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NASA NTRS1983

Asymmetries of the upper stratospheric ozone distribution between two hemispheres

In connection with the eccentricity of the earth's orbit, conditions of solar radiation are not strictly symmetrical for the two hemispheres. The intensity of solar irradiation is approximately 6.6 percent higher near perihelion than near aphelion. As the ozone densities in the upper stratosphere and mesosphere are mainly controlled by photochemical processes, the asymmetry of irradiation conditions for both hemispheres could result in corresponding asymmetries regarding the ozone content. The present investigation is concerned with this possibility. The investigation takes into account Nimbus-7 and Nimbus-4 satellite data. It is found that the hemispheric asymmetries of the ozone distribution in the summer mesosphere and upper stratosphere are fully ascribable to the hemispheric temperature differences due to the combined effects of the earth's orbital ellipticity and its tilted spin axis from the ecliptic plane. The wintertime hemispheric asymmetries imply the presence of additional effects.

Maeda, K.↗

NASA NTRS1983

Longitudinal asymmetry of the Io plasma torus

Remote observations of the Io plasma torus have revealed a persistent longitudinal asymmetry in the brightness of optical S(+) emission lines but not of ultraviolet S(2+) emission lines. The S(+) asymmetry (with respect to the corotating System III coordinates) has been attributed to an asymmetric plasma source; the question then arises, why do the higher ionization states of sulfur not reflect a similar asymmetry? The explanation proposed here is based on the fact that torus ions do not quite corotate at the System III rate because of mass loading. If the resulting System III drift period of the ions is intermediate between the ionization lifetimes of S(+) and S(2+), then the asymmetry of the source will be obscured by longitudinal drift for the relatively long-lived multiply-ionized sulfur ions, but not for short-lived S(+).

Hill, T. W.↗

NASA NTRS1984

North-south asymmetries of solar particle events in upper stratospheric ozone

Stratospheric ozone depressions, following intense solar particle events (SPE) observed by the backscattered ultraviolet (BUV) experiment on the Nimbus-4 satellite, indicate the existence of distinct asymmetries between the Northern and Southern Hemispheres. These asymmetries are observed in the magnitude of the depressions above the 5-mb level, their temporal variations, and the spatial (i.e., latitude and longitude) dependence of these variations. Possible causes of asymmetries, shown by two events on August 4, 1972 and January 25, 1971, can be attributed to: (1) tilt of the interplanetary magnetic field (IMF) with respect to the earth's dipole magnetic field which influences the precipitation of energetic solar particles into the polar atmospheres; (2) differences in ozone chemistry caused by the large change in atmospheric temperature between summer and winter hemispheres; (3) seasonal differences of the stratosphere's dynamic states which are affected by upward propagating planetary waves in winter in contrast to the relatively undisturbed zonal flows in summer; and (4) topographic asymmetry between Northern and Southern Hemispheres. These effects are shown by three-dimensional plots of the events in geographic coordinates and by color contour plots of the stratospheric ozone distributions in geomagnetic and geographic polar coordinates, respectively.

Maeda, K.↗

NASA NTRS1987

Correlating east-west asymmetries in the Jovian magnetosphere and the Io sodium cloud

Three east-west intensity asymmetries in the Jupiter system that would appear to an earth observer in optical S+, extreme ultraviolet S++ and optical Na emissions are reviewed. The three asymmetries imply that some combination of the plasma torus number densities and electron temperature is, on the long-term average, larger west of Jupiter than east of Jupiter. A small east-to-west electric field, previously proposed to explain the ion intensity asymmetries, is also shown to provide a natural explanation for the sodium intensity asymmetry. A long-term average east-to-west electric field of about 3 mV/m and a corresponding west-to-east offset of about 0.16 Jupiter radii for the plasma torus at Io's orbital distance are implied. On a shorter time scale, the east-west electric field appears to be time variable and may be readily monitored from earth by observations of the sodium cloud.

