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Meteoric Aerosols in the Middle Atmosphere
Stockholm University, Faculty of Science, Department of Meteorology.
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis concerns the fate of the meteoric smoke in the Middle Atmosphere, and its effect on ice phenomena such as noctilucent clouds (NLC) and polar stratospheric clouds (PSC).

The potential role of NLC as tracer for mesospheric processes and variability, and as a tool for monitoring this remote and inaccessible region, has generated substantial interest within the scientific community. The nucleation of ice in such a dry environment is not trivial. Supersaturation is considered too low for homogeneous nucleation. Hence, pre-existing condensation nuclei are deemed necessary, with smoke particles having long been considered the most likely candidate. Here we show that the atmospheric circulation transports meteoric smoke particles away from the polar region before they coagulate large enough to efficiently act as ice condensation nuclei. We also show that the charging of meteoric smoke, in combination with deviations from the mean thermal state, may solve this dilemma by significantly altering the ice nucleation properties of smoke. Thus, while it is highly questionable whether neutral smoke can provide sufficient amounts of condensation nuclei for ice formation at the polar summer mesopause, charged meteoric smoke proves to be a promising candidate to explain mesospheric ice phenomena as we observe them.

We further show that the bulk of the meteoric material is transported to the Arctic winter stratosphere, yielding significantly higher concentrations of meteoric smoke in the region of PSC nucleation than has previously been believed. Our new predictions of meteoric smoke in this region may thus shed new light on open questions relating to PSC nucleation.

Place, publisher, year, edition, pages
Stockholm: Meteorologiska institutionen (MISU) , 2008. , 32 p.
Keyword [en]
meteoroid, meteor, nucleation, mesosphere, stratosphere, ablation, smoke, NLC, PMSE, PSC
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences
Identifiers
URN: urn:nbn:se:su:diva-7734ISBN: 978-91-7155-676-9 (print)OAI: oai:DiVA.org:su-7734DiVA: diva2:198938
Public defence
2008-06-05, sal G, Arrheniuslaboratorierna, Svante Arrhenius väg 14-18, Stockholm, 13:00
Opponent
Supervisors
Available from: 2008-05-14 Created: 2008-05-14Bibliographically approved
List of papers
1. Distribution of meteoric smoke - sensitivity to microphysical properties and atmospheric conditions
Open this publication in new window or tab >>Distribution of meteoric smoke - sensitivity to microphysical properties and atmospheric conditions
2006 (English)In: Atmospheric chemistry and physics, ISSN 1680-7316, Vol. 6, no 12, 4415-4426 p.Article in journal (Refereed) Published
Abstract [en]

Meteoroids entering the Earth's atmosphere experience strong deceleration and ablate, whereupon the resulting material is believed to re-condense to nanometre-size "smoke particles". These particles are thought to be of great importance for many middle atmosphere phenomena, such as noctilucent clouds, polar mesospheric summer echoes, metal layers, and heterogeneous chemistry. The properties and distribution of meteoric smoke depend on poorly known or highly variable factors such as the amount, composition and velocity of incoming meteoric material, the efficiency of coagulation, and the state and circulation of the atmosphere. This work uses a one-dimensional microphysical model to investigate the sensitivities of meteoric smoke properties to these poorly known or highly variable factors. The resulting uncertainty or variability of meteoric smoke quantities such as number density, mass density, and size distribution are determined. It is found that the two most important factors are the efficiency of the coagulation and background vertical wind. The seasonal variation of the vertical wind in the mesosphere implies strong global and temporal variations in the meteoric smoke distribution. This contrasts the simplistic picture of a homogeneous global meteoric smoke layer, which is currently assumed in many studies of middle atmospheric phenomena. In particular, our results suggest a very low number of nanometre-sized smoke particles at the summer mesopause where they are thought to serve as condensation nuclei for noctilucent clouds.

Keyword
mesosphere, stratosphere, aerosol, meteoric smoke, condensation nuclei, NLC
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences
Identifiers
urn:nbn:se:su:diva-25115 (URN)
Note
Part of urn:nbn:se:su:diva-7734Available from: 2008-05-14 Created: 2008-05-14 Last updated: 2010-01-21Bibliographically approved
2. Global and temporal distribution of meteoric smoke: a two-dimensional simulation study
Open this publication in new window or tab >>Global and temporal distribution of meteoric smoke: a two-dimensional simulation study
2008 (English)In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 113, no D3, D03202- p.Article in journal (Refereed) Published
Abstract [en]

