Ozone maxima over Southern Africa : characteristics and mechanisms.
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Date
1995
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Abstract
This thesis aims to clarify the sources of, and mechanisms associated with,
the generation of ozone maxima over the southern African region. Inasmuch as,
tropospheric ozone concentration is a function of both chemistry and
meteorology, this thesis concentrates on the role of atmospheric dynamics.
Firstly, a statistical analysis of the relationship between total ozone and
meteorological parameters revealed a generally weak negative relationship
between total ozone and the height of the 500, 300 and 100 hPa geopotential
surfaces. The relationship is best expressed by the passage of a mid-latitude
cyclone while anticyclonic conditions exhibited a weak relationship. An
examination of the spatial distribution of total ozone and potential vorticity
(PV), during the passage of westerly troughs, prompted a more thorough
investigation of the exchange of ozone between the stratosphere and
troposphere.
The relationship between tropospheric ozone, and low pressure and
anticyclonic systems is investigated further using data obtained during the
South African Fire-Atmospheric Research Initiative (SAFARI) conducted in 1992.
Ozone concentrations, as expressed by ozonesonde data, reveal different
characteristic profiles for the two scenarios. Explanations for the
differences observed are sought in the observed circulation patterns during
the experiment.
Case studies at Okaukuejo (Namibia), Irene (South Africa) and Brazzaville
(Congo), which were utilised as ground stations during SAFARI, are presented
in an attempt to gain insight into the vertical distribution of ozone over the
entire expanse of the study region. The role of convective systems in the
generation of short-lived upper tropospheric ozone maxima at tropical
latitudes is illustrated while the different vertical ozone signatures,
expressed under cyclonic and anticyclonic systems as described earlier, are
reconfirmed by the Okaukuejo and Irene data.
An attempt is made to investigate dynamic links between the troposphere and
stratosphere and the concomitant exchange of ozone during the passage of
westerly trough systems. Particularly deep troughs or cut off low pressure
systems are identified as important mechanisms in the generation of upper
tropospheric ozone maxima. An examination of the vertical distribution of
ozone at Irene during the passage of a COL, using data obtained from the
SA'ARI 1994 experiment, suggests concurrence with Danielsen's (1968) model of
tropopause folding. The intrusion of high PV and dry stratospheric air,
coupled with downward flow near the tropopause, in the vicinity of the upper
tropospheric disturbance, promotes the transport of ozone-rich air to
tropospheric altitudes.
The limited availability of data has severely hampered the understanding of
tropospheric ozo~e in southern Africa in the past. This study demonstrates the
value of daily vertical ozone data, even for very short periods.
Description
Thesis (Ph.D.)-University of Natal, 1995.
Keywords
Ozone layer--South Africa., Ozone layer depletion--South Africa., Stratosphere., Theses--Geography.