Low Ozone Values Research Articles

Characteristics of episodes with extremely low ozone values in the northern middle latitudes 1957−2000

Abstract. A number of episodes are observed when the total ozone for 2 to 3 days has fallen below 220 matm-cm in the northern mid- and polar latitudes in autumn. The occurrences of such episodes represent ozone deviations of about one-third from the pre-1976 Oct-Nov-Dec monthly mean! By using primarily quality checked Dobson data, a clear identification was made of more than three dozen short spells with extremely low ozone in the 1957–1978 period. In the following twenty-two years (1979–2000), using mainly TOMS data, one can identify ~ 46 cases with ozone values falling below 220 matm-cm for longer than 1 day, with each time over an area greater than 500,000 km2 . The Ozone Mass Deficiency (O3MD) from the pre-1976 average ozone values over the affected area was ~2.8 Mt per day, i.e. four to seven times greater than it would be, assuming only a long-term trend in the Oct-Nov-Dec period. The Extremely Low Ozone (ELO3) events on the day of their appearance over the N. Atlantic/European region contribute to the O3MD by representing 16% of the deficiency due to the Oct-Nov trend in the entire 40–65° N latitudinal belt. The O3MD of the greater pool with low ozone (here taken as <260 matm-cm) surrounding the area of the lowest events could contribute on the day of their appearance in Oct-Nov up to 60% and in December, ~30% to the deficiency due to the trend over the entire 40–65° N belt. Analysis of synoptic charts, supported by a backward trajectory on the isentropic surfaces 350 and 380 K, shows that in most of the events, subtropical air masses with low ozone content were transported from the Atlantic toward the UK, Scandinavia, and in many cases, further to the western sub-polar regions of Russia. This transport was sometimes combined with upward motions above a tropospheric anticyclone which lifted low ozone mixing ratios to higher altitudes. The ELO3 events cause a significant deficiency above the tropopause where, in general, the subtropical air is injected. In fact, the overall amount of ozone is not depleted, but redistributed on the hemispheric scale. Review of low ozone events, defined as days with negative deviations from the pre-1976 averages greater than 25% show, in general, similar origin. The seasonally averaged area with ELO3 and the associated O3MD, as well as for the cases with deviations > –25%, has increased during the 1990s, which could be an indication of stronger and/or more frequent subtropical air intrusions. Their occurrences could contribute noticeably to the ozone deficiency of the middle latitude ozone during the days of ELO3 appearances; however, their contribution to the long-term trend of the ozone seasonal decline is of the order of ~10%.Key words. Atmospheric composition and structure (middle atmosphere - composition and chemistry) Meteorology and atmospheric dynamics (middle atmosphere dynamics)

Study of the interannual ozone loss and the permeability of the Antarctic polar vortex from aerosol and ozone lidar measurements in Dumont d'Urville (66.4°S, 140°E)

Systematic ground‐based measurements of the ozone and aerosol stratospheric profile performed in the Dumont d'Urville (66.4°S, 140°E) Antarctic station are used to study the air subsidence in fall, the springtime ozone loss, and the vortex confinement on an interannual basis. The data obtained mostly from March to October in the 1992–1998 time period are analyzed as a function of equivalent latitude in order to discriminate the measurements performed inside, at the edge or outside the vortex. The subsidence rate derived from the ozone measurements in the lower stratosphere prior to the destruction period and from the volcanic aerosol measurements in 1992 is in good agreement with the estimation provided by radiative transfer models. The analysis of the ozone seasonal variation shows that the ozone destruction starts in the beginning of August and affects essentially the inner vortex or inner edge regions. The destruction lasts up to the end of September and low ozone values are found up to the end of October, confirming the isolation of the polar vortex above 400 K. Ozone destruction rates of the order of 3%/d in the 400–475 K region and 1.5%/d around 550 K are derived from the data obtained inside the vortex. The ozone measurements obtained in October allow to study the vortex confinement which shows the increase of the ozone meridional gradient through the vortex edge from 400 to 650 K. A fine view of the vortex edge is provided by a near daily series of aerosol lidar measurements performed in October 1992, a period when the vortex was deformed by planetary waves and slanted with respect to the vertical direction.

