Sky temp = -38 deg C

[ChrisM]

I thought that it felt colder than usual as I walked out to the observatory just 5 minutes ago. A quick check of the sky temperature on the infrared thermometer showed it to be -38 deg C. The coldest that I've previously seen was -36, and it's usually closer to -30 at this time of year.

Does anyone else keep tabs on the sky temp? I am just using a $50 gun that was on special at Bunnings one day.

Chris

[wayne anderson (Wayne)]

Just measured sky temp here at sunshine coast QLD at 1.2 degrees and air temp 11.3 degrees sky temp is usually much less but we have thick cloud cover tonight.

[ChrisM]

Originally Posted by wayne anderson

Just measured sky temp here at sunshine coast QLD at 1.2 degrees and air temp 11.3 degrees sky temp is usually much less but we have thick cloud cover tonight.

That's right - clouds act as a big blanket. Looks like a good frost coming up here in Vic tonight if it stays clear.

[rmuhlack (Richard)]

Chris - i'm not sure to what temperature that reading really refers to.

Consulting the weatherzone 500hPa chart, it suggests an air temp of -22 to -24C over gippsland at an altitude of ~5680m. As a very rough rule of thumb, air temp drops about 0.7-0.8C per 100m of elevation. That would mean that you'd have to get to an altitude of nearly 7400m at least to see an air temp of -38 C at your long/lat.

I suspect it means that the sort of measuring device you're using can't be used to measure air temp in the manner you're describing. Point at a nearby solid object - for sure. straight up in the air - i have my doubts...

[ChrisM]

Originally Posted by rmuhlack

Chris - i'm not sure to what temperature that reading really refers to.

Consulting the weatherzone 500hPa chart, it suggests an air temp of -22 to -24C over gippsland at an altitude of ~5680m. As a very rough rule of thumb, air temp drops about 0.7-0.8C per 100m of elevation. That would mean that you'd have to get to an altitude of nearly 7400m at least to see an air temp of -38 C at your long/lat.

I suspect it means that the sort of measuring device you're using can't be used to measure air temp in the manner you're describing. Point at a nearby solid object - for sure. straight up in the air - i have my doubts...

Richard, it's not measuring the air temperature, but in the least it's giving an indication of the 'sky' temperature, and it obviously provides a sort of measure of the amount of radiation cooling occurring.

As mentioned before, point it at clouds and the temperature clearly rises, but point it at the zenith and it usually falls to somewhere between about -20 and -30 deg C. With a clear sky, the temperature rises smoothly from the zenith to the horizon. I figure that the more transparent the sky is, the colder it reads, but there are probably other factors that affect the reading too.

For my purposes, it's a cheap indicator for measuring all sorts of temperatures.

Chris