Winter Ecology Notes Winter Ecology Notes Frost, Snow, and IceFrost, Snow, and Ice

THIS STREAM IS ACTUALLY A TEAR IN THE SOIL FROM THE FROST EXPANSION IN 2003

In order for it to snow, there has to be enough In order for it to snow, there has to be enough moisture in the air, and it has to be below 32° F (0° moisture in the air, and it has to be below 32° F (0° C). If the air is warmer, it will rain or sleet instead. C). If the air is warmer, it will rain or sleet instead. Snow is basically frozen water, but it freezes in the Snow is basically frozen water, but it freezes in the air in very tiny droplets, which makes crystals. air in very tiny droplets, which makes crystals. There is a lot of air in snow, which means it is much There is a lot of air in snow, which means it is much lighter than water or ice. Sometimes there are lighter than water or ice. Sometimes there are bigger snowflakes because the tiny droplets stick bigger snowflakes because the tiny droplets stick together before they fall. If the air in the upper together before they fall. If the air in the upper atmosphere is above 32° and the air nearer the atmosphere is above 32° and the air nearer the ground is below 32°, the droplets may start as rain ground is below 32°, the droplets may start as rain but freeze as they fall into the colder air. This but freeze as they fall into the colder air. This makes sleet. makes sleet.

History can forgive fellows like Tyndall and Bentley for passing off thenucleation process as heavenly hocus-pocus. That they couldn't explain this process is not surprising. Those necks of dust and ash at the heart of every snow crystal are rather petite. Today's snow scientists can tell you that the big ones top out at around one micron—roughly the diameter of a flea's nose hair. Most nuclei are about a tenth that size. Thanks to electron microscopes, scientists can tell you that the main source of these nuclei is clay-rich dust kicked up from the earth's surface. Air pollutants come in a close second, with the balance provided by forest fires, volcanoes, bits of plant matter, wisps of sea salt, a carousel of microorganisms, and the occasional flotsam and jet-sam that sails in from outer space. They can tell you at what temperature and moisture level cloud droplets, or water vapor, will glom onto these nuclei. They can even predict that in every cubic meter (1.3 cubic yards) of the lower atmosphere, where snow forms, you will find anywhere from several hundred to many thousands of aerosol particles floating around up there, just waiting to kick up a snowstorm.

Falling for Snow, Jamie Bastedo, Red Deer Press, Canada, 2003.

CRYSYS - CRYosphere SYStem in CRYSYS - CRYosphere SYStem in CanadaCanada

- source of photos/information- source of photos/information

Snow crystals

Stellar dendrite

Sectored plates

Hollow Column

Needles

Spatial dendrite

Capped columns

Rimed snowflake

Elevation and precipitationElevation and precipitation

Snowrollers are molded by strong, gusty surface winds. They look like a rolled-up carpet or small muff and are often hollow. They can be as small as a golf-ball or as large as a 30-gallon drum,.but usually snowrollers are

about 10-12 inches in diameter and a foot wide. Snowrollers appear in open fields under specific weather conditions,

often present following the passage of a strong winter storm. First, the ground surface must have an icy, crusty snow, on which new

falling snow cannot stick. On top of this, about an inch of loose, wet snow, the sticky kind that

makes good snowballs, must accumulate. The optimum air temperature appears to be around freezing, from 28 to 34 F.

Finally, a gusty and strong wind, usually 25 mph or higher, is needed to build the snowroller.

Snowroller formation begins when the wind scoops chunks of snow out of the snowfield, they roll, bounce and tumble, like snowy tumbleweeds,

downwind. Additional snow then adheres to this seed, and the snowroller grows until it finally becomes too large for the wind to push, leaving

behind a characteristic track linking the snowroller's origin to its final resting spot.

By Bryan Yeaton

Snow Rollers

Under clear frosty nights in winter soft ice crystals might form on vegetation or any object that has been chil led below freezing point by radiat ion cooling. This deposit of ice crystals is known as hoar frost and may sometimes be so thick that i t might look l ike snow. The interlocking ice crystals become attached to branches of trees, leafs, hedgerows and grass blades and are one of the most prominent features of a typical 'winter wonderland' day. However, the f ine ' feathers' , 'needles' and 'spines' might also be found on any other object that is exposed to supersaturated air below freezing temperature.

Rime snow – wind sculpted

Rime ice – fog ice

Rime Ice – is essential ly frozen fog. Super-cooled water droplets which are suspended in clouds when temperatures dip below

freezing, wil l freeze instantly when they contact anything solid, such as

a building, road sign, etc.

Hoar frost must not be confused with r ime, which derives from

freezing fog or glaze which forms as a continuos thick layer of ice, rather

than individual frozen droplets.

Hoar FrostHoar Frost

The relat ive humidity in supersaturated air is greater then 100% and the formation of hoar frost is similar to the formation of dew with the difference that the temperature of the object on which the hoar frost forms is well below 0°C, whereas this is not the case with dew. Hoar frost crystals often form intitially on the tips of plants or other objects.