Ozone mini‐hole observed over Europe, influence of low stratospheric temperature on observations

A region of extreme low ozone values passed over North‐western Europe during November 30, and December 1, 1999. The total ozone values were measured from the ground, with a Brewer Spectrophotometer, and from space with the GOME and TOMS satellite instruments. The ozone sonde measurement and the retrieved GOME ozone profile have shown that the main reduction in the ozone column occurred between the ozone maximum (22 km) and the tropopause. The low temperatures found in the stratosphere during this event have significant consequences for the ozone retrieval algorithm, both for satellite retrievals and for the Brewer measurements.

Boundary layer vertical exchange processes and the mass budget of ozone: Observations and model results

An Eulerian chemical model is used to assess the relative importance of a variety of processes associated with producing high surface ozone episodes during selected periods of the North American Research Strategy for Tropospheric Ozone (NARSTO) 1995 field campaign over the northeastern United States. A comparison of the observed and predicted hourly surface ozone mixing ratios showed that the model qualitatively reproduced the observed ozone trends over the northeastern United States. The model had a mean hourly bias of ∼15 ppb with a wide range of skill compared to individual observing stations clustered around one node. The simulated mass budget tendency terms are compared for days with low ozone values immediately followed by days with high values. The later days showed observed and simulated ozone mixing ratios aloft to be of order twice that found on preceding days, although the associated chemical mix appeared to have relatively little potential for the subsequent generation of “new” ozone. Under conditions of shallow mixing over urban regions, simulated surface ozone production rates were negative (a net loss) throughout much of the day with convective mixing bringing newly produced ozone from aloft to the surface. It is noted that surface ozone levels appeared to be relatively insensitive to mixing layer growth rates.

Total ozone influence on the surface UV‐B radiation in the late spring‐summer 1963–1997: An analysis of multiple timescales

Monthly means and minima of total ozone for the late springs and summers (May–August) of 1963–1997 have been examined for the European Dobson stations (Arosa, Belsk, Hohenpeissenberg, Hradec Kralove, Uccle). It is shown that long‐term tendencies in total ozone means were almost similar to those in the total ozone minima. Analyses of the late spring/summer means of UV daily doses, total ozone, and global solar radiation (proxy for the overall atmospheric transparency), measured at Belsk (52°N, 21°E) for the period 1976–1996, show that an importance of the total ozone changes for the UV‐B level increases with the timescale. Decadal variations in total ozone are the main source of the UV trend at Belsk. Frequency of appearance of extreme daily total ozone values in the selected late spring/summer season seems to be important for analyses of the ozone forcing in the interannual timescale. Regional and temporal differences in the number of days with extreme low ozone values are discussed using the total ozone extrema taken at Arosa, Belsk, and Hradec Kralove in the 1963–1997 period. A statistical model is developed for diagnosis of the next day value of the UV‐B level. The changes in the overall atmospheric transparency are essential for the UV‐B level when the day‐to‐day variations in the UV forcing factors are examined.

Combined characterisation of GOME and TOMS total ozone measurements from space using ground-based observations from the NDSC

Several years of total ozone measured from space by the ERS-2 GOME, the Earth Probe TOMS, and the ADEOS TOMS, are compared with high-quality ground-based observations associated with the Network for the Detection of Stratospheric Change (NDSC), over an extended latitude range and a variety of geophysical conditions. The comparisons with each spaceborne sensor are combined altogether for investigating their respective solar zenith angle (SZA) dependence, dispersion, and difference of sensitivity. The space- and ground-based data are found to agree within a few percent on average. However, the analysis highlights for both GOME and TOMS several sources of discrepancies: (i) a SZA dependence with TOMS beyond 80° SZA; (ii) a seasonal SZA dependence with GOME beyond 70° SZA; (iii) a difference of sensitivity with GOME at high latitudes; (iv) a difference of sensitivity to low ozone values between satellite and SAOZ sensors around the southern tropics; (v) a north/south difference of TOMS with the ground-based observations; and (vi) internal inconsistencies in GOME total ozone.

