[Alumnos] IAFE-COLOQUIO: "Physics at the edge between the atmosphere and space"

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Subject: IAFE-COLOQUIO: "Physics at the edge between the atmosphere and  space"


                      PRÓXIMO COLOQUIO DEL IAFE
             Instituto de Astronomía y Física del Espacio
                           CONICET-UBA
_________________________________________________________________________

      "Physics at the edge between the atmosphere and space"

                 Franz-Josef Lübken y Ralph Latteck
        Leibniz Institute of Atmospheric Physics Schloss-Str. 6 18225
Kuehlungsborn, Alemania
                    Lunes 17 de setiembre 2012, 15:00hs.
                           Aula del Edificio IAFE

The importance of basic physical processes in the atmosphere changes
fundamentally in the mesosphere (50 to 100 km) primarily due to the
reduction of gas density being orders of magnitude smaller compared to the
troposphere. For example, molecules are no longer in thermodynamic
equilibrium with radiation and mixing ratios of inert species change with
height. Furthermore, gravity waves being generated in the troposphere
achieve large amplitudes in the mesosphere, get instable and produce
turbulence. This in turn causes a modification of the general circulation
which leads to a substantial cooling (heating) in the summer (winter)
mesosphere. Consequently, the summer mesopause (90 km) at polar latitudes
is much colder than in winter and cools down to approximately 150 Kelvin
(the coldest place in the Earth's atmosphere) despite permanent sunshine.
The extremely low temperatures lead to ice particles known as noctilucent
clouds (NLC). The same ice particles produce very strong radar echoes
(PMSE, polar mesosphere summer echoes). Since a few years NLC and PMSE are
studied in detail with lidars (light induced detecting and ranging) and
radars, respectively. This has lead to a better understanding of the
physical processes involved in ice particle formation, their influence on
the background plasma, and the importance of the background atmosphere.
Large temperature trends are observed in the mesosphere at mid latitudes.
Based on radio wave propagation experiments performed at the IAP since the
1950s a temperature decrease of up to 20 degrees in 40 years is observed,
i. e., a factor of 40 larger compared to the troposphere. Since ice
particles are very sensitive to atmospheric temperatures, NLC and PMSE are
proposed to be sensitive indicators for trends in the upper atmosphere.
The basic physical processes leading to the thermal structure of the upper
atmosphere and to NLC and PMSE are explained in the presentation and
potential long term and solar cycle variations are discussed.