Seasonal and diurnal variability of convection over the Amazonia: A comparison of different vegetation types and large scale forcing

摘要

A climatological description of the convection over Amazonia is based on the seasonal and diurnal cycle analysis. Long series of observations are used from four sites: two sites are representative of dense rainforest, either continental (Manaus) or coastal (Belem); one site is in southeast Amazonia, in a region of ecological tension where forest has been partly replaced by pasture (Vilhena); and finally, one is in the south of Amazonia, in a region typical of savanna (Brasilia). Each site has a long series of radiosonde and surface observations. Other parameters are also used: rainfall averaged from the raingauges in the vicinity of each site; vegetation monitored using NDVI averaged over 128 km x 128 km boxes centred on each site; and total and high cloud cover estimated using the 2.5° x 2.5° ISCCP products derived from satellite data. It is shown that the main differences between rainforest and savanna or deforested sites occur in the dry season, whereas the magnitude and diurnal cycle of convection as well as amount of rainfall and NDVI are quite similar during the wet season. For the savanna site the seasonal variation is well defined for every parameter, whereas for rainforest sites the vegetation and atmospheric thermodynamics show very weak seasonal variations, yet driving significant diurnal variations of the convection and precipitation. The transition season from dry to wet and the beginning of the wet season is generally the period of strongest intensity of convection.