High atmosphere
As upper atmosphere those higher areas of be Earth's atmosphere called, where the air density and the air pressure drops below a technically largely meaningless amount.
Depending on the scientific or technical application, this ( de facto fuzzy) definition concerns :
- all layers of air above the tropopause - e.g. B. from the perspective of classic meteorology or gliding
- the thermo - or ionosphere - z. B. because of reflections during telemetry or radio navigation , or direct electrodynamic interactions and other non-gravitational orbital disturbances on earth satellites
- the exosphere - for example for aspects of solar - terrestrial interactions ( solar wind , geomagnetic field ) or the magnetosphere
In contrast, the “ free atmosphere ” refers to those layers of air that lie above the peplop break or are more than 2 km from the ground. Beyond this basic layer of soil can be used for many meteorological effects, the influence of friction are neglected.
In the early days of space travel , the density of the terrestrial high atmosphere was greatly underestimated: on average, the atmosphere above about 200 km orbit height was about 7 times denser than assumed from previous research. As a result, the braking of the first earth satellites was much stronger than expected, and the planned service life was overly optimistic.
In interplanetary space travel - e.g. B. for flights to Mars - or for re-entry and return of a probe to Earth, the high atmosphere of planets can be used to brake the missile . These non-hazardous orbital maneuvers of aerobraking but must be metered very precisely.
Apparitions
Some scientists suspected early on that the air envelope extends far above the height of the clouds, primarily because of the falling stars . However, there are a number of other phenomena, the best known of which are:
- the glowing night clouds at a height of about 85 km,
- the northern lights of the Arctic and Antarctic (about 100 to 200 km high),
- the radio reflection of short waves in the D , E and F layers (see picture). They are related to the degree of ionization of the air, were predicted by Oliver Heaviside in 1902 and proven by Appleton in 1924 ,
- Influence on the earth's magnetic field (approx. 10% share of the total field, researched since ~ 1850), change in needle deviation in magnetic storms .