Smyth, William H.↗

NASA NTRS1995

Dawn-dusk asymmetries in the low-latitude boundary layer arising from the Kelvin-Helmholtz instability: A particle simulation

Along the low-latitude boundary layer (LLBL), the Kelvin-Helmholtz (K-H) instability can provide a means for injection of solar wind plasma across closed field lines of the magnetosphere. A fully electromagnetic, two-dimensional (three-velocity) particle code is used to investigate dawn-dusk asymmetries that can arise from velocity differences due to gradient drifts and electric field gradients, and ion acceleration across the narrow field transition layers in the dawn and dusk flanks. The model includes the dawn and dusk sides of the LLBL simultaneously in a slab geometry, incorporating seperate populations of ions and electrons for the magnetosphere and the magnetosheath plasmas. We report several effects: (1) asymmetries in the observed morphology of the turbulent structures, with familiar fluidlike vortex formation on the duskside, but tongues of magnetosheath plasma penetrating into the magnetosphere on the dawnside; (2) the formation of discrete current layers, characterized by strong currents and sharp gradients in the magnetic field, and discrete charge layers, having net charges and constant, weaker currents; (3) increasing asymmetry in dawn/dusk behavior with a decrease of initial currents; (3) increasing asymmetry in dawn/dusk behavior with a decrease of initial boundary layer width; and (4) enhancement of the dawn-to-dusk electric field as magnetosheath particles and momenta are transported across the magnetopause.

Wilber, M.↗

NASA NTRS1995

Magnetic reconnection in the presence of sheared flow and density asymmetry: Applications to the Earth's magnetopause

Classical models of magnetic reconnection consist of a small diffusion region bounded by two symmetric slow shocks, across which the plasma is accelerated. Asymmetries often present in space plasmas are sheared plasma flow and dissimilar plasma densities on the two sides of current sheets. In this paper, we investigate magnetic reconnection in the presence of a shear flow and an asymmetric density across the current sheet using two-dimensional magnetohydrodynamic (MHD) simulations. The results demonstrate that magnetic reconnection can occur only for a plasma flow velocity (in the frame of the X line) which is below the Alfven speed in each inflow region. This limits the velocity of the X line to a certain range for a given flow shear and provides an upper limit to the total velocity shear at which reconnection ceases to operate. Depending on the direction of the flow in the adjacent inflow region, the effects from the sheared flow and from the density asymmetry will compete with or enhance each other in respect to the magnitude and location of the currents which bound the outflow regions. The results are applied to the dayside and flank regions of the magnetosphere. For the dayside region where the magnetosheath flow is slow, the magnetic field transition region is thin and the accelerated flow is earthward of the sharp current layer (magnetopause). At the flanks tailward of the X line, shear flow and density asymmetry effects compete making the magnetic field transition layer broad with the high-speed flow contained within the transition region which explains corresponding observations. At the flanks sunward of the X line, shear flow and density asymmetry effects enhance each other and lead to a strong current sheet on the magnetosheath side of the accelerated flow. The total volume affected by magnetic reconnection is much larger than the steady state region. A large bulge region precedes the steady state region. Qualitatively, the bulge and the steady state region have similar signatures and both can explain observations. We provide criteria in order to distinguish between the bulge and the steady state region in observations.

La Belle-Hamer, A. L.↗

NASA NTRS1995

North-south asymmetry of the interplanetary magnetic helicity

Previous analyses of the north-south asymmetry of the interplanetary magnetic helicity have used the omnitape dataset and have shown that there exists a persistent and statistically significant asymmetry in the handedness of the magnetic fluctuations at 1 AU. This asymmetry is concentrated in fluctuations with spacecraft frame frequencies less than 10-5 Hz (periods greater than 30 hours) at 1 AU. Attempts to extend these analyses to include data collected in the outer heliosphere require that we consider spacecraft frame periods many times greater than 30 hours. This raises interesting questions regarding homogeneity and stationarity of the datasets at this scale and brings into question the possible breakdown of the computed correlation functions due to the sector structure of the solar wind. The likely geometry of magnetic fluctuations in the outer heliosphere provides yet another complication in the analysis. These issues will be discussed in detail and the latest results from our studies of the Voyager 1 & 2 and Pioneer 10 & 11 datasets will be presented. The analysis of Pioneer-Venus Orbiter observations will be shown as well. The potential asymmetry between the magnetic helicity of the two hemispheres has significant and measurable implications for cosmic ray propagation in the heliosphere and these implications will be reviewed in light of the new results.

