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MailTribune.com
  • Why do wind machines keep fruit from freezing?

  • Ever notice in winter that the temperature is sometimes warmer on Mount Sexton than in Medford, even though Sexton is at higher elevation?
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  • Ever notice in winter that the temperature is sometimes warmer on Mount Sexton than in Medford, even though Sexton is at higher elevation?
    Or perhaps you've been up on Roxy Ann, looked down at the valley and noticed that smoke or steam rises to a certain height and then levels out.
    These are signs of a temperature inversion. The inversion traps cold air near the ground, so it's actually warmer above the inversion layer.
    For more on inversions, see Page 140.
    This phenomenon also helps explain why wind machines can keep fruit from freezing in local orchards.
    "These inversions tend to have a ceiling, and above that point — 20 to 50 feet in the air — it's actually warmer," explains Jon Meadors, superintendent of orchard and vineyard operations at Hillcrest Orchard in east Medford.
    The wind machine, with a tower that is 40 feet tall, reaches above the layer of trapped cold air. At 18 feet in length, its blade stirs up both the trapped cold air and the warmer air above and mixes them together. The result is that the air gets just enough warmer to keep fruit from freezing.
    "They are pretty effective," Meadors says.
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