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Communication incl. Poster: BibTeX citation key:  GarciaCarreras
Garcia-Carreras, L., Parker, D. J., Murphy, J. G., Taylor, C. M. & Reeves, C. E. 2009. Observations of mesoscale atmospheric circulations induced by vegetation heterogeneity. Work presented at Third International AMMA Conference, July 20—24, at Ouagadougou, Burkina Faso.
Added by: roussot 2009-11-04 19:58:32
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Categories: Atmospheric processes, Land surface processes, Land surface-atmosphere feedback
Keywords: Atmospheric Boundary Layer, Clouds - Convection
Creators: Garcia-Carreras, Murphy, Parker, Reeves, Taylor
Publisher: African Monsoon Multidisciplinary Analyses (Ouagadougou, Burkina Faso)
Collection: Third International AMMA Conference

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Abstract
Observations from the UK BAe146 atmospheric research aircraft over Benin on 17 August 2006 are used to assess the impact of vegetation heterogeneity on the surface heat fluxes, how these affect the dynamics within the planetary boundary layer (PBL), and their subsequent impact on convection, transport and mixing. Concentrations of isoprene, a biogenic volatile organic compound emitted primarily by woody vegetation species, were measured by the aircraft, and used to link the vegetation patterns to the PBL properties.
The wind measurements at two levels show a clear mesoscale organisation of the meridional winds, with associated areas of enhanced cumulus congestus cover. Areas of low-level convergence correlate both with temperature and with isoprene gradients associated with vegetation boundaries. The results are consistent with cropland areas having higher sensible heat fluxes and lower isoprene emissions as compared with adjacent forest/shrub cover, thus producing positive temperature anomalies over the cropland. These anomalies lead to temperature gradients at the vegetation boundaries, thus causing the observed mesoscale flows. The areas of convergence were generally found on the southern edge of the warm anomalies, due to the northerly synoptic flow which displaced the convergence zones southward, and strengthened the convergence within the southerly part of the mesoscale flow. The relationships of PBL temperatures with wind velocity and with isoprene concentrations were significant down to scales of 10 and 8 km respectively, in line with aircraft observations of soil moisture induced circulations. A satellite climatology was used to look at the persistence of shallow cloud, and the potential role of the land surface in organizing convection.
Added by: roussot