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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS2015

VISIONS: Remote Observations of a Spatially-Structured Filamentary Source of Energetic Neutral Atoms near the Polar Cap Boundary During an Auroral Substorm

We report initial results from the VISualizing Ion Outflow via Neutral atom imaging during a Substorm (VISIONS) rocket that flew through and near several regions of enhanced auroral activity and also sensed regions of ion outflow both remotely and directly. The observed neutral atom fluxes were largest at the lower energies and generally higher in the auroral zone than in the polar cap. In this paper, we focus on data from the latter half of the VISIONS trajectory when the rocket traversed the polar cap region. During this period, many of the energetic neutral atom spectra show a peak at 100 electronvolts. Spectra with peaks around 100 electronvolts are also observed in the Electrostatic Ion Analyzer (EIA) data consistent with these ions comprising the source population for the energetic neutral atoms. The EIA observations of this low energy population extend only over a few tens of kilometers. Furthermore, the directionality of the arriving energetic neutral atoms is consistent with either this spatially localized source of energetic ions extending from as low as about 300 kilometers up to above 600 kilometers or a larger source of energetic ions to the southwest.

Polar Cap↗
NASA NTRS1992

Mars secular obliquity change due to the seasonal polar caps

There is a weak positive feedback mechanism between the astronomy and meteorology of Mars. The mechanism is this: the seasonal waxing and waning polar caps cause small changes in Mars' dynamical flattening. Because the changes in flattening are out of phase with the sun, there is a net annual solar torque on the planet which increases the angle between the equatorial and orbital phanes. On the basis of Viking observations of the present climate and simple atmospheric models of past climates, these seasonal shifts of mass between the atmosphere and polar caps are capable of secularly increasing Mars' obliquity by about 1 or 2 deg since the origin of the solar system. Thus, the climate, driven largely by the axial tilt, reacts back on the planet and slightly enhances the seasons on Mars as time progresses. More sophisticated models will probably not change this result much; therefore this mechanism probably produced only minor changes in Mars' climate. It causes negligible changes in the axial tilt and climate of the earth.

Rubincam, David P.↗
NASA NTRS2018

Understanding the Water Cycle Above the North Polar Cap on Mars Using MRO CRISM Retrievals of Water Vapor

The north polar cap (NPC) on Mars is the major reservoir of atmospheric water (H2O) currently on Mars. The retrieval and monitoring of atmospheric water vapor abundance are crucial for tracking the cycle of water above the NPC. The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard the Mars Reconnaissance Orbiter (MRO) has provided a wealth of data that extend over 5 + Martian years, covering the time period between 2006 and 2016. CRISM is ideally suited for spring and summer observations of the north polar region (latitudes poleward of 60 °N). The retrievals of water vapor column abundances over this extended period of time were performed over both ice-free and water ice covered surfaces, extending the coverage of the water vapor maps to include the permanent cap, where a maximum value of 90 precipitable micrometers (pr–µm) is retrieved, as compared to 60 pr–µm over ice-free regions in the North Polar Region. Away from summertime maximum, modest interannual variability in the water vapor abundance is observed. Zonal averages over all the observed Martian years combined show a developing water front that shifts northward towards summer, before dissipating over the permanent cap during mid-summer. A prominent feature at latitudes around 75 °N shows large abundances of water vapor, indicating a water vapor annulus encircling the retreating edge of the seasonal polar cap during late spring. Meridional transport of water modeled here show that the annulus may be a result of the convergence of water vapor from both south and north along the retreating edge of the NPC.

Khayat, Alain S. J.↗
NASA NTRS1971

Midday auroral observations in the oval, cusp region, and polar cap.

Evaluation of combined photographic and photometric measurements made on the 1969 NASA airborne expedition, yielding a description of the midday oval, cusp region, and polar cap auroral precipitation at low magnetic activity (Kp = 0, 1+). The observations delineate three regions through the description of the type of aurora observed and the photometrically inferred change in energy of the particles: (1) the region in and equatorward of the oval where greater than 3-keV electrons are associated with 6300 A/4278 A ratios less than or equal to 1 and with a diffuse glow or structured arcs; (2) the cusp region where electrons of several hundred electron volts and spikes of more energetic electrons are associated with 6300 A/4278 A ratios between 10 and 35 in broken, fragmented, rayed features and patches; (3) the polar cap where discrete earth-sun-aligned arcs have height luminosity profiles in 5577 A, 6300 A (forbidden O I), and 4278 A (N2(+)) that suggest incoming electrons with an energy spectrum of 2-keV characteristic energy above a low-energy (few hundred electron volts) background.

Romick, G. J.↗
NASA NTRS1992

Condensation phase of the Martian south polar cap

One type of database that can be useful in limiting models of the Mars surface-atmosphere system is the time dependent boundary of CO2 frost for the polar caps. Data acquired by the thermal infrared sensors on spacecraft are not limited by the lighting problems that hamper visual observations. The surface temperature of solid CO2 is limited by Clapeyron's equation as a function of the local partial pressure of CO2 gas. The growth was studied of the Martian south polar cap using the Viking IRTM dataset. These data are available in five bands, four of which should correspond to surface radiation in clear conditions; the 20 micron data was examined in the first phase.

