Trends in the Vertical Distribution of Ozone Randel, William J.; Stolarski, Richard S.; Cunnold, Derek M. ...
Science (American Association for the Advancement of Science),
09/1999, Letnik:
285, Številka:
5434
Journal Article
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Analyses of satellite, ground-based, and balloon measurements allow updated estimates of trends in the vertical profile of ozone since 1979. The results show overall consistency among several ...independent measurement systems, particularly for northern hemisphere midlatitudes where most balloon and ground-based measurements are made. Combined trend estimates over these latitudes for the period 1979-96 show statistically significant negative trends at all altitudes between 10 and 45 km, with two local extremes: -7.4 ± 2.0% per decade at 40 km and -7.3 ± 4.6% per decade at 15 km altitude. There is a strong seasonal variation in trends over northern midlatitudes in the altitude range of 10 to 18 km, with the largest ozone loss during winter and spring. The profile trends are in quantitative agreement with independently measured trends in column ozone, the amount of ozone in a column above the surface. The vertical profiles of ozone trends provide a fingerprint for the mechanisms of ozone depletion over the last two decades.
In situ AGAGE GC-MS measurements of methyl bromide (CH^sub 3^Br) and methyl chloride (CH^sub 3^Cl) at Mace Head, Ireland and Cape Grim, Tasmania (1998-2001) reveal a complex pattern of sources. At ...Mace Head both gases have well-defined seasonal cycles with similar average annual decreases of 3.0% yr^sup -1^ (CH^sub 3^Br) and 2.6% yr^sup -1^ (CH^sub 3^Cl), and mean northern hemisphere baseline mole fractions of 10.37 ± 0.05 ppt and 535.7 ± 2.2 ppt, respectively. We have used a Lagrangian dispersion model and local meteorological data to segregate the Mace Head observations into different source regions, and interpret the results in terms of the known sources and sinks of these two key halocarbons. At Cape Grim CH^sub 3^Br and CH^sub 3^Cl also show annual decreases in their baseline mixing ratios of 2.5% yr^sup -1^ and 1.5% yr^sup -1^, respectively. Mean baseline mole fractions were 7.94 ± 0.03 ppt (CH^sub 3^Br) and 541.3 ± 1.1 ppt (CH^sub 3^Cl). Although CH^sub 3^Cl has astrong seasonal cycle there is no well-defined seasonal cycle in the Cape Grim CH^sub 3^Br record. The fact that both gases are steadily decreasing in the atmosphere at both locations implies that a change has occurred which is affecting a common, major source of both gases (possibly biomass burning) and/or their major sink process (destruction by hydroxyl radical).PUBLICATION ABSTRACT
The current study provides a comparison of the photochemical environments for two NASA field studies focused on the western North Pacific (PEM‐West‐B (PWB) and TRACE‐P (TP)). These two studies were ...separated in calendar time by approximately 7 years. Both studies were carried out under springtime conditions, with PWB being launched in 1994 and TP being deployed in 2001 (i.e., 23 February–15 March 1994 and 10 March–15 April 2001, respectively). Because of the 7‐year time separation, these two studies presented a unique scientific opportunity to assess whether evidence could be found to support the Department of Energy's projections in 1997 that increases in anthropogenic emissions from East Asia could reach 5%/yr. Such projections would lead one to the conclusion that a significant shift in the atmospheric photochemical properties of the western North Pacific would occur. To the contrary, the findings from this study support the most recent emission inventory data Streets et al., 2003 in that they show no significant systematic trend involving increases in any O3 precursor species and no evidence for a significant shift in the level of photochemical activity over the western North Pacific. This conclusion was reached in spite of there being real differences in the concentration levels of some species as well as differences in photochemical activity between PWB and TP. However, nearly all of these differences were shown to be a result of a near 3‐week shift in TP's sampling window relative to PWB, thus placing it later in the spring season. The photochemical enhancements seen during TP were most noticeable for latitudes in the range of 25–45°N. Most important among these were increases in J(O1D), OH, and HO2 and values for photochemical ozone formation and destruction, all of which were typically two times larger than those calculated for PWB. A comparison of these airborne results with ozonesonde data from four Japanese stations provided further evidence showing that the 3‐week shift in the respective sampling windows of PWB and TP was a likely cause for the differences seen in O3 levels and in photochemical activity between the two airborne studies.
This paper investigates isentropic ozone exchange between the extratropical lower stratosphere and the subtropical upper troposphere in the Northern Hemisphere. The quantification method is based on ...the potential vorticity (PV) mapping of Stratospheric Aerosol and Gas Experiment (SAGE)-II ozone measurements and contour advection calculations using the NASA Goddard Space Center Data Assimilation Office (DAO) analysis for the year 1990. The magnitude of the annual isentropic stratosphere-to-troposphere ozone flux is calculated to be approximately twice the flux that is directed from the troposphere into the stratosphere. The net effect is that ~46 ×X 10^sup 9^ kg yr^sup -1^ of ozone are transferred quasi horizontally from the extratropical lower stratosphere into the subtropical upper troposphere between the isentropic surfaces of 330 and 370 K. The estimated monthly ozone fluxes show that the isentropic cross-tropopause ozone transport is stronger in summer/fall than in winter/ spring, and this seasonality is more obvious at the upper three levels (i.e., 345, 355, and 365 K) than at 335 K. The distributions of the estimated monthly ozone fluxes indicate that the isentropic stratosphere-to-troposphere ozone exchange is associated with wave breaking and occurs preferentially over the eastern Atlantic Ocean and northwest Africa in winter and over the Atlantic and Pacific Oceans in summer. PUBLICATION ABSTRACT
Global Atmospheric Gases Experiment/Advanced GAGE (GAGE/AGAGE) observations of CCl3F indicate that global concentrations of this compound reached a maximum in 1993 and decayed slightly in 1994; ...CCl2F2 concentrations increased approximately 7 ppt in both 1993 and 1994. The observations suggest that world emissions in these two years were smaller than industry production figures would suggest and have decreased faster than expected under the Montreal Protocol and its amendments. An analysis of regional pollution events at the Mace Head site suggest that industry may be underestimating the decline of emissions in Europe. It is argued, however, that the decline in European emissions is not biasing the background Mace Head measurements (or the GAGE global averages). Combining the chlorofluorocarbon measurements, including CCl2FCClF2, with GAGE/AGAGE measured global decreases in CH3CCl3 and CCl4 after 1992 and with Cape Grim archived air measurements of CHClF2, the measurements suggest that anthropogenic atmospheric chlorine loading from these six gases maximized in 1992 at 2.95±0.04 ppb and that it had decreased by 0.02±0.01 ppb by the beginning of 1995.
