Category: Weather

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The Smell of Rain

Electron micrograph showing
the filamentous structure of
actinomycetes
Photo Courtesy:
Soil Science Society of America

Spring is my favorite season. I love watching our landscape turn from brown to green, the first butterfly sighting, and the rain. During a recent April shower, I stepped outside and inhaled that magical springtime scent – the smell of rain. Which got me thinking – what is that smell, anyway?

What seems like a simple question, begs a complicated answer. That smell, however, does have a name – petrichor – and there are many things that contribute to its scent. One of the biggest culprits may actually be soil bacteria – mostly from the genus actinomycetes – which grow in unfathomable concentrations in soils all around the world. These bacteria play an important role in decomposition and soil health. Periods of relative dryness trigger their reproductive cycle, causing the production of spores, which are considerably more drought-tolerant. When rain finally does fall, the spores are launched into the air, where they may eventually reach our nose. Scientists have identified the chemical compound responsible for the spore’s odor and have named it geosmin, which literally translates to ‘earth smell.’

Humans noses are particularly sensitive to geosmin, but we’re not the only ones. Camels, too, are sensitive to its smell and some scientists believe this helps them find oases in the desert. Our ability to detect this odor might be a throwback to our nomadic ancestors for whom finding water in a vast landscape was of utmost importance.

But the scent trail doesn’t end with geosmin. The chemical compound ozone may also be a part of petrichor especially after a thunderstorm, as ozone is produced by lightning. Another aroma is provided by chemicals called volatile oils which are produced by all plants, and which collect on the ground during dry periods. With rain, they evaporate into the air, contributing to the musty, earthy odor. Acidic rain has also been shown to create scents by reacting with chemicals on the ground such as spilled gasoline. And further complicating the matter is the fact that rain hitting the earth throws dust and other particles from countless sources into the air.

If all of these smells are around us all the time, why is it that they are distinctly associated with rain? The answer lies in the properties of odors and how they travel. Everything that produces a scent is releasing chemical compounds into the air. The ability to evaporate – or volatility – of these compounds increases with the heat and moisture levels of the air around them. The humid air that produces rain creates ideal conditions for conveying scents to our noses.

In the end, it’s not the rain itself that causes odor, but the interaction of water and a number of chemical and organic compounds. Test this theory at home by throwing a bucket of water on the lawn or a hot driveway to see if you can recreate the smell of rain. Likewise, smell a stick, leaf, or rock when it is dry, then wet it and see how the odor changes. For those seeking answers to the origins of the smell of rain, it’s often best to follow your nose.

Thank you to the Rocky Mountain Power Foundation for supporting the research and development of this topic.

For the Stokes Nature Center and Wild About Utah, this is Andrea Liberatore.

Credits:
Images: Photo Courtesy Soil Science Society of America
Text:     Andrea Liberatore, Stokes Nature Center in Logan Canyon.
Special thanks to Joel Martin from the Utah Climate Center
Additional Reading:

National Public Radio (2007) The Sweet Smell of Rain. All Things Considered, August 11 2007. Interview of Dr. Charles Wysocki by Debbie Elliott. Transcript available online at: https://www.npr.org/templates/story/story.php?storyId=12716163

Gerritsen, V.B. (2003) The Earth’s Perfume. Protein Spotlight, Issue 35. Accessible online at: https://web.expasy.org/spotlight/back_issues/035/

Gerber, N.N, and Lechevalier, H. A., (1965) Geosmin, an Earthy-Smelling Substance Isolated from Actinomycetes. Applied Microbiology. 13,6. Accessible online at:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1058374/pdf/applmicro00362-0105.pdf

Live Worldwide Network for Lightning and Thunderstorms in Real Time, Blitzortung, https://en.blitzortung.org/live_lightning_maps.php?map=30

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Snowflakes

A free-falling snow crystal photographed as it fell on Alta Ski Area on March 6, 2011, Photo Courtesy & Copyright Tim Garrett, University of Utah
A free-falling snow crystal
photographed as it fell
Alta Ski Area on March 6, 2011
Photo Courtesy & Copyright 2011
Tim Garrett, University of Utah
Alta Snowflake Showcase

