Category Archives: Weather & Sky

Winter Solstice

Winter solstice 2012: Noon sunrise on the Bering Sea (photo by Bering Land Bridge National Preserve on Flickr)

Winter Solstice: 21 December 2019

Today the sun will pause at 11:19pm Eastern Time and begin to move north again — or so it will seem to us earthbound humans.

The far north will be dark but not inky black everywhere. At Kotzebue, Alaska, 26 miles north of the Arctic Circle, the sun will rise at 12:56pm and set 1 hour and 43 minutes later, similar to the solstice photo above, taken at Bering Land Bridge NP. Kotzebue is the furthest north I’ve ever been though I didn’t get off the plane..

Scene from the plane at Kotzebue, Alaska on the day before the summer solstice, 2019 (photo by Kate St. John)

Here in the Lower 48 we’ll have lingering sunsets …

Sunset at Kelly Brook, Spruce, Wisconsin around the winter solstice (photo by Alan Wolf via Flickr Creative Commons license)

… and the days will get longer tomorrow.

Soon the birds will think about spring for reasons described in this vintage article: In Response To Daylight.

(photos by Bering Land Bridge National Preserve, Kate St. John, and Alan Wolf on Flickr, Creative Commons licenses; click on the captions to see the originals)

Penitent Snow

On top of the world at Chajnantor Plateau, Chile. Penitente in the foreground (cropped photo from Wikimedia Commons)

If you don’t like snow, here’s some that you’ll never see in Pittsburgh.

These snow formations, called penitente, are found at elevations above 13,000 feet in the Dry Andes of Chile and Argentina. They form when the snow vaporizes — directly from solid to gas — in the cold dry wind. A feedback loop of sublimation and ablation creates snow peaks as tall as 16 feet.

Penitentes at the southern end of the Chajnantor plain (photo from Wikimedia Commons)

Penitente are named for their resemblance to kneeling penitents or the hoods worn during Spanish Holy Week. They even resemble this statue of Saint Bernadette at the grotto at Nevers.

Grotto at Nevers, France (photo from Wikimedia Commons)

Sometimes a snow field will reach across the road …

Snow field of penitentes (photo from Wikimedia Commons)

… so people get out of their cars to look at it. This one is at Agua Negra Pass on the border of Chile and Argentina, elevation 15,682 ft.

Penitentes at Paso de Agua Negra, Argentina, elev. 15,680 ft (photo from Wikimedia Commons)

The “penitent” snow creates an otherworldly scene. Click on the photo below for a panoramic view at night.

Planetary Analogue: Penitente on a starry night in the Atacama desert (photo from Wikimedia Commons)

(photos from Wikimedia Commons; click on the captions to see the originals)

Danger! Space Junk

Last month I wrote about the damage that bad space weather can do to satellites, the electric grid, radio and TV transmissions, and GPS navigation. Though space weather can kill a satellite(*) bad weather is temporary. Not so with space junk.

Since 1957 when the Space Age began, our unused equipment has created a garbage patch in outer space. Over the years we’ve launched 5,000+ satellites though only 1,300 are operational today. There’s a lot of junk up there that’s out of control (can’t be navigated anymore) and potentially explosive.

screenshot of space junk explosion from PBS Be Smart

Even if it can’t explode, space junk is dangerous to active satellites because it travels so fast. In Low Earth Orbit, where the International Space Station lives, everything travels at 17,500 miles per hour (28,000 km/hour). A crash at that speed, even with a tiny object, can destroy a satellite. When a satellite dies something electronic fails here on Earth.

Meanwhile we’re launching more satellites every year at a faster pace than before. At the end of 2018 it had taken a decade to launch 1,000 CubeSat nano-satellites, only four-inches across, but there are plans to add 1,000 more by 2021. Outer space is so crowded that NASA and the European Space Agency (ESA) work every day to steer satellites away from dangerous space debris.

The 2016 video above describes space junk and how we’ve coped with it so far. Note that it doesn’t talk about CubeSats because the video predates those plans.

ESA’s 2017 video below describes the problem in technical terms with dramatic background music. I’ve cued the video to start at Low Earth Orbit. Watch for two minutes (beyond the first fade-to-black) and you’ll see lots of collisions.

Yow! It’s crowded up there.

(videos from PBS It’s OK To Be Smart and the European Space Agency (ESA) on YouTube)

(*) Space weather killed Telstar 401 in 1997.

Angry Storm On Saturn

Saturn’s north polar vortex storm (photo from Wikimedia Commons)

This month a KDKA viewer saw unusual clouds like breaking waves in the sky as he was traveling on the Turnpike to Philadelphia.

Our planet isn’t the only one that has these clouds. This photo of Saturn’s north polar vortex shows Kelvin-Helmholtz clouds on the spinning edge. Photographed by the Cassini spacecraft in April 2013 and colorized by NASA, this image is called The Rose but is actually a violent, relentless storm. And it’s big!

