Figure 2 shows SH polar plots of V6 ozone mixing ratios at 46.4 hPa for 26 October and for 1 November, where the orbital measurements of LIMS extend only to 64^∘ S. The plot on the right shows that there are minimum ozone values of about 2.6 ppmv near 120 and 315^∘ E at 60^∘ S on 1 November, which agrees reasonably with the locations of low total ozone from the TOMS image of Fig. 1. Ozone is of the order of 3.5 to 4 ppmv at most other longitudes. Low ozone occurs within the edges of the polar vortex, based on the concurrent GPH field from the operational ECMWF Reanalysis or ERA-40 products (Uppala et al., 2005). The bold contour in Fig. 2 denotes the edge of the vortex, in the manner of Harvey et al. (2002). We define the vortex edge as the streamfunction contour coincident with maximum wind speed that also encloses a region of rotation. Meek et al. (2017) showed that this definition of the vortex edge is in good agreement with the definition of Nash et al. (1996) based on the potential vorticity gradient. We note that daily plots of GPH are also available from LIMS V6. However, they exhibit a discontinuous anomaly at the 46 hPa level for the vortex region between 29 and 31 October, due to an interpolation of National Meteorological Center (NMC) GPH analyses supplied to the Nimbus-7 Project and used for the baseline pressure level of 50 hPa for the V6 GPH product (Remsberg et al., 2004). V6 geometric height and GPH profiles above and below that level are the result of a hydrostatic integration of the LIMS-retrieved temperature versus pressure profiles of T_p. Maps of V6 GPS farther away from the 50 hPa level are very similar to those from ERA-40.

Figure 2V6 ozone mixing ratios at 46.4 hPa for 26 October and 1 November 1978. Polar plots extend from 30^∘ S to the South Pole and longitude is in ^∘ E with 0^∘ at right. Bold contours denote the vortex edge from ERA-40. The superposed, three colored dots correspond to the locations of profiles on 26 October (black and red) and on 3 September (green) in Fig. 3.

LIMS began its daily observations one week earlier than TOMS or on 25 October, and the left plot of Fig. 2 shows that the ozone for 26 October at 31^∘ E is about half of that at 119^∘ E on 1 November. The vortex on 26 October extends toward lower latitudes from about 60^∘ S, 40^∘ E. Both the vortex and region of low ozone deform and undergo a clockwise rotation from 26 October onward, such that their low values extend equatorward at 120 and at 315^∘ E on 1 November. Bodeker et al. (2002) reported that the edge of the vortex often extends to near 60^∘ S during October, and Stolarski et al. (1986, their Fig. 1) and Hassler et al. (2011) reported on an analogous clockwise rotation of the vortex during October.

The location of the vortex edge is helpful in deciding which V6 species profiles one ought to examine with regard to any constraints from HNO₃ and NO₂ on the ozone chemistry. As an example, Fig. 3 shows V6 Level 2 ozone profile segments from 11.4 to 88 hPa for two locations on 26 October, where ozone is now presented in units of partial pressure (in mPa) for a better delineation of its relative changes in the subpolar lower stratosphere. Estimates of accuracy for single V6 ozone profiles are 14 %, 26 %, and 34 % for 10, 50, and 100 hPa, respectively (see row (g) of Table 1 in Remsberg et al., 2007). The V6 ozone profile (black solid) at 54.9^∘ S, 119^∘ E is just outside the October 26 vortex, as shown by the black dot in Fig. 2, and its ozone values are nominal for subpolar latitudes. The largest contribution to total ozone from that profile in Fig. 3 occurs at the 68 hPa level. A second V6 ozone profile (solid red) is from 59.5^∘ S, 31^∘ E, and it is in a region of lower GPH as shown by the red dot in Fig. 2. Its ozone decreases rapidly from ∼8.0 mPa at the 53 hPa level to 2.6 mPa at the 88 hPa level, indicating a significant loss of ozone in the lower stratosphere sometime prior to 26 October. Komhyr et al. (1988, their Fig. 10) and Gernandt (1987) show from ozonesonde measurements that most of the observed losses of ozone for the mid-1980s occurred in the vortex in September and early October. Therefore, we also include in Fig. 3 an ozonesonde profile (solid green) from Syowa station (69^∘ S, 40^∘ E – the green dot in Fig. 2) for 3 September 1978, perhaps before there were any pronounced losses of ozone. Its ozone profile values are intermediate of those for the two V6 profiles of 26 October.

Figure 3V6 Level 2 species profiles for 59.5^∘ S, 31^∘ E (red) and 54.9^∘ S, 119.4^∘ E (black) on 26 October 1978, and from an ozonesonde at Syowa (69^∘ S, 40^∘ E – green) on 3 September 1978. Ozone (solid) has units of millipascals (mPa), while HNO₃ (dashed) and NO₂ (dot-dashed) have units of ppbv.

