Science_Illustrated_Australia_-_Issue70_2019

scienceillustrated.com.au | 55

Mountain ‘wave’

lifts glider to the

stratosphere

For only a few days a year, two major

air currents combine forces over the

Andes Mountains, producing a 30km-

high wave of wind that can lift the

Perlan II glider into the stratosphere.

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Air currents meet mountain

1

In the summer, the polar jet stream is

blowing across the Andes Mountains

in Argentina at the same time as the

polar vortex. When the two air streams pass

a mountain at altitudes of 10km and 30km

respectively, the air is forced upwards as it is

cooled one degree per 100 metres, causing

cloud formation and precipitation.

Dry air descends

2

Once the air passes the

mountain peak, it has dried,

and is consequently heavier.

Gravity will pull it downwards and

the higher temperatures close to the

ground heat the air, causing it to rise

in the form of a mountain ‘wave’.

Warm air sends powerful

waves into the stratosphere

3

Perlan II is lifted 12km by

another plane, subsequently

continuing its climb surfing on

the mountain wave. The wave grows

stronger as it ascends, because both

the pressure and the surrounding

wind speeds are gradually reduced.

The polar vortex

Stratospheric mwave ountain

The polar jet

stream

Precipitation cloud

Perlan II

The Perlan II glider

pilots expect to set an

altitude record of

27km

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