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The use of a satellite-derived cloud climatology for studying cloud-aerosol processes and the performance of regional cloud climate simulations
Stockholm University, Faculty of Science, Department of Meteorology.
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 [en]
Clouds and climate, satellite cloud climatology, validation of clouds, clouds and aerosols
National Category
Meteorology and Atmospheric Sciences
Identifiers
URN: urn:nbn:se:su:diva-1364ISBN: 91-7155-353-3 (print)OAI: oai:DiVA.org:su-1364DiVA: diva2:189967
Public defence
2006-12-18, C 609, Arrheniuslaboratoriet, Stockholm, 10:00
Opponent
Supervisors
Available from: 2006-11-18 Created: 2006-11-18Bibliographically approved
List of papers
1. Cloud climate investigations in the Nordic region using NOAA AVHRR data
Open this publication in new window or tab >>Cloud climate investigations in the Nordic region using NOAA AVHRR data
1997 (English)In: Theoretical and Applied Climatology, ISSN 0177-798X, Vol. 57, no 3-4, 181-195 p.Article in journal (Refereed) Published
Abstract [en]

A method to estimate monthly cloud conditions (monthly cloud frequencies) from multispectral satellite imagery is described. The operational cloud classification scheme SCANDIA (the SMHI Cloud ANalysis model using DIgital AVHRR data), based on high resolution imagery from the polar orbiting NOAA-satellites, has been used to produce monthly cloud frequencies for the entire year of 1993 and some additional months in 1991, 1992, 1994 and 1995. Cloud analyses were made for an area covering the Nordic countries with a horizontal resolution of four km. Examples of seasonal, monthly and diurnal variation in cloud conditions are given and an annual mean for 1993 is presented. Comparisons with existing surface observations showed very good agreement for horizontal cloud distributions but approximately 5% smaller cloud amounts were found in the satellite estimations. The most evident problems were encountered in the winter season due to difficulties in identifying low-level cloudiness at very low sun elevations. The underestimation in the summer season was partly fictious and caused by the overestimation of convective cloud cover by surface observers. SCANDIA results were compared to ISCCP (International Satellite Cloud Climatology Project) cloud climatologies for two selected months in 1991 and 1992. ISCCP cloudiness was indicated to be higher, especially during the month with anticyclonic conditions where a cloudiness excess of more than 10% were found. The regional variation of cloud conditions in the area was found to be inadequately described by ISCCP cloud climatologies. An improvement of the horizontal resolution of ISCCP data seems necessary to enable use for regional applications. The SCANDIA model is proposed as a valuable tool for local and regional monitoring of the cloud climatology at high latitudes. More extensive comparisons with ISCCP cloud climatologies are suggested as well as comparisons with modelled cloudiness from atmospheric general circulation models and climate models. Special studies of cloud conditions in the Polar areas are also proposed.

National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:su:diva-23043 (URN)10.1007/BF00863612 (DOI)A1997XM12100005 ()
Available from: 2006-11-18 Created: 2006-11-18 Last updated: 2013-12-10Bibliographically approved
2. A 10 year cloud climatology over Scandinavia derived from NOAA advanced very high resolution radiometer imagery
Open this publication in new window or tab >>A 10 year cloud climatology over Scandinavia derived from NOAA advanced very high resolution radiometer imagery
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.

National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:su:diva-23044 (URN)10.1002/joc.916 (DOI)000184388400003 ()
Available from: 2006-11-18 Created: 2006-11-18 Last updated: 2017-12-13Bibliographically approved
3. Clouds and Be-7: Perusing connections between cosmic rays and climate
Open this publication in new window or tab >>Clouds and Be-7: Perusing connections between cosmic rays and climate
Show others...
2006 (English)In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 111, no D2, D02208- p.Article in journal (Refereed) Published
Abstract [en]

[1] Time series data on Be-7, precipitation, temperature, and satellite imagery of cloud cover over Scandinavia, together with cosmic ray and sunspot activity, were used to elucidate the relationship between cosmic rays and clouds, and ultimately climate change. The results indicate a coherent negative correlation between total cloud cover and Be-7 on intraseasonal, seasonal, and decadal scales. Although the reasons behind this correlation are unclear, a full-scale implication of this feature is in the possible use of Be-7 and Be-10 records for proxy paleo-reconstruction of total cloud cover. This is a strongly needed, but generally difficult to quantify parameter in climate models.

National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:su:diva-23045 (URN)10.1029/2005JD005903 (DOI)000235157500001 ()
Available from: 2006-11-18 Created: 2006-11-18 Last updated: 2017-12-13Bibliographically approved
4. Evaluation of regional cloud climate simulations over Scandinavia using a ten-year NOAA AVHRR climatology: Part I: Compensating for limitations in observation capabilities
Open this publication in new window or tab >>Evaluation of regional cloud climate simulations over Scandinavia using a ten-year NOAA AVHRR climatology: Part I: Compensating for limitations in observation capabilities
In: Journal of Geophysical ResearchArticle in journal (Refereed) Submitted
Identifiers
urn:nbn:se:su:diva-23046 (URN)
Note
Part of urn:nbn:se:su:diva-1364Available from: 2006-11-18 Created: 2006-11-18Bibliographically approved
5. Evaluation of regional cloud climate simulations over Scandinavia using a ten-year NOAA AVHRR climatology: Part II:Validation experiment and results
Open this publication in new window or tab >>Evaluation of regional cloud climate simulations over Scandinavia using a ten-year NOAA AVHRR climatology: Part II:Validation experiment and results
In: Journal of Geophysical ResearchArticle in journal (Refereed) Submitted
Identifiers
urn:nbn:se:su:diva-23047 (URN)
Note
Part of urn:nbn:se:su:diva-1364Available from: 2006-11-18 Created: 2006-11-18Bibliographically approved

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