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Results for “tail asymmetry”

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At least 19 records

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NASA NTRS1982

Dawn-dusk asymmetry of the tail region of the magnetosphere of Saturn and the interplanetary magnetic field

In connection with the findings of the Voyager 1 mission, it appears that the tail lobe of Saturn is very different from that of earth and Jupiter, in that the latter are devoid of energetic particles, and magnetic field lines in this region are thought to be open and interconnecting with the interplanetary magnetic field at large distances in the antisolar direction. The present investigation is concerned with a possible explanation of these observations, taking into account a model of Saturn's magnetosphere. It is shown that the Voyager 1 spacecraft remained in the closed region of the magnetotail during its entire tail traversal and did not have an opportunity to penetrate into the high latitude lobe. It is concluded that Saturn probably has a tail lobe just like earth and Jupiter. However, this tail lobe was not traversed by Voyager.

Akasofu, S.-I.↗

NASA NTRS1985

North-south and dawn-dusk plasma asymmetries in the distant tail lobes - ISEE 3

ISEE 3 plasma measurements made in the distant geomagnetic tail during rapid traversals of the current sheet from one lobe to the other show that the lobe densities on opposite sides of the current sheet often differ by a factor of approximately 3-10 or more. On the dawnside of the tail the north lobe plasma has the higher density when the interplanetary magnetic field (IMF) has a +By component, and the south lobe plasma has the higher density when the IMF has a -By component. The sense of this asymmetry is reversed on the dusk-side of the tail. Such IMF-controlled asymmetries in lobe plasma density are consistent with earlier observations made much closer to earth and can be interpreted most simply as a consequence of an 'open' geomagnetic tail.

Gosling, J. T.↗

NASA NTRS1989

Results of the first statistical study of Pioneer Venus Orbiter plasma observations in the distant Venus tail - Evidence for a hemispheric asymmetry in the pickup of ionospheric ions

Pioneer Venus Orbiter plasma and magnetometer observations from the first nine tail seasons of crossings of the Venus wake are used to study ion pickup in the far wake of an unmagnetized object embedded in the solar wind. This statistical study treats all of the plasma spectra containing pickup ions in the vicinity of the Venus tail. A hemispheric asymmetry is found in the pickup of ionospheric ions, with approximately four times more O(+) events observed in the 'northern' magnetic hemisphere (where the induced electric field points outward) than in the 'southern' magnetic hemisphere. Out of a total of 167 large O(+) events, 125, or 75 percent, occurred in the northern hemisphere when position is calculated in terms of Venus radii, and 129 or 77 percent occurred in the 'northern' hemisphere when position is expressed in gyroradii. This hemispheric asymmetry in ion pickup is consistent with the prediction of the Cloutier et al. (1974) mass loading model for Venusian ions above the ionopause boundary.

Intriligator, Devrie S.↗

NASA NTRS1994

Flow-visualization study of the X-29A aircraft at high angles of attack using a 1/48-scale model

A water-tunnel study on a 1/48-scale model of the X-29A aircraft was performed at the NASA Dryden Flow Visualization Facility. The water-tunnel test enhanced the results of the X-29A flight tests by providing flow-visualization data for comparison and insights into the aerodynamic characteristics of the aircraft. The model was placed in the water tunnel at angles of attack of 20 to 55 deg. and with angles of sideslip from 0 to 5 deg. In general, flow-visualization techniques provided useful information on vortex formation, separation, and breakdown and their role in yaw asymmetries and tail buffeting. Asymmetric forebody vortices were observed at angles of attack greater than 30 deg. with 0 deg. sideslip and greater than 20 deg. with 5 deg. sideslip. While the asymmetric flows observed in the water tunnel did not agree fully with the flight data, they did show some of the same trends. In addition, the flow visualization indicated that the interaction of forebody vortices and the wing wake at angles of attack between 20 and 35 deg. may cause vertical-tail buffeting observed in flight.

Cotton, Stacey J.↗

NASA NTRS1986

Accelerated plasma flows at the near-tail magnetopause

ISEE-1 and -2 fast plasma data of ion and electron distributions at 16 energies and 16 velocities are used to study accelerated particle flow events at the near-tail dusk magnetopause. The flows separated the plasma sheet from the magnetosheath, a situation which normally arises when the local magnetosheath and plasma sheet magnetic fields are close to being antiparallel. The flows were directed tailward at speeds up to twice those in the adjoining magnetosheath and had densities similar to those in the magnetosheath. The attendant ion and electron temperatures were between those in the magnetosheath and in the plasma sheet. The flow region closest to the magnetosheath had the highest velocity and the lowest density, and a lowered-density field line region appeared on the earthward side of the accelerated flow region. The flows had the velocity changes of a tangential stress balance and are taken as the location of field line merging near (and perhaps tailward) of the dawn-dusk terminator. Significantly fewer accelerated flows are seen in the dawn tail magnetopause, an asymmetry attributed to a seasonally dependent warping of the midtail neutral sheet or a superimposition of interplanetary magnetic field lines over the dusk magnetopause.

