Author Topic: Temperature spike today for Vantage Pro 2 aspirated weather station  (Read 20470 times)

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Offline CW2274

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Re: Temperature spike today for Vantage Pro 2 aspirated weather station
« Reply #175 on: September 27, 2016, 05:42:58 PM »
Compressing air will heat it up.
No doubt, think Santa Ana winds...

Offline dendrite

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Re: Temperature spike today for Vantage Pro 2 aspirated weather station
« Reply #176 on: September 28, 2016, 10:27:42 AM »
Doesn't your powerful fan cause your temperature to run warmer at night on calm clear still nights though?
Why would that be true?

Maybe I'm way off here, but I just assume that with that much air being drawn across the sensor, the air can't "settle" quite as much leading to a higher minimum temperature. Again, maybe I'm completely off.
The higher the CFMs the more extreme your maxima and minima will be. You're going to catch those warm and cold "spikes". With less aspiration you'll get a smoothed out line graph.

Think of a hot spoon of soup. You blow on it to cool it off faster. If the temp the sensor is reading is X and you're aspirating in temp Y (Y=X-1), the faster you advect temp Y through the chamber the quicker X will approach Y.

Offline WxLover16

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Re: Temperature spike today for Vantage Pro 2 aspirated weather station
« Reply #177 on: September 28, 2016, 11:36:45 AM »
Doesn't your powerful fan cause your temperature to run warmer at night on calm clear still nights though?
Why would that be true?

Maybe I'm way off here, but I just assume that with that much air being drawn across the sensor, the air can't "settle" quite as much leading to a higher minimum temperature. Again, maybe I'm completely off.
The higher the CFMs the more extreme your maxima and minima will be. You're going to catch those warm and cold "spikes". With less aspiration you'll get a smoothed out line graph.

Think of a hot spoon of soup. You blow on it to cool it off faster. If the temp the sensor is reading is X and you're aspirating in temp Y (Y=X-1), the faster you advect temp Y through the chamber the quicker X will approach Y.

That is basically completely the opposite of what I thought. Thanks for the explanation. Also was easy to understand.
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Offline BigOkie

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Re: Temperature spike today for Vantage Pro 2 aspirated weather station
« Reply #178 on: September 28, 2016, 05:22:29 PM »
Doesn't your powerful fan cause your temperature to run warmer at night on calm clear still nights though?
Why would that be true?

Thermal dynamics?
Do you have a thermodynamic explanation? Because I can't come up with one. The only possibility could possibly be the fan exhaust getting resucked into the bottom of the FARS like it did with those old ASOS hygrothermometers. I've actually noticed slightly cooler mins due to the faster response time.

I'm not adiabatically mixing the low levels with my little 12V fan. The radiational cooling outside of the sensor chamber remains unchanged...I'm just pulling the air in.

I know meteorologists talk about this all the time.  Wind overnight makes it warmer than it otherwise would be with no wind.  I believe the term is radiation inversion.  It doesn't always happen, but knowing that cold air sinks, you can imagine.

The exact text excerpt I read was:

"A strong radiation inversion occurs when the air near the ground is much colder than the air higher up.  Ideal conditions for a strong inversion (and hence, very low nighttime temperatures) exist when the air is calm, the night is long and the air is fairly dry and cloud-free.

A windless night is essential for a strong radiation inversion because a stiff breeze tends to mix the colder air at the surface with the warmer air above.  This mixing, along with the cooling of the warmer air as it comes into contact with the cold ground, cause a vertical temperature profile that is almost isothermal (constant temperature) in a layer several meters thick.  In the absence of wind, cooler, more dense surface air does not readily mix with the warmer, less dense air above, and the inversion is more strongly developed."
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Offline Old Tele man

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Re: Temperature spike today for Vantage Pro 2 aspirated weather station
« Reply #179 on: September 28, 2016, 05:39:05 PM »
ANALOGY - Stirring a pot of stratified water (cold at bottom, medium in middle, hot at top) results in medium water throughout.
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Offline CW2274

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Re: Temperature spike today for Vantage Pro 2 aspirated weather station
« Reply #180 on: September 28, 2016, 05:58:57 PM »
ANALOGY - Stirring a pot of stratified water (cold at bottom, medium in middle, hot at top) results in medium water throughout.
Good one too.
Always know (especially common here) when the air's dry, wind's calm, and a cloudless sky, that as soon as the sun goes down, it's gonna cool in a big hurry.