According to the Cassini Mission at NASA, “Measurements have sized the eye at a staggering 1,250 miles (2,000 kilometers) across with cloud speeds as fast as 330 miles per hour (150 meters per second).”

Our own polar vortex is mild by comparison.

(photo from NASA via Wikimedia Commons; click on the caption to see the original)

Space Weather Coming Up

Aurora 3-day forecast, northern hemisphere, 11/21/2019 10pm EST to 11/22/2019, 1am EST (screenshot from NOAA Space Weather Prediction Center)

There’s a storm warning for Thursday and Friday and it’s coming from outer space. NOAA’s Space Weather Prediction Center reports:

G1 (Minor) geomagnetic storms are expected on 21-22 November 2019 due to positive polarity coronal hole high speed stream influence.

SWPC NOAA Space Weather Advisory, 19 Nov 2019

In other words, there’s a potential for mild auroras and minor electrical and magnetic disruptions this week because the solar wind (“high speed stream influence”) is going to blow hard past the Earth — but not so hard that it breaks things.

The solar wind originates from the Sun’s corona, the glowing atmosphere you see behind the moon during solar eclipses. Because the corona is fluid, it develops thin spots called coronal holes that emit the Sun’s magnetic field and charged particles. Usually the particles loop out and back into the Sun (animation below) but those that don’t return come roaring off the Sun in a solar wind that travels as fast as 500 miles/second.

Conceptual animation (not to scale) showing the Sun’s corona and solar wind. Image credit: NASA’s Goddard Space Flight Center/Lisa Poje (from NASA’s SpacePlace)

The Earth’s magnetic field shields us from the solar wind but its force distorts the shield (shown in blue below). Sometimes electromagnetic particles seep into our atmosphere and cause geomagnetic storms known as space weather.

Strong solar wind distorts Earth’s magnetic field (image from NASA Spaceplace)

Space weather messes with electronics on our satellites and increases their orbital drag. Really bad space weather — from solar flares and coronal mass ejections — disrupts our electric grid, our high frequency radio communications, and the accuracy of GPS navigation.

None of this is good so NOAA teamed up with USGS to issue a weekly Space Weather Advisory and a real time map that shows space weather’s effect in the continental U.S. Electric power grid operators use the mapping tool to prepare their infrastructure.

Sample map of Geoelectric field disruption from NOAA-USGS Space Weather Prediction Center

Space weather causes trouble but it has one very beautiful effect. When the particles follow Earth’s magnetic field lines down to the poles they create auroras that are visible during winter darkness. Here’s a stunning one at Bear Lake, Alaska in 2005.

Aurora borealis over Bear Lake, Alaska (photo from Wikimedia Commons)

Fortunately this week’s space weather will be very minor, but so will the accompanying aurora. The northern lights won’t be intense nor will they be visible in the Lower 48 states.

Check NOAA’s weekly space weather forecast on Monday afternoons to see what’s coming up. Watch their 3-day aurora forecast (or 30-minute forecast) for predictions of beauty in the sky.

(images from NOAA Space Weather Prediction Center, NASA’s SpacePlace and Wikimedia Commons; click on the captions to see the originals)

Nacreous Clouds

Nacreous clouds at Lake Mjosa, Norway (photo from Wikimedia Commons)

Near the poles in winter there are sometimes pearly-looking clouds glowing high above the Earth.

Polar stratospheric clouds (PSCs), also called nacreous clouds for their pearly appearance, form in the lower stratosphere at 49,000 to 82,000 feet — 1.5 to 2.6 times higher than a jet. They’re a winter phenomenon because they only form in the presence of super low temperatures, minus 108oF and colder.

Here you can see that they’re high above our usual clouds.

Nacreous clouds can cause trouble. Those made of water are benign but some are made of nitric acid + water that reacts with ozone in the stratosphere and creates a hole in the ozone layer. Stratospheric ozone protects Earth from the sun’s ultraviolet rays. It’s bad to have a hole in it!

Though we’ll never see these pearly clouds in Pittsburgh, we can appreciate their beauty from afar.

Polar Stratospheric Clouds over Scotland (photo from Wikimedia Commons)

p.s. The irony of ozone: Ground level ozone is bad; it burns plants and our lungs. Stratospheric ozone is good; it protects us from ultraviolet light. Ozone’s value depends on where it is.

Breaking Waves In The Sky

Kelvin-Helmholtz clouds in Wales (photo from Wikimedia Commons)

Have you ever seen breaking waves in the sky?

These unusual clouds are called fluctus or Kelvin-Helmholtz clouds. They occur when Kelvin-Helmholtz instability is present in the atmosphere, caused by a difference in temperature and wind. The air below the clouds is moving slowly, the air above them is moving fast. Since it’s an unstable condition, the clouds soon disappear.

Kelvin-Helmholtz instability creates fluctus clouds (photo from Wikimedia Commons)

Last summer Kelvin-Helmholtz clouds appeared over Smith Mountain Lake, Virginia on 18 June 2019. Meteorologist Chris Michaels at WSLS 10 News explains them in the video below.