Gosling, J. T.↗

NASA NTRS1947

Wind-Tunnel Investigation of Effects of Unsymmetrical Horizontal-Tail Arrangements on Power-on Static Longitudinal Stability of a Single-Engine Airplane Model

A wind-tunnel investigation has been made to determine the effects of unsymmetrical horizontal-tail arrangements on the power-on static longitudinal stability of a single-engine single-rotation airplane model. Although the tests and analyses showed that extreme asymmetry in the horizontal tail indicated a reduction in power effects on longitudinal stability for single-engine single-rotation airplanes, the particular "practical" arrangement tested did not show marked improvement. Differences in average downwash between the normal tail arrangement and various other tail arrangements estimated from computed values of propeller-slipstream rotation agreed with values estimated from pitching-moment test data for the flaps-up condition (low thrust and torque) and disagreed for the flaps-down condition (high thrust and torque). This disagreement indicated the necessity for continued research to determine the characteristics of the slip-stream behind various propeller-fuselage-wing combinations. Out-of-trim lateral forces and moments of the unsymmetrical tail arrangements that were best from consideration of longitudinal stability were no greater than those of the normal tail arrangement.

AIRFOILS - NACA 65(216-012(MOD ) - CHAR & MOMENTS ↗

NASA NTRS1987

Stability of the polar wind

The classical polar wind is an ambipolar outflow of thermal plasma from the terrestrial ionosphere at high latitudes. At altitudes above about 3000 km, the H(+) flow becomes supersonic and collisionless, and the H(+) velocity distribution becomes non-Maxwellian. The non-Maxwellian features include a temperature anisotropy, with the parallel H(+) temperature greater than the perpendicular temperature, and an asymmetry, with an elongated tail in the upward direction. These distortions from a Maxwellian increase as the H(+) gas escapes in the diverging geomagnetic field, and at 10 earth radii, the parallel-to-perpendicular temperature ratio is about 50 and the elongated tail is sufficiently long to move the drift velocity point off the peak of the distribution function. The stability of these highly non-Maxwellian H(+) velocity distributions was studied with regard to the excitation of electrostatic waves, and the plasma was found to be remarkably stable for a wide range of electron temperatures. This indicates that the various macroscopic formulations of the classical polar wind are valid. The stability of a perpendicularly heated polar wind was also studied, assuming bulk perpendicular heating of H(+) in the cusp, followed by the subsequent convection of the heated plasma into the polar cap. Two regions of instability were found.

Barakat, A. R.↗

NASA NTRS1976

Longitudinal asymmetry of the Jovian magnetosphere and the periodic escape of energetic particles

An earlier model of the Jovian magnetosphere is utilized in which the centrifugal stress of corotating plasma distends the outer magnetosphere and opens the tail field. Because of a longitudinal asymmetry in the ionospheric plasma source strength, caused principally by the nonaxisymmetric surface field, the closed-field region in the tail expands and contracts with the rotation period, resulting in a 10-hour modulation of the flux of energetic particles escaping from the magnetosphere into interplanetary space.

Hill, T. W.↗

NASA NTRS2012

Turbulence in a Global Magnetohydrodynamic Simulation of the Earth's Magnetosphere during Northward and Southward Interplanetary Magnetic Field

We report the results of MHD simulations of Earth's magnetosphere for idealized steady solar wind plasma and interplanetary magnetic field (IMF) conditions. The simulations feature purely northward and southward magnetic fields and were designed to study turbulence in the magnetotail plasma sheet. We found that the power spectral densities (PSDs) for both northward and southward IMF had the characteristics of turbulent flow. In both cases, the PSDs showed the three scale ranges expected from theory: the energy-containing scale, the inertial range, and the dissipative range. The results were generally consistent with in-situ observations and theoretical predictions. While the two cases studied, northward and southward IMF, had some similar characteristics, there were significant differences as well. For southward IMF, localized reconnection was the main energy source for the turbulence. For northward IMF, remnant reconnection contributed to driving the turbulence. Boundary waves may also have contributed. In both cases, the PSD slopes had spatial distributions in the dissipative range that reflected the pattern of resistive dissipation. For southward IMF there was a trend toward steeper slopes in the dissipative range with distance down the tail. For northward IMF there was a marked dusk-dawn asymmetry with steeper slopes on the dusk side of the tail. The inertial scale PSDs had a dusk-dawn symmetry during the northward IMF interval with steeper slopes on the dawn side. This asymmetry was not found in the distribution of inertial range slopes for southward IMF. The inertial range PSD slopes were clustered around values close to the theoretical expectation for both northward and southward IMF. In the dissipative range, however, the slopes were broadly distributed and the median values were significantly different, consistent with a different distribution of resistivity.

