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Assessing lidar-based classification schemes for polar stratospheric clouds based on 16 years of measurements at Esrange, Sweden
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
2014 (English)In: Journal of Geophysical Research: Atmospheres, ISSN 2169-8996, Vol. 119, no 3, 1386-1405 p.Article in journal (Refereed) Published
Abstract [en]

Lidar measurements of polar stratospheric clouds (PSCs) are commonly analyzed in classification schemes that apply the backscatter ratio and the particle depolarization ratio. This similarity of input data suggests comparable results of different classification schemes—despite measurements being performed with a variety of mostly custom-made instruments. Based on a time series of 16 years of lidar measurements at Esrange (68°N, 21°E), Sweden, we show that PSC classification differs substantially depending on the applied scheme. The discrepancies result from varying threshold values of lidar-derived parameters used to define certain PSC types. The resulting inconsistencies could impact the understanding of long-term PSC observations documented in the literature. We identify two out of seven considered classification schemes that are most likely to give reliable results and should be used in future lidar-based studies. Using polarized backscatter ratios gives the advantage of increased contrast for observations of weakly backscattering and weakly depolarizing particles. Improved confidence in PSC classification can be achieved by a more comprehensive consideration of the effect of measurement uncertainties. The particle depolarization ratio is the key to a reliable identification of different PSC types. Hence, detailed information on the calibration of the polarization-sensitive measurement channels should be provided to assess the findings of a study. Presently, most PSC measurements with lidar are performed at 532 nm only. The information from additional polarization-sensitive measurements in the near infrared could lead to an improved PSC classification. Coincident lidar-based temperature measurements at PSC level might provide useful information for an assessment of PSC classification.

Place, publisher, year, edition, pages
2014. Vol. 119, no 3, 1386-1405 p.
Keyword [en]
polar stratospheric clouds, lidar
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
URN: urn:nbn:se:su:diva-102509DOI: 10.1002/2013JD020355ISI: 000332994600019OAI: diva2:710394
Available from: 2014-04-07 Created: 2014-04-07 Last updated: 2014-05-12Bibliographically approved
In thesis
1. Lidar Measurements of Polar Stratospheric Clouds in the Arctic
Open this publication in new window or tab >>Lidar Measurements of Polar Stratospheric Clouds in the Arctic
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Polar Stratospheric Clouds (PSCs) play a key role for ozone depletion in the polar stratosphere. Its magnitude depends on the type of PSC and its lifetime and extent. This thesis presents PSC observations conducted with the Esrange lidar and the space-borne CALIPSO lidar.

PSCs are separated into three types according to their optical properties. The occurrence rate of the different types which are often observed simultaneously as well as their interaction and connection is not well understood. To better understand the processes that govern PSC formation, observations need to be combined with a detailed view of the atmospheric background in which PSCs develop, exist, and are transformed from one type to another.

This thesis introduces a new channel of the Esrange lidar for temperature profiling at heights below 35 km. The design of this channel and first temperature measurements within PSCs and cirrus clouds are presented. This is an important step since the majority of PSC-related literature extracts temperatures within PSCs from reanalysis data.

In contrast to ground–based measurements space–borne lidar does not rely on cloud–free conditions. Hence, it provides an unprecedented opportunity for studying the connection between PSCs and the underlying synoptic–scale conditions which manifest as tropospheric clouds. This thesis shows that most of the PSCs observed in the Arctic during winter 2007/08 occurred in connection with tropospheric clouds.

A combined analysis of ground-based and space-borne lidar observation of PSCs in combination with microphysical modeling can improve our understanding of PSC formation. A first case study of this approach shows how a PSC that was formed by synoptic-scale processes is transformed into another type while passing the Scandinavian mountains.

Today a variety of classification schemes provides inconsistent information on PSC properties and types. This thesis suggests a unified classification scheme for lidar measurements of PSCs.

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University, 2013. 36 p.
National Category
Natural Sciences
Research subject
Atmospheric Sciences and Oceanography
urn:nbn:se:su:diva-88054 (URN)978-91-7447-657-6 (ISBN)
Public defence
2013-04-05, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, 10:00 (English)

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Submitted. 


Available from: 2013-03-14 Created: 2013-03-04 Last updated: 2014-04-07Bibliographically approved

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