Introduction

It is well recognized that energetic proton precipitation occurring during solar events can increase the production of odd nitrogen in the upper stratosphere and mesosphere (Crutzen, 1975). Odd nitrogen is important to the ozone balance due to catalytic reactions playing a role in ozone destruction. Effect of large solar proton events on ozone and odd nitrogen have been modelled by several authors (Rusch et al., 1981; Reid et al., 1991; Jackman et al., 2000; Verronen et al., 2002). Until very recent years, very few simultaneous ozone and odd nitrogen measurements from space were available. During the large July 2000 SPE space observations from HALOE and NOAA14 SBUV/2 showed a simultaneous NOx (NO + NO2) increase and O3 depletion in the upper stratosphere at north polar latitudes (Jackman et al., 2001). The large solar storm happened end October 2003 caused the fourth largest SPE in the last 40 years. The effect of this event on NOx and O3 in the upper stratosphere has been reported by several authors due to the availability of measurements from various space sounders. Seppala et al. (2004) and Verronen et al. (2005) from ENVISAT GOMOS observed a strong enhancement of NO2 and depletion of O3 in the north polar vortex until mid-December when the vortex was destroyed by a stratospheric warming. Other observations were published by Rohen et al. (2005) from ENVISAT SCIAMACHY, Jackman et al. (2005) from HALOE and SBUV/2 and Semeniuk et al. (2005) from SciSat-I ACE. Degenstein et al. (2005) reported ODIN OSIRIS observations showing a strong mesospheric ozone depletion a few hours after the maximum proton flux. Orsolini et al. (2005) showed, from ENVISAT MIPAS data, a layer with a high HNO3 mixing ratio in the upper stratosphere during early winter, descending to 30 km in January 2004.

An enhancement of stratospheric NO and NO2 was observed in spring 2004 (March to May) in the north polar vortex by several space instruments (HALOE, MIPAS, SAGE II, POAM III) (Natarajan et al., 2004; Randall et al., 2005). The interpretation of these observations is still in discussion. Natarajan et al. (2004) attribute this enhancement to the large production of NO in the mesosphere/thermosphere during the October-November 2003 solar storm and its diabatic descent to the stratosphere during the following months when Randall et al. (2005) consider this hypothesis unlikely due to the strong mixing of stratospheric polar air after the December warming and propose a production of NOx by energetic particle precipitation in early 2004.

Here, using data from GOMOS star occultation spectrometer, on board the European satellite ENVISAT launched 1st March 2002, we give further observational evidences of the impact of the large October 2003 SPE on ozone depletion and NO2 production in the North polar vortex. We present also observations of a strong upper stratospheric NO2 enhancement in the south polar vortex in June-July 2004, tentatively attributed to an SPE with protons of moderate energy occurring in late May 2004.

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