Snowflake, Photo Courtesy and Copyright A free-falling snow crystal
photographed as it fell
Alta Ski Area
March 6, 2011
Photo Courtesy & Copyright 2011
Tim Garrett, University of Utah
Alta Snowflake Showcase

A stellar dendrite snow crystal, Photo Courtesy and Copyright Kenneth Libbrecht, Caltech University, SnowCrystals.com A stellar dendrite snow crystal Photo Courtesy & Copyright
Kenneth Libbrecht, Caltech University
SnowCrystals.com

A stellar dendrite snow crystal, Photo Courtesy and Copyright Kenneth Libbrecht, Caltech University, SnowCrystals.com A stellar dendrite snow crystal Photo Courtesy & Copyright
Kenneth Libbrecht, Caltech University
SnowCrystals.com

A hexagonal plate snow crystal, Photo Courtesy and Copyright Kenneth Libbrecht, Caltech University, SnowCrystals.com A hexagonal plate snow crystal Photo Courtesy & Copyright
Kenneth Libbrecht, Caltech University
SnowCrystals.com

As winter draws to a close, I’d like to take a moment to reflect on the amazing weather phenomenon that is a snowflake. When winter weather dumps inches of snow on us, it’s easy to overlook the tiny works of art, those intricate and delicate snowflakes, which make up the storm.

Snowflakes – or to use a more scientific term, snow crystals – come in a variety of different shapes including long, thin needles, flat hexagonal plates, columns, and irregularly-shaped pellets called graupel. The International Snow Classification System recognizes ten different shapes in all, only one of which is the traditional snowflake image. The classic six-armed snowflake shape is called a ‘stellar dendrite’ by scientists.

When teaching programs about snow, someone inevitably asks me, “Is it really true that no two snowflakes are alike?” As far as I can tell, the answer is, well, ‘maybe’, and here’s why.

Three things are needed to form these intricate crystals, and the first two are fairly obvious: water, and temperatures below freezing. The third item is a little more inconspicuous. Water cannot condense and freeze all on its own. Every snowflake needs a piece of atmospheric dust or salt at its core. This particle is referred to as a ‘nucleating agent,’ and it attracts water molecules which then condense and begin to freeze. From there, a snowflake’s overall shape is determined by a number of other variables including the atmospheric temperature, the amount of available moisture, wind speed, and mid-air collisions with other snowflakes.

To add more complexity, consider that each individual snowflake contains somewhere on the order of 10 quintillion water molecules. That’s ten with eighteen zeros behind it. While the way these molecules bind to each other is dictated by the laws of physics, the sheer number of ways in which 10 quintillion water molecules can arrange themselves as they freeze into place is mind boggling. But then again, how many snowflakes do you think fall in the typical March snowstorm in Utah? A lot. One scientist has estimated that the number of individual snowflakes that have fallen on Earth in the planet’s history is ten with 34 zeros behind it. In all of those snowflakes is it possible that two are exactly alike? Yeah, maybe… but good luck finding them!

For more information and some beautiful snowflake photographs, please visit our website at www.wildaboututah.org. Thank you to the Rocky Mountain Power Foundation for supporting the research and development of this Wild About Utah topic.

For the Stokes Nature Center and Wild About Utah, this is Andrea Liberatore.

Credits:

Photos: Courtesy Tim Garrett, University of Utah,
Kenneth Libbrecht, Caltech University
Text: Andrea Liberatore, Stokes Nature Center

Additional Reading:

Halfpenny, J.C and Ozanne, R.D. 1989. Winter: An Ecological Handbook. Boulder, CO: Johnson Books, https://www.amazon.com/Winter-Ecological-Handbook-James-Halfpenny/dp/1555660363

Gosnell, Mariana. 2007. Ice: the Nature, the History, and the Uses of an Astonishing Substance. Chicago, IL: The University of Chicago Press, https://www.amazon.com/Ice-Nature-History-Astonishing-Substance/dp/0679426086

