Austral Winter 2003

During austral winter 2003, a strong enhancement of NO2 has been observed by GOMOS in the high latitude upper stratosphere (Hauchecorne et al., 2005). The development of this enhanced NO2 can be followed on the monthly latitude-height distribution maps (Figure 5). In April, the NO2 distribution is near the climatology with highest mixing ratios at low latitudes. From 2 to 30 May GOMOS was stopped due to instrumental problems and it is not possible to compute monthly mean profiles in May. A maximum appears above 40 km at southern high latitude in June and develops and extends downwards in July. In August, the maximum decreases and peaks at 40 km. In September, the NO2 distribution is no more perturbed. There is no major SPE reported during this period to explain the strong enhancement of upper

Figure 3. Mean NO2 (left) and O3 (right) vertical profile around 70°N before and after the 28 October 2003 SPE.

Ratio (NO2 after 28 Oct) / (NO2 before 28 Oct) Ratio (O3 after 28 Oct) / (O3 before 28 Oct)

Figure 4. Ratio of NO2 (left) and O3 (right) vertical profiles around 70°N before and after the 28 October SPE.

Ratio (NO2 after 28 Oct) / (NO2 before 28 Oct) Ratio (O3 after 28 Oct) / (O3 before 28 Oct)

Figure 4. Ratio of NO2 (left) and O3 (right) vertical profiles around 70°N before and after the 28 October SPE.

stratospheric NO2. However, there is one SPE reported on 29 May 2003 with a weak flux of high energy protons but with a relatively strong flux of low energy protons. The proton flux measured by GOES 10 in the band 0.8-4 MeV (Figure 6) peaks to 3 x 104 cm-2s-1sr-1 against 8 x 104 cm-2s-1sr-1 for the 28 October 2003 SPE. These low energy protons deposit most of their energy in the mesosphere (Jackman et al., 2005) and can produce an important amount of NOx there. In June-July there is a strong diabatic descent in the south polar vortex and NOx produced in the mesosphere will descend in the upper stratosphere. This is a possible explanation of the strong NO2 enhancement observed in June-July at high southern latitudes. This hypothesis is supported by the evolution of NO2 concentration profile between May and August (Figure 7). In May, the NO2 concentration is near the level of detection above 45 km. On 13 June, NO2 concentration increases above 45 km with of a secondary maximum at 51 km. This maximum descends to 42 km on

Figure 5. Latitude-height section of monthly mean NO2 mixing ratio (in ppbv) from April to September 2003.
http://www.sec.noaa.gov/Data/goes.html)."/>
Figure 6. Proton flux measured by GOES 10 in 4 energy bands between 27 May and 30 May 2003 (from http://www.sec.noaa.gov/Data/goes.html).

27 June, 38 km on 17 July, 36 km on 1st August, 34 km on 15 August and 32 km on 26 August. Variations in NO2 concentration observed below 30 km are due to the seasonal evolution of NOx in the high latitude middle stratosphere and are not discussed here. The evolution of O3 profile from 15 April to 31 May (Figure 8) indicates a possible depletion of up to 40% around 55 km just after the SPE.

Figure 7. Evolution of NO2 profile at southern high latitude from 1 May to 26 August 2003.

Was this article helpful?

0 0

Post a comment