Effects of two large solar energetic particle events on middle atmosphere nighttime odd hydrogen and ozone content: Aura/MLS and TIMED/SABER measurements

It is well established that large solar energetic particle (SEP) events affect ozone in the middle atmosphere through chemical reactions involving odd hydrogen (HOx) species. We analyze global middle atmospheric effects at local nighttime for two large SEP events during the intervals of 7-17 November 2004 and 20-30 August 2005. Properties of the SEP events and concomitant geomagnetic storms are discussed using in situ measurements. Temporal dynamics and latitudinal distribution of HOx and ozone densities inferred from measurements by the Aura/MLS (Microwave Limb Sounder) instrument are analyzed. We show statistically significant increases of nighttime hydroxyl (OH) density in the middle atmosphere up to 5 degrees 10(6)cm(-3) in the latitude range from 70 degrees down to 50 degrees latitude in northern and to -40 degrees latitude in southern hemispheres in connection with peaks in proton fluxes of >10MeV energy range measured by GOES spacecraft. During the storm main phases, the nighttime OH density increases were observed around 50 degrees in southern and northern hemispheres in the altitude range of 65-80km. There is a correspondence between averaged nighttime OH partial column density (in 0.005 to 0.1hPa pressure range) in the polar latitudes and energetic proton (>10MeV) fluxes. Corresponding statistically significant nighttime ozone destructions up to 45% are observed from 70 degrees down to 60 degrees latitude in the northern and southern hemispheres. The SEP impulsive phases correspond to onsets of ozone density depletions. Larger relative ozone destructions are observed in the northern hemisphere in November and in the southern hemisphere in August. Simultaneous measurements of ozone density by the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED/SABER) instrument independently confirm the MLS results.