magnetohydrodynamics (MHD)↗

NASA NTRS1992

A low-speed wind tunnel study of vortex interaction control techniques on a chine-forebody/delta-wing configuration

A low speed wind tunnel evaluation was conducted of passive and active techniques proposed as a means to impede the interaction of forebody chine and delta wing vortices, when such interaction leads to undesirable aerodynamic characteristics particularly in the post stall regime. The passive method was based on physically disconnecting the chine/wing junction; the active technique employed deflection of inboard leading edge flaps. In either case, the intent was to forcibly shed the chine vortices before they encountered the downwash of wing vortices. Flow visualizations, wing pressures, and six component force/moment measurements confirmed the benefits of forced vortex de-coupling at post stall angles of attack and in sideslip, viz., alleviation of post stall zero beta asymmetry, lateral instability and twin tail buffet, with insignificant loss of maximum lift.

Rao, Dhanvada M.↗

NASA NTRS1992

A low-speed wind tunnel study of vortex interaction control techniques on a chine-forebody/delta-wing configuration

Rao, Dhanvada M.↗

NASA NTRS1990

A statistical study of ions and magnetic fields in the Venus magnetotail

A statistical characterization is made of the combined ion and magnetic field properties of the Venus magnetosheath and magnetotail, on the basis of plasma and magnetic field data from 223 Pioneer Venus orbits; no assumptions are made as to existing regions or their plasma and field characteristics. Plasma is found to flow tailward in all locations, and the magnetotail is highly draped. Weak magnetic field asymmetries are associated with the plasma dropouts. A high-E/q plasma population, previously interpreted as planetary-pickup ions, is found asymmetrically both within the tail and in the adjacent sheath. The Venus tail is filled with plasma that is primarily shocked solar wind, at fluxes that are sometimes undetectable; the tail coexists with a photoion population which generates asymmetries in the bulk plasma and magnetic field properties.

Moore, K. R.↗

NASA NTRS2010

Modeling of the Magnetosphere of Mercury at the Time of the First MESSENGER Flyby

The MESSENGER spacecraft flyby of Mercury on 14 January 2008 provided a new opportunity to study the intrinsic magnetic field of the innermost planet and its interaction with the solar wind, The model presented in this paper is based on the solution of the three-dimensional, bi-f1uid equations for solar wind protons and electrons in the absence of mass loading, In this study we provide new estimates of Mercury's intrinsic magnetic field and the solar wind conditions that prevailed at the time of the flyby. We show that the location of the boundary layers and the strength of the magnetic field along the spacecraft trajectory can be reproduced with a solar wind ram pressure P(sub sw) = 6.8 nPa and a planetary magnetic dipole having a magnitude of 210 R(sub M)(exp 3)- nT and an offset of 0.18 R(sub M) to the north of the equator, where R(sub M) is Mercury's radius. Analysis of the plasma flow reveals the existence of a stable drift belt around the planet; such a belt can account for the locations of diamagnetic decreases observed by the MESSENGER Magnetometer. Moreover, we determine that the ion impact rate at the n011hern cusp was four times higher than at the southern cusp, a result that provides a possible explanation for the observed north-south asymmetry in exospheric sodium in the neutral tail.

Benna, Mehdi↗

NASA NTRS1992

In-Flight Flow Visualization Results From the X-29A Aircraft at High Angles of Attack

Flow visualization techniques were used on the X-29A aircraft at high angles of attack to study the vortical flow off the forebody and the surface flow on the wing and tail. The forebody vortex system was studied because asymmetries in the vortex system were suspected of inducing uncommanded yawing moments at zero sideslip. Smoke enabled visualization of the vortex system and correlation of its orientation with flight yawing moment data. Good agreement was found between vortex system asymmetries and the occurrence of yawing moments. Surface flow on the forward-swept wing of the X-29A was studied using tufts and flow cones. As angle of attack increased, separated flow initiated at the root and spread outboard encompassing the full wing by 30° angle of attack. In general, the progression of the separated flow correlated well with subscale model lift data. Surface flow on the vertical tail was also studied using tufts and flow cones. As angle of attack increased, separated flow initiated at the root and spread upward. The area of separated flow on the vertical tail at angles of attack ≥ 20° correlated well with the marked decrease in aircraft directional stability.

