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    The New World Record Wind Speed: Tornadic Winds, or Not?

    February 02, 2010, 6:13:02 PM EST

    Alright, back to the discussion about the new world record wind speed. For today's entry, I will discuss the last of my main concerns that I addressed last week:

    4. Was the wind gust created by tornadic winds, which should then not compete with our record?

    The reason I bring this up is because the WMO currently has three categories for highest wind gusts in the world:

    1. Measured surface maximum wind gust 2. Measured surface tropical cyclonic wind gust 3. Measured surface tornadic wind gust

    With the verification of the wind produced by TC Olivia, Barrow Island Australia now owns the record for categories 1 and 2, where Mount Washington previously held the record for category 1.

    Take a look at this graph of the wind speed on April 10, 1996 on Barrow Island, provided by Chevron for Jesse Ferrel's blog about this event last year:


    Notice how when the 253 mph wind gust occurred, it was significantly higher than the sustained winds at the time. In fact the gust factors increased from an average of 1.33 to 2.27-2.75 at the time of the peak wind gust. This is an indication that either there was an error in measurement, or that there was a process other than just the synoptic scale storm at work here. With the WMO somehow deciding that the device was performing acceptably without testing the actual instrument, they began investigating the second possibility.

    In the report published by the WMO committee responsible for verifying this record, they bring up two mesoscale weather phenomena that could have caused this: a downdraft and a meso-vortex. The committee eventually ruled out a downdraft because other observational data from the time of the wind gust pointed to a very high unlikelihood that convective cells were present at that time. This leaves us with a meso-vortex as the only remaining possiblity.

    So what is a meso-vortex anyways?

    To put it as simply as possible, it is a small scale rotational feature and is often found around the eyewalls of intense hurricanes, or typhoons, or tropical cyclones (all the same thing). This is very similar to a tornado, but there are some fundamental differences. Dr. Roger Edwards of the U.S. Severe Storms Forecast Center talked about the differences between tornadoes and meso-vortices in the WMO report:

    a. The mini-swirl [meso-vortex] is a dynamic result of shearing instability in the zone of intense cyclonic shear that corresponds to the very tight kinematic gradient between large inner eyewall windspeed and V~0 (eye). In effect a shear eddy on steroids. These can occur at the surface or aloft, but not necessarily with veritcal connectivity. This event ocurred in the inner eyewall – precisely where mini-swirls (and also, sometimes downbursts) can be found.

    b. Vertical continuity of the eddy from the surface into the convective column isn't known without high-res aircraft or mobile radar imagery. A tornado, by definition, MUST extend vertically between surface and the convective plume aloft. Without solid evidence of such vertical vortex continuity, we can't call this a tornado.

    In more basic terms, the main difference between a meso-vortex and a tornado is that the rotating column of air making up a tornado has to extend from the surface to the cloud base, while a meso-vortex does not. I completely understand this distinction and also why we can't assume that it was a tornado. However, I don't understand why winds from a meso-vortex aren't considered tornadic in nature. They are the same kind of winds, even if they aren't created by the same phenomena. The wind that created the 231 mph wind gust on Mount Washington was a straight-line wind, very different from the winds in tornadoes and meso-vortices.

    Regardless of what kind of wind you want to classify the Barrow Island wind as, I think there should at the very least be a slight amendment to the three classes of world record winds. I think there should be a category for maximum wind gust in an extra-tropical cyclone. Mount Washington would then own this distinction, but that's not my only motivation for having this opinion. I simply think it brings a great clarification to the records, and doesn't have completely different types of winds competing with each other.

    I will be heading down tomorrow, but before I leave will post my final thoughts to bring this discussion to a close, at least on my blog. Of course, if there are any updates on the matter, I will be sure to post them. Also check back on Thursday for my bi-weekly picture summary of my latest shift. I have already scheduled that one to post!

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