Capuano, J.↗
NASA NTRS1972

Effects of interplanetary magnetic field azimuth on auroral zone and polar cap magnetic activity

During relatively quiet times in the period 1964-1968, AE is found to be greater when the interplanetary magnetic field (b sub IMF) is directed toward the sun in Jan., Feb., and Apr., and when B sub IMF is directed away from the sun in Oct. to Dec. Using Murmansk hourly H values and the AE components, AU and AL, it is shown that this sector dependence is present only in the negative H deviations. This observation supports the idea that negative bay magnitudes are determined chiefly by particle-produced ionization, while positive bay magnitudes are rather insensitive to increases in particle precipitation. The ratio of DP2-type magnetic activity in the southern polar cap to that in the northern polar cap is found to be greater by a factor of about 1.75 for B sub IMF toward the sun.

Burch, J. L.↗
NASA NTRS1992

High resolution spectroscopy of the Martian atmosphere - Study of seasonal variations of CO, O3, H2O, and T on the north polar cap and a search for SO2, H2O2, and H2CO

An overview is presented of an observational campaign which will measure (1) the seasonal variations of the CO mixing ratio on the Martian polar cap due to accumulation and depletion of CO during the condensation and evaporation of CO2, as well as (2) the early spring ozone and water vapor of the Martian north polar cap, and (3) the presence of H2CO, H2O2, and SO2. The lines of these compounds will be measured by a combined 4-m telescope and Fourier-transform spectrometer 27097.

Krasnopolsky, V. A.↗
NASA NTRS1985

A simple model for polar cap convection patterns and generation of theta auroras

An addition of the uniform interplanetary magnetic field and the earth's dipole magnetic field is used to evaluate electric field convection patterns over the polar caps that result from solar wind flow across open geomagnetic field lines. The model also accounts for field-aligned patterns within, and auroral arcs across, the polar cap. The qualitative predictions derived from the model express the electric field magnitudes, aurora intensity, sunward and antisunward flow, and the dusk-side reversal of the convection field in terms of the x and y components of the interplanetary magnetic field.

Lyons, L. R.↗
NASA NTRS1985

Escape of suprathermal O(+) ions in the polar cap

Instruments on board the Dynamics Explorer (DE) 1 and 2 spacecraft have been used to investigate the characteristics of a very low-energy (less than 10 eV) outflow of O(+) ions at high altitudes over the polar cap. The measured O(+) outflow has a relatively high Mach number (2-6) and a flux of about 2 x 10 to the 8th/(sq cm s). A statistical study using 50 orbits of retarding ion mass spectrometer data indicates that the outflows occur during active magnetic conditions, lasting for several hours over large areas of the polar cap. The observations are then discussed and analyzed in a framework based on polar wind models with particular attention paid to the new information obtained by the DE 2 Fabry-Perot interferometer, and the impact these flows have on the composition of the magnetosphere. The observed suprathermal outflow of O(+) suggests a scenario requiring both significant compositional changes in the high latitude thermosphere and significant heating of the ions and electrons in the topside ionoshpere.

Waite, J. H., Jr.↗
NASA NTRS1995

Gravity Waves Near 300 km Over the Polar Caps

Distinctive wave forms in the distributions of vertical velocity and temperature of both neutral particles and ions are frequently observed from Dynamics Explorer 2 at altitudes above 250 km over the polar caps. These are interpreted as being due to internal gravity waves propagating in the neutral atmosphere. The disturbances characterized by vertical velocity perturbations of the order of 100 m/s and horizontal wave lengths along the satellite path of about 500 km. They often extend across the entire polar cap. The associated temperature perturbations indicate that the horizontal phase progression is from the nightside to the dayside. Vertical displacements are inferred to be of the order of 10 km and the periods to be of the order of 10(exp 3) s. The waves must propagate in the neutral atmosphere, but they usually are most clearly recognizable in the observations of ion vertical velocity and ion temperature. By combining the neutral pressure calculated from the observed neutral concentration and temperature with the vertical component of the neutral velocity, an upward energy flux of the order of 0.04 erg/sq cm-s at 250 km has been calculated, which is about equal to the maximum total solar ultraviolet heat input above that altitude. Upward energy fluxes calculated from observations on orbital passes at altitudes from 250 to 560 km indicate relatively little attenuation with altitude.

