Total column ozone

Figure 1.7 shows the total column ozone measured in October at one Antarctic location, Halley Bay, as a function of year. This includes the original Farman et al. (1985) data, as well as more recent data up to 1994 (Jones and Shanklin, 1995). It is clear that starting in the late 1970 s, there was a dramatic drop in total column ozone at the end of the polar winter when sunrise occurs. Observation of such a rapid change is unprecedented and quite remarkable. 

FIGURE 1.7 Average total column ozone measured in October at Halley Bay, Antarctica, from 1957 to 1994 (adapted from Jones and Shanklin, 1995). 

The total ozone integrated through a column in the atmosphere from the earth s surface is often used as a measure of stratospheric ozone, since as seen in Fig. 12.1, about 85-90% of the total ozone is found in this region. Dobson units are used to express the amount of total column ozone. One Dobson unit (DU) is the height of the layer of pure gaseous ozone in units of 10"5 m that one would have if one separated all of the atmospheric 03 and compressed it into a layer at 1 atm and 273 K. That is, 100 DU is equivalent to a layer of pure ozone of thickness of 1 mm. 

Figure 12.9 shows some model-calculated percent changes in total column ozone due to a HSCT fleet that was projected in 2015 assuming the emission goal of El no = 5 g of NOz/kg of fuel was met (Stolarski et al., 1995). These calculations compare the change in 03 due to this fleet compared to a completely subsonic fleet in that year using the three different models for which predicted altitude changes were shown in Fig. 

FIGURE 12.9 Calculated percent change in total column ozone during March as a function of latitude due to a Mach 2.4 HSCT fleet from the three models for which results were shown in Fig. 12.7, assuming NO, emission radiation of 5 g of N02/kg of fuel. These are the predicted changes due to the projected HSCT fleet compared to a projected solely subsonic fleet (adapted from Stolarski et at., 1995). 

In 1985, Farman et al. reported that the total column ozone at Halley Bay in the Antarctic had decreased substantially at polar sunrise each year for about 5-10 years. Figure 12.16 shows the Farman et al. data supplemented by measurements taken since then (Jones and Shanklin, 1995). Clearly a major drop in column ozone has been occurring since the mid to late 1970s. The extent of this change, and the rapidity with which it occurred, were unprecedented and focused the atmospheric chemistry community s attention on the reasons for this massive destruction of stratospheric ozone in the Antarctic spring. 

Figure 12.17 shows the ozone profiles over the U.S. Amundsen-Scott Station at the South Pole in 1993 on August 23 prior to formation of the ozone hole and on October 12 after the ozone hole had developed. The total column ozone decreased from 276 DU on August 23 to only 91 DU on October 12, and, in addition, there was essentially no ozone in the region from 14 to 19 km (Hofmann et al., 1994a). During the same period at the McMurdo Station in Antarctica, the total column ozone decreased from 275 to 130 DU (B. J. Johnson et al., 1995). While similar profiles have been observed since the discovery of the ozone hole, these data show some of the most extensive ozone destruction ever observed, although 1994 and 1995 showed almost as much 03... 

A similar relationship was observed in Germany. Figure 12.36, for example, shows the deviation of the monthly mean ozone concentration after corrections for seasonal variations, long-term trends, the QBO and vortex effects, and the associated particle surface area concentration from 1991 to 1994 (Ansmann et al., 1996). The increase in the particle surface area due to Mount Pinatubo is clear associated with this increase in aerosol particles are negative monthly mean deviations in ozone that persist until fall 1993, when the surface area approaches the preeruption values. Similarly, the decrease in the total column ozone from 1980-1982 to 1993 observed at Edmonton, Alberta, Canada, and shown at the beginning of this chapter in Fig. 12.1 has been attributed to the effects of the Mount Pinatubo eruption (Kerr et al., 1993). 

Of course, it is not just the chemistry but also the dynamics that determine the net effect on total column ozone in midlatitudes. Transport of air from the tropics to midlatitudes was discussed earlier in Section A.l. There is also evidence for the influence of high-latitude air on ozone at midlatitudes. It has been proposed, for example, that the Arctic polar vortex acts more like a flowing processor than an isolated air mass. In this scenario, air flows through the polar vortex and as it does, undergoes the chemistry described earlier for the... 

In addition, there is an obseived correlation between total column ozone and the El Nino Southern Oscillation (ENSO) in the tropical troposphere, with decreases in total ozone in middle and sometimes polar latitudes following the ENSO by several months the period associated with the ENSO is 43 months (Zerefos et al., 1992). While the association between the ENSO and ozone is not well understood, it has been proposed that the warming of the troposphere in the tropics over the Pacific Ocean causes increases in the upper troposphere air temperatures and tropopause height and an upwelling in the lower stratosphere. If sufficiently large, this could have more widespread impact than just in the tropics (e.g., see Zerefos et al., 1992 and Kalicharran et al., 1993). 

Figure 13.11 is one example of variations in total column ozone in Europe, Eastern Siberia and the Far East, and Western Siberia (Bojkov et al., 1994). These data have been smoothed using a 12-month running mean, but variations due to the QBO etc. have not been removed. Figure 13.11c shows for the Western Siberia data the deviations specifically attributed to the QBO while this contributes to a significant extent to the observed trends, it clearly does not account for the entire downward trend in total ozone with time. 

FIGURE 13.11 Percentage variations in total column ozone smoothed using a 12-month running mean for a network of stations in (a) Europe, (b) Eastern Siberia and the Far East, and (c) Western Siberia from 1973 to March 1994. The arrows show the expected QBO. In (c) the dashed line shows the component that has a periodicity expected for the QBO (adapted from Bojkov et at., 1994). 

