Why is snow white? by Gillian Willis
Visible white light from the sun is made up of a series of wavelengths of light on the electromagnetic spectrum, that our eyes interpret as different colours. When white light hits an object, eg a yellow banana, different wavelengths of light are absorbed by the banana while yellow is reflected back to your eyes.
When you look at snow you are rarely ever looking at one snowflake at a time, instead you tend to look at a collection of snowflakes on the ground. As light hits the snow, it is quickly reflected and scattered in many different directions due to the complex nature of the structure of each flake.
What little sunlight is absorbed by snow is absorbed equally over the wavelengths of visible light. In other words, all the different wavelengths that could be interpreted by your eyes as different colours are scattered by the snowflakes, as the light basically bounces right back out of the snow. As a result, snow takes on a white appearance.
Saying this, snow has actually been reported to be seen in different colors!!! One famous case was reported by Charles Darwin. During one of his expeditions he noticed that the hooves of the mules were becoming stained red as they walked through the snow.The red snow was caused by the presence of certain tiny plants called algae, which had been in the athmosphere when the snow formed. In fact, some people believe that the red algae that taints snow red actually looks and tasts like watermelon!
Snow can also appear to be red if the air during the snow formation contains red dust particles. Snowflakes forming around these tainted dust particles take on a reddish colour. Red snow can sometimes be found in those parts of Europe where the air is filled with dust particles from the red sands of the Sahara Desert. I would probably not like to taste that type!!
Snow can also appear to have yellow, purple, orange or green hue.....any ideas why???
Ref.
Met Office
National Snow and Ice data Center
Gibbs, N. Science and Technology
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ReplyDeleteCan anyone guess who discovered that white light can be broken up into different colours?
ReplyDeleteNot sure what I can add to this item Gillian! I will look at coloured snow with new eyes now.
ReplyDeleteOf course, the whiteness of snow has very significant implications because of the high albedo it gives to vast areas of land in the higher latitudes and other snow-covered places. I think you should look at this in connection with issues of global warming - if the snow melts (which it is doing), what does this do to albedo and what consequences follow?
Will first have to research the term 'albedo'....never heard it before. Interesting. Will get back to you on this one.
ReplyDeleteThis is what I have found so far, tell me what you think.
ReplyDeleteThe Arctic is covered by snow and ice for much of the year, however, strange enough, this is the very reason why it is more susceptible to warming. The white colour of snow and ice makes it extremely reflective. This quality is referred to by scientist as’ the albedo effect’ or a high albedo effect in this case. It is basically a measure of how much light a surface reflects. In the Artic between 70 and 80 percent of the sun's rays that hit this kind of frozen surface are bounced right back out into space. So the land or water beneath the snowy blanket does not get a chance to absorb much of that solar radiation.
An example of the albedo effect is the snow temperature feedback. When you have a snow covered area, it reflects a lot of radiation. This is why you can get terrible sunburns when you are skiing. However, when the snow covered area warms and melts, the albedo goes down. More sunlight is absorbed in the area and the temperatures increase. Climate scientists are concerned that global warming will cause the polar ice caps to melt. With these melting caps, dark ocean water will absorb more sunlight, and contribute even more to global warming.
It has been found that the average temperature in Alaska has risen by 4 degrees Fahrenheit since 1950s, this is where the problem begins. The slightly warmer temperature has caused some of the snow and ice to melt, exposing the darker land or water underneath. These surfaces have much lower albedos. The open water for example is reported to reflect less than 10 percent of the solar energy that hits it, this leads to more hear being absorbed by the landscape. A cycle then evolves where more heat is absorbed by the darker surface, so more snow and ice melt. More of the darker surface is exposed, leading to the absorption of even more heat, more snow and ice melt, and so on. Just a small temperature rise can set this feedback cycle into motion.
The fact that the Artic is frozen for a large percentage of the year makes it fragile and easy to be affected by global warming. Climate scientists are concerned that global warming will cause the polar ice caps to melt. With these melting caps, dark ocean water will absorb more sunlight, and contribute even more to global warming. By adding freshwater to the oceans as it melts from glaciers on the land surface will change the salinity of the seas, which can affect global ocean circulation patterns. It has been predicted that as land ice melts, earthquakes could potentially occur which could further disrupt glaciers, ice shelves etc. Ecosystems are very different when frozen or thawed, or subjected to new conditions, this effect could possible lead to the extinction of certain species or maybe ….the mutation or evolution of new ones specially adapted to exist in new conditions. Scary isn’t it!
Sorry , forgot to include this:
ReplyDeleteSome of the sited that helped to inform my research.
The National Snow and Ice Data Center.
http://www.teachersdomain.
www.bbc.co.uk/programmes/p00gbg6p/qrcodeCached
http://www.carbon-info.org/carboninfo_029.htm
These are some other sites that I used as well to inform my blog:
ReplyDeletehttp://www.eoearth.org/article/Albedo?topic=54300
http://www.pbs.org/saf/1505/features/thermostat.htm
http://www.climatechangewales.org.uk/object/default.asp?id=59
http://www.ei.lehigh.edu/eli/cc/resources/handouts/Albedo_Lab_Teacher.pdf
http://principles.ou.edu/earth_planet/albedo.htm