Meteoric material entering Earth's atmosphere ablates in the mesosphere and is then expected to recondense into tiny so-called “smoke particles.” These particles are thought to be of great importance for middle atmosphere phenomena like noctilucent clouds, polar mesospheric summer echoes, metal layers, and heterogeneous chemistry. Commonly used one-dimensional (1-D) meteoric smoke profiles refer to average global conditions and yield of the order of a thousand nanometer sized particles per cubic centimeter at the mesopause, independent of latitude and time of year. Using the first two-dimensional model of both coagulation and transport of meteoric material we here show that such profiles are too simplistic, and that the distribution of smoke particles indeed is dependent on both latitude and season. The reason is that the atmospheric circulation, which cannot be properly handled by 1-D models, efficiently transports the particles to the winter hemisphere and down into the polar vortex. Using the assumptions commonly used in 1-D studies results in number densities of nanometer sized particles of around 4000 cm−3 at the winter pole, while very few particles remain at the Arctic summer mesopause. If smoke particles are the only nucleation kernel for ice in the mesosphere this would imply that there could only be of the order of 100 or less ice particles cm−3 at the Arctic summer mesopause. This is much less than the ice number densities expected for the formation of ice phenomena (noctilucent clouds and polar mesospheric summer echoes) that commonly occur in this region. However, we find that especially the uncertainty of the amount of material that is deposited in Earth's atmosphere imposes a large error bar on this number, which may allow for number densities up to 1000 cm−3 near the polar summer mesopause. This efficient transport of meteoric material to the winter hemisphere and down into the polar vortex results in higher concentrations of meteoric material in the Arctic winter stratosphere than previously thought. This is of potential importance for the formation of the so-called stratospheric condensation nuclei layer and for stratospheric nucleation processes.

National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences
Identifiers
urn:nbn:se:su:diva-25116 (URN)10.1029/2007JD009054 (DOI)000252825500004 ()
Note
Part of urn:nbn:se:su:diva-7734Available from: 2008-05-14 Created: 2008-05-14 Last updated: 2010-01-21Bibliographically approved
3. Reduced meteoric smoke abundance at the summer pole - implications for mesospheric ice particle nucleation
Open this publication in new window or tab >>Reduced meteoric smoke abundance at the summer pole - implications for mesospheric ice particle nucleation
2008 (English)In: Advances of Space Research, ISSN 0273-1177, Vol. 41, no 1, 41-49 p.Article in journal (Refereed) Published
Abstract [en]

Noctilucent clouds (NLC) and polar mesospheric summer echoes (PMSE) are phenomena that occur in the summertime polar regions due to the presence of ice particles around the mesopause. That ice particles are able to form in a region with such low water vapour concentration as the mesopause is noteworthy. Even though the summer mesopause is the coldest region on Earth, temperatures are generally not low enough for homogeneous nucleation to occur, which necessitates the presence of pre-existing condensation nuclei. The nature of these nuclei has long puzzled the scientific community and many candidates have been suggested, such as particles of meteoric origin, ion clusters, sodium bi-carbonate, sulfate aerosols and soot particles. Out of these the so-called "smoke particles", i.e. particles re-condensed from ablated meteoritic material, have long been considered the most likely. Generally, it has been believed that these particles exist in numbers of the order of thousands per cubic centimetre at the mesopause. This belief is based on 1-dimensional. studies of meteoric material. A recent 2-dimensional model study, which includes the atmospheric circulation from summer to winter pole however, suggests much lower number densities at the summer mesopause. We here investigate the implications of low number densities for the formation of ice particles. We find that even though resulting ice particle distribution may produce typical NLC brightness, the number density of ice particles is not consistent with what is expected for NLC and PMSE. In particular, it is much lower than the ice particle concentration (>1000 cm(-3)) typically expected to explain the "electron bite-outs" that are frequently observed in the vicinity of PMSE's. We therefore re-examine the assumptions and parameters that determine the smoke distribution. We show that even though the number of condensation nuclei at the polar summer mesopause can be increased within the uncertainties, the results in most scenarios remain insufficient. We show that charged particles, perhaps in combination with significant deviations from the mean mesospheric state, may be necessary for condensation of ice particles in the polar summer mesosphere. Hence, we raise the question whether the conventional ideas of nucleation on meteoric smoke, which are used in current mesospheric ice models, are correct.

Keyword
NLC, PMSE, meteoric smoke, particles, mesosphere, condensation nuclei
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences
Identifiers
urn:nbn:se:su:diva-25117 (URN)10.1016/j.asr.2007.09.006 (DOI)000253590400005 ()
Note
Part of urn:nbn:se:su:diva-7734Available from: 2008-05-14 Created: 2008-05-14 Last updated: 2010-01-22Bibliographically approved
4. The importance of charging processes for mesospheric ice nucleation
Open this publication in new window or tab >>The importance of charging processes for mesospheric ice nucleation
In: Atmospheric chemistry and physicsArticle in journal (Refereed) Submitted
Identifiers
urn:nbn:se:su:diva-25118 (URN)
Note
Part of urn:nbn:se:su:diva-7734Available from: 2008-05-14 Created: 2008-05-14Bibliographically approved
5. Meteoric Aerosols in the Middle Atmosphere
Open this publication in new window or tab >>Meteoric Aerosols in the Middle Atmosphere
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-25119 (URN)
Note
Part of urn:nbn:se:su:diva-7734Available from: 2008-05-14 Created: 2008-05-14 Last updated: 2010-01-13Bibliographically approved

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