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A 10 year cloud climatology over Scandinavia derived from NOAA advanced very high resolution radiometer imagery
Stockholm University, Faculty of Science, Department of Meteorology . The Swedish Meteorological and Hydrological Institute, Norrköping.
2003 (English)In: International Journal of Climatology, ISSN 0899-8418, E-ISSN 1097-0088, Vol. 23, no 9, 1023-1044 p.Article in journal (Refereed) Published
Abstract [en]

Results from a satellite-based method to compile regional cloud climatologies covering the Scandinavian region are presented. Systematic processing of multispectral image data from the NOAA Advanced Very High Resolution Radiometer (AVHRR) instrument has been utilized to provide monthly cloud climatologies covering the period 1991-2000. Considerable local-scale variation of cloud amounts was found in the region. The inland Baltic Sea and adjacent land areas exhibited a large-amplitude annual cycle in cloudiness (high cloud amounts in winter, low cloud amounts in summer) whereas a weak-amplitude reversed annual cycle (high cloud amounts with a weak maximum in summer) was found for the Scandinavian mountain range. As a contrast, conditions over the Norwegian Sea showed high and almost unchanged cloud amounts during the course of the year. Some interesting exceptions to these patterns were also seen locally. The quality of the satellite-derived cloud climatology was examined through comparisons with climatologies derived from surface cloud observations, from the International Satellite Cloud Climatology Project (ISCCP) and from the European Centre for Medium-range Weather Forecasts ERA-40 data set. In general, cloud amount deviations from surface observations were smaller than 10% except for some individual winter months, when the separability between clouds and snow-covered cold land surfaces is often poor. The ISCCP data set showed a weaker annual cycle in cloudiness, generally caused by higher summer-time cloud amounts in the region. Very good agreement was found with the ERA-40 data set, especially for the summer season. However, ERA-40 showed higher cloud amounts than SCANDIA and ISCCP during the winter season. The derived cloud climatology is affected by errors due to temporal AVHRR sensor degradation, but they appear to be small for this particular study. The data set is proposed as a valuable data set for validation of cloud description in numerical weather prediction and regional climate simulation models.

Place, publisher, year, edition, pages
2003. Vol. 23, no 9, 1023-1044 p.
National Category
Meteorology and Atmospheric Sciences
Identifiers
URN: urn:nbn:se:su:diva-23044DOI: 10.1002/joc.916ISI: 000184388400003OAI: oai:DiVA.org:su-23044DiVA: diva2:189963
Available from: 2006-11-18 Created: 2006-11-18 Last updated: 2017-12-13Bibliographically approved
In thesis
1. The use of a satellite-derived cloud climatology for studying cloud-aerosol processes and the performance of regional cloud climate simulations
Open this publication in new window or tab >>The use of a satellite-derived cloud climatology for studying cloud-aerosol processes and the performance of regional cloud climate simulations
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The entry of satellite-derived decadal cloud datasets with homogeneous coverage in time and space enables studies not possible before. This thesis presents two such applications. The first study deals with cloud-aerosol processes and the second with an evaluation of cloud simulations from a regional climate model.

The first part of the thesis describes the used satellite-derived dataset based on imagery from the Advanced Very High Resolution Radiometer (AVHRR) on the polar orbiting NOAA satellites. A method for cloud retrieval and the compilation of a 1991-2000 Scandinavian cloud climatology are described.

The second part reveals an intriguing anti-correlation between monthly mean satellite-derived cloudiness and the concentration of the cosmogenetic isotope Beryllium-7 in near-surface aerosol samples for three measurement sites in Sweden. Large-scale transport processes are suggested as the most likely physical mechanism for this behaviour but more complex relations to cloud microphysical processes are not ruled out.

The final part presents a thorough evaluation of cloud simulations of the SMHI Rossby Centre regional atmospheric model (RCA3). Several model-to-satellite adaptations are applied to avoid artificial biases of results. The study stresses the necessity to account for initial differences between observed and modelled clouds caused by satellite cloud detection limitations. Results show good agreement of modelled and observed cloud amounts while the vertical distribution of clouds appears largely different. RCA3 underestimates medium-level clouds while overestimating low- and high-level clouds. Also, the current use of the Maximum cloud overlap approach in the radiation scheme and an indicated excess of cloud condensate in modelled clouds appear to create excessive cloud optical thicknesses with serious implications for the surface radiation budget.

Future applications are outlined based on greatly enhanced satellite-derived cloud and radiation budget datasets.

Place, publisher, year, edition, pages
Stockholm: Meteorologiska institutionen (MISU), 2006. 142 p.
Keyword
Clouds and climate, satellite cloud climatology, validation of clouds, clouds and aerosols
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:su:diva-1364 (URN)91-7155-353-3 (ISBN)
Public defence
2006-12-18, C 609, Arrheniuslaboratoriet, Stockholm, 10:00
Opponent
Supervisors
Available from: 2006-11-18 Created: 2006-11-18Bibliographically approved

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