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Name: Sandra D.
Status: other
Age: 40s
Location: N/A
Country: N/A
Date: 2001

When snow melts, does it melt from the top surface as a result of the sun and/or air temperature or from the ground surface. the snow does not appear to change in its' surface appearance and this creates a debate in our family each spring.

The melting occurs at either the top or the bottom depending on the temperature of the air and the ground respectively. If the ground temp is below freezing, the snow will not freeze, correspondingly if the temperature at the ground is above freezing the snow will melt at the interface of the ground and snow. Same arguments apply for the air.

Dr. Harold Myron

Both mechanisms operate depending upon conditions. Snow reflects a lot of incident sunlight, but not all, and warm air also melts ice. Both these occur from the top ----> down. As the water trickles through the snow it too melts ice from the inside if it is warm enough, or it may re-freeze depending upon the snow temperature. On the other hand, if there is any blacktop, ground, or even concrete nearby, it heats up rather quickly and the heat is conducted through the underneath "stuff" and the snow bank melts from the bottom up.

Vince Calder

Sandra, just to stir up even more debate at the next family dinner, toss this out: some snow sublimates. That is a fancy way of saying that some of the solid snow on top goes directly from the ice (solid) state to the gas (evaporated) state, without melting (you know, like dry ice goes from solid to gas without passing through the liquid phase). This can happen even if the air temp stays below freezing. Ever notice how some snow will disappear even though it has not really warmed up? Enjoy :)

Paul Mahoney, PhD

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