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weather & performance

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Aircraft Systems, General Aviation, Instrument Rating, Private Pilot, Weather

Does temperature inversions have an affect on altimeter readings?

1.) We know that the altimeter reads the altitude based on the pressure. Less pressure and the altimeter will read a higher altitude. More pressure and the altimeter will read a lower altitude. 

2.) We know that temperature has an affect on density and pressure. Higher temperatures means that the air will rise and spread out (less dense) and we know that cold air will sink and shrink(more dense). 

3.) We also know that there is four types of temperature inversions, mostly dealing with radiation temperature inversions.  Temperature inversions means that as altitude increases, temperature increases. Over the cold long nights the temperature from the ground tends to get colder but the air above the ground doesn't necessarily get cold due to the fact that air is a poor conductor. Causing to have the air above the ground to be less cold than the air close to the ground. 

If flying at or above a temperature inversion how would you know which altimeter setting to adjust the altimeter? 

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2 Answers



  1. ayavner on Sep 07, 2018

    Interesting question. If I understand the question, my instinct is to say you use whichever altimeter setting you were given – I think the important thing is that everyone’s altimeter is set to the same in a given area. Even if the pressure is somewhat different above the inversion layer, everyone will be off by the same amount at that level. Assuming you are talking below the flight levels?

    Should be an interesting discussion!
    adam

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  2. John D Collins on Sep 08, 2018

    Temperature and temperature inversions will affect what an altimeter indicates for any given true altitude above where the altimeter setting is determined. The altimeter setting is determined at the surface at some location and only reflects the correction for temperature and pressure at that location. The farther away one is from the point of altimeter setting determination, the greater the potential error and the higher one is above that point, the greater the error. This is because the altimeter is designed to indicate altitude based on the ambient pressure based on a standard model of the atmosphere which involves a standard pressure and temperature lapse rate. When the conditions don’t match the model, the altimeter will not indicate the true altitude. Generally, with colder conditions than standard for the altitude, the altimeter will indicate higher than the actual altitude and with warmer temperatures the altimeter will indicate lower than the actual altitude.

    The error for temperature is zero at the point of measurement because the altitude is known and the altimeter setting is essentially determined by adjusting the altimeter to the known altitude and reading off the altimeter setting. This can be accomplished manually or using automation and sensors.

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