Montane climates are shaped by high spatial variability that depends on net radiation and synoptic weather, and much on elevation and topographic features of terrain. We measured near-ground meteorological variables using a weather station network during 14 months, in a valley-shaped basin in southeast Brazil, to address the spatiotemporal climate variability at the meso-γ atmospheric scale. The terrestrial climatic gradients were evident in the cross-valley direction of the basin, where the valley tended to warm/wet up at day and cool/dry down at night relatively from the slopes. The temperature at noon showed high variability and decreased at a mean gradients of about −0.7 C (100 m) −1 . The nocturnal air temperature increased with height up to a maximum at about 200 m (the thermal belt), and showed seasonal rates higher/less in dry/wet season of +1.1/+0.2 C (100 m) −1 over the full altitude. The vapour pressure decreased from the valley bottom upwards, in general below −0.5 hPa (100 m) −1 , whereas the wind speed increased at a rate of 0.9 m s −1 (100 m) −1 . We noted significant differential warming along the valley and mountain sides. The middle valley was circumstantially colder at night and warmer at daytime, relatively to the upper catchment, under mean magnitudes below 1.0 C. The west slope at upper catchment was slightly warmer at night, and colder in the afternoon, at magnitudes below 0.5 C, highlighting the control of hills' aspect at daytime, and the sheltering to flow aloft in east side. The cross-valley gradients appeared to be well associated with local circulation, where downslope wind and positive temperature gradients, as well as upslope wind and negative temperature gradients strictly coexisted during the morning. The terrestrial gradients and the thermal circulation were in general dampened by cloudiness and mechanical mixing.

There is growing evidence that modification of tropical forests to pasture or other anthropic uses (anthropization) leads to land surface warming at local and regional scales; however, the degree of this effect is unknown given the dependence on physiographic and atmospheric conditions. We investigated the dependence of satellite land surface temperature (LST) on the fraction of anthropized area index, defined as the fraction of non-forested percentual area within 120m square boxes, sampled over a large tropical forest dominated ecosystem spatial domain in the Atlantic Forest biome, southeastern Brazil. The LST estimated at a 30 m resolution, showed a significant dependence on elevation and topographic aspect, which controlled the average thermal regime by 2~4°C and 1~2°C, respectively. The correction of LST by these topographic factors allowed to detect a dependence of LST on the fraction of non-forested area. Accordingly, the relationship between LST and the fraction of non-forested area showed a positive linear relationship (R2 = 0.63), whereby each 25% increase of non-forest area resulted in increased 1°C. As such, increase of the maximum temperature (~4°C) would occur in the case of 100% increase of non-forested area. We conclude that our study area, composed to Atlantic forest, appears to show regulatory characteristics of temperature attenuation as a local climatic ecosystem service, which may have mitigation effects on the accelerated global warming.

RESUMOO principal objetivo deste estudo foi analisar de forma comparativa a estimativa do saldo de radiação à superfície (Rn) a partir de imagens orbitais com dados de superfície medidos, bem como os componentes do Rn, para dois diferentes tipos de cobertura vegetal (pastagem e floresta) sob condições atmosféricas tropical-úmida. Este estudo foi realizado no estado de Rondônia, no noroeste do Brasil. Para realizar as análises através de técnicas de sensoriamento remoto foram utilizadas sete imagens orbitais do sensor MODIS a bordo do satélite Aqua, para a aplicação do algoritmo e os dados de superfície medidos por duas torres micrometeorológicas, sendo instaladas em área de pastagem e de floresta. Os principais resultados obtidos a partir das imagens MODIS mostram erro percentual (EP) máximos e mínimos coerentes para o Rn de 3% e 0,02%, para a área de floresta e para a área de pastagem apresentou valores de EP de 10% e 0,7%. Esses resultados mostram que o sensoriamento remoto orbital é uma ferramenta importante e eficaz em estudos hidrológicos e ambientais. Palavras-chave: sensoriamento remoto, micrometeorologia, SEBAL, balanço de radiação ABSTRACT: OBTAINING THE NET RADIATION IN PASTURES AND FOREST AREAS IN AMAZON (DRY SEASON) BY THE MODIS SENSORThe main objective of this study was to analyze comparatively the estimate of net radiation at surface (Rn) from orbital images with surface measured data as well as the components of Rn, for two different types of vegetation (pasture and forest) under tropical-humid climate. This study was conducted at Rondônia State in northwestern Brazil. To carry out the analysis using remote sensing techniques seven orbital images of MODIS sensor aboard the Aqua satellite were used for the algorithm implementation, and the measured surface data at two micrometeorological towers installed in the pasture and forest locations. The main results obtained from MODIS images show consistent maximum and minimum percentage error (PE) for Rn , 3% and 0.02% for the forest area and 10% and 0.7% for the pasture area. These results show that remote sensing is an important and effective tool in environmental and hydrological studies.