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What caused the exceptional mid-latitudinal Noctilucent Cloud event in July 2009?
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology .
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2011 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 73, no 14-15, 2125-2131 p.Article in journal (Refereed) Published
Abstract [en]

Noctilucent Clouds (NLCs) are rarely observed at mid-latitudes. In July 2009, strong NLCs were recorded from both Paris and Nebraska, located at latitudes 48 degrees N and 41 degrees N, respectively. The main focus of this work is on the atmospheric conditions that have led to NLCs at these latitudes. We investigate to what extent these clouds may be explained by local formation or by transport from higher latitudes. The dynamical situation is analyzed in terms of wind fields created from Aura/MLS temperature data and measured by radar. We discuss possible tidal effects on the transport and examine the general planetary wave activity during these days. The winds do not seem sufficient to transport NLC particles long southward distances. Hence a local formation is rather likely. In order to investigate the possibility of local NLC formation, the CARMA microphysical model has been applied with temperature data from MLS as input. The results from the large-scale datasets are compared to NLC observations by Odin and to local NLC, temperature and wind measurements by lidar and radar. The reason for the exceptional NLC formation is most likely a combination of local temperature variations by diurnal tides, advantageously located large-scale planetary waves, and general mesospheric temperature conditions that were 5-10 K colder than in previous years. The results also point to that NLCs are very unlikely to occur at latitudes below 50 degrees N during daytime. This conclusion can be made from a tidal temperature mode with cold temperatures during nighttime and temperatures above the limit for NLC occurrence during daytime. The best time for observing mid-latitude NLCs is during the early morning hours.

Place, publisher, year, edition, pages
2011. Vol. 73, no 14-15, 2125-2131 p.
Keyword [en]
Mesosphere, Noctilucent Clouds, Atmospheric dynamics
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:su:diva-67286DOI: 10.1016/j.jastp.2010.12.008ISI: 000295551000010OAI: oai:DiVA.org:su-67286DiVA: diva2:470910
Note
authorCount :7Available from: 2011-12-30 Created: 2011-12-27 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Tomographic views of the middle atmosphere from a satellite platform
Open this publication in new window or tab >>Tomographic views of the middle atmosphere from a satellite platform
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The middle atmosphere is a very important part of the Earth system. Until recently, we did not realize the importance of the structure of this vaporous shell and of the fundamental role it plays in both creating and sustaining life on the planet. Thanks to the development and improvement of new sounding methods and techniques, our knowledge of the composition of the atmosphere has become more detailed than ever before. We have also learned how to reveal complex interactions between different species and how they react to the incoming solar radiation.

The middle part of the Earth’s atmosphere serves as a host for the Polar Mesospheric Clouds. These clouds consist of a thin layer of water-ice particles, only exsisting during the summer months and only close to the poles. There are indications that the occurrence of Polar Mesospheric Clouds may be linked to climate change. It has been pointed out that the first sightings coincide with the industrial revolution. Satellite observations have shown that Polar Mesospheric Clouds have become brighter and possibly more widely distributed during the 20th century. The clouds might therefore be suited as indicators of the variability of the climate - a good reason for studying this night-shimmering phenomena. The clouds can also be used as a proxy for middle atmospheric dynamics. In order to fully utilize Polar Mesospheric Clouds as tracers for atmospheric variability and dynamics, we need to better understand their local properties.

The Optical Spectrograph and Infra-Red Imager System (OSIRIS) is one of two instruments installed on the Odin satellite. The optical spectrograph of this instrument observes sunlight scattered by the atmosphere and thus the Polar Mesospheric Clouds. This thesis deals with a tomographic technique that can reconstruct both horizontal and vertical structures of the clouds by using observations from various angles of the atmospheric region. From this information, microphysical properties such as particle sizes and number densities are obtained.

The tomographic technique presented in this thesis also provides a basis for a new satellite concept - MATS. The idea behind the MATS satellite mission is to analyze wave activity in the atmosphere over a wide range of spatial and temporal scales, based on the scientific heritage from Odin/OSIRIS and the tomographic algorithms presented in this thesis.

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University, 2014. 53 p.
Keyword
Atmosphere, Mesosphere, Noctilucent Clouds, Polar Mesospheric Clouds, Tomography, Remote sensing, Odin, OSIRIS
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-106833 (URN)978-91-7447-974-4 (ISBN)
Public defence
2014-10-03, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 10:00 (English)
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Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper3: Submitted. Paper 4: Manuscript.

Available from: 2014-09-11 Created: 2014-08-23 Last updated: 2014-10-22Bibliographically approved

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