Archive for the 'Weather & Sky' Category

Feb 16 2013

Hold Onto Your Hats

Published by under Weather & Sky

Chelyabinsk meteor trace, 15 February 2013 (photo by Nikita Plekhanov via Wikipedia)

There we were, focusing our attention on an asteroid that was going to miss Earth when Bang!  a real live meteor zipped low over Russia yesterday morning.

The meteor taught me a lot more than the asteroid.  After it lit the sky, made an explosive boom, blew out windows, and injured more than 1,000 people I learned from NASA:

  • Its light was brighter than the sun.
  • Its contrail was 300 miles long. (That’s the distance from Pittsburgh to Philadelphia).
  • Eyewitnesses said the sonic boom lagged by three minutes … just long enough for everyone to go to their windows to watch.
  • The meteor was about the size of a bus (55 feet) but it weighed 10,000 tons –> 1,400 times heavier than a bus.
  • The atmosphere really did help after all.  When the meteor exploded it was still 12-15 miles up.  At least twice as high up as a jetliner.
  • If it was only the size of a bus and 2 to 4 times higher up than a jet, why did it cause such a problem?   Well, it was traveling at 40,000 mph!

So, hold onto your hats.  It’s the stuff we aren’t worried about that gets us.

Click here for scientific analysis (video) from The Telegraph UK.

 

(photo of the Chelyabinsk meteor’s trace by Nikita Plekhanov via Wikipedia. Click on the image to see the original)

p.s.  The meteor also taught me two things about Russian culture:  (1) Russians have dashboard cameras in their cars to protect against corrupt policemen and disputed traffic accidents, and (2) They have already made a joke about it, quoted from the Houston Chronicle: “The meteorite was supposed to fall on Dec. 21, 2012 — when many believed the Mayan calendar predicted the end of the world — but was delivered late by Russia’s notoriously inefficient postal service.”

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Feb 11 2013

An Icy Parfait

Published by under Weather & Sky

Sea ice in the Arctic (photo courtesy Univeersity of Washington)

Even when scientists develop an answer to why something happened, they still test the idea to make sure they’re right.

That’s what happened with the Great Arctic Cyclone of August 2012.

Last August a rare, massive cyclone formed in Siberia and swirled out over the Arctic Ocean for days.  During its transit the sea ice disappeared faster than anyone had ever seen.  (See the swirl here.)

By September Arctic sea ice was at an all time low.  Some said the cyclone caused the lowest ice extent since record-keeping began.  Did it?  Or would the ice have melted anyway due to warm temperatures?

Scientists at the University of Washington’s Applied Physics Laboratory ran two computer simulations of last summer’s Arctic weather.  One matched the actual weather.  The other included everything except the cyclone.

The result showed that yes, “the effect is huge in the immediate aftermath of the cyclone, but after about two weeks the effect gets smaller.  By September, most of the ice that melted would have melted with or without the cyclone,” said lead author Jinlun Zhang.

Why?  Because of mixing.

Back in September most thought that the wind broke up the thin ice or pushed it into a warmer part of the ocean.  Since then scientists have learned that the ocean underneath the ice is like a layered parfait.  Just below thin ice is a layer of ice-cold fresh water.  About 65 feet down is a layer of salty water warmed by the sun.  The cyclone stirred the parfait.  The ice was exposed to the warm water beneath and it melted.

The cyclone did cause the ice to melt 10 days sooner, but in the end it made less than 5% difference in the ice extent.

So yes, the sea ice melted because it was hot last year.

Click on the photo to read more about the study in Science Daily.

(photo courtesy University of Washington)

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Feb 09 2013

Easy To See In Snow

Horned Lark (photo by Bobby Greene)

In snow-covered fields horned larks are easy to see because their brown backs don’t completely blend into the background.

Without snow these birds match the dirt.  The only way I find them is by luck — I hear them and then search for movement in the mud.

When the blizzard finally ends on the East Coast today, it will be easy to see horned larks against all that snow.  In the meantime in Pittsburgh our snow will melt in tomorrow’s 50 degree temperatures.

Despite the challenge of muddy fields I think I’d rather have a hard time seeing horned larks.  ;)

(photo by Bobby Greene)

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Jan 31 2013

Walking Down Vortex Street

I know almost nothing about fluid dynamics but my article about wingtip vortices two weeks ago piqued my interest in the subject.

Last weekend I learned about this amazing phenomenon, the von Kármán vortex street, animated above by Cesareo de La Rosa Siqueira.

Von Kármán vortex streets occur when a fluid flows past a stationary object and generates a long line of vortices that swirl in opposite directions.  The phenomenon was named for Theodore von Kármán, the man who described it, and is probably called a street because it looks like one.

We usually don’t see von Kármán vortex streets in the wind, but it’s important that engineers plan for them.  If a tall structure is uniformly straight the vortices can make it fall down.  Click here to read about a famous mistake.

On a small scale, von Kármán vortex streets make telephone wires sing in the wind.  On a large scale they’re visible from outer space when clouds blow past a tall island.

Here’s a picture taken from the space shuttle that shows cloud cover blowing past Rishiri Island, Japan.  When the wind encounters Mt. Rishiri the clouds form a von Kármán vortex street on the downwind side.

Pretty cool, huh?

There are more than twenty islands that reliably generate von Kármán vortex streets.  Click here to see more pictures from NASA.

(Vortex animation by Cesareo de La Rosa Siqueira via Wikimedia Commons.  Space shuttle photo from NASA via Wikimedia Commons. Click on the images to see the originals)

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Jan 29 2013

Open Water

Female buffelhead at Bosque del Apache (photo by Steve Valasek)

The long spate of cold weather froze all our ponds and lakes.  Even the rivers were beginning to freeze until Monday’s warmth reversed the trend.

