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(6) Aeronomy

Introduction to Geophysics and Planetary Physics. Geophysics 129. (6) Aeronomy. Geophysics 130. What is Aeronomy?. Aeronomy is the science of the upper atmosphere – where dissociation and ionization becomes important.

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(6) Aeronomy

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  1. Introduction to Geophysics and Planetary Physics Geophysics 129 (6) Aeronomy

  2. Geophysics 130 What is Aeronomy? Aeronomy is the science of the upper atmosphere – where dissociation and ionization becomes important. If we look at the structure of the atmosphere in terms of composition, this will primarily happen in the Heterosphere and in the Exosphere (picture credit: M. L. Salby).

  3. Geophysics 131 Spheres In terms of the average temperature profile we have to consider the Thermosphere (and aslo the Mesosphere) – and by definition – the Ionosphere (if we look at the atmosphere in terms of electric properties (picture credit: Thomson). Some (most) aspects have already been covered in the lectures by Günter Kargl.

  4. Geophysics 130 Plasmasphere Above the Ionosphere (which is partly ionized) we find (above ~1000 km) the Plasmasphere, which is almost entirely ionized (mainly hydrogen), and – largely – co-rotates with the Earth.

  5. Geophysics 131 Mesosphere Mean zonal winds in December (NRL): The Mesosphere is characterized by strong (geostrophic) zonal winds, reaching 70 m/s and more, with westerlies in the winter-, and easterlies in the summer hemisphere.

  6. Geophysics 132 Mesopause The upper atmosphere is very dry, but Polar Mesospheric Clouds (PMCs) frequently mark the Mesopause – where the atmosphere is coldest (Credit: P.M. Heden)

  7. Geophysics 133 Noctilucent Clouds Observers on the ground (not only at polar latitudes) know them as Noctilucent Clouds (NLCs). They frequently show features of Gravity Waves (Credit: D. Weir, NASA (right)).

  8. Geophysics 134 Polar Mesospheric Clouds The satellite perspective (AIM) reveals the typical spatial distribution, the ISS the appearance (Credit: NASA).

  9. Geophysics 135 Anthropogenic Clouds Shuttle launches (Hydrogen + Oxygen) were a significant water vapor source for the upper atmosphere, producing artificial clouds (Credit: Ken Thornsley (l), NASA (r)).

  10. Geophysics 136 Transient Luminous Events The Mesosphere (“Ignorosphere”) is home to (still) strange phenomena, summarized under Transient Luminous Events (Credit: NOAA).

  11. Geophysics 137 Red Sprites and Elves Red Sprites (“Kobolde”) are large-scale electric discharges over active thunderstorms, triggered by (rare) positive cloud-to-ground lightnings (Credit: NOAA (l), H. Stenbaek-Nielsen (r)). They typically start at ~70 km altitude, last just milliseconds, propagate downwards downwards at speeds of ~107 m/s – and are still not really understood. Elves are rapidly expanding (up to 500 km across) disk-shaped regions of luminosity, lasting less than a millisecond, which occur high above energetic cloud-to-ground lightning of positive or negative polarity. Elves most likely result when an energetic electromagnetic pulse (EMP) propagates into the ionosphere. Though they can be accompanied by sprites. Elves got their name as an acronym for Emission of Light and Very Low Frequency perturbations due to Electromagnetic Pulse Sources.

  12. Geophysics 138 Gigantic Jets and Blue Jets Gigantic Jets also appear above thunderclouds, but without associated lightnings (Credit: Natur (l), H. T. Su et al. (r)). They propagate upwards – and are still not really understood. Blue jets are optical ejections from the top of the electrically active core regions of thunderstorms, but not directly associated with cloud-to-ground lightning. They typically propagate upward in narrow cones of about 15 degrees.

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