Johnson, F. S.↗
NASA NTRS1998

35 GHz Measurements of CO2 Crystals for Simulating Observations of the Martian Polar Caps

In order to learn more about the Martian polar caps, it is important to compare and contrast the behavior of both frozen H2O and CO2 in different parts of the electromagnetic spectrum. Relatively little attention has been given, thus far, to observing the thermal microwave part of the spectrum. In this experiment, passive microwave radiation emanating from within a 33 cm snowpack was measured with a 35 GHz hand-held radiometer, and in addition to the natural snow measurements, the radiometer was used to measure the microwave emission and scattering from layers of manufactured CO2 (dry ice). A 1 m x 2 m plate of aluminum sheet metal was positioned beneath the natural snow so that microwave emissions from the underlying soil layers would be minimized. Compared to the natural snow crystals, results for the dry ice layers exhibit lower' microwave brightness temperatures for similar thicknesses, regardless of the incidence angle of the radiometer. For example, at 50 degree H (horizontal polarization) and with a covering of 21 cm of snow and 18 cm of dry ice, the brightness temperatures were 150 K and 76 K, respectively. When the snow depth was 33 cm, the brightness temperature was 144 K, and when the total thickness of the dry ice was 27 cm, the brightness temperature was 86 K. The lower brightness temperatures are due to a combination of the lower physical temperature and the larger crystal sizes of the commercial CO2 Crystals compared to the snow crystals. As the crystal size approaches the size of the microwave wavelength, it scatters microwave radiation more effectively, thus lowering the brightness temperature. The dry ice crystals in this experiment were about an order of magnitude larger than the snow crystals and three orders of magnitude larger than the CO2 Crystals produced in the cold stage of a scanning electron microscope. Spreading soil, approximately 2 mm in thickness, on the dry ice appeared to have no effect on the brightness temperatures.

Foster, J. L.↗
NASA NTRS1984

Thermospheric circulation, temperature, and compositional structure of the southern hemisphere polar cap during October-November 1981

Results of NCAR thermospheric general circulation model (TGCM) simulations were compared with Dynamics Explorer (DE2) data on the neutral wind, temperature and O and N2 number variations over the south polar cap in the F region in October-November 1981. Attention was focused on variations in the thermospheric characteristics. All variations reached a maximum over the magnetic polar cap, with the largest O and N2 changes being present in the dawn sector of the auroral oval, where Joule heating was maximized. The TGCM simulations for conditions similar to the DE2 passes agreed well with the satellite data, indicating that the variations in the wind, temperature and compositional characteristics are dependent on the magnitude of magnetospheric convection and influenced by the separation between the geomagnetic and geographic poles.

Roble, R. G.↗
NASA NTRS1982

Mars residual north polar cap - Earth-based spectroscopic confirmation of water ice as a major constituent and evidence for hydrated minerals

A description is presented of new earth-based reflectance spectra of the Martian north residual polar cap. The spectra indicate that the composition is at least mostly water ice plus another component with a 'gray' reflectance. The other minerals in the ice cap appear to be hydrated. The data were obtained with a cooled circular variable filter spectrometer on February 20, 1978, using the 2.2-m telescope on Mauna Kea, Hawaii. It is pointed out that the identification of water ice in the north polar cap alone does not indicate that water makes up all or even most of the bulk of the cap. Kieffer (1970) has shown that a small amount of water will mask the spectral features of CO2.

Clark, R. N.↗
NASA NTRS1983

Polar cap electron densities from DE 1 plasma wave observations

Electric-field-spectum measurements from the plasma-wave instrument on the Dynamics Explorer 1 spacecraft are used to study the local electron density at high altitudes in the northern polar-cap region. The electron density is determined from the upper cutoff of whistler-mode radiation at the electron plasma frequency. Median density values over the polar cap at L greater than 10 are found to vary from 35.2 + or - 8.5 cu cm at 2.1 earth radii to 0.99 + or - 0.51 cu cm at 4.66 earth radii. The steady-state radial-outflow model is examined for consistency with the observed density profile. A power-law fit to the radial variation of the electron density yields an exponent of - 3.85 + or - 0.32, which for the radial-outflow model implies a flow velocity increasing nearly linearly with incresing radial distance. Comparison of the observed electron densities with theoretical polar-wind densities yields consistent results up to 2.8 earth radii. A comparison of the observed electron densities with low-altitude density profiles from the Alouette II and ISIS 1 spacecraft illustrates transitions in the slope of the profile at 1.16 earth radii and between 1.55 and 2.0 earth radii. The changes in the density profile suggest that changes occur in the basic radial-transport processes at these altitudes.

Persoon, A. M.↗
NASA NTRS1993

Parameterized study of the ionospheric modification associated with sun-aligned polar cap arcs

The local ionospheric modification that is due to a generalized steady state solar aligned (SA) arc structure is addressed. For a representative set of SA arc parameters which includes both convection and precipitation, emphasis is placed on the modification by SA polar cap arcs upon the F region electron density and the height integrated conductivity. At low fluxes and low characteristic energies, SA polar cap arcs have the most pronounced relative effect at F region altitudes in darkness for winter solar minimum conditions. The absolute enhancement in summer solar minimum and winter solar maximum is equivalent to that of winter solar minimum, but the higher ambient densities make the relative enhancement less. The TEC enhancement associated with an SA arc may be used to indicate the degree of plasma cross flow across the arc.

Crain, D. J.↗