Decadal evolution of atmospheric ozone and remote sensing of tropospheric ozone
<p>Monitoring and preservation of the Earth's ozone layer has engaged scientists intensively in the 20th century especially after the discovery of the Antarctic ozone hole by Farman et al. (1985). There is increasing evidence that ozone depletion occurs on a global scale such as in the...
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| Format: | Others |
| Language: | en |
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1997
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| Online Access: | https://thesis.library.caltech.edu/7434/2/Jiang_y_1997.pdf Jiang, Yibo (1997) Decadal evolution of atmospheric ozone and remote sensing of tropospheric ozone. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/40ec-pk63. https://resolver.caltech.edu/CaltechTHESIS:01242013-141747377 <https://resolver.caltech.edu/CaltechTHESIS:01242013-141747377> |
| Summary: | <p>Monitoring and preservation of the Earth's ozone layer has engaged scientists intensively
in the 20th century especially after the discovery of the Antarctic ozone hole by
Farman et al. (1985). There is increasing evidence that ozone depletion occurs on a
global scale such as in the Arctic and at midlatitudes. Following the understanding
of the the catalytic destruction of ozone in the stratosphere by chlorine derived from
chlorofluorocarbons (CFC's), there is a growing realization that the consequences of
anthropogenic pollution can be felt in unpredictable ways in near and faraway places.</p>
<p>The atmosphere is a complex mixture of more than a thousand trace chemicals
that are constantly reacting and redistributing. The need to understand the sources
and distribution of these chemicals, along with the mechanisms by which they are
transformed, transported, and ultimately removed from the atmosphere, has grown in
parallel with the increased concern about air pollution and its consequences. Therefore,
the exploration of the mechanism controlling both spatial and temporal variation of
the atmosphere is a key component of the atmosphere science research (as part
of the global change) and it requires an interdisciplinary approach and innovative
application of the traditional techniques of chemistry, physics, and meteorology.</p>
<p>Monitoring the composition of the troposphere and stratosphere globally is particularly
interesting in this context for ozone which is the key component regulating
the photochemistry of the atmosphere.</p>
<p>In chapter 1, the decadal evolution of the Antarctic ozone hole is studied by using
ozone column amounts obtained by the total ozone mapping spectrometer (TOMS) in
the southern polar region during late austral winter and spring (Days 240 - 300) for
1980 - 1991 using area-mapping techniques and area-weighted vortex averages. The
vortex here is defined using the -50 PVU (1 PVU = 1.0 x 10^(-6)K kg^(-1) m^2 s^(-1)) contour
on the 500 K isentropic surface. The principal result is that there is a distinct change
after 1985 in the vortex averaged column ozone depletion rate during September and
October, the period of maximum ozone loss. The mean ozone depletion rate in the
vortex between Day 240 and the day of minimum vortex-averaged ozone is about 1
DU/day at the beginning of the decade, increasing to about 1.8 DU /day by 1985,
and then apparently saturating thereafter. The vortex-average column ozone during
September and October has declined at the rate of 11.3 DU / yr (3.8%) from 1980
to 1987 (90 DU over 8 yrs), and at a smaller rate of 2 DU / yr (0.9%) from 1987 to
1991 (10 DU over 5 years, excluding the anomalous year 1988). We interpret the
year-to-year trend in the ozone depletion rate during the earlier part of the decade
as due to the rise of anthropogenic chlorine in the atmosphere. The slower trend at
the end of the decade indicates saturation of ozone depletion in the vortex interior, in
that chlorine amounts in the mid-80s were already sufficiently high to deplete most of
the ozone in air within the isolated regions of the lower stratospheric polar vortex. In
subsequent years, increases in stratospheric chlorine may have enhanced wintertime
chemical loss of ozone in the south polar vortex even before major losses during the
Antarctic spring.</p>
<p>In chapter 2, we will show that standard deviation of column ozone from the zonal
mean (COSDZ) provides a measure of the longitudinal inhomogeneity in column ozone
and dynamical wave activities in the atmosphere. We point out that simulation of this
quantity by three-dimensional (3-D) models could provide a sensitive check on the
wave activities in the stratosphere that are responsible for ozone transport. Analysis
of the Total Ozone Mapping Spectrometer (TOMS) data shows a profound secular
change in COSDZ from 1979 to 1992. The changes are not symmetric between the
southern and northern atmospheres. In the southern higher latitudes, COSDZ shows
a significant increase around 65° in August and September, while the changes are
much smaller in the northern higher latitudes in the boreal spring. We interpret most
of the observed changes to be caused by enhanced ozone losses in the polar vortices in
the springtime of the two respective hemispheres. There is also evidence for secular
dynamical changes at mid-latitudes.</p>
<p>In chapter 3, an estimate of tropospheric ozone levels over tropical pacific south
America is obtained from the difference in the TOMS (Total Ozone Mapping Spectrometer)
data between the high Andes and the Pacific Ocean. From 1979 to 1992
tropospheric ozone apparently increased by 1.47 ± 0.40 %/yr or 0.21 ± 0.06 DU / yr
over South America and the surrounding oceans. An increase in biomass burning in
the Southern Hemisphere can account for this trend in tropospheric ozone levels.</p>
<p>Due to larger multiple scattering effects in the troposphere compared to that in
the stratosphere, the optical path of tropospheric ozone is markedly enhanced (as
compared with that of stratospheric ozone) in the Huggins bands from 310 nm to
345 nm. By using this principle, we model the direct and diffuse solar fluxes on the
ground shows differences between tropospheric and stratospheric ozone in chapter 4.
The characteristic signature of tropospheric ozone enables us to distinguish a change
in tropospheric ozone from that of stratospheric ozone. A simple retrieval algorithm
is used to recover the tropospheric column ozone from simulated data.</p>
<p>Light reflected or transmitted by a planetary atmosphere contains information
about the particles and molecules in the atmosphere. Therefore, accurately calculating
the radiation field is necessary. In the appendix, the doubling-adding method for
plane-parallel polarized radiative transfer model is studied in detail. A special Fourier
expansion leading to a compact notation is developed for the azimuth-dependent
quantities. The multi-layer model for a vertically inhomogeneous atmosphere is implemented and several numerical results are presented for verification and comparison.
Preliminary runs from this model in the Huggins bands show the distinct features of
linear polarization in the reflection spectrum due to the multiple Rayleigh scattering
in the troposphere.</p>
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