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Thread: What exactly is the Hook Echo?

  1. #1
    Member John Cameron's Avatar
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    Default What exactly is the Hook Echo?

    When we see a hook echo on radar, are we seeing heavy precip bring drawn around the mesocyclone? Or, is it being drawn around the tornado vortex? Is it precip under the influence of RFD? Is it precip being shoved upwind by focused, accelerating inflow?

    I've never heard the explination of what causes what we're seeing on radar. I thought this may be a good "beginner" topic.
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  2. #2
    Joey Ketcham
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    A hook echo is the result of precipitation being wrapped around the area of rotation, on radar it appears just as that.. a hook.



    This is a radar image which shows a hook echo on the southwest side of the storm just west of Newcastle, OK.

  3. #3
    Administrator Team Skip Talbot's Avatar
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    Yes, its being wrapped around the mesocyclone of the storm. The radar images you typically see hooks on are from looking at the midlevels of the storm where the mesocyclone is. To see precip wrapping around the tornado you'll need a much higher resolution radar with a beam lower to the ground (like Josh Wurman's radar). Also keep in mind that many storms with hook echoes do not produce tornadoes. RFD is also marked by the hook. As the hook approaches you will get hit by outflow which is RFD and then heavy rain and/or hail.

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    This grab has been detailed;

    Stephen Locke
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  5. #5
    Stormtrack supporter John Wetter's Avatar
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    hook echo—A pendant, curve-shaped region of reflectivity caused when precipitation is drawn into the cyclonic spiral of a mesocyclone.
    The hook echo is a fairly shallow feature, typically extending only up to 3–4 km in height before becoming part of a bounded weak echo region (BWER).
    Fujita, T., 1958: Mesoanalysis of the Illinois tornadoes of 9 April 1953. J. Meteor., 15, 288–296.
    John Wetter, K0WDJ
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    The picture is a bit misleading as you really need to look aloft to see the BWER. I'll add that during my M.S. thesis, only 20% of hook echoes were tornadic, so you defintely don't need a tornado.

    As a matter of fact, I would even hypothesize many appendages we label as hook echoes may have less to do with near-sfc rotation. Instead, they form as precipitation is advected around the mesocyclone aloft and then fall out to the surface. I've seen plenty of appendages form more of an L like echo with the echo trailing the updraft. In other cases, you'll see the mesocyclone (incipient tornado cyclone?) strengthen aloft, precip wraps and becomes collocated with the rotation and THEN descends to the surface (like a DRC or what some call a "finger"). In other cases, this intensification in vorticity seems to occur at all levels, and there is no descent in the reflectivity field.
    Aaron Kennedy
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  7. #7
    Member Scott Nelson's Avatar
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    Not stepping on John's thread here but would a storm producing multi vortex tornadoes have a multiple hook signature/echo too? Storms that generate this power fasinate me more than anything.

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    Stormtrack supporter Karla Dorman's Avatar
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    So: is the hook echo after the tornado (as depicted on radar) behind the actual circulation/tornado? Appreciate any answers/help ...
    Karla Dorman: have cane, will travel - PorchChaser!!

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  9. #9
    Administrator Team Skip Talbot's Avatar
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    The hook does not have to correlate with the tornado at all. A mesocylconic tornado can spawn north of the hook in an area with no radar reflectivity (I think this is more common actually) or even further north of there in the precip core, or back inside of the hook (like in many HP's). Also remember that non mesocyclonic tornadoes including gustnadoes and spouts can form in a wide variety of places along the storm. All the hook indicates is that the storm may have a mesocyclone, and these storms have a tendancy to be the tornado producers. I wouldn't try to directly pin a tornado on a hook, especially since your are not looking at the ground level slice of the storm.

  10. #10
    Member L.B. LaForce's Avatar
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    yes, here is a smoothed image from GR3 showing the same hook echo as posted above.


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