Increased shear in the North Atlantic upper-level jet stream over the past four decades

Earth’s equator-to-pole temperature gradient drives westerly mid-latitude jet streams through thermal wind balance. In the upper atmosphere, anthropogenic climate change is strengthening this meridional temperature gradient by cooling the polar lower stratosphere and warming the tropical upper troposphere acting to strengthen the upper-level jet stream. In contrast, in the lower atmosphere, Arctic amplification of global warming is weakening the meridional temperature gradient acting to weaken the upper-level jet stream. Therefore, trends in the speed of the upper-level jet stream represent a closely balanced tug-of-war between two competing effects at different altitudes. It is possible to isolate one of the competing effects by analysing the vertical shear—the change in wind speed with height—instead of the wind speed, but this approach has not previously been taken. Here we show that, although the zonal wind speed in the North Atlantic polar jet stream at 250 hectopascals has not changed since the start of the observational satellite era in 1979, the vertical shear has increased by 15 per cent (with a range of 11–17 per cent) according to three different reanalysis datasets. We further show that this trend is attributable to the thermal wind response to the enhanced upper-level meridional temperature gradient. Our results indicate that climate change may be having a larger impact on the North Atlantic jet stream than previously thought. The increased vertical shear is consistent with the intensification of shear-driven clear-air turbulence expected from climate change which will affect aviation in the busy transatlantic flight corridor by creating a more turbulent flying environment for aircraft. We conclude that the effects of climate change and variability on the upper-level jet stream are being partly obscured by the traditional focus on wind speed rather than wind shear

Marginalization of end-use technologies in energy innovation for climate protection

Mitigating climate change requires directed innovation efforts to develop and deploy energy technologies. Innovation activities are directed towards the outcome of climate protection by public institutions, policies and resources that in turn shape market behaviour. We analyse diverse indicators of activity throughout the innovation system to assess these efforts. We find efficient end-use technologies contribute large potential emission reductions and provide higher social returns on investment than energy-supply technologies. Yet public institutions, policies and financial resources pervasively privilege energy-supply technologies. Directed innovation efforts are strikingly misaligned with the needs of an emissions-constrained world. Significantly greater effort is needed to develop the full potential of efficient end-use technologies

Mems resonators: Numerical modeling

The thermal stability of the natural frequency of a double-ended tuning-fork MicroElectroMechanical Systems (MEMS) resonator is studied for different orientations of the structure on the silicon wafer and for several doping levels of the single-crystal silicon. An intrinsic minimum for the frequency variation in temperature is found for each doping level and we prove that it is always possible to find the optimal orientation of the structure on the silicon wafer that allows to reach this minimum. The quality factor Q is another fundamental property to take into account during the design process of a MEMS resonator. We prove that the orientation of the mechanical structure on the silicon wafer and the doping level do not influence the Q significatively. An optimization procedure is proposed to maximize the Q by adding slots in the deformable arms of the resonating structure. The best geometry in terms of Q is combined with the best orientation of the structure in terms of thermal stability of the natural frequency and an optimal design for the DETF resonator is obtained. Two prototypes are fabricated and experimental tests are currently in progress

Design of photovoltaics-based manufacturing system using computer-aided design

Carbon dioxide has increased drastically in the last decades due to energy production, exacerbating the global warming problem. To address this issue, researchers have focused on developing energy production technologies from renewable sources. From the renewable energy sources, solar has shown great promise chiefly due to its high availability. The conversion of solar energy into electricity (photovoltaics) requires specialized equipment such as solar cells, and a coordinated supply chain to be able to manufacture this technology in a sustainable way and at low cost. Therefore, this chapter proposes an approach based on mathematical programming for the optimal design of a solar photovoltaics manufacturing system considering diverse criteria linked to economic and environmental variables such as minimum sustainable price, transportation costs, and technical limits. In addition, the dependence of the minimum sustainable price over inflation, electricity price, and weighted average capital cost is analyzed, showing that a variation of minimum sustainable price could significantly change the manufacturing supply chain topology