Posted on 19 November 2010 at 14:51h
Not exactly a lollipop but it is ice on a stick. I've noticed this phenomenon for many years and often wondered what caused it. On cold mornings , even when there isn't frost on the ground, large crystals of ice grow out of small twigs. The only explanation can think of is that the twig contacts squeezing sap out of small pores (twigs have pores I think) as the liquid squeezes out it freezes. Well not much of an explanation but its all I can think of.
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But why does it only appear on twigs and not stones or anything else? See the leaves in the background have only a bit of frost on them but the twig has loads. I don't think this is rime, we have lots of that here at the moment and this stuff is different, much more fragile and fibrous like asbestos. It tends to appear when its not that cold, sometimes the only frost around is coming out of twigs. I'll get some better photos.
Posted by on 30 November 2010 at 18:25h
Chris, what you are observing is called hoar frost or more particularly rime. You also see it on fence posts when winter mountaineering in Scottish hills etc. The twig cools (by radiation) to a temperature below zero and if the air is supersaturated water droplets condense on the twig. Mist and fog droplets are smaller than rain droplets so the heat released as they crystallise (freeze) can be quickly conducted away so the whole droplet freezes rapidly. As more and more cold mist droplets hit the windward side of the object they build up a mass of porous ice (called rime). In winter mountaineering it is a way to see what the prevailing winds were and whether they have now changed direction which can give information on fronts passing over etc – I’ve told you before that climbing gives you a good education!
Posted by Geoff Neuss on 27 November 2010 at 09:29h