THERMAL INVERSION, THE CASE OF THE CANARY ISLANDS

Graphic of the 2 main layers in The Canary islands

In the most superficial layer of the Earth it is normal for the temperature to fall as we climb but there are certain layers where the opposite occurs, if we raise the temperature increases. This is mainly due to two causes; the cooling of the planet during the night and the atmospheric pressure.

We can see how temperature normally decrease when we gain height BUT not always
Real graphic of temperature on Teide


During the day the Sun radiates us energy making the temperature of the surface rise, at night the Earth releases that energy in the form of infrared rays and these rays tend to heat a layer of air in height, the result is that we have a layer of air warmer above a cooler one, therefore a thermal ceiling is formed that does not allow the air to pass upwards since when the updrafts reach it the temperature of both masses is balanced and there is nothing that makes them rise, for now. This situation is less common in the Atlantic Islands since their small surface area is not significant enough to influence the entire mass of air that surrounds them, but in these areas what is common is that atmospheric pressure has the same effect. Remember that in areas of high pressure the air descends and is compressed on itself, this compression takes its proper increase in temperature. It is like an hourglass where each grain is falling on another and that friction that occurs at the top of the mound is the equivalent of heating a layer in height of the troposphere.

Graphic of the 2 main layers in The Canary islands
Trade winds, upper and lower

The high altitude of some islands in relation to their surface defines different climatic conditions according to their altitude. A humid subtropical climate almost permanent in the lower layers and another much more extreme and dry, almost alpine continental, in the upper layers.

Tenerife with its high altitude presents up to three climatic floors with great differences: the sea moisture blocked in the lower layer, a stable band at medium height and the typical extreme and unstable mountain conditions on the summits.

This is another of the key factors to understand the flight conditions in the Canary Islands: The thermal inversion. This appears when the anticyclone grows or approaches the islands since inside the anticyclones the air descends or subsides generating greater pressure and with it increases its temperature, forming this stable layer where the temperature increases with the height instead of descending as it would be normal. This layer usually ranges between 700 and 1400 meters and delimits two quite different air currents between them, below the lower Trade Wind, cool and humid which is controlled by the isobars and above the upper Trade Wind, warm and dry, which obeys the general West current.

It is a common characteristic of the climate of the Canary Islands and is present more than 90% of the time. This inversion, usually of about 3 or 4 degrees Celsius, almost physically, blocks the connectivity of the lower and upper air masses, preventing the wind from ascending the summits of the island and falling again, forcing it to surround it like the profile of a wing .

Flying above the inversion layer

If the inversion disappears is that the anticyclone has also done it and a storm is approaching, so the cloudiness increases dramatically and with it the rain appears.

The singularity of the general morphology of the island in the form of an arrow, oriented in the opposite direction to the usual northeast winds, produces a deviation of the wind flow from the lower layers by its laterals and generates a series of local aerodynamic effects suitable for free flying. 

The triangular shape of the Island also defines a perimeter with three points that severely limits the Coanda effect of the wind on its profile and prevents it from turning when it reaches them, being thrown into the sea while generating calm areas. Therefore, in almost any weather condition, we will always find a place protected to the lee of this imposing volcanic massif, a microclimate or “bubble” of good weather that is incredible for pilots who visit the island for the first time.

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