What is the Boundary Layer, and where is aloft?


a l o f t 
/əˈlɒft/ adverb, adjective
in or into a high or higher place; up above
Word Origin: from Old Norse ā lopt (in the air)
Translation to other languages:
German: oben, empor, hoch droben
French: en haut, en l'air
Italian: in alto
Spanish: en alto, en vuelo, en el aire, arriba
Hungarian: Fenn, a magasban
Norwegian: værs
Swedish: högt upp
Polish: wysoko
The Boundary Layer
The term boundary layer is used in meteorology, 
In meteorology the planetary boundary layer (PBL), also known as the atmospheric boundary layer (ABL), is the lowest part of the atmosphere. Its behavior is directly influenced by its contact with a planetary surface.
This is where we play and fly!
 
In meteorology the planetary boundary layer (PBL), also known as the atmospheric boundary layer (ABL), is the lowest part of the atmosphere. It's behavior is directly influenced by its contact with a planetary surface. On Earth it usually responds to changes in surface radiative forces in an hour or less. In this layer physical quantities such as flow velocity, temperature, moisture, etc., display rapid fluctuations (turbulence)  and are strong. Above the PBL is the "free atmosphere" where the wind is approximately parallel to the isobars while within the PBL the wind is affected by surface drag and turns across the isobars. The free atmosphere is usually nonturbulent, or only intermittently turbulent. 
The depth of the boundary layer is the area from the planet’s surface to the height where the surface no longer mixes with the air mass aloft.
Although most paraglider and hang glider pilots can only exploit the upward movement in the boundary layer from thermals rising through it, the boundary layer can also take the shape of mixing air influenced by the surface that is not usable by pilots. You can read more about this here:

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