Flight Testing↗

NASA NTRS1992

In-flight flow visualization results from the X-29A aircraft at high angles of attack

Flow visualization techniques were used on the X-29A aircraft at high angles of attack to study the vortical flow off the forebody and the surface flow on the wing and tail. The forebody vortex system was studied because asymmetries in the vortex system were suspected of inducing uncommanded yawing moments at zero sideslip. Smoke enabled visualization of the vortex system and correlation of its orientation with flight yawing moment data. Good agreement was found between vortex system asymmetries and the occurrence of yawing moments. Surface flow on the forward-swept wing of the X-29A was studied using tufts and flow cones. As angle of attack increased, separated flow initiated at the root and spread outboard encompassing the full wing by 30 deg angle of attack. In general, the progression of the separated flow correlated well with subscale model lift data. Surface flow on the vertical tail was also studied using tufts and flow cones. As angle of attack increased, separated flow initiated at the root and spread upward. The area of separated flow on the vertical tail at angles of attack greater than 20 deg correlated well with the marked decrease in aircraft directional stability.

Delfrate, John H.↗

NASA NTRS1992

Coma imaging of comet P/Brorsen-Metcalf at Calar Alto in late July to mid August 1989

Comet P/Brorsen-Metcalf was observed on 1989/07/28+30 and on 1989/08/04+12(+14) with the 3.5 m telescope and the 0.8 m Schmidt camera at Calar Alto/Spain. The images exhibit a narrow plasma tail pointing into anti-solar direction. On 1989/07/30 a triple tail was found which can be interpreted as tail ray event. The coma isophotes show prominent asymmetries with the nucleus located on the tailward side of the isophote foci and with a slightly higher brightness in the Northern Hemisphere of the coma. A strong curved jet feature was detected in the coma on 1989/07/30. The jet extended at least 30,000 km into the sunward coma hemisphere. The rotation period of about 1.3 days, estimated from the curvature of the coma jet, needs verification by other observations.

Boehnhardt, Hermann↗

NASA NTRS1992

System III variations in apparent distance of Io plasma torus from Jupiter

System III variations in apparent distance of the Io plasma torus from Jupiter are examined on the basis of data obtained from UVS scans across Jupiter's satellite system. The displacement of the dawn and dusk ansae are found to be unexpectedly complex. The displacements are unequal and both ansae are in motion with the motion of the approaching ansa being the lesser of the two. The radial motions, as measured from either the center of Jupiter or the offset-tilted dipole, are of unequal magnitude and have the System III periodicity. It is concluded that the cross-tail electric field that causes these torus motions is concentrated on the dusk ansa, varied with the System III period, and shows magnetic-anomaly phase control. It is found that the dawn-dust asymmetry in brightness is not explained simply by the cross-tail electric field. It is concluded that there is a heating mechanism that causes the dusk side of the Io plasma torus to be brighter than the dawn side.

Dessler, A. J.↗

NASA NTRS2024

JWST-TST High Contrast: Asymmetries, Dust Populations, and Hints of a Collision in the β Pictoris Disk with NIRCam and MIRI

We present the first JWST Mid-Infrared Instrument (MIRI) and Near Infrared Camera (NIRCam) observations of the prominent debris disk around βPictoris. Coronagraphic observations in eight filters spanning from 1.8 to 23 μm provide an unprecedentedly clear view of the disk at these wavelengths. The objectives of the observing program were to investigate the dust composition and distribution and to investigate the presence of planets in the system. In this paper, we focus on the disk components, providing surface brightness measurements for all images and a detailed investigation of the asymmetries observed. A companion paper by Kammerer et al. will focus on the planets in this system using the same data. We report for the first time the presence of an extended secondary disk in thermal emission, with a curved extension bent away from the plane of the disk. This feature, which we refer to as the “cat’s tail,” seems to be connected with the previously reported CO clump, mid-infrared asymmetry detected on the southwest side of the disk, and the warp observed in scattered light. We present a model of this secondary disk sporadically producing dust that broadly reproduces the morphology, flux, and color of the cat’s tail, as well as other features observed in the disk, and which suggests the secondary disk is composed largely of porous, organic refractory dust grains.

Isabel Rebollido↗