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Reduced meteoric smoke abundance at the summer pole - implications for mesospheric ice particle nucleation
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology .
Leibniz Inst Atmospher Phys, Kuhlungsborn, Germany .
USN, Res Lab, EO Hulburt Ctr Space Res, Washington, DC 20375 USA .
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.

Place, publisher, year, edition, pages
2008. Vol. 41, no 1, 41-49 p.
Keyword [en]
NLC, PMSE, meteoric smoke, particles, mesosphere, condensation nuclei
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences
Identifiers
URN: urn:nbn:se:su:diva-25117DOI: 10.1016/j.asr.2007.09.006ISI: 000253590400005OAI: oai:DiVA.org:su-25117DiVA: diva2:198935
Note
Part of urn:nbn:se:su:diva-7734Available from: 2008-05-14 Created: 2008-05-14 Last updated: 2010-01-22Bibliographically approved
In thesis
1. Meteoric Aerosols in the Middle Atmosphere
Open this publication in new window or tab >>Meteoric Aerosols in the Middle Atmosphere
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
meteoroid, meteor, nucleation, mesosphere, stratosphere, ablation, smoke, NLC, PMSE, PSC
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences
Identifiers
urn:nbn:se:su:diva-7734 (URN)978-91-7155-676-9 (ISBN)
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

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