Very low zonally asymmetric ozone values in March 1997 above the North Atlantic-European region, induced by dynamic processes

Abstract. The total ozone distribution in March 1997 showed very low values in the North Atlantic-European region, even lower than in the years before. A spatial pattern correlation between the zonally asymmetric part of total ozone and that of the 300 hPa surface geopotential of the Northern Hemisphere was applied to examine the spatial structure of the low ozone values and its dynamic dependence. A trend analysis in the North Atlantic-European region was carried out to determine to what extent the low March 1997 ozone values are related to the decadal change of meteorological parameters in the lower stratosphere, observed since the 1980s, in comparison to the interannual variability. The conclusion is that the very low ozone values above the North Atlantic-European region in March 1997 were mainly induced by dynamic processes, namely their decadal change as well as their interannual variability.Key words. Meteorology and atmospheric dynamics (climatology; middle atmosphere dynamics)

Spectral characteristics of the quasi-biennial oscillation of total Ozone

The 12-month running means of the 50 hPa low latitude zonal wind and total ozone values for the latitude zones NP (North Polar), NT (North Temperate), TRO (Tropical), ST (South Temperate), SP (South Polar) were subjected to special analysis, separately over the two successive 18 year intervals, 1958-1975 and 1976-1993. In the interval 1958-1975, the wind had a prominent peak at 2.45 years and two smaller but significant peaks at 1.98 and 3.05 years. For ozone only NP. NT and ST had roughly similar peaks (2.37, 2.41, 2.48 years), while TRO and SP had different peaks (2.27 and 2.12 years). All ozone series had significant peaks at 20-21 months, barely significant in the wind series. Ozone peaks were noticed in the 3-5 years band also. In the interval 1976-1993, the patterns were different. The wind had only one prominent peak at 2.51 years. For ozone, NP, NT, ST had roughly similar peaks (2.41, 2.45, 2.45 years) while TRO. Speed different peaks (2.32 and 2.29 years). All ozone series had significant peaks at 20-22 months and in the 3-5 year band; but these were absent in the wind series. The 3-5 year band probably indicates ENSO effects. A cross-correlation analysis between wind and ozone showed that TRO maxima coincided with westerly wind maxima. while NT, ST and NT, NP were phase shifted by 4 and 6 seasons.

Very low zonally asymmetric ozone values in March 1997 above the North Atlantic-European region, induced by dynamic processes

The total ozone distribution in March 1997 showed very low values in the North Atlantic-European region, even lower than in the years before. A spatial pattern correlation between the zonally asymmetric part of total ozone and that of the 300 hPa surface geopotential of the Northern Hemisphere was applied to examine the spatial structure of the low ozone values and its dynamic dependence. A trend analysis in the North Atlantic-European region was carried out to determine to what extent the low March 1997 ozone values are related to the decadal change of meteorological parameters in the lower stratosphere, observed since the 1980s, in comparison to the interannual variability. The conclusion is that the very low ozone values above the North Atlantic-European region in March 1997 were mainly induced by dynamic processes, namely their decadal change as well as their interannual variability.Key words. Meteorology and atmospheric dynamics (climatology; middle atmosphere dynamics)

The 1997 Arctic Ozone depletion quantified from three‐dimensional model simulations

Three‐dimensional simulations of total ozone are reported for the 1996–97 Arctic winter. The record low ozone values observed by satellite in late March are well reproduced by the chemistry‐transport model. The comparison between the chemically integrated ozone and a passive tracer with identical initialization allows us to discrimate chemical changes from variations due to dynamical processes. In addition to a substantial total ozone chemical loss (60 to 120 Dobson Units), the simulation reveals an dynamically‐induced reduction of ∼70 DU also responsible for the ozone minimum observed in the Arctic in late March 1997.

Ozone variability in the high latitude summer stratosphere

Observations made by the HALOE instrument aboard UARS show very low stratospheric ozone in the Arctic and Antarctic summers of 1992 and 1993 [Park and Russell, 1994]. Large longitudinal variability is seen in ozone between 8 and 45 mb, poleward of 60° during late summer. This paper examines the cause of this variability using isentropic trajectory analysis and photochemical calculations. According to trajectory analysis using UKMO wind fields, air parcels with higher ozone mixing ratios move to 73°N from lower latitudes in the longitude sector 180°E ‐ 225°E over a 9 day period beginning on 10 August, 1993. Low ozone values seen in the HALOE data around 100°E at 73°N correspond to air parcels that remain mostly in higher latitudes. We present results from photochemical calculations conducted in conjunction with UARS data, and conclude that the longitudinal asymmetry in ozone can be be explained by transport along isentropic trajectories with standard chemistry.

