Decadal evolution of atmospheric ozone and remote sensing of tropospheric ozone

• Main Author: Jiang, Yibo
• Format: Others
• Language: en
• Published: 1997
• 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>

<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>