Airborne pollen transport over the Andes: statistical study of trajectories.

63. C. F. PÉREZ, M. E. CASTAÑEDA, M. I. GASMANN Y M. M. BIANCHI

Santiago de Chile, Chile

Conferencia; 4th Alexander von Humboldt International Conference - The Andes: Challenge for Geosciences"; 2008

Airborne pollen transport over the Andes: statisticalstudy of trajectoriesC. F. Pérez (1,3), M. E. Castañeda (1,3), M. I. Gassmann (1,3), M. M. Bianchi (2,3)(1) Departamento de Ciencias de la Atmósfera y los Océanos, FCEN, UBA. Pabellón II, 2dopiso, Ciudad Universitaria, (1428) Buenos Aires, Argentina, (2)INIBIOMA-CONICET-UNCo, calle Quintral 1250,(8400) San Carlos de Bariloche, RioNegro, Argentina, (3) CONICET (perez@at.fcen.uba.ar/54 011 4576 3364)Comprehension of atmospheric pollen transport episodes requires proper knowledgeof the role of interacting mechanisms from different time and space scales. Examplesof these mechanisms are: turbulent mixing, dry and wet deposition, synoptical weathersystems, location, strength and phenology of vegetation sources. Airborne pollen is ofgreat importance due to its interest for many fields of science, from palaeoecologyto allergology. Studies of pollen transport in South America are particularly scarce.Recent airborne pollen records in Southern Patagonia, suggest that pollen transporttakes place from the west to the east slope of the Andes but, the main atmosphericcharacteristics responsible of this phenomenon are not studied yet. The aim of thispaper is to assess potential source areas and to describe the involved synoptic mechanismswhich drive airborne pollen transport above the Andes. Methodology relies onthe analysis of backward trajectories of air masses calculated for particular days whereairborne pollen of Weinmannia trichosperma Cav. was detected at Bariloche aerobiologicalstation (41.143S, 71.375W) located east of the Andes. This pollen type wasselected due to the geographical distribution of their source plants located mainly onthe west slope of the Andes. Eighty-eight backward trajectories were calculated withthe HYSPLIT 4.5 regional model developed by the National Oceanic and AtmosphericAdministration (http://www.arl.noaa.gov/ready.html) for events recorded between Octoberand March for the period 2002 -2006. Correspondence between trajectories andthe position of potential sources were checked throw GIS maps provided by the Laboratoriode teledetección -SIG-INTA-EEA Bariloche. Mode T, Principal ComponentAnalysis (PCA) with Varimax rotation was used to identify the main spatial structureof geopotential height anomalies leading the calculated trajectories. Meteorologicaldata came from daily NCEP reanalysis provided by the NOAA-CIRES Climate DiagnosticCenter, stored at their web site (http://www.cdc.noaa.gov/). Results show twotrajectory patterns. The first one is mainly from the west, passing over the Chileanregion of W. trichosperma distribution, while the second one come first from the westto later return to Bariloche area with an E-NE direction. This pattern is not directlyrelated with potential source areas. Analysis of the first PC scores (31.17% of the totalvariance) show a pattern of negative anomalies at high and mid latitudes and positiveones extending towards the tropics; the more negative at higher latitudes while themore positive show the position of semi-permanent anticyclones. Composite fields ofmean geopotential heights at 1000, 850 and 700 Hpa constructed with significant PCloadings, show the characteristic field of strong westerlies over Patagonia, which supportthe quasizonal trajectories displayed in 70% of the selected cases. The secondPC scores (26.12% of the total variance) show the presence of an anticyclone centredat 40S, 68W. This pattern supports those cases where trajectories showed E-NEcomponents before Weinmannia pollen were finally collected.