ALBERT

Description: Tidal power can be described as harnessing the kinetic energy of the in and out flows known as tides created by the changing gravitational pull of the moon and the sun on the oceans of the world. As the relative positions of the sun and moon can be accurately predicted, so can the resultant tidal movements, making tidal energy such a valuable resource and an attractive option for renewable power generation. However, the high costs and difficulties associated with the deployment of underwater turbines, which includes anchoring, are prohibitive factors in the widespread utilisation of tidal power technology. Existing turbine fixation methods are primarily based on the use of large gravity anchors or monopole structures to secure the turbine to the seabed. In an effort to reduce size, environmental impact on the seafloor and installation cost, a hydrofoil-based anchor could be considered. The objective of this study is to experimentally test the lift and drag force behaviour of a finite-span hydrofoil with endplates, whose profile was selected based on simplified two-dimensional (2D) numerical simulations using the vortex panel method. A customised lift and drag force measurement system for this prototype hydrofoil was designed, fabricated and calibrated, and subsequently installed and tested in the Dutch Tidal Testing Centre (TTC) in Den Oever, the Netherlands. A series of tests with force and flow velocity measurements are described for different angles-of-attack under realistic tidal flow conditions. Results for the lift and drag coefficients as a function of angle-of-attack are compared to numerical simulation data and revealed that the real-world lift force is predicted well, whereas the drag force is underpredicted by the numerical predictions. These findings provide useful information for the design of anchoring systems based of hydrofoil profiles.

Description: Previous research has shown that nations that controlled global-scale empires over the most recent centuries and presently possess great per-capita wealth are in Earth’s two largest regions of regular moderate rainfall. That rainfall regime is the pattern of atmospheric precipitation most supportive of agriculture and water-wheel-powered industry, both of which presumably contributed to those nations’ advancement. Those regions of regular moderate rainfall ring the North Atlantic, and this article reviews the evidence that the Gulf Stream delivers warm vapor-releasing water in the upper limb of the Atlantic Meridional Overturning Circulation, generating the distinctive climate of western Europe and eastern North America. Ocean circulation’s control on continental climate has thus contributed significantly to the Euro-American concentration of wealth and geopolitical power that has dominated the last few centuries of human history. However, comparison of the present apparent weakening or failure of the Atlantic Meridional Overturning Circulation with both the early Holocene 8.2 ka event and modeling of the Atlantic Meridional Overturning Circulation’s diminished generation of water vapor suggests that Europe and eastern North America may lose their beneficent climate pattern as rainfall there lessens.

Description: This paper presents the intercomparison of wave hindcasts using the third-generation models WAM and WAVEWATCH-III for the North Indian Ocean over 1° × 1° (latitude × longitude) grid resolutions, which reveals the first assessment of their relative performance through intercomparison of the model results. Hindcast wave parameters such as significant wave height, mean wave period, and swell wave height obtained from the simulations using Oceansat-2 scatterometer winds are analyzed to understand the quality and variability associated with the individual model outputs in the Indian Ocean. WAM and WAVEWATCH-III intercomparison studies are carried out for four different cases (January and June 2010, and January and June 2011). A comparative study of the relative performances of these two models is evaluated through extensive and robust statistical error analysis. Based on both qualitative and quantitative assessment of the model results, this study clearly indicates that both WAM and WAVEWATCH-III performed well in the common model domain using Oceansat-2 scatterometer winds, and they can be confidently used for long-term hindcasting in the North Indian Ocean, which will be very useful for most of the user community dealing with various coastal/offshore activities. The study also suggests that it would be preferable to consider available long-term wave measurements both in deep and coastal waters of the North Indian Ocean to validate and intercompare WAM and WAVEWATCH-III further.

Description: Selection of sustainable and environmental friendly technologies is very important in meeting strict environmental regulations on industrial emissions of volatile organic compounds and greenhouse gases. Many of the industrial volatile organic compounds are toxic and carcinogenic, and they are regulated under Clean Air Act for hazardous air pollutants. Similarly, global environmental agreements such as European Union’s 2015 Paris Agreement and Kyoto Protocol restrict carbon emission, which is responsible for global warming, sea-level rise, flooding, and ecological imbalance. It is essential that industries choose suitable technologies that reduce not only toxic volatile organic compounds in the air but also greenhouse gas emissions. In this communication, biotechnological methods are discussed and compared with conventional processes, which are used for control of volatile organic compounds. The readers may find this article useful in the selection of an appropriate technology for their application while minimizing the greenhouse gas emissions.

Description: This study examines the influence of intertropical discontinuity movement on seasonality and distribution of atmospheric aerosols over Nigeria, using remote sensing approach. The Moderate Resolution Imaging Spectroradiometer (MODIS) Terra aerosol optical depth, wind speed and precipitation/intertropical discontinuity (ITD) dataset were used. Geospatial interpolation model was used to analyse the aerosol seasonal distribution. Correlations analysis was used to evaluate the degree of influence of wind and ITD on the monthly distribution of aerosol. The results show significant variations in monthly mean distributions of aerosol, but the variation is much more extraordinary during Harmattan season than Wet and Dry seasons, with 0.29 ⩽ aerosol optical depth ⩾ 0.46. In other ecological zones, the highest mean aerosol optical depth values were observed in the months of December, January and February with 0.30 ⩽ aerosol optical depth ⩾ 0.60, with highest value in Sahel ecological zone. Generally, the results further show a strong relationship between aerosol optical depth distribution and migration of ITD with correlation r2 ⩾ 0.60 @ p = 0.05 mostly during Dry and Harmattan seasons but relatively low correlation r2 ⩽ 0.40 @ p = 0.05 during Wet season. The major findings of this study are that seasonal shifts in the location of the ITD considerably affect not only rainfall distribution, resulting in the Wet and Dry seasons in the study area, but also have significant impacts on atmospheric aerosol distributions. Although not all aerosols presented in this study are dust originated from Sahara desert, since biomass-burning activities frequently occur in the study area, the study concludes that satellite-based aerosol optical depth datasets continue to be advantageous to understand atmospheric aerosols distribution in a region where there is fewer ground aerosols data.

