Profile of an updraft

Discussion in 'Advanced weather & chasing' started by Jeff Duda, May 28, 2017.

  1. Jeff Duda

    Jeff Duda Resident meteorological expert
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    An OU grad student and researcher for the CLAMPS field experiment was sending up balloons every few hours leading up to initiation in south-central Oklahoma on Saturday's chase. During the evening, the group sent a rawinsonde directly into the updraft of the intense storms down there, and the result was this:

    DA4gHLLUMAAigYj.jpg

    Note the deep saturation and generally moist-adiabatic lapse rates from 900-400 mb. Also note the rather extreme horizontal winds and hodograph shape. You can find model soundings that look a lot like this if you pick a location that has received high precipitation in the most recent slot of time.

    Use this as a reference for knowing when you're looking at a forecast sounding that looks extreme...if the location of the sounding has high precip or simulated reflectivity in it, then you know it's going through the updraft of a modeled storm and does not represent the large-scale environment in which the storm exists.

    Final treat: measured ascent rates of this balloon ranged from 28-46 m/s. 46 m/s (~102 mph) is probably within a few m/s of the fastest upward velocities you will ever see. The caveat to this is that the balloon itself has a background upward motion (because it has to if you want it to ascend and measure the atmosphere) that is mixed in with the measured ascent rate. I think the typical value of ascent (near the ground at least) is about 5 m/s, but it depends on the size of the balloon and the payload. These might have been smaller balloons than the ones NWS offices send up twice a day. In that case the background ascent rate was probably lower than 5 m/s. Maybe 3 or 4.
     
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  2. Bob Schafer

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    In trying to understand why those lateral velocities were so high, I took a look at the OUN sounding from 00z. At 700mb OUN recorded about 25-30 kts. At 300 it was 60. The CLAMPS group's data more than doubled those numbers (at those two particular heights). So, the differences are (partly) explained by the tilt of the updraft, right? If the updraft was vertical there should not have been much difference. Further, because of that tilt, the actual velocity of the updraft was much greater than 102 mph, but not the purely vertical component. Add the differences from the ambient (background) and updraft lateral velocities to the ascent (102) for a ballpark of the velocity of the tilted updraft, no?
     
  3. Jeff Duda

    Jeff Duda Resident meteorological expert
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    If the balloon went through a mesocyclone, that would explain the lateral speeds. Given typical mesocyclonic vorticity values of 10^-3 s^-1 and a diameter of 10 km, a parcel rotating around in there would be moving laterally at 31 m/s (~60 kts).
     
  4. Bob Schafer

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    I considered that, but then you would have a crazy looking hodo as the balloon went around and around in the meso.
     
  5. Jeff Duda

    Jeff Duda Resident meteorological expert
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    Not if it only went through part of it. At 10^-3 s^-1, a full revolution of the meso would take 104 minutes. The person who launched the sounding said the balloon went from launch to 250 mb in about 15 minutes, which means it wouldn't have even gone halfway around the meso in the time it ascended. It must also be considered if the balloon took a direct path through the meso as opposed to a glancing blow. Hard to tell for sure.
     
  6. Randy Jennings

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    Bet it was fun to fill that balloon near a storm. It would be interesting to know what size balloon, what the payload weight is, and how much gas they used. I've done a lot of HAB (High Altitude Balloon) launches with my local radio club and we have never see ascent like that.
     
  7. Jeff Duda

    Jeff Duda Resident meteorological expert
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    I think this video shows the entire package and launch pretty well: https://twitter.com/MesonetMan/status/868527741435600899
     
  8. Jeff Duda

    Jeff Duda Resident meteorological expert
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  9. James Hyde

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