BGR Bundesanstalt für Geowissenschaften und Rohstoffe

Giraf

 

Coming soon: GIRAF 2011 Workshop

5. - 9. December 2011
Dar es Salaam, Tanzania
Organised by the IUGS-CGI and UNESCO
Hosting Organisation: SEAMIC

 

GIRAF: Geoscience InfoRmation AFrica. Logo

Mesosphere

 

The stratosphere and the mesosphere are sometimes collectively referred to as the "middle atmosphere", which spans altitudes between approximately 10 and 100 kilometers above the Earth's surface. The mesopause, at an altitude of 8090 km (5056 mi), separates the mesosphere from the thermosphere+the second-outermost layer of the Earth's atmosphere. This is also approximately the same altitude as the turbopause, below which different chemical species are well-mixed due to turbulent eddies. Above this level the atmosphere becomes non-uniform because the scale heights of different chemical species differ according to their molecular masses.

The term near space is also sometimes used to refer to altitudes within the mesosphere. This term does not have a technical definition, but typically refers to the region of the atmosphere up to 100 kilometres (62 mi; 330,000 ft), roughly between the Armstrong limit (above which humans require a pressure suit in order to survive) and the Karman line (where astrodynamics must take over from aerodynamics in order to achieve flight); or, by another definition, to the range of altitudes below which commercial airliners fly but above which satellites orbit the Earth. Some sources distinguish between the terms "near space" and "upper atmosphere", so that only the layers closest to the Karman line are described as "near space".

The main dynamic features in this region are strong zonal (East-West) winds, atmospheric tides, internal atmospheric gravity waves (commonly called "gravity waves"), and planetary waves. Most of these tides and waves start in the troposphere and lower stratosphere, and propagate to the mesosphere. In the mesosphere, gravity-wave amplitudes can become so large that the waves become unstable and dissipate. This dissipation deposits momentum into the mesosphere and largely drives global circulation. This helps the Earth.

Noctilucent clouds are located in the mesosphere. The upper mesosphere is also the region of the ionosphere known as the D layer. The D layer is only present during the day when some ionization occurs with nitric oxide being ionized by Lyman series-alpha hydrogen radiation. The ionization is so weak that when night falls, and the source of ionization is removed, the free electron and ion form back into a neutral molecule. The mesosphere has been called the "ignorosphere" because it is poorly studied relative to the stratosphere (which can be accessed with high-altitude balloons) and the thermosphere (in which satellites can orbit).

The mesosphere lies above altitude records for aircraft, while only the lowest few kilometers are accessible to balloons, for which the altitude record is 53.0 km. Meanwhile, the mesosphere is below the minimum altitude for orbital spacecraft due to high atmospheric drag. It has only been accessed through the use of sounding rockets, which are only capable of taking mesospheric measurements for a few minutes per mission. As a result, it is the least-understood part of the atmosphere, resulting in the humorous moniker ignorosphere.[18] The presence of red sprites and blue jets (electrical discharges or lightning within the lower mesosphere), noctilucent clouds, and density shears within this poorly understood layer are of current scientific interest.

Near space was first explored in the 1930s. The early flights flew to the edge of space without computers, spacesuits, and with only crude life support systems. Notable people who flew in near space were Jean Piccard and his wife Jeannette, on the nearcraft The Century of Progress. Later exploration was mainly carried out by unmanned craft, although there have been skydiving attempts made from high-altitude balloons.

High-altitude platform stations have been proposed for applications such as communications relays. There has been a resurgence of interest in near space to launch manned spacecraft by man. Groups like ARCASPACE, as well as the da Vinci Project are planning on launching manned suborbital space vehicles from high-altitude balloons. JP Aerospace has a proposal for a spaceport in near space, as part of their Airship to Orbit program.

Near space has long been used for scientific ballooning, for applications such as submillimetre astronomy. High-altitude balloons are often flown by students and by amateur groups to altitudes on the order of 100,000 ft (30,000 m), for both scientific and educational purposes.

Contact

    
Dr. Kristine Asch
Phone: +49-(0)511-643-3324
Fax: +49-(0)511-643-3782