Outward Wind Research Articles

Two-dimensional MHD modelling of switchbacks from jetlets in the slow solar wind

Solar wind switchbacks are polarity reversals of the magnetic field, recently frequently measured by Parker Solar Probe inside 0.2 AU. In this Letter we show that magnetic switchbacks, similar to those observed by PSP, are reproduced by injecting a time-limited collimated high-speed stream in the Parker spiral. We performed a 2D magnetohydrodynamics simulation with the PLUTO code of a slightly inclined jet at 1000 km s−1 between 5 and 60 R⊙. The jet rapidly develops a field inversion at its wings and, at the same time, it is bent by the Parker spiral. The match with the radial outward wind field creates two asymmetric switchbacks, one that bends to the anti-clockwise and one that bends to the clockwise direction in the ecliptic plane, with the last one being the most extended. The simulation shows that such S-shaped magnetic features travel with the jet and persist for several hours and to large distances from the Sun (beyond 20 R⊙). We show the evolution of physical quantities as they would be measured by a hypothetical detector at a fixed position when crossed by the switchback, for comparison with in situ measurements.

Research and Application of the technology of Forced Ventilation Diversion to Control and Reduce Dust in Comprehensive Excavation Face

In order to solve the problem of dust pollution in the comprehensive excavation face, the matching relationship between the long forced ventilation and the short dust removal sucking was grasped, and reasonable control dust removal process parameters were obtained. In this paper, the 3-1 coal return air roadway in Hongliulin Coal Mine is taken as the research object. By establishing the working face physical model and adopting the numerical simulation method, the different axial diameter outward air ratio is compared and analyzed. Combined with the field measurement, it is verified to obtain the optimal range of dust axial diameter outward air ratio. The application results show that a swirl air curtain is formed along the sidewall of the roadway after the adoption of the attached air duct, and a dust control air curtain pointing to the head is gradually formed after entering the section of the roadheader. When the axial diameter outward wind ratio is 1:2∼1:3, the breathing dust at the driver's position can be controlled within 17 mg/m3, and the dust removal efficiency can be increased to more than 93%, which greatly improves the working environment and ensures the occupational health and safety of workers.

Stability and solution of the time-dependent Bondi–Parker flow

ABSTRACT Bondi and Parker derived a steady-state solution for Bernoulli’s equation in spherical symmetry around a point mass for two cases, respectively, an inward accretion flow and an outward wind. Left unanswered were the stability of the steady-state solution, the solution itself of time-dependent flows, whether the time-dependent flows would evolve to the steady state, and under what conditions a transonic flow would develop. In a Hamiltonian description, we find that the steady-state solution is equivalent to the Lagrangian implying that time-dependent flows evolve to the steady state. We find that the second variation is definite in sign for isothermal and adiabatic flows, implying at least linear stability. We solve the partial differential equation for the time-dependent flow as an initial-value problem and find that a transonic flow develops under a wide range of realistic initial conditions. We present some examples of time-dependent solutions.

Observational constraints on the cometary impact flux on Mars and Earth

While dynamical models indicate that both cometary and asteroid collisions likely contribute to the population of bodies that impact the inner solar system, the distinction between the craters produced by the two populations remains uncertain. Although cometary impacts larger than 10 km in diameter are rare, dynamical studies cannot confidently eliminate their possible contribution to the total impact population at levels lower than ~10%. Due to the speed and volatile content of comets, their impact should couple more energy with a planetary atmosphere and result in observable signatures. The tenuous atmosphere of Mars makes the planet an ideal location to recognize such signatures. Here we use computational simulations and laboratory experiments to model both asteroid and cometary impacts on Mars. We explore the relationship between such impacts and enigmatic radial streaks that form around certain impact craters due to high-speed, long-duration winds. While lower speed asteroid impacts into thick (500 m) surface ices also can produce intense outward winds, the global distribution of craters with impact-generated wind streaks limits this mode of origin to just a few candidates; the rest are likely cometary. Based on the occurrence and relatively young age of these craters, we conclude that ~1% of the impactors on Mars over the last 2 Ga resulted from Long-Period cometary impacts, which should be about 6 times higher on Earth. Inclusion of Jupiter-Family and Haley-type comets (but not including cometary asteroids) then predicts that ~ 16% of all terrestrial impacts, with important implications for future impact hazards on Earth.

Experimental constraints on impact-induced winds

A new class of wind streaks on Mars uniquely associated with impact craters is most clearly detected in nighttime thermal infrared imaging. Thermally bright streaks radiate from some well-preserved impact craters and are related to the impact process. Using laboratory experiments performed at the NASA Ames Vertical Gun Range, we test the hypothesis that these streaks are formed from either the winds within an air-blast or winds set up by expanding impact vapor interacting with the atmosphere. The experiments use a variety of tracers and instruments to document three interrelated processes occurring in the impact of a Pyrex projectile into an easily vaporized powdered dolomite target: (1) a surface roughening spreading outward from the impact point, (2) an expanding vapor plume, and (3) outward winds made visible by dust trails from vertically placed, dusty pipe cleaners. The clear connection between the surface roughening, vapor expansion, and outward winds implicate an expanding vapor interacting with the atmosphere as the controlling process.

