Friday, January 3, 2014

Parhelia and Cryoseisms

We woke this morning to sundogs out the window, and news reports of frost quakes in southern Ontario.   And a temperature of -29°C, the coldest I can remember here.  The sundogs or 'parhelia' were striking this morning, perhaps the brightest I've ever seen.

This wide shot shows the pair of sundogs off to the right and left of the sun.  They're caused by fine ice particles sometimes called 'diamond dust' in the atmosphere in very cold temperatures.  If the tiny ice crystals sink to the lower atmosphere and line up vertically, they form sundogs like this; if they're higher and not lined up, they can form a halo around the sun or moon.  Sorry about the sun flare in this shot.

The westerly sundog was most spectacular when I first saw them, and out in the open so I could get a picture while poking my camera out the door into the frigid arctic atmosphere!

The easterly sundog was partly obscured by the trees that sometimes hide my sunrises, but still very bright.  Note that the colour banding is opposite in the two parhelia, the red closest to the sun on each.

But they did foreshow a bright sunny cloudless day, with brilliant blue skies.  It was too cold for me for snowshoeing or skiing, so I went on a 'photography drive' (after putting on as many layers as I could).  This could have been any of the numerous roads I drove down, cold, crisp and sunny.

In patches here and there I found quite a bit of frost on the trees.  I had been assuming that frost occurs uniformly when it does, but I'm wrong.  It obviously develops in local patches as small as a few acres when conditions are right.  This entire woodlot looked frosty.

And as for the 'cryoseisms' or frost quakes, they are heard rather than felt, in the form of loud booms overnight or early on very cold mornings.  There have been numerous reports of such frost quakes across southern Ontario these days, apparently caused by moisture in the ground suddenly freezing and expanding.  After reading about it, I realized I probably heard one the other night, when I heard a loud boom, and put it down to ice falling off the roof - but none had fallen.

I was interested to find this distribution map when I looked up 'cryoseisms' in Wikipedia.  Apparently they occur in this band, from Wisconsin through into New England, and (missing from this map), Ontario and Quebec (as well as Alaska).  I would guess this is the part of the continent that has enough moisture in the soil, combined with sometimes extremely cold winter temperatures, to make this happen.  Interesting!

Linking to:
http://skyley.blogspot.ca/

14 comments:

  1. Interesting post. I've heard of sundogs; we have them here but not very frequently. I was unfamiliar with the term parhelia but I see that it comes from the prefix "para" (meaning beside) and helios, or sun. Maybe next time I hear the word I'll remember what it means.

    As for cryoseisms, we don't have them in Virginia. I've been complaining that it's cold here but nothing like you have there.

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  2. Wow, this was a wonderful and informative post! I did not know about 'cryoseisms'. That was really interesting. Your photos are just beautiful too. I've seen a sundog or two in my day. I haven't even been out with a camera yet this new year. We've been sick ever since leaving Alaska from our Christmas with family.

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  3. Yesterday the skies were beautiful. I didn't see any sundogs so I'm feeling a bit envious! Very intresting about 'cryoseisms' - I had never heard of them before.

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  4. It is interesting, isn't it?
    Cheers from Cottage Country Ontario , ON, Canada!

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  5. I captured a right side sundog the other day too. I think we might have had frost quakes the other day. There is no other explanation for the loud boom we heard. An interesting event that I've not heard of before. The forecast for Monday is +7 and up to 30 mm of rain!! Should be interesting. Keep warm.

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  6. Huh, I never heard of a frost quake!

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  7. i have never heard of sun dogs or a frost quake.....i don't think we have those here at the jersey shore. your images are beautiful!!

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  8. Hi! This post has certainly taught me a few things. Never heard of a 'sundog' in my life, but goodness they are beautiful! And what a contrast to such vivid blue sky later in the day.
    I live in the Pacific Northwest (WA state) and our winters here are typically mild and cloudy. In fact, the last time my area got any real snow was five years ago: a whole 6 inches and you'd think the world was ending. Personally, I love it (snow), but obviously my love is rather ideal since I don't live with it much. :) Stay warm!

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  9. Brrr that is cold. I've never heard of sundogs before, but wow they are beautiful. Such a bright blue sky!!

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  10. I have seen sundogs, but never heard of frost quakes. Thank you for telling us about them. I suppose the quakes happen in spots where snow does not accumulate much because of the wind pattern or some other reason and does not provide insulation.

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  11. Wonderful photos! Interesting post because I´ve never heard of these weather phenomenons.

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  12. Great stuff! I caught a sun dog last year some time. The frost quakes are nifty. I think I've heard a few in my lifetime but not recently. The wide shot with both sides of the sun dog is awesome!

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  13. I've never heard of either of those terms. Really cool. Literally!

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  14. I've never heard of these super cold events before, very interesting. I'm glad it doesn't get that cold here for the sake of our animals.

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