Friday, 25 May, 2012

Why do bridges ice before the road? People in cold climates are used to signs warning that “bridge freezes before road.” Water on surface will freeze once the surface becomes cold enough, but why does the road cool faster? ENLARGE Photo: Petelewisr Beware of the bridge on an icy day! Warming and cooling result from [...]

How do ice ridges form on a lake? ENLARGE Photo: Jeff Miller Pressure ridge near shore on Lake Mendota in Madison, WI Lake ice formation is dynamic. Even when a lake is completely frozen, the ice is not stagnant. It expands and contracts as it warms and cools. Differences in day and night temperatures can [...]

Do all snowflakes have unique shapes? It is highly unlikely that you’ll find two identical snowflakes. Feel free to try to prove us wrong, but your search may involve some cold feet! If you compared 1 million snowflakes (a minuscule fraction of the flakes in a single snowstorm), performing two comparisons per second, you’d need [...]

What is ‘black ice’? The term ‘black ice’ refers to either a new layer of transparent ice on water, which allows us to see the deep water below, or a layer of clear ice on a roadway, which makes for hazardous driving. In both cases, the ice is transparent, not black, and so it shows [...]

How does a lake freeze? Enlarge Photo: NOAA Ice forming around the shore of Lake Michigan Lakes freeze from the top down. Ice is less dense than water, which is why ice floats. The density of liquid water is determined by its temperature, and water is most dense at about 40 F. Why is that [...]

How does frost form? Heavy frost on Burr Oak tree in Wisconsin Frost on objects is just water vapor in the air that has condensed as ice onto a surface. Frost forms on objects close to the ground, such as blades of grass. At night, a blade of grass loses energy by emitting a non-lethal [...]

Why are clouds white? Photograph of Cumulus clouds in fair weather taken by Michael Jastremsk Clouds are made of water and clean water is clear. So why are clouds white? Because clouds are made of billions of small water droplets and ice crystals. When light beams interact with particles suspended in air, some of the [...]

Snow can make both ‘squeaky’ and ‘crunchy’ sounds. Snow is a mixture of ice crystals, liquid water and air, and the sound it makes when you walk on it depends on the proportions of this mixture.

Yes, this is a real picture. More accurately, it’s 165 pictures pasted together from NASA’s Cassini spacecraft’s flyby of Saturn as the planet between the probe and the sun. From this unique vantage point, the contrast of light and shadow enabled astronomers to discern new bands of ice and dust — perhaps the remnants of [...]

Frosty questions: Are some snowflakes identical? How do flakes form, and how does weather affect their shape? How does ice in the atmosphere affect weather and climate? And where does the jet stream fit in this picture?