ISA. Does it get colder at night?

[glum]

Having looked at the International Standard Atmosphere temperature changes with altitude, I can't find any reference to a day / night difference.

Surely the sun has some measurable effect on the air temp, even at cruising altitudes. Can anybody enlighten me?

[ShyTorque]

The ISA is just that. It's not meant to be a "real" atmosphere, only a datum to work from. ;)

[dixi188]

The ISA is just a set of standards to compare your actual conditions with. There is no day or night version.

[barit1]

Just as there is no summer/winter difference, nor clear / high cloud / low cloud.

[glum]

Ah yes, good points!

In which case, does anyone have an idea of the usual variation of day to night temperatures, be they summer or winter - i.e.

"It's usually 20 degrees colder at night than during the day for the same time of year / lattittude / altitude?"

[Check Airman]

Not being a meteorologist, I'd hazard a guess and say that there's no standard day/night temperature variation- it would depend largely on the climate. In the middle of the Sahara, the variation would be more than your beach front condo in Aruba:ok:

[Mark 1]

At surface level, the changes are largest but they depend on cloud cover, duration of darkness, wind speed, coastal effects etc.

The higher you go, the smaller the variation between day and night temperature in the troposphere.

ISA is approximately an average for the whole globe.

[phiggsbroadband]

Hi Glum, I think it all depends upon which country you are in.

In arid countries (Spain and desert regions.) where the sky remains clear
overnight, the variation can be, as you say, 20 deg C or more.

However in an overcast UK the night-time temperature can be the same (or more.) than the daytime temp... It all depends upon wind direction here.

[john_tullamarine]

My recollection is that the ISA is based on now well dated readings for North America.

The Industry has used a range of "standard" reference atmospheres over the years for different purposes, mainly test work.

As has been observed in earlier posts, we need two criteria to be met ..

(a) the reference atmosphere needs to bear some resemblance to what happens in the real world but is then idealised

(b) the driving requirement is to have a reference standard (whatever it may be) for purposes such as test reduction and comparison.

Much the same sort of philosophy as the aircraft design certification standards when you come to think about it ..

[mohamedarab]

temperature changes with altitude
Dear all
I think the IAS temp. is just a calculation method depends on the altitude and the day/ night has no effect.The atmosphere is a gaseous envelope surrounding the earth. Its
characteristics are different throughout the world. For this reason, it is necessary to
adopt an average set of conditions called the International Standard Atmosphere
This ISA model is used as a reference to compare real atmospheric conditions
and the corresponding engine/aircraft performance. The atmospheric conditions will
therefore be expressed as ISA +/- ΔISA at a given flight level day or night

[Northbeach]

Surely the sun has some measurable effect on the air temp, even at cruising altitudes.

I do not think so; I have never noticed, read any or seen any data linking change of temperature at higher altitudes in relation to the sun setting or sun rising. Nor is there any real difference between summer and winter.

The sun is the main energy source for most of the planet’s weather. It provides the initial heating (direct light) and cooling (darkness) for the planet’s continental/maritime/tropic/polar air masses that then mix. So, yes the sun has a huge effect on temperatures, including temperatures at altitude. However a given sunset at FL370 does not result in an immediate decrease in temperature as the sun dips below the horizon.

[Checkboard]

In which case, does anyone have an idea of the usual variation of day to night temperatures, be they summer or winter - i.e.

Really? :rolleyes: You do know that Summer to Winter variation is different in .. umm .. Siberia ... to ... umm Alice Springs? :confused:

Seasonality - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Seasonality)

Diurnal temperature variation - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Diurnal_temperature_variation)

[glum]

I do. Hence asking about variations from the same lattitude...

The sun causes the earth to heat, which of course causes warm air to rise leading to all sorts of things happening in the atmosphere.

At night the heating effect isn't there so I would expect the air to be colder - not immediately, but as the earth cools so will the air above it.

Surely there are some with experience of this from their own cockpit?

[Lancman]

A foot is a foot, a metre is a metre, a kiss is still a kiss.......................

[glum]

:confused:

[Lancman]

The International Standard Atmosphere is a concept, a datum point, it exists only in your head. At any particular point on the Earth's surface that is at sea level the actual temperature may be +30 degrees Centigrade and we can say that it is ISA +15. At night it may have gone down to +5, and we say that it is ISA -10. ISA hasn't changed; it's a universally accepted Standard.

[glum]

Sure, I understood that in post 5.

My question has expanded to ask if there are observations people have made for a common change between day and night relative to where they are in the world / time of year.

[Tinstaafl]

I think you have in mind average seasonal diurnal temp. minima & maxima, usually given for each month often on tourist/travel & meteorology websites.

[westhawk]

glum:

If you're asking whether the temperature at typical jet cruising levels varies according to whether it's night or day then I'll offer my own observation. No, not that I've ever noticed. Temperature variations at typical cruising altitudes are attributable to upper air pressure patterns and the associated meandering of the jet stream. Large variations in temperature aloft are often noted in the vicinity of large frontal systems and convective activity.

Understanding the complex nature of climate and meteorology is a lifelong pursuit consisting of specific education, training and continuing study. Pilots with a basic understanding have a unique opportunity to compare the standard atmospheric models they've become familiar with through training to what they see while flying their aircraft. It is a highly interesting pursuit that I try not to confuse with the actual scientific understanding possessed by actual meteorological experts! But I hope your question has been addressed.

westhawk

[compressor stall]

There is an embryonic theory that there is quite a significant amount of localised cooling in the atmosphere after the passage of a total solar eclipse.

After we experienced some turbulence in the lee of the shadow of the last total solar eclipse (37,000 feet) that was not there prior to the shadow's passage (same location) there are some weather balloons being organised to fly before and after the next one in November.

Nothing to do with ISA though, but tangential to the discussion. :E

[glum]

Thanks Westhawk, that's exactly what I was hoping for.

As an aircraft design engineer I'm mindful of the ever increasing heat output from power electronics, galleys, people etc. and how we can better reject that heat in the various phases of flight or indeed on the ground when parked or taxiing.