Latitudinal dependence of the stratospheric ozone and temperature response to solar particles’ forcing оn 20 January 2005

Abstract

This study examines the latitudinal-altitudinal variations of the midday O3and temperature response to the forcing of the enhanced flux of energetic particles, during January 2005 Solar Proton Event (SPE). We show that short-term response of the stratospheric O3 depends strongly on the latitude and the energy of precipitating particles. At polar latitudes, where the relativistic electrons and “soft” protons are able to penetrate deeper into the atmosphere, we found a reduction of the peak ozone density in periods of enhanced particles’ fluxes. Such a response is widely explained by the activation of HOx and NOx ozone destructive cycles. At mid-latitudes, however, the stratospheric part of the O3profile remains insensitive to these lower energy particles, because they affect only the thermospheric and mesospheric O3. On the other hand, the “hard” protons, emitted during the third solar flare on 20 January, are able to propagate much deeper, affecting even the stratospheric ozone and reducing its density. As a consequence of the thinning of the ozone optical depth, the solar UV penetrates deeper into the atmosphere, activating the Slanger’s mechanism for ozone production at lower levels –known also as ozone self-restoration. This could be an explanation for the obtained raise of the mid-latitude peak O3density in the period of atmospheric restoration after the SPE’2005. The earlier raise of the polar ozone maximal density –i.e. between 18 and 21 January –could be related to the fact that at the moment of SPE’2005it has been already diminished by the relativistic electrons and “soft” protons, getting ahead of the strongest proton flare. So the further ozone destruction (by particles with mixed energies) triggered the activation of its restoration several days earlier. Consequently, the latitudinal differences in the ozone response –found in ERA Interim data –could be attributed to the different energetic spectrum of solar flares, the depth of the particles’ penetration into the atmosphere and the zenith angle of stratosphere illumination by the solar UV radiation. Enhancement of the lower and middle stratospheric temperature during the SPE’2005 has to be attributed to the increased ozone density and the more solar UV radiation absorbed.