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Loss of ozone due to reactive chlorine chemistry proceeds effectively in the presence of air that has undergone denitrification (Solomon, 1999; Müller et al., 2008). Lambert et al. (2016) somewhat loosely set an HNO₃ threshold of < 5 ppbv for indicating denitrification at 46 hPa, based on Microwave Limb Sounder (MLS) data of 2008. Nitrous oxide is the source molecule for odd nitrogen (mainly HNO₃) in the lower stratosphere, and its tropospheric values have grown by only a small amount from 1975 (∼296 ppbv) through 2008 (∼322 ppbv) (WMO, 2018); the HNO₃ threshold of 5 ppbv should also be representative of 1978. Thus, in Fig. 3 we also show the accompanying V6 profiles of HNO₃ and nighttime NO₂ for the same two locations on 26 October. HNO₃ and NO₂ at 31^∘ E are a half (or 3 ppbv) and a third (or < 1 ppbv), respectively, of those at 119^∘ E below about the 31 hPa level. Thus, both species indicate that there was a denitrification of the air in the vortex region and a likely loss of ozone due to reactive chlorine chemistry in the presence of polar stratospheric clouds (PSCs) several weeks earlier (Solomon, 1999; WMO, 2018). Although the V6 temperature at 31^∘ E on 26 October was 206 K (at 53 hPa), it is normal to find temperatures in the Antarctic vortex that are below the chlorine activation threshold value of 195 K and in the presence of PSCs during September and early October (WMO, 2018).

Figure 4As in Fig. 2, but for V6 HNO₃.

Figure 4 shows the corresponding V6 plots of HNO₃ at 46 hPa in terms of its mixing ratios, which have an estimated accuracy of ∼9 % (Remsberg et al., 2010, Table 10). There are very low values of HNO₃ on 26 October poleward of 60^∘ S and from 31^∘ E to at least 90^∘ E, indicating an earlier conversion of HNO₃ from vapor to condensed phase and the sedimentation of larger HNO₃ containing particles rather than an advection of low HNO₃ from lower latitudes. Low HNO₃ mixing ratios are also present within the vortex region on 1 November. Analogous polar plots of the nighttime NO₂ fields are quite noisy (not shown) due to the large uncertainties for tangent layer NO₂ in the lower stratosphere. Nevertheless, most of the odd nitrogen reservoir at 46 hPa comes from HNO₃, not NO₂. Together, they indicate the extent of denitrification of the air in the vortex region during late October 1978.

We show in Figs. 5 and 6 the details of the changing ozone and nitric acid from late October through November. Figure 5 displays time–longitude or Hovmöller diagrams for both species at 60^∘ S; thick black contours indicate the vortex edge and dotted horizontal lines the vortex interior. The occurrence of lowest species mixing ratios is shown clearly in the vortex region in late October. Figure 6 extends the findings of Fig. 5 through the end of November, and there is an eastward progression of the region of low values from late October to early November. Reduced mixing ratios of those species occur inside the vortex until about 25 November, as expected for chemicals that are tracers of air motions in the lower stratosphere. The vortex distorts and then exhibits a stationary wave-1 pattern from November 5 onward, where height is lowest near 0^∘ E. Mixing of air across the vortex edge appears slow for both ozone and HNO₃ during that time.

Figure 5Time–longitude or Hovmöller plots of LIMS ozone (a) and HNO₃ (b) for 60^∘ S and 46 hPa. The ERA-40 vortex edge is shown as thick black contours, and the vortex interior has horizontal dotted lines.

Figure 6As in Fig. 5, but extended in time from 25 October to 30 November 1978.

The LIMS V6 data archive is at the NASA EARTHDATA site of EOSDIS and its website: https://search.earthdata.nasa.gov/search?q=LIMS (Remsberg et al., 2020). Nimbus 7 TOMS ozone is at https://disc.gsfc.nasa.gov/datacollection/TOMSN7L2_008.html (TOMS Science Team, 2020). ECC ozonesonde ozone profiles are available from the World Ozone and Ultraviolet Radiation Data Centre or WOUDC at https://woudc.org/data/explore.php (WOUDC, 2020). ECMWF Reanalysis (ERA-40) data are accessible through https://climatedataguide.ucar.edu/climate-data/era40 (National Center for Atmospheric Research Staff, 2020).

ER and VLH wrote the manuscript and prepared the figures with input from all the other co-authors. AK provided information about the TOMS ozone images. LG led the development of the LIMS Version 6 algorithms. JCG and JMR are the co-principal investigators of the LIMS experiment. They also commented on the new insight from the findings about ozone and nitric acid of October 1978.

The authors declare that they have no conflict of interest.

This research has been supported by the NASA Langley Research Center (Science Directorate).

This paper was edited by Rolf Müller and reviewed by two anonymous referees.