Smith, Charles W.↗

NASA NTRS1995

Titan's stratospheric temperature asymmetry: a radiative origin?

During the 1981 Voyager encounter, Titan's stratosphere exhibited a large thermal asymmetry, with high northern latitudes being colder than comparable southern latitudes. Given the short radiative time constant, this asymmetry would not be expected at the season of the Voyager observations (spring equinox), if the infrared and solar opacity sources were distributed symmetrically. We have investigated the radiative budget of Titan's stratosphere, using two selections of Voyager IRIS spectra recorded at symmetric northern and southern latitudes. In the region 0.1-1 mbar, temperatures are 7 K colder at 50 degrees N than at 53 degrees S and the difference reaches approximately 13 K at 5 mbar. On the other hand, the northern region is strongly enriched in nitriles and hydrocarbons, and the haze optical depth derived from the continuum emission between 8 and 15 micrometers is twice as large as in the south. Cooling rate profiles have been computed at the two locations, using the gas and haze abundances derived from the IRIS measurements. We find that, despite lower temperatures, the cooling rate profiles in the pressure range 0.15-5 mbar are 20 to 40% larger in the north than in the south, because of the enhanced concentrations of infrared radiators. Because the northern hemisphere appears darker than the southern one in the Voyager images, enhanced solar heating is also expected to take place at 50 degrees N. Solar heating rate profiles have been calculated, with two different assumptions on the origin of the hemispheric asymmetry. In the most likely case where it results from a variation in the absorbance of the haze material, the heating rates are found to be 12-15% larger at the northern location than at the southern one, a smaller increase than that in the cooling rates. If the lower albedo in the north results from an increase in the particle number density, a 55 to 75% difference is found for the pressure range 0.15-5 mbar, thus larger than that calculated for the cooling rates. Considering the uncertainties in the haze model, dynamical heat transport may significantly contribute to the meridional temperature gradients observed in the stratosphere. On the other hand, the latitudinal variation in gas and haze composition may be sufficient to explain the entire temperature asymmetry observed, without invoking a lag in the thermal response of the atmosphere due to dynamical inertia.

NASA Program Exobiology↗

NASA NTRS1989

Auxin asymmetry during gravitropism by tomato hypocotyls

Gravitropic asymmetry of auxin was observed in hypocotyls of tomato (Lycopersicon esculentum Mill.) soon after horizontal placement: the ratio of apically supplied [3H]IAA collected from the lower sides to that from the upper sides was about 1.4 between 5 and 10 minutes. This was adequately early to account for the beginning of curvature. The auxin asymmetry ratio rose to about 2.5 between 20 and 25 minutes, and to 3.5 during the main phase of curvature. This compares reasonably well with the roughly 3.9 ratio for elongation on the lower side to elongation on the upper side that is the basis for the curvature. These data extend evidence that the Went-Cholodny theory for the mediation of tropisms is valid for dicot stems. Also consistent with the theory, an auxin asymmetry ratio of 2.5 was observed when wrong-way gravitropic curvature developed following application of a high level of auxin. In addition to reversing the asymmetry of elongation, the large supplement of auxin resulted in lower net elongation. Previous data established that ethylene is not involved in this decrease of growth as a function of increasing level of auxin.