Silver FrostSilver Frost

Hoar frost might form as liquid dew that has Hoar frost might form as liquid dew that has subsequently frozen with a drop in temperature, which is subsequently frozen with a drop in temperature, which is then known as silver frost or white frost. Usually the dew then known as silver frost or white frost. Usually the dew drops do not freeze immediately, even if the air drops do not freeze immediately, even if the air temperature is slightly below zero. Rather they become temperature is slightly below zero. Rather they become supercooledsupercooled dew droplets at first. Supercooled dew will dew droplets at first. Supercooled dew will eventually freeze if the temperature falls below about eventually freeze if the temperature falls below about -3°C to -5°C. Hoar frost deposits might also derive by -3°C to -5°C. Hoar frost deposits might also derive by sublimation, when water vapour is forming ice directly on sublimation, when water vapour is forming ice directly on the surfaces concerned. In most cases hoar frost will the surfaces concerned. In most cases hoar frost will have formed by a combination of the processes above. have formed by a combination of the processes above.

Icicles

Ice cave - Apostles

Ice curtainIce curtains

Icicle formationIcicle formation

When the snowmelt flows When the snowmelt flows down the roof, the competition down the roof, the competition between gravity — pulling the between gravity — pulling the water downward — and water downward — and surface tension — trying to surface tension — trying to keep the water flow flat — keep the water flow flat — leads to the formation of leads to the formation of evenly-spaced ripples along evenly-spaced ripples along the flow front. These ripples the flow front. These ripples will freeze when and where the will freeze when and where the surface temperature dips surface temperature dips below 0oC (32oF), and the below 0oC (32oF), and the frozen ripples become the frozen ripples become the icicle roots. icicle roots.

Ridge formationRidge formationAfter a period of continuous After a period of continuous growth, icicles display prominent growth, icicles display prominent horizontal ribbing which encircles horizontal ribbing which encircles the icicle to form a series of the icicle to form a series of progressively smaller rings toward progressively smaller rings toward the tip. Each ring is separated the tip. Each ring is separated from those surrounding it by from those surrounding it by shallow constrictions in the ice. shallow constrictions in the ice. Typically, rings extend outward Typically, rings extend outward less than a centimeter (half an less than a centimeter (half an inch). During active icicle growth, inch). During active icicle growth, the rings are initially composed of the rings are initially composed of fragile, thin ice plates growing fragile, thin ice plates growing randomly outward, but the spaces randomly outward, but the spaces between them are soon filled with between them are soon filled with downward flowing melt water. downward flowing melt water.

The tip of a growing icicle is primarily The tip of a growing icicle is primarily liquid water with a pendent drop on the liquid water with a pendent drop on the

tip end.tip end.

Spin drift

Sastrugi

Sastrugi and frost flowers

Frost flowers

Frost flowers on ice

Fern frostFern frost

The mystery circle

What happens to all that snow? What happens to all that snow? It piles up, gradually It piles up, gradually compressing in compressing in firn,firn, a kind of a kind of limbo state for crystals in limbo state for crystals in transition from snow to glacial k transition from snow to glacial k In its youthful phase, firn is In its youthful phase, firn is nothing more than a mass of nothing more than a mass of BB-sized blobs ice riddled with BB-sized blobs ice riddled with serpentine air spaces. Under serpentine air spaces. Under increasing pressure from increasing pressure from above, air within the ice is above, air within the ice is steadily squeezed out, while steadily squeezed out, while meltwater seeps in, eventually meltwater seeps in, eventually freezing and recrystallizing until freezing and recrystallizing until the deeper layers of firn are the deeper layers of firn are transmuted into true glacial ice. transmuted into true glacial ice. This process can take several This process can take several years, or even decades years, or even decades depending on the amount of depending on the amount of annual dump of snow up on annual dump of snow up on top. One glaciogist boldly calls top. One glaciogist boldly calls the end product a "mono-the end product a "mono-mineralic rock" since, like mineralic rock" since, like quartz or diamonds, glacial ice quartz or diamonds, glacial ice is no more than a consolidated is no more than a consolidated mass of a single mineral—in mass of a single mineral—in this case, frozen water.this case, frozen water.

TransitionsTransitionsBY Patty BensonBY Patty Benson

Coated by rimeCoated by rime

After wind has tumbled crystalsAfter wind has tumbled crystals

Rounding evidentRounding evident

Transition viewTransition view

Small Small rounded rounded grainsgrains

Melting snowpack absorbs Melting snowpack absorbs waterwater

Melting snowpack with free waterMelting snowpack with free water

Fractured Fractured hailhail

Pukak or Sugar SnowPukak or Sugar Snow

We dug down to rock We dug down to rock bottom. "I've saved bottom. "I've saved the best till last, the best till last, Arthur." I showed him Arthur." I showed him pukak,pukak, the large the large chunky crystals, chunky crystals, sometimes called sometimes called "depth hoar," found "depth hoar," found at the very base of a at the very base of a mature snowcover. mature snowcover. PukakPukak is an aboriginal is an aboriginal term from northwest term from northwest Alaska; the street Alaska; the street term is "sugar snow.“term is "sugar snow.“Falling for SnowFalling for Snow, Jamie , Jamie Bastedo, Red Deer Press, Bastedo, Red Deer Press, Canada, 2003. Canada, 2003.