Camada limite amazônica: aspectos observacionais e de modelagem

Fisch, Gilberto

doi:10.1590/s0102-261x1999000100010

Cited by 12 publications

(11 citation statements)

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“…Additional statistics are listed in Table 1. Earlier studies focused largely on the dry season [26] or the dry-to-wet transition season [16]. Santos [10], however, carried out measurements in the wet season.…”

Section: Resultsmentioning

confidence: 99%

“…One of the pioneering studies on the characteristics of the Amazonian NBL was carried out by Fisch [26], followed by other robust studies in different seasons by Santos [10] and Neves et al [16]. In these previous studies, vertical profiles of potential temperature and specific humidity were the main observations used to estimate the NBL height [16,27].…”

Section: Introductionmentioning

confidence: 99%

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Vertical Profiles of Ozone Concentration Collected by an Unmanned Aerial Vehicle and the Mixing of the Nighttime Boundary Layer over an Amazonian Urban Area

Guimaraes

Batista

et al. 2019

Atmosphere

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The nighttime boundary layer was studied in an urban area surrounded by tropical forest by use of a copter-type unmanned aerial vehicle (UAV) in central Amazonia during the wet season. Fifty-seven vertical profiles of ozone concentration, potential temperature, and specific humidity were collected from surface to 500 m above ground level (a.g.l.) at high vertical and temporal resolutions by use of embedded sensors on the UAV. Abrupt changes in ozone concentration with altitude served as a proxy of nighttime boundary layer (NBL) height for the case of a normal, undisturbed, stratified nighttime atmosphere, corresponding to 40% of the cases. The median height of the boundary layer was 300 m. A turbulent mixing NBL constituted 28% of the profiles, while the median height of the boundary layer was 290 m. The remaining 32% of profiles corresponded to complex atmospheres without clear boundary layer heights. The occurrence of the three different cases correlated well with relative cloud cover. The results show that the standard nighttime model widely implemented in chemical transport models holds just 40% of the time, suggesting new challenges in modeling of regional nighttime chemistry. The boundary layer heights were also somewhat higher than observed previously over forested and pasture areas in Amazonia, indicating the important effect of the urban heat island.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Vertical Profiles of Ozone Concentration Collected by an Unmanned Aerial Vehicle and the Mixing of the Nighttime Boundary Layer over an Amazonian Urban Area

Guimaraes

Batista

et al. 2019

Atmosphere

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“…Determining the consequences of Amazon deforestation has been the focus of many numerical model studies (Nobre et al, 1991;Lean & Rowntree, 1993;Dolman et al, 1999). Observational studies specifically aimed to determine the impact of deforestation on climate and carbon exchange in the Amazon include the ABRACOS project (Anglo-Brazilian Amazonian Climate Observation Study; Shuttleworth et al, 1991;Fisch, 1996;Gash et al, 1996) and LBA (Large-Scale Biosphere-Atmosphere Experiment in Amazonia) field experiments.…”

Section: Introductionmentioning

confidence: 99%

Land‐use change effects on local energy, water, and carbon balances in an Amazonian agricultural field

Sakai

Fitzjarrald

Moraes

et al. 2004

Global Change Biology

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To study how changing agricultural practices in the eastern Amazon affect carbon, heat and water exchanges, a 20 m tower was installed in a field in August 2000. Measurements include turbulent fluxes (momentum, heat, water vapor, and CO 2 ) using the eddy covariance (EC) approach, soil heat flux, wind, and scalar profiles (T, q, and CO 2 ), soil moisture content, terrestrial, total solar radiation, and photosynthetically active radiation (PAR, 400-700 nm). At the beginning of the measurements, in September 2000, the field was a pasture. On November 2001, the pasture was burned, plowed, and planted in upland (nonirrigated) rice.Calm nights were the norm in this site. Anomalously low values of net ecosystem exchange (NEE) were found using the EC method, even when the common criterion u Ã o0.2 m s À1 was used to identify and exclude poor performance nights. We observed more plausible values of NEE using criterion u Ã o0.08 m s À1 , indicating that the criterion must be revised downward for flow over surfaces smoother than forests. However, even using the lower threshold, u Ã was lower than this limit for 82% of nights, and this led to nocturnal respiration underestimates. We compensate for this difficulty by estimating the respiration rate using the nocturnal boundary layer budget method.Land-use change from pasture to rice cultivation strongly affected both diurnal rates of turbulent exchange but also the pattern of seasonal variation. Seasonal wet and dry season differences in vegetation state were clearly detected in the albedo and PARalbedo. These reflectivity changes were accompanied by modified net radiative flux, turbulent heat flux and evaporation rates. The highest evaporation rate was observed during the rice crop, when the field had total evaporation approximately half the precipitation input, less than that of the surrounding forest. Effects of the land-cover changes were also detected in the carbon budget. For the pasture, the maximum CO 2 uptake occurred in May, appreciably delayed from the start of the rainy season. After the field was plowed and the soil was exposed and there was efflux of CO 2 to the atmosphere day and night for an extended period. Highest values of carbon uptake occurred during the rice plantation. Although the upland rice took up carbon at double the rate of the pasture that it replaced, the field was left fallow for much of the year, during the dry season.

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“…Furthermore, the Rondonia Boundary Layer Experiments II and III have provided the ®rst experimental evidence of large dierences between the structure and growth of the boundary layer over forest and pasture (Fisch, 1996). During the dry season, simultaneous measurements of boundary layer temperature and humidity show that the boundary layer over the pasture is between 500 to 1000 m deeper and up to 2 K warmer.…”

Section: Introductionmentioning

confidence: 99%

Meso-scale effects of tropical deforestation in Amazonia: preparatory LBA modelling studies

Dolman¹,

Dias²,

Calvet

et al. 1999

Ann. Geophys.

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Abstract. As part of the preparation for the Large-Scale Biosphere Atmosphere Experiment in Amazonia, a meso-scale modelling study was executed to highlight de®ciencies in the current understanding of land surface atmosphere interaction at local to sub-continental scales in the dry season. Meso-scale models were run in 1-D and 3-D mode for the area of Rondonia State, Brazil. The important conclusions are that without calibration it is dicult to model the energy partitioning of pasture; modelling that of forest is easier due to the absence of a strong moisture de®cit signal. The simulation of the boundary layer above forest is good, above deforested areas (pasture) poor. The models' underestimate of the temperature of the boundary layer is likely to be caused by the neglect of the radiative eects of aerosols caused by biomass burning, but other factors such as lack of sucient entrainment in the model at the mixed layer top may also contribute. The Andes generate patterns of subsidence and gravity waves, the eects of which are felt far into the Rondonian area The results show that the picture presented by GCM modelling studies may need to be balanced by an increased understanding of what happens at the meso-scale. The results are used to identify key measurements for the LBA atmospheric meso-scale campaign needed to improve the model simulations. Similar modelling studies are proposed for the wet season in Rondonia, when convection plays a major role.

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Camada limite amazônica: aspectos observacionais e de modelagem

Cited by 12 publications

References 0 publications

Vertical Profiles of Ozone Concentration Collected by an Unmanned Aerial Vehicle and the Mixing of the Nighttime Boundary Layer over an Amazonian Urban Area

Vertical Profiles of Ozone Concentration Collected by an Unmanned Aerial Vehicle and the Mixing of the Nighttime Boundary Layer over an Amazonian Urban Area

Land‐use change effects on local energy, water, and carbon balances in an Amazonian agricultural field

Meso-scale effects of tropical deforestation in Amazonia: preparatory LBA modelling studies

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