NASA Program Space Biology↗

NASA NTRS2011

Modification of Otolith Reflex Asymmetries Following Space Flight

We hypothesize that changes in otolith-mediated reflexes adapted for microgravity contribute to perceptual, gaze and postural disturbances upon return to Earth s gravity. Our goal was to determine pre- versus post-fight differences in unilateral otolith reflexes that reflect these adaptive changes. This study represents the first comprehensive examination of unilateral otolith function following space flight. Ten astronauts participated in unilateral otolith function tests three times pre-flight and up to four times after Shuttle flights from landing day through the subsequent 10 days. During unilateral centrifugation (UC, +/- 3.5cm at 400deg/s), utricular function was examined by the perceptual changes reflected by the subjective visual vertical (SVV) and by video-oculographic measurement of the otolith-mediated ocular counter-roll (OOR). Unilateral saccular reflexes were recorded by measurement of collic Vestibular Evoked Myogenic Potential (cVEMP). Although data from a few subjects were not obtained early post-flight, a general increase in asymmetry of otolith responses was observed on landing day relative to pre-flight baseline, with a subsequent reversal in asymmetry within 2-3 days. Recovery to baseline levels was achieved within 10 days. This fluctuation in the asymmetry measures appeared strongest for SVV, in a consistent direction for OOR, and in an opposite direction for cVEMP. These results are consistent with our hypothesis that space flight results in adaptive changes in central nervous system processing of otolith input. Adaptation to microgravity may reveal asymmetries in otolith function upon to return to Earth that were not detected prior to the flight due to compensatory mechanisms.

Clarke, Andrew H.↗

NASA NTRS2013

The North-South Asymmetry of the Heliospheric Current Sheet: Results of an MHD Simulation

A displacement of the heliospheric current sheet (HCS) south of the helioequator by approx.10deg was proposed by Simpson et al. (1996) as a possible explanation of the north-south asymmetry in the galactic cosmic rays observed by Ulysses during its first fast transit in 1994-1995. The idea was not supported by magnetic field measurements on Ulysses and, on this ground, was dismissed by Simpson et al. (1996). In addition, Erdos & Balogh (1998) argued that any north-south symmetry was unlikely as there should be flux balance between the magnetic sectors of opposite polarity. Nonetheless, many in the scientific community have accepted the original suggestion of Simpson et al. (1996) that a displacement of the HCS was responsible for the cosmic ray asymmetry. In this paper, using a magnetohydrodynamic model of the solar corona and solar wind that includes both dipole and quadrupole magnetic source terms, we show that a north-south asymmetry of the magnetic field on the Sun does not give rise to a displacement of the HCS. The lack of displacement of the HCS results from a latitudinal redistribution of magnetic flux near the Sun where the plasma beta much < 1. The latitudinal redistribution is a direct consequence of the magnetic field gradient between pole and equator. Near the Sun, the latitudinal gradient in magnetic field generates meridional flows directed equatorward that tend to relax the gradient in the magnetic field (to make it more latitude-independent) as heliocentric distance increases. If there is an asymmetry between north and south magnetic field strength then the meridional flows are also asymmetric (i.e., stronger in the hemisphere of stronger magnetic field). Because the magnetic fluxes (positive and negative) in the hemispheres must be equal, the redistribution shifts the HCS into balance by approx. 16 R(solar mass). At larger distances, where the magnetic field is relatively weak (beta much > 1), the HCS can be displaced if there is a difference in total pressure between the hemispheres.

solar wind↗

NASA NTRS2015

Impact of Stratospheric Ozone Zonal Asymmetries on the Tropospheric Circulation

The depletion and recovery of Antarctic ozone plays a major role in changes of Southern Hemisphere (SH) tropospheric climate. Recent studies indicate that the lack of polar ozone asymmetries in chemistry climate models (CCM) leads to a weaker and warmer Antarctic vortex, and smaller trends in the tropospheric mid-latitude jet and the surface pressure. However, the tropospheric response to ozone asymmetries is not well understood. In this study we report on a series of integrations of the Goddard Earth Observing System Chemistry Climate Model (GEOS CCM) to further examine the effect of zonal asymmetries on the state of the stratosphere and troposphere. Integrations with the full, interactive stratospheric chemistry are compared against identical simulations using the same CCM except that (1) the monthly mean zonal mean stratospheric ozone from first simulation is prescribed and (2) ozone is relaxed to the monthly mean zonal mean ozone on a three day time scale. To analyze the tropospheric response to ozone asymmetries, we examine trends and quantify the differences in temperatures, zonal wind and surface pressure among the integrations.