Don’t expect to see a lot of birds at Lake Arthur right now.  Waterfowl who rely on open water for food or to get airborne have left for open water.  Some are at our rivers, most have left town completely.

This female bufflehead was on the other side of the U.S. — at Bosque del Apache, New Mexico — when Steve Valasek took her picture.

No, she didn’t leave Pittsburgh for New Mexico, but Steve did.

(photo by Steve Valasek)

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Jan 20 2013

Wind Effect

Published by under Weather & Sky

As I write this morning before dawn, the wind is whipping around the house as a winter storm approaches from the west.

If I was at the roof peak I’d be blown away.  The wind is even faster up there (see red lines at top) where it converges to clear the house.

Outside my window on the downwind side, the air is swirling in updrafts like the turquoise lines at left.

I suppose I could find a few calm spots within the swirls if I went outdoors to experiment, but it’s not worth it.  At particularly gusty moments I hear garbage cans rattle down the alley in the dark.

(diagram by Barani on Wikimedia Commons.  Click the image to see the original)

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Jan 08 2013

Why Don’t They Just Move?

When bird habitat disappears some people say, “Birds can fly.  They should just move and they’ll be fine.”

A new study published last month in Ecology Letters shows why that idea doesn’t work.

Oxford University scientists, lead by Dr. Alex Pigot, studied the ovenbird(*) (Furnariidae) family in South America.  They found that closely related species who evolved similar feeding strategies do not live in the same area.  This isn’t just a local exclusion, it’s regional.

Feeding strategies are often characterized by the shape of the bird’s beak and Furnariidae have some amazing ones!  This bird, the black-billed scythebill, pulls insects out of bark, bamboo and bromeliads.  The large range of his close relative, the red-billed scythebill, barely overlaps.  Each species has its niche.

What happens to displaced birds when habitat is lost?   Obviously, the homeless birds find a new location but other species are already there and successfully exploiting the niche the new birds need.  Out-competed by locals, the new arrivals may not survive.

Thus the study suggests that the effects of climate change will not be a simple shifting of bird populations but new layers of competition in a changing world.

Read more about this study of beaks and ranges here in Science Daily.

(photo of a black-billed scythebill in Brazil from Wikimedia Commons.  Click on the image to see the original)

 

(*) Furnariidae are not related to our ovenbird warbler though both build nests that look like little Dutch ovens.

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Dec 21 2012

The Sun As Pearls

Published by under Weather & Sky

Like a three-strand necklace of pearls, this composite photo shows the sun’s position hour by hour at the summer solstice, the vernal equinox, and the winter solstice.

It was taken at the same location in Bursa, Turkey over a period of six months by award-winning amateur astronomer and night sky photographer Tunç Tezel, a member of The World At Night.

The top strand is the sun’s transit during the summer solstice in June, the longest day of the year.  You can tell the sun was up for 15 hours because there are fifteen pearls on that strand.

The middle strand was taken during the equinox when every place on earth has 12 hours of daylight.

The lowest strand was taken on this day, the winter solstice, when there are 9 hours of sunlight in northern Turkey.

There are nine hours of daylight in Pittsburgh today, too.

Northern Turkey and western Pennsylvania are on approximately the same latitude so these sun tracks are what we see here in Pittsburgh.

The whole world shares the same sky.  We all can see the sun as pearls.

 

(photo copyright by Tunç Tezel, member of The World At Night (TWAN).  This photo was NASA’s Astronomy Photo Of the Day on September 23, 2012.  Click on the photo to see the original and learn more about its creation.)

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Dec 01 2012

Weak Winter Sun

Published by under Weather & Sky

Today’s weather is supposed to be “partly sunny” but in winter that can mean the sun looks like this for part of the day.

This photo could have been taken anywhere in western Pennsylvania in early December.  Brown fields, bare trees, power lines, crows.  Can you guess where it was taken?

Click here and then on the Google Maps link to see the photo’s location, or click on the image to read the description.  You’re in for a surprise.

 

(photo by Pauline Eccles via Wikimedia Commons. Click on the photo to see the original)

p.s. The coordinates are 51° 53′ 50.63″ N, 2° 29′ 38.14″ W

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Nov 14 2012

Hazy Inversion

Published by under Weather & Sky

Three weeks ago I wrote about radiation fog and inversions.  We had another inversion recently, this time without fog.

Here is the view last Sunday from the Allegheny Front Hawk Watch.  It looks like a bad picture of beautiful scenery but it’s actually a good illustration of a hazy inversion.  Notice how the near trees are colorful and Wills Mountain, 10.5 miles away,  is bland and washed out.  You can’t see the fire tower on Kinton Knob.  The colors are cancelled by bad air.

This was a classic temperature inversion but the first time I was able to measure it.  As I drove to the hawk watch my car’s outdoor thermometer registered 43o in the Laurel Highland valleys and 57o on top of the mountain.  Normally the hawk watch site is far colder than anywhere else in western PA.

The weather was topsy-turvy.  Warm air aloft trapped cold air below and with it pollutants that made the air smell bad in the cold zones.

Bad air was not limited to cities and industrial zones.  On my way to the Allegheny Front I saw quite a few outdoor wood boilers creating thick white smoke that blanketed rural areas.  These relatively new devices burn wood in backyard sheds to heat water for radiators in homes.  Because outdoor wood boilers are small scale polluters they weren’t on the bad air radar at first, but their smoke is much worse than typical burning because the fire smolders when indoor heat demand is low.  I saw valleys where wood smoke enveloped nearby homes and neighbors.

At the hawk watch the air was nice and warm.

So when there’s an inversion, go to the mountain.

(photo by Kate St. John)

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