Two examples of how the total ozone is influenced by the upper air circulation pattern

Abstract Two winter months, February 1993 and February 1994, with quite different circulation patterns in the Atlantic area have been studied. February 1993 was dominated by a strong southwesterly upper air current with correspondingly strong ascending motion in the area. This resulted in a reduced ozone column in the lower stratosphere and also a low total ozone column. This was especially true in Scandinavia and Northwestern Europe. February 1994 had a more normal circulation in the same area with weaker horizontal and ascending motions. The ozone column was back to “normal” in Scandinavia and Northwestern Europe. Several of recent years have had an increased southwesterly upper air circulation over the Atlantic ocean with low ozone values in Northwestern Europe. This altered circulation might then add to the negative trend, which has been observed during the two last decades.

Analysis of tropospheric ozone measurements in Greenland

The Danish Meteorological Institute (DMI) initiated continuous measurements of surface ozone concentrations in Greenland during spring 1994 as a part of the EU-project ARCtic Tropospheric Ozone Chemistry (ARCTOC). In 1995 and 1996, several events of deep ozone depletion were recorded at Thule and Søndre Strømfjord connected with passing frontal systems (cold fronts) from the west or north-west with rising pressure and falling temperature. At Scoresbysund, minor episodes were observed both in 1995 and 1996. The major episodes could definitely be assigned to cold air masses moving from the Arctic Ocean over the Canadian Archipelago across Baffin Bay and Davis Strait and further crossing Greenland. Analyses of backward trajectories calculated by a 3-D transport model developed at DMI utilising meteorological data from the numerical weather prediction model DMI-HIRLAM (HIgh Resolution Limited Area Model) have been performed. Results from these studies show that air parcels with low ozone values at the receptor point generally have passed the northern Canadian Archipelago or the Arctic Ocean a few days before the arrival at the receptor point.

Limits on heterogeneous processing in the Antarctic spring vortex from a comparison of measured and modeled chlorine

Forty‐day photochemical model runs are compared with ground‐based stratospheric ClO observations taken during the austral spring of 1993. Our purpose is to explore the range of required heterogeneous processing within which we can reproduce the duration and degree of chlorine activation within the Antarctic spring vortex. Heterogeneous processing on nitric acid trihydrate (NAT) polar stratospheric clouds (PSCs) or supercooled ternary solution (STS) ‐type particles is shown to be necessary to maintain chlorine in active forms during ozone hole formation in September, even for small HNO3 amounts, or chlorine deactivates sooner than observed. The lower limits for the surface areas required are quite small, however. Thus the record ozone losses observed during September of 1993 may be attributed to catalytic loss due to chlorine maintained in active forms by heterogeneous processing despite the sparse particle loading of the Antarctic lower stratosphere at that time. The ozone loss rates predicted by the model during the formation of the springtime Antarctic ozone hole indeed agree quite well with observations. The one‐dimensional model is also able to reproduce both the observed timing and rate for subsequent deactivation of chlorine. Renitrification from PSC evaporation is not required for this deactivation, as HCl reformation is very rapid at low ozone values.

The role of stratospheric minor warmings in producing the total ozone deficiencies over Europe in 1992 and 1993

During 1992 and 1993, record low total ozone values were observed over the middle and high northern latitudes. The ozone data from the long-operating station at Belsk, Poland, have been used to examine their departures from climatological behaviour in 1992 and 1993. It seems that not only do the exceptionally low ozone amounts recorded over the northern mid-latitudes need an explanation but also their occurrence for two years in a row. One of the possible mechanisms which may be responsible for this event is suggested to be connected with the occurrence of stratospheric minor warmings. They occur without a breakdown of the polar vortex but only with the displacement of very cold air towards lower latitudes (as in January 1992 and February 1993). It is known that air masses in the polar vortex have been chemically disturbed and, when they arrive over the sunlit middle latitudes, chemical destruction of ozone is likely to occur. During the periods under study, the strongest negative total ozone deviations correspond to strong negative temperature deviations at 30 hPa and to large potential vorticity values; this points to the presence over Europe of air masses of polar vortex origin. It has been shown that the characteristics of mid-winter stratospheric warmings and the interannual variability of winter-spring total ozone averages at Belsk are associated with each other.