Chemistry-Climate Modeling↗

NASA NTRS2024

Investigating Zonal Asymmetries in Stratospheric Ozone Trends From Satellite Limb Observations and a Chemical Transport Model

This study investigates the origin of a zonal asymmetry in stratospheric ozone trends at northern high latitudes, identified in satellite limb observations over the past two decades. We use a merged data set consisting of ozone profiles retrieved at the University of Bremen from SCIAMACHY and OMPS-LP measurements to derive ozone trends. We also use TOMCAT chemical transport model (CTM) simulations, forced by ERA5 reanalyses, to investigate the factors that drive the asymmetry observed in the long-term changes. By studying seasonally and longitudinally resolved observation-based ozone trends, we find, especially during spring, a well-pronounced asymmetry at polar latitudes with values up to +6 % per decade over Greenland and −5 % per decade over western Russia. The control CTM simulation agrees well with these observed trends, whereas sensitivity simulations indicate that chemical mechanisms involved in the production and removal of ozone, or their changes, are unlikely to explain the observed behavior. The decomposition of TOMCAT ozone time series and ERA5 geopotential height into the first two wavenumber components shows a clear correlation between the two variables in the middle stratosphere and demonstrates a weakening and a shift in the wavenumber-1 planetary wave activity over the past two decades. Finally, the analysis of the polar vortex position and strength points to a decadal oscillation with a reversal pattern at the beginning of the century. The same is found in the ozone trend asymmetry. This further stresses the link between changes in the polar vortex position and the identified ozone trend pattern.

Instrumentation↗

NASA NTRS1974

Effect of a progressive sound wave on the profiles of spectral lines. 2: Asymmetry of faint Fraunhofer lines

The absorption coefficient profile was calculated for lines of different chemical elements in a medium with progressive sound waves. Calculations show that (1) the degree and direction of asymmetry depend on the atomic ionization potential and the potential of lower level excitation of the individual line; (2) the degree of asymmetry of a line decreases from the center toward the limb of the solar disc; and (3) turbulent motions 'suppress' the asymmetry.

Kostyk, R. I.↗

NASA NTRS1975

High-order magnetic multipoles as a source of gross asymmetry in the distant Jovian magnetosphere

The longitudinal asymmetry of the surface magnetic-field strength at Jupiter causes a longitudinal asymmetry in the equatorial plasma mass density within the Jovian magnetosphere. The rotation of these density variations with the planet causes a diurnal variation of the radial distance on the night side at which the centrifugal stress of the magnetospheric plasma exceeds the local magnetic-field tension. This is approximately the distance at which the magnetic field opens to interplanetary space; we estimate that the opening distance can vary by as much as 14% as a result of the observed surface field asymmetry. Such a diurnal variation of the boundary of the particle trapping region can account for the observed ten-hour modulation of relativistic electrons emitted from Jupiter into interplanetary space.

Dessler, A. J.↗

NASA NTRS1980

Functional asymmetry of posture and body system regulation

The manifestation of functional asymmetry during the regulation of an athlete's posture and a system of bodies and its effect on the execution of individual and group acrobatic exercises were studied. Functional asymmetry of posture regulation was recorded in acrobats during the execution of individual and group exercises. It was shown that stability is maintained at the expense of bending and twisting motions. It is important to consider whether the functional asymmetry of posture regulation is left or right sided in making up pairs and groups of acrobats.

Boloban, V. N.↗

NASA NTRS1984

Magnetopause merging site asymmetries

Regions where a draped model magnetosheath magnetic field is nearly antiparallel to a model geomagnetic field are shown to be asymmetric for an interplanetary magnetic field (IMF) at the garden hose angle, as suggested by Heelis. When the IMF has a southward component, the asymmetry favors the dawn region for both IMF polarities. The dusk region is favored when the IMF has a northward component. If the regions of antiparallel fields are assumed to be sites of maximum magnetic merging, then the asymmetry is consistent with observed seasonal variations of geomagnetic activity and with dawn-displaced magnetospheric phenomena. In the alternate merging geometry of a line passing through the subsolar region, the asymmetry is predominantly north-south rather than dawn-dusk. Merging line geometry is consistent with the seasonal variations but not with the dawn-displaced phenomena.

Crooker, N. U.↗

NASA NTRS1985

Magnetopause merging site asymmetries

Crooker, N. U.↗