Up Side Down
New Zealand is a wonderful place for Ice Needles. The sky is often crystal clear and the radiation losses great. Just the right conditions for ice needle formation. LTER's own David Greenland, not a New Zealander, to the best of my knowledge, studied New Zealand ice needles and made them in his lab. He assures me that their hypothesis that Southern Hemisphere ice needles grow upside down was rejected both by field observations and laboratory growth trials. The classy, glassy details are in Soons, J. M. and D. Greenland. 1970. "Observations on the Growth of Needle Ice. " Water Resources Research 6(2):579-593.
Prospecting for needle ice is a pedagogical endeavor. The crunching sound, like glass breaking, may indicate a needle ice find under foot. The columns of ice grow upward through soil at the expense of frozen soil water waiting for the footfall. The core of this micro story is an advertisement for one of the very best non-fiction books to cross my desk in quite long time. Mariana Gosnell titled it ICE! Over 500 pages, it is encyclopedic in its scope.
Once abscission happens, the energy budget of the forest floor is maxing-out, the upward bound infrared radiation and ice needle season begins.
My Australian ice needles experience was on Tasmania. It was a family vacation with a rented car. Our "motel" was an airstream trailer park no-longer fit for the highway. On ours the wheels were gone. We were there in the Southern Hemisphere winter enjoying continental polar air from Antarctica. There was very little water vapor in the air to retard the outgoing radiation from the surface. Our surface was the skin of our airstream trailer. It seemed like every rivet holding the Trailer together was having a difficult time. Each rivet was singing a part of a symphony of groans. It got colder by the minute. Our sweatpants were worn like hats. We turned on the propane stove. I took first watch, my wife second. We made it through the night.
Icicles are not needle ice. The North Island (Tropical) and the South Island (sub-polar) are as different as ice needles and icicles. Icicles grow downward. Now we can understand Soons’ and Greenland’s paper "Observations on the Growth of Needle Ice." The reader can benefit by following the path of Google on ice needles followed by a hit on the images button. You now have an atlas of ice crystals. The second image is classic ice needle.