A new approach to the characterization of long-term changes in total atmospheric ozone: Determination and application of frequency distributions

This paper sets forth a new approach for describing long-term changes in total ozone by using frequency distributions and analyzing the extreme values. We applied this methodology to the database of column ozone provided by the Total Ozone Mapping Spectrometer aboard Nimbus 7. We examined a geographic region measuring 7.0° in latitude by 6.25° in longitude in the midwestern United States from 1979 to 1991. On any given spring day, individual ozone measurements in this region show a large variability, where the differences between the local noon maximum and minimum total ozone values sometimes exceed 100 Dobson units. Daily variability in total column ozone was shown to be greater in the spring than in the fall. Based on frequency distribution results, the most probable values for the spring season decreased from 1979–1982 to 1989–1991. During spring, the frequency of extremely low ozone values decreased from the six-year period 1980–1985 to the 1986–1991 time period, while the opposite situation prevailed during fall. Preliminary results indicate that this approach can illuminate the detailed behavior of TOZ within each season in a particular region.

Climate Assessment for 1995

The El Niño-Southern Oscillation (ENSO) phenomenon is a major contributor to the observed year-to-year variability in the Pacific Ocean and in the global atmospheric circulation. The short-term climate system witnessed the return to the mature phase of warm ENSO conditions (commonly referred to as the El Nino) during early 1995 for the third time in four years. This frequency of occurrence is unprecedented in the last 50 years and is comparable to that observed during the prolonged 1911–15 ENSO episode. These warm ENSO conditions contributed to a large-scale disruption of the normal patterns of wind, rainfall, and temperature over much of the tropics and middle latitudes, particularly during the December 1994–February 1995 period. This period was followed by a dramatic decrease in sea surface temperatures in the tropical Pacific, resulting in a complete disappearance of all warm episode conditions during June–August and in the development of weak coldepisode conditions during September–November. Changes in the tropical Pacific were accompanied by pronounced, large-scale changes in the atmospheric circulation patterns from those that had prevailed during much of the early 1990s. Particular examples of these changes include 1) a dramatic return to a very active hurricane season over the North Atlantic, following four consecutive years of significantly below-normal hurricane activity; 2) the return to above-normal rainfall throughout Indonesia, northern Australia, and southern Africa, following a prolonged period of below-normal rainfall and periodic drought; and 3) a northward shift of the jet stream and storm track position over the eastern half of the North Pacific during the latter part of the year, following several winter seasons (three in the last four) characterized by a significant strengthening, southward shift, and eastward extension of these features toward the southwestern United States. Other regional climate anomalies during 1995 included extreme warmth throughout western and central Asia during January–May and colder than normal conditions in this region during November–December, severe flooding in the midwestern United States (April–May), abnormally wet conditions in California and the southwestern United States (December–February) combined with near-record warmth over eastern North America, deadly heat waves in the central United States (mid-July) and India (first three weeks of June), drought in the northeastern United States (August), a drier-than-normal rainy season in central Brazil (September–December), and an intensification of drier-than-normal conditions over southern Brazil, Uruguay, and northeastern Argentina at the end of the year. The global annual mean surface temperature for land and marine areas during 1995 averaged 0.40°C above the 1961–90 mean. This value exceeds the previous warmest year in the record (1990) by 0.04°C. The Northern Hemisphere also recorded its warmest year on record during 1995, with a mean departure from normal of 0.55°C. The global annual mean surface temperature for land areas only during 1995 was the second warmest since 1951. The year also witnessed near-record low ozone amounts in the Southern Hemisphere stratosphere, with minimum values only slightly higher than the record low values observed in 1993. The areal extent of very low ozone values during 1995 was as widespread over Antarctica as in the record low year of 1993.

