacts of global warming and the changes in climate that result.

Continue reading “Long hot summer”

Nice weather for ducks

Duck.jpg A couple of days ago, NIWA published its climate summary for 2008 — a comprehensive overview of all the weather events that went together to make last year what it was. In general, 2008 was sunny and warm for New Zealand, but with many notable extreme weather events — a “rollercoaster” of a year, according to NIWA principal scientist Jim Renwick (who’s been a guest poster here). The Herald picked up on the rollercoaster reference, but Stuff latched on to something else Jim said:

[…] Renwick said the extremes could be a preview of how global climate change would affect New Zealand weather. “I am not saying 2008 was a result of climate change, but we should expect to see more years like that,” he said. “The idea of a sunny year, but with some pretty violent storms, is consistent with climate change. We should expect to see more of those rainfall extremes.”

The last time I looked at my weather records was last February. After musing on a heavy rain event, my comment then was “if you were to ask me what will Canterbury’s climate be like in 2030, I’d have to answer – just like this summer…” For our property in the Waipara Valley, 2007 was a dry year — only 496 mm of rain. 2008 was much wetter: 809 mm in the year, 10% over the average for the last 11 years, and the second wettest in my record. That’s been good news.

However, when I look back at the year, nearly 40% of that rain came in just three events — a big fall in February to break the dry spell, and then two big storms in late July and August, the latter severe enough to cause dramatic flooding in the region. Roughly 320 mm fell in those three events. I had to wash mud out of the garage three times, dig a drainage trench through the truffiere (truffles don’t like drowning), gullies eroded, the road slumped, and the Waipara River lowered its bed by half a metre in places.

Take away those big storms, and we had only 489 mm for the year — a dry year by my standards. Over the ten years up to 2008, we had a total of three comparable heavy rain events (Aug 2000, Jan 2002 and Sept 2003), and then like London buses, three came along at once.

What does this prove? Precisely nothing. I don’t have records going back far enough to know whether there’s any sort of statistical significance in 2008’s North Canterbury rainstorms. But… remember what Jim said earlier? The impact of global warming on the east coast of NZ is expected to increase the frequency of drought, but because warming also means more water vapour in the atmosphere — more “fuel” for weather — when rain does fall, it could come in floods. So if you were to ask me what Canterbury’s climate will be like in twenty year’s time, I’d have to answer – just like last year.

[Lemon Jelly]