Libbrecht, Kenneth .1999. A Snowflake Primer: the basic facts about snowflakes and snow crystals. https://www.its.caltech.edu/~atomic/snowcrystals/primer
/primer.htm

 

 

 

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Best Snow

Skier at Brian Head
Photo Courtesy USDA Forest Service

As the mountains begin to take on hues of scarlet, gold and russet, many Utahns might be looking eagerly toward the coming months when those slopes will be blanketed in white. The Utah ski industry nurtures a whopping annual income of about $800 million dollars. It’s no surprise, therefore, that the state claims to have the “greatest snow on earth.” In fact, the state of Utah managed to make their slogan a federal trademark in 1995 after winning a lawsuit brought by the Ringling Brothers and Barnum & Bailey circus group, who felt the catchy marketing phrase might be confused with their slogan, the Greatest Show on Earth.

The trademark must have worked, because Utah draws so many visitors to its slopes, it racks up about 4 million skier days annually. But disregard plenty of evidence that we do indeed draw a crowd, and the statement is pretty subjective. So what’s the science behind our legendary powder?

The ideal condition skiers hope for is a deep, fluffy snow that creates the illusion of bottomless powder. And finding it is a bit like the Goldilocks story. Too wet, and you bog down. Too dry, and there’s not enough body to create a floating sensation beneath the ski. If the terrain is too steep, the powder won’t stick. And if it’s not steep enough, you can’t build sufficient momentum to glide over the top.

To get to the bottom of why Utah’s snow is just right, we actually have to look even further westward, toward the slow warm waters of the North Pacific current. As water laden clouds move inland, snow first falls over the Cascades in the north and the Sierra Nevadas further south, with an average moisture content of 12%. Even in areas like Washington’s Mt. Baker, where annual snowfall comes in greater quantities than Utah, the moister maritime snow creates a heavy base that bogs down skis. By the time these winter storms cross the Great Basin and reach the skiers’ Mecca of Alta and the Wasatch Range, the moisture content will have decreased to about 8.5%. And that seems to be the sweet spot. The moisture content of Utah’s intermountain snow is just enough that powder from our first storms settles into a soft but voluminous base. As winter progresses, fresh snow falls in a cold and mostly arid environment, forming very fine, symmetrical crystals called dendrites. The microscopic structure of dendrites allows them to accumulate in well ventilated, incompact drifts, much like the puffy down in your favorite pillow or ski jacket.

And perfect powder isn’t the only advantage Utah’s ski resorts have over their neighbors. Our mountainous topography, with its wealth of winding canyons, means we have an abundance of slopes well protected from strong winds which could compact or carry away fresh snowfall. And while so many cold and overcast days might get you down, it also protects our top powder from radiation and air mass effect, which can create a crust along the surface. And that means our freshly fallen powder sticks around for longer.

So consider that Utah offers 26,000 acres of mountain, blanketed in more than 500 annual inches of perfect intermountain snow, and it’s no wonder we enjoy 5 times the number of “powder days” as our neighbors. “The Greatest Snow on Earth” starts sounding a lot less subjective, and more like truth. In fact, you just might be tempted to make like Goldilocks and make yourself at home.

For Wild About Utah and Stokes Nature Center, I’m Ru Mahoney.

Credits:
Image: Courtesy USDA Forest Service, fs.usda.gov
Text:     Ru Mahoney, Stokes Nature Center in Logan Canyon.


Additional Reading:

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Wind and Sagebrush

Wind and Sagebrush

Wind and Sagebrush: Mountain big sagebrush (Artemisia tridentata subsp. Vaseyana) in flower - Photo Courtesy and Copyright Dr. Leila Shultz
Mountain big sagebrush (Artemisia tridentata subsp. Vaseyana) in flower – Photo Courtesy and Copyright Dr. Leila Shultz

Wind and Sagebrush:Three-tip sage (Artemisia tripartite) with visible yellow flowers. - Photo Courtesy and Copyright Dr. Leila ShultzThree-tip sage (Artemisia tripartite) with visible yellow flowers. – Photo Courtesy and Copyright Dr. Leila Shultz

Hi, I’m Holly Strand of the Quinney College of Natural Resources at Utah State University.

