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August 18th, 2005, 01:24
| #1 |
| Old Skool  Join Date: Feb 2002 Location: Phoenix, AZ
Posts: 2,169
|  lowest temp in 24 hr period The lowest temperature in a 24 hour period is usually after sunrise. I don't understand that. I would think that right before sunrise is when the lowest temperature occurs. Any takers on why that is? |
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August 18th, 2005, 02:03
| #2 |
| Administrator  Join Date: Feb 2003 Location: Pinal Airpark
Posts: 6,897
| Re: lowest temp in 24 hr period [ QUOTE ] The lowest temperature in a 24 hour period is usually after sunrise. I don't understand that. I would think that right before sunrise is when the lowest temperature occurs. Any takers on why that is? [/ QUOTE ] It's usually some time just after sunrise. All through the night, the ground and air are nocturnally cooling. When the sun rises, it's still at low angle and not very effective in reversing the trend and causing heating just yet, since cooling is still going on. Once it's gets further above the horizon and can begin reversing the cooling trend, that's the time of lowest temp. This is the critical time for IR based sensors and weapons, since this time of "diurnal crossover" is where the surrounding temp of land matches the temp of objects on that land, so an IR sensor sees everything the same, or in essence, sees nothing. |
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August 18th, 2005, 22:35
| #3 |
| Senior Member Join Date: Dec 2001 Location: Redding, CA
Posts: 619
| Re: lowest temp in 24 hr period last winter, many times I waled out to my airplane at 5:25 AM, just as thesun was coming up andthere was dew all over the airplane. I learned to wipe it all off then because y 6:00 AM it often turned to frost, even though the sun had risen. I had always thought this was called thermal lag or diurnal lag or something like that, but I just searched and couldnt ocnfirm that... |
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August 19th, 2005, 16:54
| #4 |
| Senior Member  Join Date: Jun 2002 Location: Home:SFO Work:MSP
Posts: 1,035
 | Re: lowest temp in 24 hr period [ QUOTE ] last winter, many times I waled out to my airplane at 5:25 AM, just as thesun was coming up andthere was dew all over the airplane. I learned to wipe it all off then because y 6:00 AM it often turned to frost, even though the sun had risen. I had always thought this was called thermal lag or diurnal lag or something like that, but I just searched and couldnt ocnfirm that... [/ QUOTE ] Good info! I never came across that scenario before so I will file it in my brain for later use someday. |
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August 24th, 2005, 05:52
| #5 |
| Junior Member  Join Date: Mar 2002 Location: RKNN
Posts: 185
| Re: lowest temp in 24 hr period Shh... don't give away any sar info,.. wouldnt want people to use diurnal crossover to their advantage  -Perpetual  |
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