Is climage change affecting ISA basis, altimeter

[LongRoadBob]

I'm on to the Meteorology book in ground school. Had already gone through rudimentary concepts about International Standard Atmosphere and how the altimeter works. Only now am getting into how one actually sets (to the height above sea level the airport is, or to sea level) the altimeter, and it's a little confusing so far.

But the idea of standard atmosphere, where 15degC at sea level, dry air, 29.92 " etc. and that density changes at a certain rate when going up from there.

Not getting political, but just theoretically say the climate is changing, that temperatures are rising, I'm trying to figure out (and believe) if so we can still use standard atmosphere, since we adjust it for the actual conditions anyway, but is there ever a point where it ought to be "adjusted" so as to be more....um, standard. More fitting with the phsyical average or norm?

 

[MAKG1]

ISA is much too rough to distinguish a few deg.

If you take it too seriously, it's 59 deg at the North Pole on the winter solstice. Needless to say, the real atmosphere is NEVER standard and never has been.

 

[LongRoadBob]

ISA is much too rough to distinguish a few deg.

If you take it too seriously, it's 59 deg at the North Pole on the winter solstice. Needless to say, the real atmosphere is NEVER standard and never has been.

Thanks. I think I get it somewhat anyway. I knew that it would be a VERY special day if all the computations of standard were met and would never happen all over the globe at the same time unless it was ragnarok.

I was only wondering if there was advantage, I mean like Celsius decided to have freezing at 0 deg, and boiling water (at sea level) at 100 deg. That at some point in time when they defined standard atmosphere they must have had some thought to "ok. Where should the ground zero be and what temperature, what pressure and density, humidity?"

I am just guessing but I think it might be they averaged the temp to get 15 deg Celcius, decided to rule out any humidity, and averaged pressure density, etc.? But like you say, it almost (virtually) never is the real situation so it doesn't matter I guess.

 

[coloradobluesky]

It doesn't matter what the actual average temperature and pressure are. They have to normalize it to something, so they picked 29.92 and 59F. If it's something different, the system would still work. Hmmm, well, thats my theory. Not absolutely sure its right. Throw it out there and see, I guess.

 

[azure]

As you say, maybe someday "standard temperature" will be defined to be something else, like, say, 17C instead of 15. But there's little reason to redefine it since it is just a reference, and actual conditions are very rarely standard.

More important is not taking things like "standard lapse rate" too seriously, or you could, someday far from any weather reporting station, find yourself unexpectedly up against the bases of clouds you thought were much higher.

 

[fiveoboy01]

What azure said. It's just a number, a starting point. We could change it, but I don't think there would be much point.

 

[MAKG1]

If it were getting (a lot) colder there would be a point.

But ISA is used for two things: keeping airplanes from banging into each other, and keeping airplanes from banging into immovable objects. For the first, there is no reason whatsoever to label the altimeter in feet. It could be in frobnitzes or femtoparsecs or (even better) hPa. For the second, warm temperatures mean it reads lower than actual above reporting stations. You're further above obstacles than your altimeter says.

 

[EdFred]

If it were getting (a lot) colder there would be a point.

But ISA is used for two things: keeping airplanes from banging into each other, and keeping airplanes from banging into immovable objects. For the first, there is no reason whatsoever to label the altimeter in feet. It could be in frobnitzes or femtoparsecs or (even better) hPa. For the second, warm temperatures mean it reads lower than actual above reporting stations. You're further above obstacles than your altimeter says.

Except then all the charts would be useless when they put the elevations on things.
"What is the airport elevation?"
"Blah blah hectopascals"
"Um...that's a constantly changing value"

 

[MAKG1]

Except then all the charts would be useless when they put the elevations on things.
"What is the airport elevation?"
"Blah blah hectopascals"
"Um...that's a constantly changing value"

Yes, that's the "immovable object" thing. For other aircraft, especially in the flight levels, it doesn't matter. As long as everyone does it the same way.

 

[LDJones]

The "change" in climate change is in tenths of a degree. A non-issue for our aviation purposes.

 

[Let'sgoflying!]

its also used to adjust power charted power settings.

 

[luvflyin]

I'm on to the Meteorology book in ground school. Had already gone through rudimentary concepts about International Standard Atmosphere and how the altimeter works. Only now am getting into how one actually sets (to the height above sea level the airport is, or to sea level) the altimeter, and it's a little confusing so far.

But the idea of standard atmosphere, where 15degC at sea level, dry air, 29.92 " etc. and that density changes at a certain rate when going up from there.

Not getting political, but just theoretically say the climate is changing, that temperatures are rising, I'm trying to figure out (and believe) if so we can still use standard atmosphere, since we adjust it for the actual conditions anyway, but is there ever a point where it ought to be "adjusted" so as to be more....um, standard. More fitting with the phsyical average or norm?

Sure we can keep using 15 and 2992. It's relative. The only thing that matters is we all are using the same numbers. I doubt if "standard atmosphere" is going to be changed over a few degrees, requiring the republishing of thousands of documents. I'm not going to bet a whole paycheck against it though. Some me of the stuff the "committees" come up with never cease to amaze me. If it happens, I'm going to blame you for bringing it up, LOL.

 

[LongRoadBob]

Sure we can keep using 15 and 2992. It's relative. The only thing that matters is we all are using the same numbers. I doubt if "standard atmosphere" is going to be changed over a few degrees, requiring the republishing of thousands of documents. I'm not going to bet a whole paycheck against it though. Some me of the stuff the "committees" come up with never cease to amaze me. If it happens, I'm going to blame you for bringing it up, LOL.

I didn't happen to mention I just bought stock in a printing company?