Julio Tóta

On the influences of the El Niño, La Niña and Atlantic dipole pattern on the Amazonian rainfall during 1960-1998.

The influence of the large-scale climatic variability dominant modes in the Pacific and in the Atlantic on Amazonian rainfall is investigated. The composite technique of the Amazon precipitation anomalies is used in this work. The basis years for these composites arc those in the period 1960-1998 with occurrences of extremes in the Southern Oscillation (El Nino or La Nina) and the north/south warm (or cold) sea surface temperature (SST) anomalies dipole pattern in the tropical Atlantic. Warm (cold) dipole means positive (negative) anomalies in the tropical North Atlantic and negative (positive) anomalies in the tropical South Atlantic. Austral summer and autumn composites for extremes in the Southern Oscillation (El Nino or La Nina) and independently for north/south dipole pattern (warm or cold) of the SST anomalies in the tropical Atlantic present values (magnitude and sign) consistent with those found in previous works on the relationship between Amazon rainfall variations and the SST anomalies in the tropical Pacific and Atlantic. However, austral summer and autumn composites for the years with simultaneous occurrences of El Nino and warm north/south dipole of the SST anomalies in the tropical Atlantic show negative precipitation anomalies extending eastward over the center-eastern Amazon. This result indicates the important role played by the tropical Atlantic in the Amazon anomalous rainfall distribution.

The Green Ocean Amazon Experiment (GoAmazon2014/5) Observes Pollution Affecting Gases, Aerosols, Clouds, and Rainfall over the Rain Forest

AbstractThe Observations and Modeling of the Green Ocean Amazon 2014–2015 (GoAmazon2014/5) experiment took place around the urban region of Manaus in central Amazonia across 2 years. The urban pollution plume was used to study the susceptibility of gases, aerosols, clouds, and rainfall to human activities in a tropical environment. Many aspects of air quality, weather, terrestrial ecosystems, and climate work differently in the tropics than in the more thoroughly studied temperate regions of Earth. GoAmazon2014/5, a cooperative project of Brazil, Germany, and the United States, employed an unparalleled suite of measurements at nine ground sites and on board two aircraft to investigate the flow of background air into Manaus, the emissions into the air over the city, and the advection of the pollution downwind of the city. Herein, to visualize this train of processes and its effects, observations aboard a low-flying aircraft are presented. Comparative measurements within and adjacent to the plume followed t...

Amazon Rainforest Exchange of Carbon and Subcanopy Air Flow: Manaus LBA Site—A Complex Terrain Condition

On the moderately complex terrain covered by dense tropical Amazon Rainforest (Reserva Biologica do Cuieiras—ZF2—02°36′17.1′′ S, 60°12′24.4′′ W), subcanopy horizontal and vertical gradients of the air temperature, CO2 concentration and wind field were measured for the dry and wet periods in 2006. We tested the hypothesis that horizontal drainage flow over this study area is significant and can affect the interpretation of the high carbon uptake rates reported by previous works at this site. A similar experimental design as the one by Tóta et al. (2008) was used with a network of wind, air temperature, and CO2 sensors above and below the forest canopy. A persistent and systematic subcanopy nighttime upslope (positive buoyancy) and daytime downslope (negative buoyancy) flow pattern on a moderately inclined slope (12%) was observed. The microcirculations observed above the canopy (38 m) over the sloping area during nighttime presents a downward motion indicating vertical convergence and correspondent horizontal divergence toward the valley area. During the daytime an inverse pattern was observed. The micro-circulations above the canopy were driven mainly by buoyancy balancing the pressure gradient forces. In the subcanopy space the microcirculations were also driven by the same physical mechanisms but probably with the stress forcing contribution. The results also indicated that the horizontal and vertical scalar gradients (e.g., CO2) were modulated by these micro-circulations above and below the canopy, suggesting that estimates of advection using previous experimental approaches are not appropriate due to the tridimensional nature of the vertical and horizontal transport locally. This work also indicates that carbon budget from tower-based measurement is not enough to close the system, and one needs to include horizontal and vertical advection transport of CO2 into those estimates.

Airborne observations reveal elevational gradient in tropical forest isoprene emissions

Isoprene dominates global non-methane volatile organic compound emissions, and impacts tropospheric chemistry by influencing oxidants and aerosols. Isoprene emission rates vary over several orders of magnitude for different plants, and characterizing this immense biological chemodiversity is a challenge for estimating isoprene emission from tropical forests. Here we present the isoprene emission estimates from aircraft eddy covariance measurements over the Amazonian forest. We report isoprene emission rates that are three times higher than satellite top-down estimates and 35% higher than model predictions. The results reveal strong correlations between observed isoprene emission rates and terrain elevations, which are confirmed by similar correlations between satellite-derived isoprene emissions and terrain elevations. We propose that the elevational gradient in the Amazonian forest isoprene emission capacity is determined by plant species distributions and can substantially explain isoprene emission variability in tropical forests, and use a model to demonstrate the resulting impacts on regional air quality.

