Abstract. We have investigated a magnetohydrodynamic mechanism that accounts for several fundam6ntal properties of the slow solar wind, in particular its variability, latitudinal extent, and bulk acceleration. In view of the well-established association between the streamer belt and the slow wind, our model begins with a simplified representation of a streamer beyond the underlying coronal helmet: a neutral sheet embedded in a plane fluid wake. This wake-neutral sheet configuration is characterized by two parameters that vary with distance from the Sun: the ratio of the cross-stream velocity scale to the neutral sheet width, and the ratio of the typical Alfv6n velocity to the typical flow speed far from the neutral sheet. Depending on the values of these parameters, our linear theory predicts that three kinds of instability can develop when this system is perturbed: a tearing instability and two ideal fluid instabilities with different cross-stream symmetries (varicose and sinuous). In the innermost, magnetically dominated region beyond the helmet cusp, we find that the streamer is resistively and ideally unstable, evolving from tearing-type reconnection in the linear regime to a nonlinear varicose fluid instability. Traveling magnetic islands are formed which are similar to features recently revealed by the large-angle spectroscopic coronagraph on the joint European Space Agency/NASA Solar and Heliospheric Observatory (SOHO) [Brueckner et al., 1995]. During this process, the center of the wake is accelerated and broadened slightly. Past the Alfv6n point, where the kinetic energy exceeds the magnetic energy, the tearing mode is suppressed, but an ideal sinuous fluid mode can develop, producing additional acceleration up to typical slow wind speeds and substantial broadening of the wake. Farther from the Sun, the system becomes highly turbulent as a result of the development of ideal secondary instabilities, thus halting the acceleration and producing strong filamentation throughout the core of the wake. We discuss the implications of this model for the origin and evolution of the slow solar wind, and compare the predicted properties with current observations from SOHO. IntroductionThe solar wind has two distinct components: the fast wind

The linear and nonlinear evolution of the plane current–vortex sheet, with a basic magnetic field given by B0(y)=tanh yêz, and a basic velocity field given by W0(y)=V tanh Ryêz, is examined. The discovery of an ideal instability in a large region of parameter space previously found to be stable is reported. In this paper numerical evidence is presented that this parameter regime is in fact highly unstable, with growth rates exceeding those of the modes existing in the region of parameter space previously found to be unstable. An examination of the perturbation energy balance indicates that enhanced energy transfer from the basic velocity field to the perturbed velocity and magnetic fields is responsible for the enhanced growth rate. This occurs due to processes absent from both the resistive and Kelvin–Helmholtz instabilities. Nonlinearly it is found that magnetic reconnection can occur on an ideal time scale in certain cases. These faster instabilities lead to a more violent cascade of excitation in the streamwise direction, as evidenced by the rapid formation of higher harmonics of the initial disturbance. A nonlinear saturation due to increased correlation of the perturbed velocity and magnetic field occurs for all cases.

Major pasta industries have started to evaluate the environmental footprint of their productions exploiting both Life Cycle Assessment (LCA) and, in some cases, Environmental Product Declaration (EPD) methodologies. In this research, two different pasta production chains were considered: a “high-quality pasta” chain (referred here as “local or regional scenario”), which follows traditional procedures in a Tuscan farm that uses only ancient wheat varieties; and a “conventional pasta” one (referred here as “global or industrial scenario”), in which pasta is produced using national and international grains, following industrial processes. An integrated methodology based on both an Environmental Impacts ANalysis (EIAN) approach and the LCA has been developed, analyzing five environmental compartments (i.e., soil, water, air, resources, climate change) and a total number of ten expected environmental pressures. As a result, the high-quality pasta chain shows a better performance in terms of risk reduction of soil degradation and agrobiodiversity loss, as well as the consumption of non-renewable resources; this is mainly due to the use of lower quantity of chemicals, a lower mechanization level in the agricultural phase, and the use of ancient grains. However, the conventional pasta chain prevails in terms of a more efficient exploitation of land and water resources, due to higher yields and the use of more efficient sprayers, and also in reducing noise emitted by the overall production equipment.

The linear and nonlinear evolution of the plane magnetized jet, a magnetohydrodynamic configuration consisting of a plane fluid jet embedded in a neutral sheet, is examined. At low Alfvén number (A=ratio of the characteristic Alfvén speed to the characteristic flow speed), two ideally unstable modes are found that correspond to the sinuous and varicose modes of the fluid plane jet. Increasing A leads to a stabilization of both of these modes. For large A there is a separate resistively unstable mode. The ideal varicose mode and the resistive varicose mode are distinct modes with similar properties in a given range of A. A magnetohydrodynamic generalization of the Howard semicircle theorem indicates that a strong enough magnetic field will damp out all ideal modes. The stability properties of the two modes are studied in terms of their perturbation energy balances. The nonlinear evolution is quite different for the three modes in terms of time scales and of the properties and spatial location of the small-scale structures that strongly modify the initial configuration. The two ideal modes have in common the capability of accelerating the fluid initially at rest in a much more efficient way than the resistive one.

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