Erdfernerkundung - Numerische Physik: Modellierung

5.5. CAWSES 273
Abbildung 5.40: Ion–pair production due to energetic charged particles during the solar cycle
time, NOx is depleted in the mesosphere by photochemical reactions – its life time in the
stratosphere is much longer and with time it sinks slowly to lower altitudes with its maximum
around the height of the ozone layer.
§ 908 Ozone depletion (bottom panel in Fig. 5.39) is regulated by both species: initially in
the event there is a strong depletion in the mesosphere above 60 km due to the combined
effects of HOx and NOx. The pronounced depletion around 40 km, on the other hand, is
due to NOx as can be inferred from the long time scales. Owing to different temperatures,
the NOx-induced ozone depletion is larger in the stratosphere than in the mesosphere. The
most remarkable effect, however, is the persistent ozone depletion by a few percent right in
the middle of the ozone layer around 25 km lasting for more than a year. Such a persistent
anomaly bears the seed for possible cumulative effects of solar energetic particle events – in
particular during magnetic field reversals where the effects of individual events will be even
larger than in the present day atmosphere.
Ionization through the Solar Cycle
§ 909 The first approach on long–term studies is a view on the solar cycle. Figure 5.40
shows ion–pair production rates from 1988 to 2005, that is almost 2 solar cycles. Times
of high solar activity are clearly visible as times with increased ion–pair production rates
between 1989 and 1992 and again between 2000 and 2005. Solar minimum is around 1996.
The sharp drop in ionization rate at 20 km is ‘instrumental’: the highest energies observed
by the GOES particle detector are 800 MeV protons which stop at that height. At lower
altitudes, ionization expected from higher energies is ignored in this figure – this does not
pose a problem for modeling because the subsequent atmospheric chemistry model is limited
to the stratosphere and mesosphere and thus is not influenced by neglect of tropospheric
ionization. 14
14 Such a limitation for a chemistry module is validated by the fact that the tropopause is a boundary
which strongly inhibits transport of matter and thus almost completely decouples the troposphere from the
atmosphere above.
c○ M.-B. Kallenrode 2. Juli 2008