Description: We estimate long-range persistence in ocean surface temperature off the coast of central California, a region where similar observations have not been made. The database consists of 20-year records of daily sea surface temperature from three locations: Pacific Grove and Granite Canyon along the coast, and Southeast Farallon Island located 40 km off the coast and slightly further north. Long-range persistence is important for a number of reasons: on the negative side, it can have serious detrimental effects for statistical inference and on the positive side, it provides access to the ocean’s memory which can lead to a greater understanding of the processes involved and thus to better prediction. Long-range persistence also provides important insights into the relationship between the scaling that is obtained and the time scales employed. The first step in the analysis was to remove the annual cycle from the data at each location because of its detrimental effect on estimating long-range persistence. Then detrended fluctuation analysis was used to calculate long-range persistence where a single scaling exponent is obtained that relates the magnitudes of the fluctuations in the data to the time scales involved. Similar scaling exponents were obtained for Granite Canyon and Pacific Grove with values of 1.04 and 1.05, respectively. At Southeast Farallon Island, a value of 1.16 was obtained. The increase in the scaling exponent at Southeast Farallon Island is consistent with observations made elsewhere and model results, which indicate that as coastal influence decreases further offshore, the scaling exponents for sea surface temperature tend to increase. Because Southeast Farallon Island is exposed to subarctic waters offshore, whereas Pacific Grove and Granite Canyon are exposed to warmer waters from the California Undercurrent along the coast, these exposures to different water masses may contribute to the observed change in scaling behavior.

Description: Tidal inlets get disconnected depending on the seasons due to the formation of sand bars near its mouth are termed as “seasonally open tidal inlets.” These inlets are usually small of width of about 100 m and occur in micro-tide (tidal range not exceeding 1 m). Since the east coast of India experiences a net littoral drift of up to about 0.8 Mm3/annum, which is one of the largest in magnitudes that needs to be considered in the analysis of modeling of the sand bar formation and the associated phenomena. Kondurpalem inlet situated along the South east coast of India is considered as a case study. A frequency domain wave model (STeady-state spectral WAVE) has been used to compute the nearshore wave climate. The wave-induced currents have been obtained, and the longshore sediment transport rate is obtained through empirical relations. The tidal prism is found from measured depth and tidal velocity by solving shallow water equations. The stability of the inlet is investigated by applying the criteria developed by Bruun (1986). The effect of a pair of training walls on maintaining the stability of the mouth is reassessed over the periods.

Description: We present an analysis of turbulent kinetic energy dissipation rates in the upper ocean using in situ measurements collected by a coherent Doppler sonar in the Labrador Sea during summer 2004. The sonar recorded horizontal velocity fluctuations of the upper 2 m with an uncommonly small spatial resolution of 0.8 cm, allowing direct calculations of wavenumber spectra and the application of Kolmogorov theory to obtain turbulent kinetic energy dissipation rates for the first time in this area. The project presented a unique opportunity for the study of air–sea exchange during a phytoplankton bloom, being the first time a specialized air–sea interaction spar buoy was deployed during such particular event. An additional uniqueness of this experiment resulted from being the first turbulent kinetic energy dissipation rate observations obtained at higher latitudes, coincidentally in a well-known region of dense water formation, with a fundamental role in both global circulation and forecasting studies of global climate change. Focusing on the relationship between turbulent kinetic energy dissipation rates and wave phase in the upper 2 m, we estimated O[Formula: see text] turbulent kinetic energy dissipation rates, consistent with previous estimates obtained through similar devices and methods. A T-test between dissipation rates calculated at the crest and at the trough of waves showed no dependency of turbulent kinetic energy dissipation rates on the wave phase at 2 m depth, coinciding with many of the earlier findings available. a comparison with previous research showing conflicting results with our values is also discussed here linking them to the relative roles of experimental design variations, diverse dynamical frames, and particular environmental conditions.

Description: Indian Space Research Organization had launched Oceansat-2 on 23 September 2009, and the scatterometer onboard was a space-borne sensor capable of providing ocean surface winds (both speed and direction) over the globe for a mission life of 5 years. The observations of ocean surface winds from such a space-borne sensor are the potential source of data covering the global oceans and useful for driving the state-of-the-art numerical models for simulating ocean state if assimilated/blended with weather prediction model products. In this study, an efficient interpolation technique of inverse distance and time is demonstrated using the Oceansat-2 wind measurements alone for a selected month of June 2010 to generate gridded outputs. As the data are available only along the satellite tracks and there are obvious data gaps due to various other reasons, Oceansat-2 winds were subjected to spatio-temporal interpolation, and 6-hour global wind fields for the global oceans were generated over 1 × 1 degree grid resolution. Such interpolated wind fields can be used to drive the state-of-the-art numerical models to predict/hindcast ocean-state so as to experiment and test the utility/performance of satellite measurements alone in the absence of blended fields. The technique can be tested for other satellites, which provide wind speed as well as direction data. However, the accuracy of input winds is obviously expected to have a perceptible influence on the predicted ocean-state parameters. Here, some attempts are also made to compare the interpolated Oceansat-2 winds with available buoy measurements and it was found that they are reasonably in good agreement with a correlation coefficient of R 〉 0.8 and mean deviation 1.04 m/s and 25° for wind speed and direction, respectively.