A similar observation of record low total column ozone over Lauder, New Zealand, down to 222 DU compared to the 1985-1996 average of 340 DU was reported by Brinksma et al. (1998). They attributed the low ozone in part to a portion of the Antarctic polar vortex passing over this location at altitudes of 25-35 km and in part to injection at lower altitudes ( 22 km) of ozone-poor subtropical air. 

Because of the strong absorption of ultraviolet (UV) radiation starting at 320 nm by 03, one of the major impacts of decreased stratospheric ozone is expected to be increased UV at the earth s surface, with associated effects such as increases in skin cancer and cataracts and damage to plants and other ecosystem components. It has therefore been of great interest to determine whether such a relationship can be detected and, if so, what the magnitude of the effect is. The latter is commonly expressed as an amplification factor (AF) or radiation amplification factor (RAF), defined as the fractional change in radiation (R) per fractional change in total column ozone (03) ... 

Zerefos, C. S., K. Tourpali, B. R. Bojkov, D. S. Balis, B. Rognerund, and I. S. A. Isaksen, Solar Activity-Total Column Ozone Relationships Observations and Model Studies with Heterogeneous Chemistry, J. Geophys. Res., 102, 1561-1569 (1997). 

Measured total column ozone has fallen between about 1970 and 1994. Ultraviolet irradiation increases at the surface of the earth due to ozone depletion should peak at about 15% in midlatitudes. The incidence of harmful health effects of UV radiation can be expected to rise, eventually, at midlatitudes. Public health action is still necessary to reduce sun exposure, increase protection against the sun, and develop clear policies on the action that should be taken on early detection and treatment of skin cancers (Armstrong, 1997). 

The 10 min sums of erythemal solar irradiances measured simultaneously during ten months at two locations in the Czech Republic were analysed. The altitude effect is about 4 to 8% per 1000 m, the radiation amplification factor is about 1.1 and both numbers vary only slightly with solar zenith angle. The statistical model relating erythemal solar irradiance with total column ozone and solar zenith angle was developed. This model and the annual cycles of the mean and variability of total column ozone are used to estimate variability of annual and daily cycles of mean erythemal solar irradiance. 

Figure 1. Trend in annual and monthly means of total column ozone in Hradec Kralove determined from 1962-90 and 1962-97 series. The vertical lines demarcate the standard error of the estimated trend.

Figure 2. Dependence of sun-visible eiythemal solar irradiance (normalised for the mean total column ozone, 339 DU. and the mean Earth-Sun distance) on solar zenith angle. HIC(data) data measured in Hradec Kr lovd (smoothed averages of 10 min sums) HK(model) statistical model for Hradec Krilovi MIL(model) statistical model for MileSovka MIL/HK the ratio of models for Hradec Krdlovi and MileSovka.

Figure 3 Variability of total column ozone in Hradec Krfilovd and die minimum values of daily average total ozone in 1962-97 (circles). The variability of total ozone is represented by smoothed average, A, and standard deviation, S, determined from Dobson measurements made during 1962-90. The thick black line represents the smoothed mean determined from 1991-97.

Figure 4 The annual cycle of variability of model UV-ERY irradiance related to variability of total column ozone, Q. Heavy solid line model UV-ERY irradiance for the mean 1962-90 total ozone concentration circles model UV-ERY irradiance for the mean 1991-97 total ozone concentration shaded lines model UV-ERY irTadiance for Q=A+S (lower line) and Q=A-S (upper line), where A and Sare average and standard deviation of total column ozone in Hradec Krdlovi, 1962-90 medium solid lines model UV-ERY irradiance for Q AOS., thin solid lines model UV-ERY irradiance for 0= 35 thin dashed line solar zenith angle at noon.

Figure 5. Daily cycle of model UV-ERY irradiance for June 21 and various levels of total column ozone. See Fig. 4 for the legend.

The altitude effect (Sec. 3) and the radiation amplification factor (Sec. 4) were derived from UV-ERY measurements made simultaneously at two locations in the Czech Republic. The value of RAF obtained from the present data agrees with previous studies of other authors. The value of the amplitude effect agrees with the value used by National Weather Service and EPA [10] but is lower than the values obtained by other authors [2, 9]. The statistical model relating UV-ERY irradiance with total ozone and solar zenith angle was developed (Sec. 5 Fig. 2). Although the information on the total ozone does not satisfactorily improves accuracy of the UV-ERY forecast (further variables should be incorporated into the model to improve its accuracy), the model may be used to estimate annual and daily cycles of sun-visible UV-ERY irradiance for various total ozone levels. The results obtained show variability of the model UV-ERY irradiance related to variability of total column ozone. Specifically, it is demonstrated that the UV-ERY irradiance may exceed the annual/daily normal-ozone maxima during non-negligible portion of the year/day (about 214 months/hours) if the total ozone... 

Ozone data includes measurements from 380 quality controlled Vaisala ECC-ozone soundings. Ozone profiles from soundings have been inspected visually and by comparing the profile based total column ozone to the spectrometric column ozone measured preferably by Dobson spectroradiometer in Marambio or by satellite based TOMS-instrument. No normalisation factor was used to correct the profiles dubious spikes were nevertheless corrected. Soundings were made twice a month from January until July and twice a week from August until January. Occasional interruptions of soundings have existed. 

Figure 1. Observations of the trend in total column ozone (%/decade) from 1979 to 1997, relative to 1979 values, shown as a function of latitude and day of year. Contour interval is 2 %/decade and ozone decreases are shown dotted. Data are from the WMO Ozone Assessment (WMO (1999)) and were provided courtesy of Lime Bishop and Vitali Fioletov.

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