HR: 1340h
AN: A43B-1149    [Abstracts]
TI: Recent Summer Sunshine Duration Variability and Trends Over the Iberian Peninsula: Relation With Changes in Circulation Patterns and Teleconnection With the Sahel Rainfall
AU: * Sanchez-Lorenzo, A
EM: asanchezlorenzo@ub.edu
AF: Group of Climatology, University of Barcelona, C/ Montalegre, no. 6, Barcelona, E-08001, Spain
AU: Calbo, J
AF: Group of Environmental Physics, University of Girona, Campus Montilivi, EPS II, Girona, E- 17071, Spain
AU: Martin-Vide, J
AF: Group of Climatology, University of Barcelona, C/ Montalegre, no. 6, Barcelona, E-08001, Spain
AU: Querol, X
AF: Institute of Earth Sciences "Jaume Almera" (CSIC), C/ Lluis Sole i Sabaris s/n, Barcelona, E-08028, Spain
AU: Brunetti, M
AF: Institute of Atmospheric Sciences and Climate (NRC), Via Gobetti, 101, Bologna, I-40129, Italy
AB: This work describes the summer (July and August) time evolution and trends of sunshine duration (SunD) over the Iberian Peninsula (IP) covering the 1961-2004 period. We used the homogenized and gridded SUNDUIB database. The temporal evolution of the mean summer series for the whole IP shows a decrease in SunD from the 1960s to the early 1980s, followed by a slightly increase up to the end of the 20th century, which matches the "global dimming" and the subsequent "brightening" described for other regions in international scientific literature. The trend analysis applied to the IP series highlights a dominant decrease in SunD, with a negative and significant trend of about -0.6% per decade.

These temporal variability and trends of the summer SunD in the IP are related to changes in the frequency of circulation patterns that were classified applying a Principal Component Analysis in T-Mode and then performing a Cluster Analysis on the most relevant extracted principal components, using a non-hierarchical k-means method as clustering algorithm. The analysis was carried out using the daily sea level pressure (SLP) data and the geopotential fields at 850 and 700 hPa, derived from the NCEP/NCAR reanalysis at a resolution of 2.5ºx2.5º, and in a selected area between 20°W-15°E longitude and 20º-45°N latitude. The results of the classification show that the most satisfactory results are those obtained with 12 circulation patterns. We calculated the time series of absolute frequency of occurrence of the above mentioned patterns, and correlated them with the summer SunD series. Four of these patterns are negatively and significantly correlated with the SunD series, while other four patterns are positively and significantly correlated. Grouping together the absolute frequency of the circulation patterns with positive significant correlation and those with negative significant correlation, the correlations increase to r=0.73 and r=-0.85, respectivaly. These two series of absolute frequencies are strongly and negatively correlated between them (r=-0.83), and show significant trends with opposite sign: -4.4 days and +2.6 days per decade, respectively. We completed the analysis using total cloud cover data over the 1961-2004 period, and data of TSP (total suspended particles) and PM10 (suspended particles <10 µm) from 14 air quality monitoring stations recorded in rural areas of Spain over the 1996-2004 period. The results show that the changes in the SunD over the IP can hardly be explained only by changes in the total cloud cover, and it is reasonable to affirm that there is also a contribution from the African dust episodes and resuspension processes in the incoming solar radiation that reach the IP, especially in the southern and central areas.

Finally, we studied the relationship between SunD and Sahel rainfall variability measured by means of the Sahel index. There is a positive and significant correlation between the two variables, with the strongest values in the southern and central areas of the IP. The results suggest a possible link between the precipitation in the Sahel area and the SunD over the IP, due to an increase (decrease) in the dust intrusions and cloudiness during the years with negative (positive) anomalies of precipitation in the Sahel area.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 3309 Climatology (1616, 1620, 3305, 4215, 8408)
DE: 3311 Clouds and aerosols
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting