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At least 1,747 records · Page 97
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

The sound of a Martian dust devil

Dust devils (convective vortices loaded with dust) are common at the surface of Mars, particularly at Jezero crater, the landing site of the Perseverance rover. They are indicators of atmospheric turbulence and are an important lifting mechanism for the Martian dust cycle. Improving our understanding of dust lifting and atmospheric transport is key for accurate simulation of the dust cycle and for the prediction of dust storms, in addition to being important for future space exploration as grain impacts are implicated in the degradation of hardware on the surface of Mars. Here we describe the sound of a Martian dust devil as recorded by the SuperCam instrument on the Perseverance rover. The dust devil encounter was also simultaneously imaged by the Perseverance rover’s Navigation Camera and observed by several sensors in the Mars Environmental Dynamics Analyzer instrument. Combining these unique multi-sensorial data with modelling, we show that the dust devil was around 25 m large, at least 118 m tall, and passed directly over the rover travelling at approximately 5 m s –1 . Acoustic signals of grain impacts recorded during the vortex encounter provide quantitative information about the number density of particles in the vortex. The sound of a Martian dust devil was inaccessible until SuperCam microphone recordings. This chance dust devil encounter demonstrates the potential of acoustic data for resolving the rapid wind structure of the Martian atmosphere and for directly quantifying wind-blown grain fluxes on Mars.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1975

Variations in the solar wind stand-off distance at Mercury

The intrinsic dipole model of the magnetosphere of Mercury is combined with statistics on the solar wind dynamic pressure from Explorers 33 and 35 to obtain histograms of the solar wind stand-off distance for aphelion, perihelion and median distance of Mercury from the sun. The results show that even at perihelion the stand-off distance lies above the surface the great majority of the time. On rare occasions, direct impact of the solar wind onto the surface will occur.

Siscoe, G.↗
NASA NTRS1981

Interplanetary ions during an energetic storm particle event - The distribution function from solar wind thermal energies to 1.6 MeV

An ion velocity distribution function of the postshock phase of an energetic storm particle (ESP) event is obtained from data from the ISEE 2 and ISEE 3 experiments. The distribution function is roughly isotropic in the solar wind frame from solar wind thermal energies to 1.6 MeV. The ESP event studied (8/27/78) is superposed upon a more energetic particle event which was predominantly field-aligned and which was probably of solar origin. The observations suggest that the ESP population is accelerated directly out of the solar wind thermal population or its quiescent suprathermal tail by a stochastic process associated with shock wave disturbance. The acceleration mechanism is sufficiently efficient so that approximately 1% of the solar wind population is accelerated to suprathermal energies. These suprathermal particles have an energy density of approximately 290 eV cubic centimeters.

Gosling, J. T.↗
NASA NTRS1981

Forced shelf circulation by an alongshore wind band

The forced circulation over a continental shelf generated by the alongshore wind stress is studied within the frictional regime. The model alongshore wind stress has a finite extent in the alongshore direction and oscillates monochromatically, resembling a series of anticyclones traveling across the coastline. Both the shelf-wave response and the localized non-wavelike response exist within the wind band. The numerical results show that the interaction of shelf waves with locally wind-forced response generates a large increase in the phase speed within the wind band. Given an alongshore variation in the alongshore wind stress, a right-bounded phase propagation is possible even in the absence of continental shelf waves. Given a reasonable friction currently accepted for the east coast of the United States, the resonance mechanism at the cutoff frequency may not be important, and lower frequency wind events generate larger amplitude continental shelf circulation. By reducing the friction, energy at cutoff fequencies leaks out of the wind band in both directions effectively. It also is shown that non-wavelike response depends only on the local wind stress and is not affected significantly by friction.

Chao, S.-Y.↗
NASA NTRS1979

On the angle between the average interplanetary magnetic field and the propagation direction of plane large amplitude Alfven waves

The paper shows that the experimentally observed close alignment of magnetic field minimum variance direction with the average magnetic field for Alfven waves in the solar wind is consistent with theoretically predicted properties of plane large amplitude Alfven waves in the MHD approximation. The theoretical properties of these Alfven waves constrain the time averaged magnetic field to cluster around the direction of minimum variance, which is aligned with the wave normal. Thus, spacecraft magnetometer observations in the solar wind of minimum variance directions strongly peaked about the average magnetic field direction are consistent with plane large amplitude Alfven waves which have wave normals aligned with the directions of minimum variance. This does not imply that geometrical hydromagnetic calculations for Alfven wave propagation direction in the solar wind are incorrect, but there is a discrepancy between geometrical hydromagnetics theory and observations that IMF minimum variance directions tend to be aligned with the ideal Parker spiral instead of the radial direction.

Lichtenstein, B. R.↗
NASA NTRS1980

Solar wind flow past Venus - Theory and comparisons

Advanced computational procedures are applied to an improved model of solar wind flow past Venus to calculate the locations of the ionopause and bow wave and the properties of the flowing ionosheath plasma in the intervening region. The theoretical method is based on a single-fluid, steady, dissipationless, magneto-hydrodynamic continuum model and is appropriate for the calculation of axisymmetric supersonic, super-Alfvenic solar wind flow past a nonmagnetic planet possessing a sufficiently dense ionosphere to stand off the flowing plasma above the subsolar point and elsewhere. Determination of time histories of plasma and magnetic field properties along an arbitrary spacecraft trajectory and provision for an arbitrary oncoming direction of the interplanetary solar wind have been incorporated in the model. An outline is provided of the underlying theory and computational procedures, and sample comparisons of the results are presented with observations from the Pioneer Venus orbiter.

Spreiter, J. R.↗
NASA NTRSDate not supplied

The Solar Wind Defines Space Weather Safety Zones

During the ARTEMIS era, humans again will venture beyond the protection of the Earth’s atmosphere and magnetosphere into the solar wind. It is now well established that the solar wind is responsible for carving out a cavity in cosmic ray flux in the inner heliosphere. The resulting reduction in blood-forming organ dose rate basically enables human exploration. Lesser known or acknowledged is the important role the solar wind plays in shaping the directivity and extents of solar energetic particle events. This influence leads to an effective offset of the source location of the Sun that has the most potential to harm explorers through radiation exposure from major solar eruptions. This presentation will discuss how the solar wind influence renders current measures ineffective but instead demands new and immediate strategies to protect human explorers over the first decades of ARTEMIS exploration missions.

exploration↗
NASA NTRS1973

Comparison of aircraft noise measured in flight test and in the NASA Ames 40- by 80-foot wind tunnel.

A method to determine free-field aircraft noise spectra from wind-tunnel measurements has been developed. The crux of the method is the correction for reverberations. Calibrated loud speakers are used to simulate model sound sources in the wind tunnel. Corrections based on the difference between the direct and reverberant field levels are applied to wind-tunnel data for a wide range of aircraft noise sources. To establish the validity of the correction method, two research aircraft - one propeller-driven (YOV-10A) and one turbojet-powered (XV-5B) - were flown in free field and then tested in the wind tunnel. Corrected noise spectra from the two environments agree closely.

Atencio, A., Jr.↗
NASA NTRS1984

The case for aeolian control of meter-scale surface texture on Mars

The origin of Mars surface units and the extent of subsequent cratering play key roles in determining surface texture. At scale sizes of 0.1-10 meters, however, there is a growing body of evidence that wind is the dominant force. The direct and indirect evidence which implies that meter-scale surface texture on Mars is controlled by the wind is presented. Since radar is uniquely sensitive to structure on these scales, radio wave scattering data can provide insight on aeolian activity available from no other source.

Simpson, R. A.↗
NASA NTRS1981

Structure of thunderstorms along a squall line on May 2, 1979

Preliminary results are presented concerning the structure of a developing squall line in Oklahoma on May 2, 1979, during SESAME. It is shown that the line developed ahead of a cold front with explosive growth. A synthesis of radar, satellite, sounding, and surface data is presented. The combined use of satellite and radar data is found to be of considerable value in describing the evolution of cells along the squall line. These are found to interact strongly with one another at all heights. Three preliminary conclusions are made. The first is that many of the cells initially move with the direction of the upper level winds and then turn to the right of all tropospheric winds. An explanation for this rightward turn is given in terms of the motion of the cold front relative to the cells. The second conclusion is that the updrafts in two of the cells at 0030 were quite vertical, and the upper level divergent region is almost directly above the low-level frontal windshift. The third conclusion is that the strongest downdrafts occurred from mid to upper levels and resulted from the strong convergence produced between the divergent outflow regions of two adjacent cells.

Heymsfield, G. M.↗
NASA NTRS2019

Does the Solar Wind Electric Field Control the Reconnection Rate at Earth's Subsolar Magnetopause?

We demonstrate that the reconnection rate at the subsolar magnetopause is stronglycontrolled by the solar wind electric field and depends weakly on the local properties of the dissipationregion. Our approach is to match the solar wind and magnetospheric states in an internal boundarylayer described by the Cassak and Shay (2007, https://doi.org/10.1063/1.2795630) expression fortwo-dimensional asymmetric reconnection. Faraday's law along the Sun-Earth line determinesthe variation of the solar wind electric field from the bow shock to the magnetopause. While themagnetospheric plasma exerts some control over the reconnection rate, magnetic flux pileup in the sheathpartially compensates for any local reduction in the reconnection rate. For a fixed magnetospheric state,the reconnection rate is shown to be directly proportional to the solar wind electric field, thus explainingwhy the solar wind electric field correlates well with geomagnetic indices.

Dorelli, John C.↗
NASA NTRS1976

A low speed wind tunnel test of a 0.050 scale model of shuttle orbiter (model 089B) to investigate the longitudinal and lateral directional effects of canard and tail configurational modifications in the LTV LSWT (MA14)

A low speed wind tunnel test was conducted to determine the effects of 6 canard configurations on the 0.050 scale model of shuttle orbiter 089B. In addition, two horizontal tail configurations were tested at two positions on the model as were two wing configurations. Since this test was restricted to 103 runs, only a limited number of permutations of the configurational changes could be tested. The testing was done in the 15 by 20 foot section of the LSWT and consisted of pitch polars, one yawed polar and several yaw runs. The pitch polars encompassed an alpha range from 0 to 28 deg; the yawed polar was run at beta = +2 degrees and the yaw runs covered a beta range from -6 to +6 deg at angles-of-attack of 0, 4, 10, 16, and 20 deg.

Chambliss, E. B.↗
NASA NTRS1994

Coronal mass ejections in the solar wind at high solar latitudes: An overview

Ulysses provided the first direct measurements of coronal mass ejections (CME's) in the solar wind at high heliographic latitudes. An overview of new results from the plasma experiment on Ulysses and magnetic field measurements, during the spacecraft's first excursion to high solar latitudes are summarized. A striking aspect of the high-latitude CME's observed is that they all had high speeds, with the overall average speed being 730 km/sec. A new class of forward-reverse shock pairs, associated with expansion of CME's was discovered at high latitudes. Of six certain CME's observed at high latitudes, three have associated shock pairs of this nature. Combined Ulysses and Yohkoh observations suggest that the flux rope topology characteristic of some CME's results from reconnection within the legs of neighboring magnetic loops embedded within the escaping CME's.

Gosling, Jack T.↗
NASA NTRS1981

Solar flare acceleration of solar wind - Influence of active region magnetic field

The direction of the photospheric magnetic field at the site of a solar flare is a good predictor of whether the flare will accelerate solar wind plasma. If the field has a southward component, high-speed solar wind plasma is usually observed near the earth about 4 days later. If the field has a northward component, such high-speed solar wind is almost never observed. Southward-field flares may then be expected to have much larger terrestrial effects than northward flares.

Lundstedt, H.↗
NASA NTRS1984

Interplanetary field enhancements in the solar wind Statistical properties at 0.72 AU

A new class of disturbance in the interplanetary magnetic field has been discovered. This disturbance consists of an enhancement in the magnetic field strength lasting tens of minutes to hours. The strength of the enhancement is variable ranging up to over double the background field strength. The peak field pressure can be as high as 10 percent of the solar wind dynamic pressure. These events occur randomly with respect to the position of the spacecraft relative to Venus but not randomly with respect to Venus solar ecliptic longitude. There is a significant tendency for these events to cluster near certain ecliptic longitudes. The field distortion is often greater in the direction perpendicular to the solar wind flow rather than along it. These characteristics suggest that the source of the disturbances are weakly outgassing objects, possibly dispersed along their orbits such as in meteor streams.

Russell, C. T.↗
NASA NTRS1994

Computational analysis of forebody tangential slot blowing

An overview of the computational effort to analyze forebody tangential slot blowing is presented. Tangential slot blowing generates side force and yawing moment which may be used to control an aircraft flying at high-angle-of-attack. Two different geometries are used in the analysis: (1) The High Alpha Research Vehicle; and (2) a generic chined forebody. Computations using the isolated F/A-18 forebody are obtained at full-scale wind tunnel test conditions for direct comparison with available experimental data. The effects of over- and under-blowing on force and moment production are analyzed. Time-accurate solutions using the isolated forebody are obtained to study the force onset timelag of tangential slot blowing. Computations using the generic chined forebody are obtained at experimental wind tunnel conditions, and the results compared with available experimental data. This computational analysis compliments the experimental results and provides a detailed understanding of the effects of tangential slot blowing on the flow field about simple and complex geometries.

Gee, Ken↗