Comparação da Radiação Solar Global Incidente Obtida por Diferentes Fontes de Dados para o Norte de SP

O objetivo deste trabalho foi comparar os dados de radiaçãosolar global incidente de três torres micrometeorológicas localizados naregião norte do estado de São Paulo, com os dados disponíveis de outrasfontes: estações meteorológicas de superfície mais próximas e estimativasa partir de satélites (modelo GL1.2). A regressão linear entre as estimativasde radiação do modelo GL1.2 com as observações na área decerrado indicou um ajuste melhor do que o obtido com a estaçãometeorológica mais próxima. Esses resultados sugerem que as estimativasde radiação do modelo GL1.2 podem ser usadas para o preenchimentode falhas de Ki medida nas torres micrometeorológicas e potencialmentecomo forçante em esquemas de superfície e modelos hidrológicosaplicados a bacias hidrográficas da região

Fluxes of CO2 above a plantation of Eucalyptus in southeast Brazil

Eddy-covariance measurements of net ecosystem exchange of CO2 (NEE) and estimates of gross ecosystem productivity (GEP) and ecosystem respiration (RE) were obtained in a 2–4 year old Eucalyptus plantation during two years with very different winter rainfall. In the first (drier) year the annual NEE, GEP and RE were lower than the sums in the second (normal) year, and conversely the total respiratory costs of assimilated carbon were higher in the dry year than in the normal year. Although the net primary production (NPP) in the first year was 23% lower than that of the second year, the decrease in the carbon use efficiency (CUE = NPP/GEP) was 11% and autotrophic respiration utilized more resources in the first, dry year than in the second, normal year. The time variations in NEE were followed by NPP, because in these young Eucalyptus plantations NEE is very largely dominated by NPP, and heterotrophic respiration plays only a relatively minor role. During the dry season a pronounced hysteresis was observed in the relationship between NEE and photosynthetically active radiation, and NEE fluxes were inversely proportional to humidity saturation deficit values greater than 0.8 kPa. Nighttime fluxes of CO2 during calm conditions when the friction velocity (u*) was below the threshold (0.25 m s−1) were estimated based on a Q10 temperature-dependence relationship adjusted separately for different classes of soil moisture content, which regulated the temperature sensitivity of ecosystem respiratio