Disentangling the role of the Pacific and Atlantic Oceans during the Amazonian droughts in 2015

Theoretical and Applied Climatology - El Niño events lead to worldwide changes in the inter-annual variability of precipitation, and more in particular to South America droughts. In the year...     

Dynamics of arrays of floating point-absorber wave energy converters with inter-body and bottom slack-mooring connections

If point absorbers are employed in the extensive exploitation of the offshore wave energy resource, they should be deployed in arrays, the distance between the elements in the array being possibly tens of meters. In such cases, it may be more convenient that the array is spread moored to the sea bottom through only some of its elements, located in the periphery, while the other array elements are prevented from drifting and colliding with each other by connections to adjacent elements. An array of identical floating point absorbers located at the grid points of an equilateral triangular grid is considered in the paper. A spread set of slack-mooring lines connect the peripheric floaters to the bottom. A weight is located at the centre of each triangle whose function is to pull the three floaters towards each other and keep the inter-body mooring lines under tension. The power take-off system (PTO) is a linear damper activated by the buoy heaving motion. The whole system–buoys, moorings and power take-off systems–is assumed linear, so that a frequency domain analysis may be employed. Hydrodynamic interference between the oscillating buoys in array is accounted for. Equations are presented for a set of three identical point absorbers. This is then extended to more complex equilateral triangular grid arrays. Results from numerical simulations, with regular and irregular waves, are presented for the motions and power absorption of hemispherical converters in arrays of three and seven elements and for different mooring parameters and wave incidence angles. Comparisons are given with the unmoored and independently-moored buoy situations.     

Removal of phenolic compounds in olive mill wastewater by silica–alginate–fungi biocomposites

This study aims to attempt a treatment strategy based on fungi immobilized on silica-alginate (biocomposites) for removal of phenolic compounds in olive oil mill wastewater (OMW), OMW supplemented (OMWS) with phenolic compounds and water supplemented (WS) with phenolic compounds, thus decreasing its potential impact in the receiving waters. Active (alive) or inactive (death by sterilization) Pleurotus sajor caju was encapsulated in alginate beads. Five beads containing active and inactive fungus were placed in a mold and filled with silica hydrogel (biocomposites). The biocomposites were added to batch reactors containing the OMW, OMWS and WS. The treatment of OMW, OMWS and WS by active and inactive biocomposites was performed throughout 28 days at 25 °C. The efficiency of treatment was evaluated by measuring the removal of targeted organic compounds, chemical oxygen demand (COD) and relative absorbance ratio along the time. Active P. sajor caju biocomposites were able to remove 64.6–88.4 % of phenolic compounds from OMW and OMWS and 91.8–97.5 % in water. Furthermore, in the case of OMW there was also a removal of 30.0–38.1 % of fatty acids, 68.7 % of the sterol and 35 % of COD. The silica–alginate–fungi biocomposites showed a high removal of phenolic compounds from OMW and water. Furthermore, in the application of biocomposites to the treatment of OMW it was observed also a decrease on the concentration of fatty acids and sterols as well as a reduction on the COD.     

Surface temperature control in the North and tropical Pacific during the last glacial maximum

Based on coupled modelling evidence we argue that topographically-induced modifications of the large-scale atmospheric circulation during the last glacial maximum may have led to a reduction of the westerlies, and a slowdown of the Pacific subtropical gyre as well as to an intensification of the Pacific subtropical cell. These oceanic circulation changes generate an eastern North Pacific warming, an associated cooling in the Kuroshio area, as well as a cooling of the tropical oceans, respectively. The tropical cooling pattern resembles a permanent La Niña state which in turn forces atmospheric teleconnection patterns that lead to an enhancement of the subtropical warming by reduced latent and sensible cooling of the ocean. In addition, the radiative cooling due to atmospheric CO₂ and water vapor reductions imposes a cooling tendency in the tropics and subtropics, thereby intensifying the permanent La Niña conditions. The remote North Pacific response results in a warming tendency of the eastern North Pacific which may level off the effect of the local radiative cooling. Hence, a delicate balance between oceanic circulation changes, remotely induced atmospheric flux anomalies as well local radiative cooling is established which controls the tropical and North Pacific temperature anomalies during the last glacial maximum. Furthermore, we discuss how the aftermath of a Heinrich event may have affected glacial temperatures in the Pacific Ocean.     

