Investigation of mesospheric and thermospheric magnesium species from space [Elektronische Ressource] / vorgelegt von Marco Scharringhausen

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• Publié par: universitat_bremen
• Publié le: 01 janvier 2007
• Nombre de lectures: 7
• Langue: English
• Poids de l'ouvrage: 3 Mo

Extrait

Investigation of Mesospheric and Thermospheric
Magnesium Species from Space
Dissertation zur Erlangung des Grades
Dr. rer. nat.
der Universität Bremen, Fachbereich 1 (Physik/Elektrotechnik)
vorgelegt von
Dipl. Math. Marco Scharringhausen
Abgabe: 11.6.2007
1. Gutachter: Prof. Dr. John P. Burrows, FB 1
2.hter: Prof. Dr. Justus Notholt, FB 1
Kolloquium: 19.10.2007Für meine ElternContents
Abstract 5
I Introduction 7
1Introduction 9
1.1 Origin and role of metal species in the upper atmosphere 9
1.2 Purpose and outline of this study 11
2 General review of the atmosphere 13
2.1 Vertical structure 13
2.2 Mesospheric and thermospheric chemistry 13
3Airglow 17
3.1 Resonance fluorescence 17
3.2 Photodissociation 18
3.3 Dissociative recombination 18
3.4 SCIAMACHY measurements of airglow emissions 19
+4 Chemistry of Mg and Mg 23
4.1 Why magnesium? 23
4.2 Major chemical compounds and reactions 23
II Methodology 29
5 The SCIAMACHY instrument 31
5.1 Spectral characteristics 31
5.2 Spatial characteristics and measurement modes 32
5.3 Limb-Nadir-Matching 33
6 A 2D retrieval scheme for SCIAMACHY limb and nadir data 35
6.1 Horizontal resolution of a single limb scan – absorption data and emissions 35
6.2 Retrieval principle 37
6.3 Obtaining column densities 39
6.4 Instrument noise 52
6.5 Systematic errors 56
6.6 Comparison with other measurements and model calculations 60
6.7 Reconstruction of synthetic data 61
III Results 65
7 Review of the complete SCIAMACHY data set 67
7.1 Observations 67
7.2 Discussion 74
8 Magnesium species and meteor activity 79
8.1 Observations 79
8.2 Quadrantids (January 1 – January 5) 80
8.3 η-Aquarids (April 19 – May 28) 80
8.4 Perseids (July 17 – August 24) 81
8.5 Leonids (November 14 – November 21) 81
34 Contents
8.6 Geminids (December 7 – December 17) 82
8.7 Conclusions 82
9 Estimation of the total influx of cosmic dust from total content and loss
rates of Mg 89
10 Correlation with solar activity 93
10.1 Correlation with proton fluxes 95
10.2 C with the 10.7 cm radio flux 96
10.3 Conclusions 99
11 Solar proton events and upper atmosphere magnesium 101
11.1 Observations 102
11.2 Discussion 120
12 The 2005 magnesium anomaly 123
12.1 Observations 123
12.2 Discussion 123
13 Summary, conclusions and outlook 129
13.1 Summary and conclusions 129
13.2 Outlook 130
Appendix 131
A Bibliography 133
B Danke! 137Abstract
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 thermosphere
region (MLT) extending from approximately 70 to 500 km altitude.
The major source of metal species in the upper atmosphere is influx from cosmic dust. Along
with Earth, a variety of celestial bodies orbit the Sun. The asteroid belt between Earth and Mars
and the Kuiper belt outside the orbit of Neptune are well-known regions of high abundance of
those objects. In addition, a number of regularly returning cometary objects present sources of
cosmic material. The origin of these comets is believed to be the Oort cloud surrounding the
solar system. After entering the atmosphere, particles from either source are then subject to
frictional 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 meteoric
cosmic material into the atmosphere is highly uncertain. Metal species are suggested to impact
the removal of ozone in the upper stratosphere and the formation of water vapour in the
mesosphere. Additionally, the role of meteoric particles in the formation of stratospheric clouds
is of scientific interest.
Space-borne measurements present the most powerful method to investigate global distri-
butions of metal species with moderate vertical and horizontal resolution. The SCIAMACHY
instrument is capable to observe emission signals from mesospheric and thermospheric magne-
sium species on a global scale with good spatial and temporal coverage. This work comprises
results from the first six years of measurement (2002 – 2007) of the SCIAMACHY instru-
ment. The results presented here represent the first vertically resolved satellite measurements
