In my last blog, I said I would explain how wind machines work to raise the temperatures in the vineyards, and also under what conditions, they don’t.
This will be the short course for those of you only interested in the basics. I’ll be taking bits & pieces from 2 websites that go into more depth than the average person needs or wants to know.
On this website:
http://biomet.ucdavis.edu/frostprotection/Principles%20of%20Frost%20Protection/FP005.html
Richard L. Snyder, Extension Biometeorologist University of California, Atmospheric Science, Davis, CA, had this to say:
More economic losses occur due to freeze damage in the United States than to any other weather related hazard.
…
TYPES OF FROST EVENTS
Advection Frost
An advection frost occurs when cold air blows into an area to replace warmer air that was present before the weather change. It is associated with moderate to strong winds, no temperature inversion, and low humidity. Often temperatures will drop below 32F (0F) and stay there all day. Advection frosts are difficult to protect against, but fortunately they are rare in California fruit growing regions.
Radiation Frost
Radiation frosts are common occurrences in California. They are characterized by clear skies, calm winds, and temperature inversions. Radiation frosts occur because of heat losses in the form of radiant energy. Under clear, nighttime skies, more heat is radiated away from an orchard than it receives, so the temperature drops. The temperature falls faster near the radiating surface causing a temperature inversion to form (temperature increases with height above the ground).
===================
I’ll limit this discussion to the two types of frost noted above; Advection & Radiation. These will be easiest to explain in pictures, provided by Iowa State University. Just pretend those trees in the graphics are really grape vines.
First, the Radiation Freeze:
The Radiation Freeze is a condition that can be mitigated by the use of wind machines. Since there is “warmer” air above the vineyard, the challenge is to bring that air down to the vineyard.
The use of wind machines can perform that function.
But in an Advection Freeze, there is no warmer air to bring down.
Operating a wind machine during an advection freeze can actually do more harm than good.
Well, that about sums up the short course. But if you enjoyed those graphics and want to see more that include the use of heaters, bonfires, smoke (of no value), tower-less wind machines, helicopters, sprinklers, etc., just click on the following:
http://viticulture.hort.iastate.edu/info/06iawgmtg/vineyardfrostprotection.pdf
So the next time the wind machines wake you up and somebody at the store or your work or gym mentions that “…it sure got cold last night”, you might be able to impress them by saying; “Yes, but luckily for the farmers, it was a radiation freeze and not an advection freeze”.
This will be the short course for those of you only interested in the basics. I’ll be taking bits & pieces from 2 websites that go into more depth than the average person needs or wants to know.
On this website:
http://biomet.ucdavis.edu/frostprotection/Principles%20of%20Frost%20Protection/FP005.html
Richard L. Snyder, Extension Biometeorologist University of California, Atmospheric Science, Davis, CA, had this to say:
More economic losses occur due to freeze damage in the United States than to any other weather related hazard.
…
TYPES OF FROST EVENTS
Advection Frost
An advection frost occurs when cold air blows into an area to replace warmer air that was present before the weather change. It is associated with moderate to strong winds, no temperature inversion, and low humidity. Often temperatures will drop below 32F (0F) and stay there all day. Advection frosts are difficult to protect against, but fortunately they are rare in California fruit growing regions.
Radiation Frost
Radiation frosts are common occurrences in California. They are characterized by clear skies, calm winds, and temperature inversions. Radiation frosts occur because of heat losses in the form of radiant energy. Under clear, nighttime skies, more heat is radiated away from an orchard than it receives, so the temperature drops. The temperature falls faster near the radiating surface causing a temperature inversion to form (temperature increases with height above the ground).
===================
I’ll limit this discussion to the two types of frost noted above; Advection & Radiation. These will be easiest to explain in pictures, provided by Iowa State University. Just pretend those trees in the graphics are really grape vines.
First, the Radiation Freeze:
The Radiation Freeze is a condition that can be mitigated by the use of wind machines. Since there is “warmer” air above the vineyard, the challenge is to bring that air down to the vineyard.The use of wind machines can perform that function.But in an Advection Freeze, there is no warmer air to bring down.
Operating a wind machine during an advection freeze can actually do more harm than good.Well, that about sums up the short course. But if you enjoyed those graphics and want to see more that include the use of heaters, bonfires, smoke (of no value), tower-less wind machines, helicopters, sprinklers, etc., just click on the following:
http://viticulture.hort.iastate.edu/info/06iawgmtg/vineyardfrostprotection.pdf
So the next time the wind machines wake you up and somebody at the store or your work or gym mentions that “…it sure got cold last night”, you might be able to impress them by saying; “Yes, but luckily for the farmers, it was a radiation freeze and not an advection freeze”.
2 comments:
Ranndy,
Here in Central CA the wind machines run to protect the citrus. As a youngster I woke many early winter mornings to the cloudy smog of smudgepots and the hum of wind machines. Even now the sound of wind machines is a calming noise, though to my citrus growing friends it is fearful sound.
Steve in Exeter, CA
Steve,
I doubt that many readers will understand that comment "the sound of wind machines is a calming noise", but I do.
Post a Comment