Spatiotemporal variability of vegetation due to drought dynamics (2012–2017): a case study of the Upper Paraíba River basin,Brazil

Natural Hazards - Vegetation indices have been widely used for monitoring the spatiotemporal variables of vegetation and characterizing droughts, primarily in semiarid regions. Drought is a...     

Influence of Antarctic ice sheet lowering on the Southern Hemisphere climate: modeling experiments mimicking the mid-Miocene

A coupled global atmosphere-ocean model is used to study the influence of the Antarctica ice sheet in a configuration that mimics that of the early Miocene on the atmospheric and oceanic circulations. Based on different climate simulations of the present day (CTR) and conducted with distinct Antarctic ice sheet topography (AIS-EXP), it is found that the reduction of the Antarctic ice sheet topography (AIS) induces warming of the Southern Hemisphere and reduces the meridional thermal gradient. Consequently, the atmospheric transient low level eddy heat flux $[(\overline{v^{\prime}T^{\prime}})]$ and the eddy momentum flux $[(\overline{u^{\prime}v^{\prime}})]$ are reduced causing the reduced transport of heat from the mid-latitudes to the pole. The stationary flow and transient wave anomalies generate changes in the SSTs which modify the rate of deep water formation, strengthening the formation of the Antarctic Bottom Water. Substantial changes are predicted to occur in the atmospheric and oceanic heat transport and a comparison between the total heat transport of the atmosphere-ocean system, as simulated by the AIS-EXP and the CTR runs, shows that the reduction of the AIS height leads to reduced Southern Hemisphere poleward and increased equatorward heat transport. These results are in agreement with reduced storm track activities and baroclinicity.     

Modeling the photosynthetically active radiation in South West Amazonia under all sky conditions

Accurate estimates of photosynthetically active radiation (PAR) are critical for the development of realistic models of plant productivity. However, in many areas such as the vast Amazon region of South America, there have been few empirical studies of PAR. Here, we analyzed the relationship between PAR and broadband solar irradiance (R _s) and formulated models to estimate PAR in two experimental sites (pasture and forest) in the Brazilian Amazon. Three different models of increasing complexity were developed based on information from R _s (model 1), R _s and clearness index (k _t; model 2), and R _s, k _t, and water vapor pressure (model 3). Estimates of PAR were generated for each season and for the entire year. All models had very high determination coefficients and indices of agreement for both pasture and forest sites. This strongly supports the use of R _s and k _t to produce robust estimates of PAR. The results obtained by annual models were close than that found by seasonal models, demonstrating that a single annual model is able to estimate PAR, albeit with lower accuracy.     

OWC wave energy devices with air flow control

A theoretical model is developed to simulate the energy conversion, from wave to turbine shaft, of an oscillating-water-column (OWC) plant equipped with a Wells air-turbine and with a valve (in series or in parallel with the turbine) for air-flow control. Numerical simulations show that the use of a control valve, by preventing or reducing the aerodynamic stall losses at the turbine rotor blades, may provide a way of substantially increasing the amount of energy produced by the plant, particularly at the higher incident wave power levels. From the hydrodynamic point of view, a by-pass valve or a throttle valve should be used depending on whether the wave energy absorbing system is over-damped or under-damped by the turbine.     

Climate change impacts on sugarcane attainable yield in southern Brazil

This study evaluated the effects of climate change on sugarcane yield, water use efficiency, and irrigation needs in southern Brazil, based on downscaled outputs of two general circulation models (PRECIS and CSIRO) and a sugarcane growth model. For three harvest cycles every year, the DSSAT/CANEGRO model was used to simulate the baseline and four future climate scenarios for stalk yield for the 2050s. The model was calibrated for the main cultivar currently grown in Brazil based on five field experiments under several soil and climate conditions. The sensitivity of simulated stalk fresh mass (SFM) to air temperature, CO₂ concentration [CO₂] and rainfall was also analyzed. Simulated SFM responses to [CO₂], air temperature and rainfall variations were consistent with the literature. There were increases in simulated SFM and water usage efficiency (WUE) for all scenarios. On average, for the current sugarcane area in the State of São Paulo, SFM would increase 24 % and WUE 34 % for rainfed sugarcane. The WUE rise is relevant because of the current concern about water supply in southern Brazil. Considering the current technological improvement rate, projected yields for 2050 ranged from 96 to 129 t?ha^?1, which are respectively 15 and 59 % higher than the current state average yield.