Visit this vintage blog, Making Waves, for a video that shows what happens when the waves break.

(photos from Wikimedia Commons; click on the caption to see the original. Video embedded from WSLS TV)

How To Get Happy When Skies Are Gray

Fields of rapeseed on a cloudy day in France (photo from Wikimedia Commons)

Today in Pittsburgh it’s “cloudy” but a better description would be gloomy. Gray skies are depressing. How can we cope? Let’s look at yellow.

In an ongoing international survey (6,625 people in 55 countries to date) participants are asked, “What emotions do colors represent?” The data shows that most people say yellow is joyful but this isn’t true worldwide. It’s very joyful in the United States, exceptionally joyful in Finland, but in desert regions it’s not.

Researchers led by Domicele Jonauskaite at University of Lausanne, wondered if the attitude toward yellow was cultural or environmental: “What if people’s physical surroundings affect their feelings about certain colors?” They mapped the data here. (Darkest means the greatest yellow-joy; see Finland, Iceland, New Zealand.)

Likelihood of yellow-joy association (map from Science Direct, The Sun Is No Fun Without Rain)

They found that environment and cloud cover matter. The sun is not your friend in hot, dry, cloudless places. The study aptly named itself, “The sun is no fun without rain.”

Finland loves yellow. I think I know why. The first time I saw an intense field of yellow, like the one shown at top, was in Finland. I made my friends stop the car. So yellow! So happy! What is this plant? Rapeseed!

Rapeseed (Brassica napus) is the crop that makes canola oil.

Rapeseed in bloom (photo from Wikimedia Commons)

We don’t grow rapeseed in Pittsburgh, but I found a joyful yellow patch of chrysanthemums at the corner of Forbes Avenue and South Bouquet Street.

Go find some yellow and get happy.

(rapeseed photos from Wikimedia Commons; click on the captions to see the originals. Chrysanthemums by Kate St. John)

Which Personality Survives Bad Storms?

Comb-footed spider in the Everglades (photo from Wikimedia Commons)

Comb-footed spiders (Anelosimus studiosus) have a lot of personality. These social cobweb spiders live in colonies of 40-100 individuals, build their webs around branches, and hunt cooperatively to capture large prey.

The spiders exhibit either aggressive or docile personalities. If you know what to look for you can tell the difference. In the evening aggressive A.studiosus attack each other and then retire to opposite corners of the web; docile spiders rest side by side. Aggressive spiders come out to attack when their web is disturbed, the docile ones stay inside.

What happens to these spiders when they’re hit by a tropical storm or hurricane? Is there a difference in which spiders survive?

A 2018 study led by Jonathan Pruitt of U.C. Santa Barbara tracked 240 Anelosimus studiosus colonies in seven states including Florida, Alabama and the Carolinas. For baseline data they recorded the locations and personalities of the spider colonies. Later they searched for spider webs after a tropical storm or hurricane had passed.

You might think it’s futile to look for cobwebs after hurricanes, but individual spiders do survive, stay on their home territory, and rebuild. While humans are picking up the pieces, the spiders are too.

Damage from Hurricane Michael, 2018 (photo from Wikimedia Commons)

The study found that the storms always wiped out the docile spiders but the aggressive ones survived.

The relentless pressure of weather and nature is changing the spider population. Among comb-footed spiders, only the strong personalities survive.

For more information see Science Magazine: “Tropical storms are making these spiders more aggressive” and “For spiders, it’s cruel to be kind

UPDATE 31 JAN 2020: Is this research true? The work of biologist Jonathan Pruitt is being called into question: Spider biologist denies suspicions of widespread data fraud in his animal personality research

(photos from Wikimedia Commons; click on the captions to see the originals)

Morning Glories Roll In

Morning glory clouds, Gulf of Carpentaria, Australia (photo from Wikimedia Commons)

These jelly roll clouds, called morning glories, are so rare that the only reliable place to find them is at the Gulf of Carpentaria during Australia’s spring, August to November. They form there because of Cape York Peninsula’s shape and orientation to the wind.

Map of Gulf of Carpentaria, Australia (from Wikimedia Commons)

In photographs from above these clouds look peaceful. From the ground they are awe-inspiring, rolling across the landscape on their horizontal axis as shown in this video from Leelanau State Park, Michigan in 2016.

Morning glory clouds are extremely rare in the U.S. but I have an idea why one formed at Grand Traverse Bay. Notice the shape and orientation of the Leelanau Peninsula. It’s like Cape York on a smaller scale.

Location of Leelanau State Park, Michigan (screenshot from Google maps)

Read more about morning glories and why glider pilots love them in this vintage article: Morning Glory.

(photo and Gulf of Carpentaria map from Wikimedia Commons, video by Chad Bousamra on YouTube, Michigan map screenshot from Google Maps; click on the captions to see the originals)