Total ozone variations in the tropical belt: An application for quality of ground based measurements

The study of the regime of ozone variations in the huge tropical belt (25° S to 25° N), which are, in general, very small and zonally nearly symmetric, permits to establish a statistical model for estimating the ozone deviations using Total Ozone Mapping Spectrometer (TOMS) data. The equatorial stratospheric winds at 25 and 50hPa and the solar flux at 10.7 cm are used as major predictors and the linear trend was also estimated. The 10m/sec stratospheric wind change is related to≈1.2% ozone change at the equator, to practically no change in the 8–15° belts and up to 1.4% change with opposite phase over the tropics in spring but nearly zero change in fall. The solar cycle related amplitude is about 1.4% per 100 units of 10.7 cm solar flux. The ozone trends are negative: not significant over the equator and about −2% per decade (significant at 95% level) over the tropics. The latter could have been enforced by the 2 to 4% lower ozone values during 1991–1993, part of which might be related to the effects of the Mt. Pinatubo eruption, but might also be due to the strong QBO. The estimated deviations are verified versus reliable observations and the very good agreement permits applying the model for quantitative quality control of the reported ozone data from previous years. The standard deviation of the difference between observed ozone deviations and those estimated from the model is only 0.9–1.6% for yearly mean, that means instruments used for total ozone observations in the tropical belt should have systematic error of less than 1%. Cases when the discrepancies between the model and reported observations at a given station exceed 2–3% for time interval of 2 or more years should be verified.

Atmospheric sampling of Supertyphoon Mireille with NASA DC‐8 aircraft on September 27,1991, during PEM‐West A

The DC‐8 mission of September 27, 1991, was designed to sample air flowing into Typhoon Mireille in the boundary layer, air in the upper tropospheric eye region, and air emerging from the typhoon and ahead of the system, also in the upper troposphere. The objective was to find how a typhoon redistributes trace constituents in the West Pacific region and whether any such redistribution is important on the global scale. The boundary layer air (300 m), in a region to the SE of the eye, contained low mixing ratios of the tracer species O3, CO, C2H6, C2H2, C3H8, C6H6 and CS2 but high values of dimethylsulfide (DMS). The eye region relative to the boundary layer, showed somewhat elevated levels of CO, substantially increased levels of O3, CS2 and all nonmethane hydrocarbons (NMHCs), and somewhat reduced levels of DMS. Ahead of the eye, CO and the NMHCs remained unchanged, O3 and CS2 showed a modest decrease, and DMS showed a substantial decrease. There was no evidence from lidar cross sections of ozone for the downward entrainment of stratospheric air into the eye region; these sections show that low ozone values were measured in the troposphere. The DMS data suggest substantial entrainment of boundary layer air into the system, particularly into the eye wall region. Estimates of the DMS sulphur flux between the boundary layer and the free troposphere, based on computations of velocity potential and divergent winds, gave values of about 69 μg S m−2 d−1 averaged over a 17.5° grid square encompassing the typhoon. A few hours after sampling with the DC‐8, Mireille passed over Oki Island, just to the north of Japan, producing surface values of ozone of 5.5 ppbv. These O3 levels are consistent with the low tropospheric values found by lidar and are more typical of equatorial regions. We suggest that the central eye region may act like a Taylor column which has moved poleward from low latitudes. The high‐altitude photochemical environment within Typhoon Mireille was found to be quite active as evidenced by significant levels of measured gas phase H2O2 and CH3OOH and model‐computed levels of OH.

Meteor‐3/TOMS observations of the 1994 ozone hole

The development of the 1994 springtime (September–November) Antarctic ozone hole was observed by the Meteor‐3/TOMS (Total Ozone Mapping Spectrometer) to result in a very low minimum ozone value, 90±5 DU (Dobson Units) on September 28, 1994. During late September and early October, the region of extremely low ozone values was centered on the geographical pole between 85°S and 90°S. The geographical extent of the ozone hole region, the area within the 220 DU contour, reached a maximum during the first week in October with an elliptical area covering 24 × 106 km², reaching to the southern tip of South America. This approximately matched previous area records. After the maximum area was reached in early October, the 1994 ozone hole region was very similar to the 1993 ozone hole throughout the remainder of the month. The area of low temperatures (<196 K), where polar stratospheric clouds (PSCs) can form and heterogeneous chemistry is significant, has not increased over the past 16 years. During this period, the large trends in the area and minimum ozone amounts of the Antarctic ozone hole do not appear to be related to atmospheric temperature trends.