Offline dendrite

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Re: Temperature spike today for Vantage Pro 2 aspirated weather station
« Reply #181 on: September 29, 2016, 12:31:05 PM »
ANALOGY - Stirring a pot of stratified water (cold at bottom, medium in middle, hot at top) results in medium water throughout.
Of course if you mix any layer of the atmosphere you won't get the same temperature throughout that layer. A well mixed layer will warm adiabatically toward the surface (dry adiabatically unless the layer is saturated...then it's moist adiabatically). You analogy makes the same premise though.

Offline dendrite

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Re: Temperature spike today for Vantage Pro 2 aspirated weather station
« Reply #182 on: September 29, 2016, 12:41:46 PM »
Doesn't your powerful fan cause your temperature to run warmer at night on calm clear still nights though?
Why would that be true?

Thermal dynamics?
Do you have a thermodynamic explanation? Because I can't come up with one. The only possibility could possibly be the fan exhaust getting resucked into the bottom of the FARS like it did with those old ASOS hygrothermometers. I've actually noticed slightly cooler mins due to the faster response time.

I'm not adiabatically mixing the low levels with my little 12V fan. The radiational cooling outside of the sensor chamber remains unchanged...I'm just pulling the air in.

I know meteorologists talk about this all the time.  Wind overnight makes it warmer than it otherwise would be with no wind.  I believe the term is radiation inversion.  It doesn't always happen, but knowing that cold air sinks, you can imagine.

The exact text excerpt I read was:

"A strong radiation inversion occurs when the air near the ground is much colder than the air higher up.  Ideal conditions for a strong inversion (and hence, very low nighttime temperatures) exist when the air is calm, the night is long and the air is fairly dry and cloud-free.

A windless night is essential for a strong radiation inversion because a stiff breeze tends to mix the colder air at the surface with the warmer air above.  This mixing, along with the cooling of the warmer air as it comes into contact with the cold ground, cause a vertical temperature profile that is almost isothermal (constant temperature) in a layer several meters thick.  In the absence of wind, cooler, more dense surface air does not readily mix with the warmer, less dense air above, and the inversion is more strongly developed."
Yeah...most of our diurnal swings in temperature are due to net radiation. The shortwave radiation from the sun warms the ground, we get rising thermals, and the low levels mix and warm. At night, with clear skies, we lose the incoming shortwave radiation and our net is negative due to the outgoing longwave infrared radiation lost to space. The ground loses heat and cools it off at 2m via conduction. You don't have to go too far up to get above that radiation inversion and get back into the mixed layer. If you have clouds at night, the longwave infrared is absorbed by the cloud and re-radiated back to the earth's surface which keeps your temp warmer. Some of those deep northern mountain valleys never mix out during the day in the winter and they keep the cold inversion all day. I doubt CW2274 has that problem in Tucson. ;)

Offline CW2274

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Re: Temperature spike today for Vantage Pro 2 aspirated weather station
« Reply #183 on: September 29, 2016, 04:36:41 PM »
We do get inversions here, almost exclusively in the cold months. You can always can tell when the smog gets trapped at the low levels and the visibility takes a nose dive. Ugly too.

Offline Scalphunter

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Re: Temperature spike today for Vantage Pro 2 aspirated weather station
« Reply #184 on: September 30, 2016, 01:05:20 PM »
That is Fairbanks in the winter. Air piles up in the bowl with no movement and is capped by inversion layer. It can be 20 degrees warm just few miles away at top of ridges surrounding the city. Ice fog and wood smoke  prevails in the city produce heavy pollution.

John

Offline CW2274

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Re: Temperature spike today for Vantage Pro 2 aspirated weather station
« Reply #185 on: September 30, 2016, 02:45:57 PM »
That is Fairbanks in the winter. Air piles up in the bowl with no movement and is capped by inversion layer. It can be 20 degrees warm just few miles away at top of ridges surrounding the city. Ice fog and wood smoke  prevails in the city produce heavy pollution.

John
Yeah, I'll bet. As a matter of fact, wood burning fireplaces were banned from being built here in new homes within the city limits in 2000, fake ones only.

Offline Old Tele man

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Re: Temperature spike today for Vantage Pro 2 aspirated weather station
« Reply #186 on: September 30, 2016, 04:38:09 PM »
Yeah only 'grandfather' Tucsonians have real fire places (double entendre' intentional)!
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Offline CW2274

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Re: Temperature spike today for Vantage Pro 2 aspirated weather station
« Reply #187 on: September 30, 2016, 05:03:23 PM »
When I had my place built, the ban had just taken effect and was asked if I wanted a fake one instead, ummmmm, no, I'll use the space otherwise.  ;)