of 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 meso-
+spheric magnesium species (Mg and Mg ) in the upper mesosphere and lower thermosphere is
provided. Seasonal variations are investigated. In the northern hemisphere, a pronounced sea-
+sonal variation with summer maxima has been found for the ionized species Mg . The neutral
species does not exhibit such variation.
An estimation of the total influx of meteoric material has been derived from the total content
of 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 total
content of magnesium species in the upper atmosphere. The impact of meteoric showers on the
total content has been found to be undetectable. It can thus be concluded that the additional
mass 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 inves-
tigated. This includes a general long-term consideration over all six years of measurement as
well as short-term observations made during a large outburst of solar particles in October and
+November 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 particle
flux, however, strong enhancements in both magnesium species have been observed.
5Part I
Introduction1 Introduction
1.1 Origin and role of metal species in the upper
atmosphere
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 thermosphere
region (MLT) extending from approximately 70 to 500 km altitude. This region forms the
boundary between the atmosphere and space and is subject to a number of energy inputs in
the form of solar radiation such as solar wind and electromagnetic radiation. Gravity waves,
tides and planetary waves present energy influx from lower altitudes.
The major source of metal species in the upper atmosphere is influx from cosmic dust.
Along with Earth, a variety of celestial bodies orbit the Sun. The asteroid belt between Earth
and Mars and the Kuiper belt outside the orbit of Neptune are well-known regions of high
abundance of those objects. As a result of perturbations by gravitational forces, small particles
of micrometer sizes as well as larger objects of sizes up to several meters leave their natural
orbits and enter the Earth’s gravitational field. In addition, a number of regularly returning
cometary objects present sources of cosmic material. The origin of these comets is believed
to be the Oort cloud surrounding the solar system. The radius of this cloud is estimated to
be several thousand astronomical units. While approaching the Sun, the cometary material is
evaporating and sublimating from the comets, forming trails that can often be observed by eye
from the ground. This phenomenon lead to the term ”comet”, derive from the ancient Greek
word ”kometes” – ”star with hairs”. Passes of the Earth through these trails result in material
influx into the atmosphere (Goldberg and Aikin, 1973).
Meteoric particles are categorized by their composition. Most particles fall into one of four
categories:
– Iron meteorites: These meteorites consist of mainly iron and nickel. The amount of nickel
ranges from 5 to 60% of the iron mass, with an average of 10%. The major part of the whole
mass is made up by iron, up to 30% sulfides, metal compounds (containing Mg, Ca and other
species) and silicates may be contained in the meteorite.
– Stony irons: These type of meteorites features an iron-nickel-silicate composition. The iron-
nickel part forms 30 – 70% of the total mass, realized in chunks or granules embedded in the
ambient silicates.
– Achondrites: These are silicate rich meteorites containing a broad range of minerals and metal
compounds. The iron-nickel fraction is rather small and makes up at most 5% of the total
mass.
– Chondrites: Though the chemical composition of chondrites is not much different from all of
the above mentioned types – the iron-nickel fraction makes up between 1 and 35%, and the
rest is formed from silicate compounds – the physical manifestation is much more granular
and grainy than that of the other three types. This is a result of the ’cooler’ history of
the chondrites. These particles may originate in accretion or weak collisions between larger
bodies, releasing energies too weak to melt the complete particle and thus resulting in partial
melting and mixing.
After entering the atmosphere, particles from either source are then subject to frictional
heating. This leads to sublimation of metallic species from the surfac