By late summer, most of Utah’s flowering plants have fizzled out for the year—those that remain are looking pretty spent. But not true for the sagebrush. It’s show time for over 20 types of sagebrush of the Intermountain West.

Like grasses and conifers, sagebrush plants are pollinated by the wind. They have no need for the specialized traits designed to attract live pollinators. Instead, they have evolved other strategies to survive and multiply.

For instance, wind-pollinated plants don’t need showy, colorful petals to attract insects or birds. The wind is going to do its job anyway regardless of visual cues. Thus sagebrush flowers are very small and nondescript. In fact, when passing by flowering sagebrush you might not even notice that it’s in bloom. Look for long spikes with clusters of tiny flower heads. The pale yellow flowers are concealed by petal-like bracts, which are the very same color as the rest of the plant.

While the flowers of sagebrush lack in beauty, they make up in quantity. A single flowering stem of the most common sagebrush—known simply as big sagebrush–can hold hundreds of flower heads that produce a massive amount of pollen. Most wind-blown pollen grains won’t end up anywhere near the female part of another plant. So to make up for this risky method of fertilization, individual plants must produce greater volumes of pollen. In contrast, plants with live pollinators get door to door service during fertilization. Far less pollen is needed to get the same job done.

Scent is another way for plants to attract live pollinators. Species pollinated by bees and flies have sweet scents, whereas those pollinated by beetles have strong musty, spicy, or fruity odors. However, the iconic western scent of the sagebrush has absolutely nothing to do with pollination. Instead, the pungent aroma of the sagebrush is a by-product of certain chemicals produced in the leaves. These chemicals evolved to repel animals and to reduce the odds of being eaten or grazed.

The chemicals—bitter terpenes, camphors and other secondary compounds–—peak in early spring. But as the late-summer flowering period approaches, the chemicals start to break down. By winter, browsers like deer and elk can nibble on the protein-rich seed heads without getting a nasty aftertaste.

Thanks to botanist Leila Shultz for sharing her knowledge of sagebrush. For a link to the online version of Leila’s book Pocket Guide to Sagebrush, go to www.wildaboututah.org
If you’d like a hard copy of this Pocket Guide, send an email to wildaboututah@gmail.com We have 5 copies to give away to listeners from across the state.

For Wild About Utah and the Quinney College of Natural Resources, I’m Holly Strand.

NOTE: The copies are gone. You can view the book as a .pdf here or check here for the next printing from https://www.sagestep.org/pubs/brushguide.html.

Credits:

Photo Courtesy & Copyright 2007 Dr. Leila Shultz
Text: Holly Strand, Quinney College of Natural Resources at Utah State University

Additional Reading:

Dudareva, Natalia. 2005. Why do flowers have scents? Scientific American April 18. https://www.scientificamerican.com/article/why-do-flowers-have-scent/

Shultz, Leila. 2012. Pocket Guide to Sagebrush. PRBO Conservation Science. https://digitalcommons.usu.edu/sagestep_reports/20/
As pdf: https://rdjzr2agvvkijm6n3b66365n-wpengine.netdna-ssl.com/wp-content/uploads/2018/06/sagebrush_pock_guide_reduced.pdf

Shultz, L. M. 2006. The Genus Artemisia (Asteraceae: Anthemideae). In The Flora of North America north of Mexico, vol. 19: Asterales, pp. 503–534. Flora of North America Editorial Committee, eds. Oxford University Press. New York and Oxford.

USDA, NRCS. 2012. The PLANTS Database, National Plant Data Team, United States Department of Agriculture (USDA), Natural Resource Conservation Service (NRCS): https://www.plants.usda.gov

VanBuren, R., J. C. Cooper, L. M. Shultz and K. T. Harper. 2011. Woody Plants of Utah. Utah State University Press & Univ. Colorado. 513 pp. https://upcolorado.com/utah-state-university-press/item/2323-woody-plants-of-utah