Linking meteorology, turbulence, and air chemistry in the Amazon Rain Forest

AbstractWe describe the salient features of a field study whose goals are to quantify the vertical distribution of plant-emitted hydrocarbons and their contribution to aerosol and cloud condensation nuclei production above a central Amazonian rain forest. Using observing systems deployed on a 50-m meteorological tower, complemented with tethered balloon deployments, the vertical distribution of hydrocarbons and aerosols was determined under different boundary layer thermodynamic states. The rain forest emits sufficient reactive hydrocarbons, such as isoprene and monoterpenes, to provide precursors of secondary organic aerosols and cloud condensation nuclei. Mesoscale convective systems transport ozone from the middle troposphere, enriching the atmospheric boundary layer as well as the forest canopy and surface layer. Through multiple chemical transformations, the ozone-enriched atmospheric surface layer can oxidize rain forest–emitted hydrocarbons. One conclusion derived from the field studies is that the...

Observing and Modeling the Vertical Wind Profile at Multiple Sites in and above the Amazon Rain Forest Canopy

We analyzed the vertical wind profile measured at six experimental tower sites in dense forest in the Amazon Basin and examined how well two simple models can reproduce these observations. In general, the vertical wind profile below the canopy is strongly affected by the forest structure. From the forest floor to 0.65h (where h = 35 m is the average height of the forest canopy for sites considered), the wind profile is approximately constant with height with speeds less than 1 ms−1. Above 0.65 to 2.25h, the wind speed increases with height. Testing these data with the Yi and Souza models showed that each was able to reproduce satisfactorily the vertical wind profile for different experimental sites in the Amazon. Using the Souza Model, it was possible to use fewer input variables necessary to simulate the profile.

Estabilidade e estrutura da turbulência sob a influência de jatos de baixos níveis noturnos no sudoeste da amazônia

The aim of this study was to evaluate how the occurrence of nocturnal Low Level Jets (LLJs) may influence the atmospheric turbulence structure and atmospheric stability at the surface. Using data collected from both radiosondes and Eddy Covariance Systems during the WetAMC-LBA campaign, three atmospheric stability regimes were defined at the surface: weakly stable; transition, and very stable. Relating these regimes and the turbulence structure of strong, weak-type 1 (occurring above 500 m) and weak-type 2 (occurring below 500 m) LLJs, it was observed that 22% of the strong LLJ cases were within the weakly stable regime, whereas only 3% of the weak LLJ cases (type 1 and 2) were in this regime. Another interesting result is that in the weak type 1 LLJ cases, the highest percentage were within the very stable regime (approximately 54%). During strong-LLJs, mean friction velocity and mean turbulence kinetic energy were 0.09 ms-1 and 0.13 m2s-2, respectively. For weak-type 1-LLJs, these variables presented respectively values of 0.04 ms-1 and 0.02 m2 s-2, whereas for weak-type 2-LLJs values were 0.06 ms-1 and 0.03 m2s-2, respectively. These results suggest that LLJs with sufficiently high velocities may increase turbulence and introduce weak atmospheric stability at near surface, depending on the height of occurrence.

Hydroclimatic variables associated with El Nino and La Nina events at the Curuá-Una hydroelectric reservoir, Central Amazonia

The anomalies of Sea Surface Temperature (SST) influence rainfall and therefore the regime of the rise and fall in the level of the rivers in the Amazon region. The aim of this study was to investigate the influence of the El Nino-Southern Oscillation (ENSO) on hydroclimatic variables and identify the existence of trends on these variables in the Curua-Una hydroelectric reservoir in the West of the State of Para. It was used 27 years of monthly precipitation and water flow data to identify possible trends using a non-parametric test (Mann Kendall, p<0.05), and the standardized precipitation index (SPI) was also calculated. The results indicate a positive tendency of the influence of the ENSO on hydroclimatic variables, although it was observed that the rainfall did not increase over the period of 1977 to 2004. The SPI indicates that extreme events of precipitation are related to El Nino and La Nina and that lower precipitation periods were more intense in the decades of the 80´s and 90s. The results show that El Nino events can directly affect the water balance at the micro-watershed of Curua-Una, as was observed in 2015.

ANALYSIS OF THE CO2 VERTICAL PROFILE OF IN A FOREST AREA IN THE CENTRAL AMAZON

This study aimed to describe the vertical profile of CO2 concentration during least rainy period and rainy periods of 2006 , into an area of tropical forest in the Central Amazon, Brazil . It were used data of CO2, collected at various heights by a system of measures including an infrared gas analyzer (Licor 7000), in a tower with 40 meters of height. From the data collected it was observed that the concentration of CO2 decreases as one moves from the ground to the top of the canopy. This suggests that the largest source of CO2 is from the soil, due to processes such as respiration and decomposition of plant biomass. When is compared the least rainy and the most rainy periods, it is noted significant differences in the amounts of CO2 concentration in these periods. The highest concentrations were observed during least rainy period, with monthly mean values above 440 ppm near the surface.

JATOS DE BAIXOS NÍVEIS NO SUDOESTE DA AMAZÔNIA

This study presents an analysis of the occurrence of Low Level Jets (LLJs) in a grassland area in the southwestern Amazon. Using the wind vertical profile data obtained by atmospheric radiosonde, it was observed that about 60% of total analyzed profiles showed LLJs. This percentage is higher than found in several studies in the Amazon and is linked to the LLJs selection criteria used in this work. Another interesting result is the tendency of weak LLJs is associated with lower heights, whereas strong LLJs preferentially develop in greater heights. This result suggests that different mechanisms may have generated the LLJs of different intensities.