Category: Weather

Posted on

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

Posted on

Snow Pack Dynamics

Click for more information on Snow Layers. Graphic Courtesy Forest Service Avalanche Center www.fsavalanche.org
Snow Layers
Courtesy:
Forest Service Avalanche Center
Jim Conway, Graphic Artist
Formerly fsavalanche.org
See: https://avalanche.org/avalanche-encyclopedia/#snow-layer

Click for more information on Depth Hoar. Graphic Courtesy Forest Service Avalanche Center www.fsavalanche.orgDepth Hoar
Click to watch archived animation
Courtesy:
Forest Service Avalanche Center
Jim Conway, Graphic Artist
Formerly fsavalanche.org
See: https://avalanche.org/avalanche-encyclopedia/#depth-hoar-basal-facets

See Archived Avalanche Encyclopedia https://web.archive.org/web/20100312232112/http://www.avalanche.org/~uac/encyclopedia/

Water is our planet’s magical molecule, changing states faster than a presidential candidate. Snowpacks vaporize, ice melts and re-freezes, lakes evaporate, and cooled water vapor condenses back as clouds, snowflakes and hoarfrost. The muffled silence of the winter snowpack belies its dramatic pace of transformation.

In his book entitled “Life in the Cold”, author Peter Marchand explains the dynamic nature of the snowpack. Within a few hours after a snow storm, destructive metamorphism sets to work on the newly fallen snow. The delicate crystalline structure of each snowflake is quickly degraded. The intricate flakes transform to amorphous icy grains. Wind, warmth and compression accelerate destructive metamorphism, leaving a firmer, denser snowpack. At the surface, not only does snow strongly reflect the weak warmth of winter sunlight, but on a clear night, it radiates energy, greatly cooling the surface.

Meanwhile, the soil beneath the snowpack is typically warmer than the overlying snow, which is why springs can run all winter long. Three feet underground, soil temperature is within a few degrees of that location’s average annual air temperature. Sandwiched between the warm soil and the cold air, the blanket of snow is a great thermal insulator; fresh snow is the equal of fiberglass insulation. As a result, soil warmth transforms snow deep under the snowpack into water vapor. This moisture spreads through air spaces in the snowpack, following the thermal gradient to the chilly snow surface. As the moisture vacates the lower layers, a brittle porous layer develops in the snowpack. Termed “depth hoar”, it is weak, icy and prone to collapse. When the heavy overlying snowpack shifts, the crumbly depth hoar can release an avalanche, a powerful reminder of snowpack transformations for any backcountry traveler.

Come spring, every particle of Utah’s snowpack undertakes its final transformation. Some sublimates to waft away on warm springtime winds. Most of it melts away to feed the groundwater, springs and streams that give us cool relief on a hot summer day and provide the precious water that every Utahn depends on.

This is Linda Kervin for Bridgerland Audubon Society.

Credits:

Graphics: Courtesy Forest Service Avalanche Center, https://www.fsavalanche.org/
Text: Jim Cane, Bridgerland Audubon Society

Additional Reading:

Life in the Cold by Peter Marchand:https://www.upne.com/9619460.html

Forest Service National Avalanche Center, Avalanche Awareness Website: https://www.fsavalanche.org/

Depth Hoar: https://www.fsavalanche.org/encyclopedia/depth_hoar.htm

Utah Avalanche Center: https://utahavalanchecenter.org/

Posted on

Utah’s Changing Climate and Weather

Utah's Changing Climate and Weather: History of global surface temperature since 1880 Click to visit https://www.climate.gov/news-features/understanding-climate/climate-change-global-temperature and explore interactive graph. Courtesy NOAA Climate.gov
History of global surface temperature since 1880
Click to visit https://www.climate.gov/news-features/understanding-climate/climate-change-global-temperature and explore interactive graph.
Courtesy NOAA Climate.gov
Hi, this is Mark Larese-Casanova from the Utah Master Naturalist Program at Utah State University Extension.Utah’s Changing Climate and Weather

When I’m standing in line at the post office on a cold, snowy day, I inevitably hear someone make a sarcastic comment about global warming. The reality is, weather and climate are two distinctly different measures. Weather is the combination of current atmospheric conditions, such as temperature, humidity, precipitation, and wind. It changes from day to day, sometimes from minute to minute. It affects our choices of clothing each day, or whether we carry an umbrella.

Climate, however, is a prediction of future weather conditions based on data that have been collected during at least the past few decades. Climate can change as well, but this occurs more slowly over greater time scales. Climate determines which plants we can grow and how much we insulate our homes.

During the last 500 million years, the earth has experienced several different climates from very warm periods to ice ages. Between about one hundred thousand to ten thousand years ago, the planet was impacted by an Ice Age where 30% of the earth was covered by ice extending from the poles. During part of this time, much of Utah was covered by Lake Bonneville, and was home to several now-extinct mammals, such as mammoths, saber-toothed cats, and ground-sloths.

The modern era has also seen climatic changes. Ocean sediments and polar ice core data show that from 900-1300 A.D., the earth’s climate was warmer than normal. However, between about 1300-1900 A.D., the earth experienced a little ice age. Scientists believe this was caused by a combination of three major, natural events- less solar radiation reaching Earth, five major volcanic eruptions, and the disruption of ocean circulation due to melting polar ice caps.