Pull-Out Strength of Screws in Screw Chases: Part 2

This paper (Part 2 of 2) presents a study of the structural behavior of tension-loaded screws installed in screw chases in extruded aluminum profiles. This connection is commonly used to resist outward wind load on glass in curtainwalls and skylights. See Part 1 for details of the pull-out testing. Two types of chase, each with 1/4 in. (6.35 mm) diameter stainless steel screws were used: a flat chase with AB tapping screws (1/4-14; 14 threads per 25.4 mm) and F tapping screws (1/4-20; 20 threads per 25.4 mm), and a longitudinally ribbed chase with UNC-thread machine screws (1/4-20). The extrusions included six cross-section shapes (three with flat chases and three with ribbed chases) and three alloy-tempers.

Pull-Out Strength of Screws in Screw Chases: Part 1

This paper presents test results and a proposed pull-out strength equation for tension-loaded screws installed in chases in extruded aluminum profiles. The screws are perpendicular to the extrusion's length. This connection is commonly used to resist outward wind load on glass in curtain walls and skylights. Two types of chase, each with 1/4 in. (6.35 mm) diameter 300 series stainless steel screws were used: a flat chase with AB tapping screws (1/4-14; 14 threads per 25.4 mm) and F tapping screws (1/4-20; 20 threads per 25.4 mm), and a longitudinally ribbed chase with UNC-thread machine screws (1/4-20). The extrusions included six cross-section shapes (three with flat chases and three with ribbed chases) and three alloy-tempers. Pull-out tests of 150 single screws were conducted. The Aluminum Design Manual [1] does not include pull-out strength equations for screws in chases; this research was intended to develop such equations. Pull-out strength increased with an increase in engaged length of screw threads with the chase. The shape and dimensions of the chase also affected the pull-out strength.

Generation of a North/South Magnetic Field Component from Variations in the Photospheric Magnetic Field

We address the problem of calculating the transverse magnetic field in the solar wind outside of the hypothetical sphere called the source surface where the solar wind originates. This calculation must overcome a widely used fundamental assumption about the source surface -- the field is normally required to purely radial at the source surface. Our model rests on the fact that a change in the radial field strength at the source surface is a change in the field line density. Surrounding field lines must move laterally in order to accommodate this field line density change. As the outward wind velocity drags field lines past the source surface this lateral component of motion produces a tilt implying there is a transverse component to the field. An analytic method of calculating the lateral translation speed of the field lines is developed. We apply the technique to an interval of approximately two Carrington rotations at the beginning of 2011 using 2-h averages of data from the Helioseismic Magnetic Imager instrument on the Solar Dynamics Observatory spacecraft. We find that the value of the transverse magnetic field is dominated on a global scale by the effects of high latitude concentrations of field lines being buffetted by supergranular motions.

A Hydrodynamical Model of a Rotating Wind Source and Its Effects on the Collapse of a Rotating Core

This work presents three-dimensional hydrodynamical simulations with the fully parallel GAGDET2 code, to model a rotating source that emits wind in order to study the subsequent dynamics of the wind in three independent scenarios. In the first scenario we consider several models of the wind source, which is characterized by a rotation velocityVrotand an escape velocityVesc, so that the models have a radially outward wind velocity magnitudeVradgiven by 1, 2, 4, 6, and 8 timesVrot. In the second scenario, we study the interaction of winds emitted from a binary system in two kinds of models: one in which the source remains during the wind emission and a second one in which all the source itself becomes wind. In the third scenario we consider the interaction of a rotating source that emits wind within a collapsing and rotating core. In this scenario we consider only wind models of the second kind built over a new initial radial mesh, such that the angular velocity of the windΩwis 1, 100, and 1000 times the angular velocity of the coreΩc.

Evolutionary characteristics of a dust storm over Oman on 2 February 2008

The evolutionary characteristics of a dust storm over Oman on 2 February 2008 were studied by analyzing the weather associated with it. The National Center for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) reanalysis wind flow pattern at 1,000 hPa showed a clockwise and outward wind flow pattern over the study region, a manifestation of a high-pressure cold air mass. In addition, ground truth observations for surface temperature and surface winds showed cold northerly winds until the early morning of 2 February 2008. A strong wind shear resulted from differences in wind speed between warm air and trapped cold air. This vertical wind shear enhanced instability. Furthermore, the weakening of the inversion in the lower troposphere and the formation of a mixed layer due to transfer of horizontal momentum from upper air towards the surface led to strong surface winds. These strong winds lifted a large amount of dust particles off the ground, resulting in the dust event of 2 February 2008.

Black Hole Magnetospheres around Thin Disks Driving Inward and Outward Winds

We construct a simple model for stationary, axisymmetric black hole magnetospheres, in which the poloidal magnetic field is generated by a toroidal electric current in a thin disk with an inner edge, by solving the vacuum Maxwell equations in the Schwarzschild background. In this work, to obtain a concise analytical form of the magnetic stream function, we use the approximation that the inner edge is far distant from the event horizon. The global magnetospheric structure with a closed-loop and open field lines threading the inner and outer parts of the disk is explicitly shown, claiming that the model is useful as a starting point to study astrophysical problems involving inward disk-driven winds to a black hole and outward ones to infinity. The asymptotic shape of the field lines at the event horizon becomes nearly cylindrical, while at infinity it becomes conical. The magnetic spot in the disk connected with the black hole through the loop field lines occupies a very narrow region with the ring area roughly equal to the horizon area. By taking account of the existence of a uniform (external) magnetic field, we also obtain a model for collimated open field lines. Then, it is found that the magnetic connection between the black hole and the disk breaks down if the uniform field is strong enough. Considering slow rotation of the magnetosphere and angular momentum transfer by inward winds from the disk, the final discussion is devoted to gradual disruption of the closed loops due to radial accretion of disk plasma toward the black hole.