Cold!!! Pretty Ice Pillars (Weather Series)


 My friend, Niki, got me thinking of this one.  As she was shoveling snow, she noticed the ice pillars in the sky.  Yes, finally winter has arrived.  With a vengeance, I may add.  The last few days have given us the coldest air in several years after many consecutive months of ridiculous to slightly above normal temperatures.  If you don’t know or recall what these look like, especially if you are smartly hibernating during these cold days, here is a cool picture of some.

pillars_tape_big

Anyway…I love the ice pillars for two reasons.  One, they remind me of the northern lights because of their streaky, vertical patterns and that they pick up the color of the lights that make them.  Two, they only occur in bitter cold air.  Ok, reason number two does make me sound crazy but bitter cold air is sort of exhilarating in a crazy way…like running a marathon and getting the runner’s high.

In this blog, I am speaking of ground based ice pillars.  You can have a light pillar even with warm ground temperatures if you are seeing them through high, thin, cold clouds.

So what is it about ice pillars that make them work?  Well first of all they are known by different names, light column or ice columns being two of them.  They are caused by the same thing – light reflecting through small plate shaped ice crystals.  Another blogger has a great visual of how these work:

 Ice-pillar-formation-KeithCHeidorn-400x239

The figure above shows it is a plate structure of the crystal that does the trick.  So why do plates form?  Well, water is a neat substance for many reasons.  One of the reasons is that depending on the humidity and the temperature, you get different crystal shapes!  Water isn’t the only substance that does this but because it is so ubiquitous in our lives, we tend to experience it commonly.  Here is a diagram showing water crystals as a function of a measure of humidity (vertical axis) vs. temperature (horizontal axis).

morphologydiagram

The pillars you see are not above the light source as the second figure shows.  They will appear to be above the source no matter what direction you are standing.

On my way to work today, I saw a pulsing ice pillar.  As I approached the airport where I work, my hunch was confirmed.  As the beacon on top of the traffic control tower rotated to point at me, a momentary ice pillar formed.  A split second later it was gone.  This conclusively shows it is only the position of the observer and the light source that matters.  Anyone else would have seen the pillar when and only when the beacon rotated to point towards them.

The plate crystals appear only when fairly cold temperatures exist (see the third figure) but because they have to be nearly horizontal to reflect light, they have to be able to stay that way as they slowly fall through the air.  That requires some calm winds and hence why you usually, but not always, see them in calm mostly clear air.

In southern lower Michigan, we usually see ice pillars a number of times in the winter.  As you can tell, they only form at ground level if the ground level temperatures are about 10 degrees or lower and they tend to form with relatively dry air which we get when arctic air comes by.  The same conditions can also give rise to our famous lake effect snow which I will cover in a future blog but dry air doesn’t give us much lake effect snow but does make for tiny plates that give us our beautiful ice columns this time of year.

I love to run and I like bitter cold but usually not together.  But when I am up on a Saturday morning trying to feel my hands on a long run in the depth of winter, ice columns make my runs so much better!

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Categories: fun sciencey stuff.

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