Recent findings, based on both ground-based and satellite measurements, have established that there has been an apparent downward trend in the total column amount of ozone over mid-latitude areas of the Northern Hemisphere in all seasons. Measurements of the altitude profile of the change in the ozone concentration have established that decreases are taking place in the lower stratosphere in the region of highest ozone concentration. Analysis of updated ozone records, through March of 1991, including 29 stations in the former Soviet Union, and analysis of independently calibrated satellite data records from the Total Ozone Mapping Spectrometer and Stratospheric Aerosol and Gas Experiment instruments confirm many of the findings originally derived from the Dobson record concerning northern midlatitude changes in ozone. The data from many instruments now provide a fairly consistent picture of the change that has occurred in stratospheric ozone levels.
A seasonal trend analysis of Dobson total ozone data that have been critically reevaluated and revised is performed for 29 northern hemisphere stations located between 19°N and 64°N latitude using data through 1986. The trend model considered for these data allows for a different linear trend for each month of the year, so that the seasonal as well as the latitudinal and regional nature of the total ozone trend behavior can be examined. The trend model also incorporates the 10.7‐cm solar flux series and the 50‐hPa equatorial zonal wind series as additional explanatory factors for solar and quasi‐biennial oscillation induced ozone variations. Regression random effects models are then used for the individual station seasonal trend estimates to obtain trend estimates as a function of latitude for different seasons of the year. The results of this seasonal trend analysis indicate significantly more negative trends during the winter months (December‐March) than during the summer months (May–August), notably at higher latitudes, with the trends in winter becoming more negative with increasing latitude. The trends in the winter are estimated to be of the order of −1.2%, −2.1%, and −3.0% per decade for latitudes 35°N, 45°N, and 55°N, respectively, while trends during the summer are of the order of −0.6% per decade with no distinct pattern as a function of latitude. The year‐round or annual trend over all latitudes is estimated to be about −0.84±0.82% per decade. The trends are found to display some regional variation, with trends in Japan being considerably less negative than those in North America and Europe. Sensitivity studies are also performed to investigate the effects on ozone trend estimates due to certain factors such as abnormal ozone behavior in 1983 and 1985, the use of ozone data prior to 1965, and nuclear weapons testing in the early 1960s. The seasonal trend analysis is also performed using published (unrevised) Dobson data. Trend results based on published data are on average less negative than trends from revised Dobson data for European stations, by about 1.0% per decade across all seasons, with only small average differences for stations in North America and Japan.
The interannual variability of the ozone layer is studied with the largest available revised Dobson (RD) total ozone records through March 1991. The analysis of this new data set, as well as the revised Total Ozone Mapping Spectrometer (TOMS) zonal mean total ozone, shows that the phase of the ozone Ouasi-Biennial Oscillation (OBO) relative to the 50 hPa zonal wind at Singapore varies linearly with latitude, being nearly in-phase at low latitudes and more symmetric about the equator than published in earlier studies. The phase progression of the OBO is about 2 months per 10 degrees of latitude, ozone following the 50 hPa zonal wind at Singapore. After removing the OBO and solar cycles from the RD total ozone records, a relatively large part of the remaining total ozone variance can be explained by El Nino/Southern Oscillation (ENSO) events in the tropics. It is also shown that only very lfirge ENSO events (1982-1983 and possibly 1972) are followed within a few months time lag by low total ozone values in middle and even higher latitudes. This analysis also shows that at individual stations there are other significant total ozone anomalies which cannot be explained by the OBO or ENSO. Tentative circulational aspects of the ENSO disturbance and its relation to total ozone are also discussed. INTRODUCTION The purpose of this paper is to provide a new look atthe most prominent interhnnual fluctuations of total ozone, by using the longest available, revised by Bojkov, Dobson (RD) total ozone records, used in NASA/World Meteorological Organization (WMO) [1988] Ozone Report 18 and their extension until March 1991 for the WMO [1991] Ozone Report 25. These fluctuations include the Quasi-Biennial Oscillation (QBO), the 11-year solar-related oscillation and the El Nino/Southern Oscillation (ENSO). There are, of course, other anomalies in the interannual ozone variability which are not yet fully understood. The QBO in total ozone and its relation to the 26-30 month oscillation of zonal winds in the equatorial stratosphere have been extensively studied during the past three decades [Funk and Graham, 1962; Dutsch and Ling, 1973; Wilcox et aL, 1977; Oltmans and London, 1982; Zerefos, 1983, Hasebe, IQR•;/•nc,•,11 and •nrehnw, r 1 QR•' NA•A/V•MC} 1QRR' Jqnwman, 1989]. Many features of the QBO in total ozone have been successfully reproduced in a two-dimensional model by Gray and Pyle [ 1989]. In most of these studies the latitudinal variation of the phase of the QBO in total ozone was considered to be relatively simple; nearly in-phase with zonal winds at 50 hPa over the equatorial region and out-of-phase at latitudes greater than about the 35 degree latitude circles in both hemispheres. The chances of such a simple relationship are, however, small because it has been proposed that the QBO may be modified by either the solar activity cycle Angell, 1989] and/or a quasi-four-year oscillation [Hasebe, 1983; Schuster et al., 1989]. With regard to the proposed ENSO-ozone relationship, there is now evidence that large ENSO events can e...
All available total ozone data from over 150 past and present Global Ozone Observing System (GO3OS) stations, after careful quality control and reevaluation, have been analyzed in order to deduce the basic global ozone characteristics both for pre‐ozone‐hole and during “ozone hole” time periods. Utilizing Total Ozone Mapping Spectrometer (TOMS) data, the longitudinal inhomogeneity of the total ozone distribution was estimated. That permitted the use of ground‐based data for establishing long‐term zonal as well as hemispheric and global ozone variations for the 1964–1994 period. The difference between the estimations of monthly zonal variations from ground‐based and TOMS data for the overlapping period of 1979–1993 is less than 1% in latitudes 40°S–60°N. The ozone changes are several times larger than possible errors of the estimated values; therefore the results are highly reliable. They show that the northern hemisphere average ozone was ∼312 and the southern average was ∼300 matm cm in the pre‐ozone‐hole decades (1964–1980) and that the global average for the 1984–1993 period was lower by ∼3% (from 306.4±1.0 down to 297.7±2.2 matm cm). The southern hemisphere contributed ∼64% of the overall ozone decline. The levels of annual ozone maximum have been reduced by 5.8% in the southern hemisphere and 3.2% in the northern hemisphere, and the levels of ozone minimum have been reduced by 2.1% and 1.2%, respectively. The ozone trends for midlatitudinal bands (35–65°) show a pronounced seasonal dependence varying from ∼3% to 8 % (and even more for the southern hemisphere) for the cumulative decline since 1970. The ozone decline calculated in percent per decade from 1980 is almost twice as large as the decline calculated from 1970. The cumulative year‐round global ozone decline is 4.8±0.6%; however, the cumulative year‐round decline over middle and polar latitudes is more than 7%. The advantages of establishing ozone “norms” for estimations of long‐term ozone variations from ground‐based data are emphasized.
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