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#1
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At what temeprature do you get frost
Header says it all really but what does the temperature have to drop to
before you get a 'frost' Cheers Jim -- Remove BRAIN before replying |
#2
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At what temeprature do you get frost
In message , JimM
writes Header says it all really but what does the temperature have to drop to before you get a 'frost' Jim You can get a grass frost with air temperatures (4 feet above ground level in a screen) as high as 4 or even 5C. For an air frost, the reading in a screen has to be -0.1C or lower. Having said that, plants are rarely damaged by a slight grass frost unless it is prolonged. Just my opinion of course. -- Steve Jackson, Bablake Weather Station, Coventry, UK http://www.netlink.co.uk/users/bws |
#3
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At what temeprature do you get frost
That's about it.
Frost is when (pure) water freezes at 0°C. When the night sky is clear, the ground can radiate heat to outer space & get slightly below zero even if the air is a bit warm. Conversely, a wave of cold air can arrive at any time, even if the ground is above freezing. Plants cool down quicker than the soil. Regards "Steve Jackson" a écrit dans le message de news: ... In message , JimM writes Header says it all really but what does the temperature have to drop to before you get a 'frost' Jim You can get a grass frost with air temperatures (4 feet above ground level in a screen) as high as 4 or even 5C. For an air frost, the reading in a screen has to be -0.1C or lower. Having said that, plants are rarely damaged by a slight grass frost unless it is prolonged. Just my opinion of course. -- Steve Jackson, Bablake Weather Station, Coventry, UK http://www.netlink.co.uk/users/bws |
#4
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At what temeprature do you get frost
JimM wrote:
Header says it all really but what does the temperature have to drop to before you get a 'frost' Cheers Jim -- Remove BRAIN before replying Freezing point ;-)) Sorry - I guess the point is that you can get very strong temperature gradients close to surfaces. The temperature at the surface will depend on heat loss by radiation plus heat loss/gain by conduction from the surrounding air. The steepness of the temperature gradient will be influenced by many factors. For example: Wind speed - moderate winds will often prevent frost by ensuring "warm" air is always moving across the surface. Commercial fruit growers use large "fans" to generate gentle breezes across orchards to prevent late frosts damaging blossom. Cloud cover - radiative cooling rates will depend on what the surface is "looking" at, a clear "cold" sky or warm clouds. Mist or fog - odd as it sounds, fine water droplets freezing in the air release heat, preventing the temperature dropping too low. Again, this is used to practical effect in California where commercial citrus growers spray water into the air above the trees to prevent late frosts damaging blossom. The angle of the surface - on a night with a clear, dark sky, a vertical surface (which doesn't "see" the sky) radiates slighty less heat than a horizontal surface. This is why you will sometimes find ice on the car windscreen/rear window but water on the side windows. Of course, all this becomes incidental when general air temperatures drop below freezing point. -- Larry Stoter |
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