The isentropic cross-tropopause ozone transport has been estimated in both hemispheres in 1999 based on the potential vorticity mapping of Stratospheric Aerosol and Gas Experiment 11 ozone ...measurements and contour advection calculations using the NASA Goddard Space Flight Center Global and Modeling Assimilation Office analysis. The estimated net isentropic stratosphere-to-troposphere ozone flux is approx.118 +/- 61 x 10(exp9)kg/yr globally within the layer between 330 and 370 K in 1999; 60% of it is found in the Northern Hemisphere, and 40% is found in the Southern Hemisphere. The monthly average ozone fluxes are strongest in summer and weakest in winter in both hemispheres. The seasonal variations of ozone in the lower stratosphere (LS) and upper troposphere (UT) have been analyzed using ozonesonde observations from ozonesonde stations in the extratropics and subtropics, respectively. It is shown that observed ozone levels increase in the UT over subtropical ozonesonde stations and decrease in the LS over extratropical stations in late spring/early summer and that the ozone increases in the summertime subtropical UT are unlikely to be explained by photochemical ozone production and diabatic transport alone. We conclude that isentropic transport is a significant contributor to ozone levels in the subtropical upper troposphere, especially in summer.
Long-term ozone variations at 60-70degS in spring are investigated using ground-based and satellite measurements. Strong positive correlation is shown between year-to-year variations of ozone and ...temperature in the Antarctic collar region in Septembers and Octobers. Based on this relationship, the effect of year-to-year variations in vortex dynamics has been filtered out. This process results in an ozone time series that shows increasing springtime ozone losses over the Antarctic until the mid-1990s. Since approximately 1997 the ozone losses have leveled off. The analysis confirms that this change is consistent across all instruments and is statistically significant at the 95% confidence level. This analysis quantifies the beginning of the recovery of the ozone hole, which is expected from the leveling off of stratospheric halogen loading due to the ban on CFCs and other halocarbons initiated by the Montreal Protocol.
SAGE (version 5.96) ozone trends in the lower stratosphere Cunnold, D. M.; Wang, H. J.; Thomason, L. W. ...
Journal of Geophysical Research, Washington, DC,
27 February 2000, Letnik:
105, Številka:
D4
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
Ozone retrievals from Stratospheric Aerosol and Gas Experiment (SAGE) II version 5.96 (v5.96) below ∼25 km altitude are discussed. This version of the algorithm includes improved constraints on the ...wavelength dependence of aerosol extinctions based on the ensemble of aerosol size distribution measurements. This results in a reduction of SAGE ozone errors in the 2 years after the Mount Pinatubo eruption. However, SAGE ozone concentrations are still ∼10% larger than ozonesonde and Halogen Occultation Experiment (HALOE) measurements below 20 km altitude under nonvolcanic conditions (and by more than this in the tropics). The analysis by Steele and Turco 1997 suggests that the SAGE ozone overpredictions are in the wrong direction to be explained by aerosol extinction extrapolation errors. Moreover, preliminary SAGE II v6.0a retrievals suggest that they are partially accounted for by geometric difficulties at low altitudes in v5.96 and prior retrievals. SAGE ozone trends for the 1979–1996 and 1984–1996 periods are calculated and compared, and the sources of trend errors are discussed. These calculations are made after filtering out ozone data during periods of high, local aerosol extinctions. In the lower stratosphere, below ∼28 km altitude, there is shown to be excellent agreement in the altitudinal structure of ozone decreases at 45°N between SAGE and ozonesondes with the largest decrease in both between 1979 and 1996 having occurred below 20 km altitude, amounting to 0.9±0.7% yr−1 (2σ) at 16 km altitude. However, in contrast to the fairly steady decreases at 45°N, both SAGE measurements and Lauder ozonesondes show ozone increases at 45°S over the period from the mid‐1980s to 1996 of 0.2±0.5% yr−1 (2σ) from 15 to 20 km altitude. The SAGE data suggest that this increase is a wintertime phenomenon which occurs in the 15–20 km height range. Changes in dynamics are suggested as the most likely cause of this increase. These hemispheric differences in ozone trends are supported by ozone column measurements by the Total Ozone Mapping Spectrometer (TOMS).
Tropospheric measurements of ozone from SAGE II (version 6.1) in the tropics have been analyzed using 12 years of data (1985–1990, 1994–1999). The seasonally averaged vertical profiles of the ozone ...mixing ratio in the upper troposphere have been presented for the first time from satellite measurements. These profiles show qualitative similarities with corresponding seasonal mean ozonesonde profiles at northern and southern tropical stations and are about 40–50% less than the sonde values. Despite this systematic offset, the measurements appear to be consistent with a zonal wave one pattern in the upper tropospheric column ozone and with the recently predicted summertime ozone enhancement over the Middle East. These results thus affirm the usefulness of the occultation method in studying tropospheric ozone.
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