Even though Utah has the second driest climate in the country, annual precipitation has actually increased 14% since the late 1800’s. Sounds great, right? Well, during this same time period, the average temperature has increased three degrees Fahrenheit. This means that more of Utah’s precipitation is falling as rain rather than snow. Because water is released from snowpack at a slower rate, we are provided with water throughout the year. If more of this water comes from rain, it could result in increased stream flow in winter and spring, but decreased stream flow in summer and fall. Furthermore, it is predicted that Utah will be faced with a reduction in snowpack upwards of 50% by the year 2085.

While those of us who enjoy winter sports might experience a gradually shortening ski season, less snowpack is likely to affect us all throughout the year. With Utah’s population expected to double around the year 2050, we’ll need to find creative solutions to an increased demand on water resources.

For Wild About Utah, I’m Mark Larese-Casanova.

Credits:
Utah’s Changing Climate and Weather
Images:
Text:     Mark Larese-Casanova, Utah Master Naturalist Program at Utah State University Extension.
Utah’s Changing Climate and Weather
Additional Reading:

Climate Change and Utah. 1998. US Environmental Protection Agency. EPA 236-F-98-007z. Available at: https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=40000PTI.PDF

Hotter Utah- Not All Bad? 2007. Deseret News. March 18, 2007. Available at: https://www.deseretnews.com/article/660204298/Hotter-Utah–not-all-bad.html

Global Warming: What about Water? 2006. Salt Lake Tribune. October 30, 2006. Available at: https://archive.sltrib.com/article.php?id=4149629&itype=NGPSID

Lindsey, Rebecca and Dahlman, LuAnn, Climate Change: Global Temperature, Climate.gov, NOAA,

Steenburgh, Jim, Wasatch Weather Weenies https://wasatchweatherweenies.blogspot.com/

Weatern Regional Headquarters, National Weather Service, National Oceanographic and Atmospheric Administration(NOAA) https://www.weather.gov/wrh/

Posted on

Wind, Hold on to Your Hat!

Graphical Forecasts – Central Rockies
NOAA National Weather Service
Western Regional Headquarters

Hi I’m Holly Strand.

On a recent camping trip on Utah’s Colorado Plateau, my brother and I were buffeted by strong sand-blasting winds for two days straight. Setting up camp was nearly impossible. Strong gusts ripped the tent away from us. Catching only the guylines, we flew the big green tent like a kite through the sagebrush. Eventually we pulled it down and got stakes in the ground. Unable to make a fire, we ate a cold dinner and tried to sleep –until the tent collapsed under the persistent onslaught of meteorological Furies. The next day, the sand-infused wind whipped us painfully as we descended into Horseshoe Canyon. Dust devils pursued us along the canyon floor.

Arriving home I read up on the cause of our discomfort. In simplest terms wind is caused by air moving from high to low pressure. The steeper the air pressure gradient—that is –the change in air pressure per unit distance–the stronger the resulting wind speed. Differences in air pressure are often caused by localized warming of air temperature. The warm air rises creating a spot of relatively low pressure ; then cooler air from a high pressure region rushes in to replace it.

Wind tends to blow much more forcefully near a frontal boundary. And our camp was located very close to the low pressure center of a stationary front. Although the wind was a nuisance, it was probably only blowing around 35 miles an hour. Meanwhile the record in Utah is 124 miles an hour –a wind gust measured at 11000 feet Snowbird. The strongest wind gust here in Logan was 94 miles an hour. Compare this to the highest wind on record anywhere—a gust measuring 253 miles per hour on Australia’s Barrow Island during a tropical cyclone. The record in the United States is 231 miles per hour on top of Mt. Washington in New Hampshire. Higher wind speeds than these may occur in tornadoes, but anemometers tend to malfunction at extreme speeds .

Luckily, we don’t have to worry much about tornadoes. Utah ranks very low in terms of tornado frequency. We average 2-33 a year with most of them occurring May through August. Utah tornadoes tend to be small and not last very long. Whirlwinds or dust devils are much more common. About 90% of them occur in the West Desert where there is plenty of loose, dry dust and sand to swirl around in the air.

Thanks to Marty Booth of the Utah Climate Center for help in developing this Wild About Utah episode.

For Wild About Utah, I’m Holly Strand.

Credits:

Photos: Courtesy US NOAA
Text: Holly Strand

Sources & Additional Reading:

National Weather Service (NOAA) “Dust Devils” https://www.wrh.noaa.gov/fgz/science/dustdvl.php?wfo=fgz [Accessed June 15, 2011]

National Weather Service (NOAA) Jetstream Online School for Weather. “Origin of Wind” https://www.srh.noaa.gov/srh/jetstream/synoptic/wind.htm [Accessed June 15, 2011]

National Weather Service (NOAA) Daily weather maps https://www.hpc.ncep.noaa.gov/dailywxmap/ [Accessed June 15, 2011]

Utah Climate Center https://climate.usurf.usu.edu/

Pope, Dan and Clayton Brough (eds.) Utah’s Weather and Climate. 1996. Salt Lake City: Publisher’s Press. https://www.amazon.com/Utah-Weather-Climate-D-Pope/dp/1567131743

https://www.photolib.noaa.gov