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  • Writer's pictureRuben GT

Low altitude temperature Inversion and sounding

Updated: 7 days ago

You have certainly already noticed this phenomenon, usually during the summer here on the Island, and even if you don't live in Madeira, at a global level the effect is similar.

When the atmospheric pressure remains very high for several days, representing high atmospheric stability, there is a tendency to form this phenomenon that we call temperature inversion.

Temperature inversion real life examples

The image above represents a normal day, the one below a day with low thermal inversion.

Please note that temperature inversions occur often, the one that "interests" us is the one that forms at very low altitude, around 300 meters or lower.

We can clearly perceive the presence of this effect a few days before using a tool called Sounding.

Or on the day itself, due to the presence of a grayish-colored fog at low altitude, formed by dust and various forms of pollution, trapped in the lower layer of the thermal inversion, as if the latter made a shield similar to the greenhouse effect, and the result is similar.

Calheta beach in a low temperature inversion day

The effect of the temperature Inversion can be clearly seen in this image, with the dust particles and pollution.

The explanation for this is that, as a rule, the temperature drops with altitude, with the air being colder in the mountains than near the sea.

However, on these days, the temperature, instead of decreasing, increases with altitude, up to a certain point, being, as a general rule, warmer in higher areas than near the sea.

In terms of Free Flight (Paragliding and Hang Gliding) what does a temperature inversion tell us?

Hot air is less dense and so it rises, helping us to rise with it.

This is what happens on a normal day, allowing us to gain altitude in flight and be able to stay flying for a long time.

If the air above is warmer than in the lower layer, then the air becomes "stagnant" in this lower layer, not allowing us to rise, making flights as a general rule shorter and sometimes a little turbulent when passing through the inversion layer.

Also using the Sounding graph we are able to determine the dew point, indicating that in addition to being warmer, the air is also often drier with altitude, on days with low temperature inversions.

Sounding graph

Sounding of a normal flight day in terms of temperature (notice that the inversion almost always happens, however when it occurs higher up it doesn't accumulate pollution close to the ground and it allows some higher altitude gains for Free Flight

Low temperature inversion Sounding graph

Day with temperature Inversion at low altitude

Notice how the temperature curve, in red, evolves on a normal day when compared to the inversion day.

To fully understand this graph an advanced training is required, but for this type of reading it is relatively simple to read, the numbers on the right in red correspond to temperature values and the values on the left correspond to atmospheric pressure, representing different altitudes.

Below you will find the complete description of the data obtained through this graph.

Don't try to understand them all, use just the ones that help you understand the effect of a temperature inversion.

Sounding information available

Just as a curiosity, here is all the data that can be used from a (Sounding)

The dew point, just as a quick parenthesis so as not to prolong this post too much, is the temperature at which the air cannot hold more moisture and condensates, that is, if for example, at 500 meters the dew point is 15º and the temperature at that same altitude is 15º, the probability of cloud formation at that level is almost 100%

In this order of ideas, you will easily understand that the further "away" the dew point is from the temperature, for a given altitude, the drier the air will be at that level.

As pilots we use this tool, among others, to help us draw up a flight plan and help us understand what the conditions will be like in terms of forecast.

However, it is also possible to use these basic notions for everyday life, knowing how to read the basics of a sounding, we can get to know the temperature, dew point and wind speed with altitude, with this we can decide whether to go to the beach, to the mountains or to the interior where we might be more sheltered from the wind and heat.

This does not in any way replace the meteorology classes on a Paragliding course, or other more advanced meteorology courses, on the other hand, it helps to make a little more simple readings of this great tool that is the Sounding.

Simplified explanation of the temperature Inversion phenomenon, using hot and cold water bottles by Iberê of manual do mundo

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