Investigation of Mesospheric and Thermospheric Magnesium Species from Space

Abstract

The scope of this study is the investigation of mesospheric and thermospheric metallic species.The methodology used in this work provides results in the mesosphere/lower thermosphereregion (MLT) extending from approximately 70 to 500 km altitude.The major source of metal species in the upper atmosphere is influx from cosmic dust. Alongwith Earth, a variety of celestial bodies orbit the Sun. The asteroid belt between Earth and Marsand the Kuiper belt outside the orbit of Neptune are well-known regions of high abundance ofthose objects. In addition, a number of regularly returning cometary objects present sources ofcosmic material. The origin of these comets is believed to be the Oort cloud surrounding thesolar system. After entering the atmosphere, particles from either source are then subject tofrictional heating. This leads to sublimation of metallic species from the surface of the particles.The impact of metal species on the chemistry and physics of the upper and middle (and,eventually, the lower) atmosphere is still a field of intense research. The total influx of meteoriccosmic material into the atmosphere is highly uncertain. Metal species are suggested to impactthe removal of ozone in the upper stratosphere and the formation of water vapour in themesosphere. Additionally, the role of meteoric particles in the formation of stratospheric cloudsis of scientific interest.Space-borne measurements present the most powerful method to investigate global distributionsof metal species with moderate vertical and horizontal resolution. The SCIAMACHYinstrument is capable to observe emission signals from mesospheric and thermospheric magnesiumspecies on a global scale with good spatial and temporal coverage. This work comprisesresults from the first six years of measurement (2002 - 2007) of the SCIAMACHY instrument.The results presented here represent the first vertically resolved satellite measurementsof mesospheric magnesium species on a global scale and a long period of time.A comprehensive review of the distribution and variability of the two major atomic mesosphericmagnesium species (Mg and Mg ) in the upper mesosphere and lower thermosphere isprovided. Seasonal variations are investigated. In the northern hemisphere, a pronounced seasonalvariation with summer maxima has been found for the ionized species Mg . The neutralspecies does not exhibit such variation.An estimation of the total influx of meteoric material has been derived from the total contentof Mg. A total amount of approximately 55 t enters the atmosphere per day.A long-term study has been carried out to analyze the impact of meteor showers on the totalcontent of magnesium species in the upper atmosphere. The impact of meteoric showers on thetotal content has been found to be undetectable. It can thus be concluded that the additionalmass influx of meteor showers is negligible compared to the average background flux.The correlation between the abundance of magnesium species and the solar activity is investigated.This includes a general long-term consideration over all six years of measurement aswell as short-term observations made during a large outburst of solar particles in October andNovember 2003. No impact of variations in the solar activity on the total content of either Mg or Mg has been observed. During the October/November 2003 period of high solar particleflux, however, strong enhancements in both magnesium species have been observed.