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Ozone maxima over Southern Africa : characteristics and mechanisms.Combrink, Jane. January 1995 (has links)
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. / Thesis (Ph.D.)-University of Natal, 1995.
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Role of synoptic weather systems in surface ozone concentration in Durban region.Langa, Mduduzi Amos. January 1995 (has links)
Measurements of surface ozone in Durban have been
undertaken since September 1994 until August 1995 using a Dasibi ozone monitor model 1108. There is a seasonal
variation in surface ozone with a small amplitude of 6.5 ppb. The mean maximum of 12.5 ppb is experienced in August and the minimum in December (6 ppb). The late winter peak and the sharp rise from June to July is possibly related to the greater accumulation of ozone at the surface due to the poor dispersion, higher frequency of inversions and lower mixing depth.
The study also focuses on the relationship between synoptic weather systems and daily ozone concentrations in an attempt to establish if any relationship exists. The analysis suggests that there is an increase in ozone concentration during the pre-frontal and established high pressure systems and a reduction in ozone under postfrontal conditions.
The mean diurnal variation in surface ozone depicts a maximum between solar noon and 14:00, which is typical of an urban-industrial environment, in which ozone precursor gases have built up during the morning. However, a secondary peak in the early morning during winter and autumn was more difficult to explain and is thought to be due to the transport of ozone from the interior in the mountain-plain wind systems.
Comparison of ozone values at Durban with results available from the other locations in South Africa such as Cape Point and the Eastern Transvaal Highveld has been undertaken.
Ozone values at Durban are lower than Cape Point, which is a representative of a background monitoring station. It ls hypothesised that those low ozone concentrations may be due to high NOx which in turn depletes ozone. / Thesis (M.Sc.)-University of Natal, 1995.
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