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Discussion of the amplitude of bulk velocities associated with upward-propagating Alfven waves in the lower solar atmosphere. It is shown that, for a given wave energy flux, the bulk velocities can be appreciably lower in cases when the wavelength is much larger than the scale height, than in situations where the wavelength is smaller than the scale height.
Spectral line profiles, curves of growth, and curves for the equivalent width of a line as a function of Venus phase angle are computed for a Rayleigh scattering cloud and compared with those for a cloud of isotropic scatterers. The results are similar for the two kinds of scattering, with the exception for the curves of equivalent width as a function of Venus phase angle. These latter curves exhibit the inverse phase effect and rule out the possibility that the scale height of the clouds can be much less than half the scale height of the gas.
A preliminary profile of the atmosphere of Jupiter in the South Equatorial Belt shows (1) the tropopause occurring at a pressure level of 100 millibars and temperature of about 113 K, (2) a higher warm inversion layer at about the 35-millibar level, and (3) a lower-altitude constant lapse rate matching the adiabatic value of about 2 K/km, with the temperature reaching 150 K at the 600-millibar level. Preliminary afternoon and predawn ionospheric profiles at 12 deg and near the equator, respectively, have topside plasma scale heights of 590 km changing to 960 km above an altitude of 3500 km for the dayside, and about 960 km at all measured heights above the peak for the nightside. The higher value of scale height corresponds to a plasma temperature of 1100 K under the assumption of a plasma of protons and electrons in ambipolar diffusive equilibrium. The peak electron concentration in the upper ionosphere is approximately 200,000/cu cm for the dayside and about a factor of 10 less for the nightside. These peaks occur at altitudes of 1600 and 2300 km, respectively. Continuing analyses are expected to extend and refine these results, and to be used to investigate other regions and phenomena.
The mass-loss process in S stars is studied using 65 S stars from the listing of Wing and Yorka (1977). The role of pulsations in the mass-loss process is examined. It is detected that stars with larger mass-loss rates have a greater amplitude of pulsations. The dust-to-gas ratio for the S stars is estimated as 0.002 and the average mass-loss rate is about 6 x 10 to the -8th solar masses/yr. Some of the properties of the S stars, such as scale height, surface density, and lifetime, are measured. It is determined that scale height is 200 pc; the total duration of the S star phase is greater than or equal to 30,000 yr; and the stars inject 3 x 10 to the -6th solar masses/sq kpc yr into the interstellar medium.
We compare the images of Jovian lightning taken by Galileo spacecraft with the images of terrestrial lightning observed by Lightning Imaging Spectrometer (LIS) onboard the TERRA spacecraft. Both data sets have good spatial resolution: Galileo's pixel is 25 km, or about half the atmospheric scale height, LIS pixel is 3-6 km, also about half of the scale height. This good resolution allows us to see that both Jovian and terrestrial lightning spots look diffuse because of the scattering in the clouds above. Previously we used the appearance of the diffuse spots on Jupiter to model lightning depths and the opacity and shape of the overlying clouds (Dyudina and Ingersoll, 2000). The comparison with LIS data allowed us to verify that the model is valid for terrestrial lightning. The irregular shapes of large terrestrial lightning suggests 30-km scale horizontal bolts. On Jupiter the spots, projected onto the horizontal plane, are nearly circular suggesting that the large size of the spots is mostly due to the horizontal diffusion of the photons scattered in the clouds. Unlike the Galileo observations, LIS has fine temporal resolution of 2 ms, or about 250 frames per single lightning flash. We will discuss the temporal evolution of terrestrial flashes and its implications for Jupiter.
To improve existing ice accretion simulation codes, more data regarding ice roughness and its effects on convective heat transfer are required. To build on existing research on this topic, this study used the Vertical Icing Studies Tunnel (VIST) at NASA Glenn Research to model realistic ice roughness in the stagnation region of a NACA 0012 airfoil. Using the VIST, a test plate representing the leading 2% chord of the airfoil was subjected to flows of 7.62 m/s (25 ft/s), 12.19 m/s (40 ft/s), and 16.76 m/s (55 ft/s). The test plate was fitted with 3 surfaces, each with a different representation of ice roughness: 1) a control surface with no ice roughness, 2) a surface with ice roughness with element height scaled by 10x and streamwise rough zone width from the stagnation point scaled by 10x, and 3) a surface with ice roughness with element height scaled by 10x and streamwise rough zone width from the stagnation point scaled by 25x. Temperature data from the tests were recorded using an infrared camera and thermocouples imbedded in the test plate. From the temperature data, a convective heat transfer coefficient map was created for each case. Additional testing was also performed to validate the VIST's flow quality. These tests included five-hole probe and hot-wire probe velocity traces to provide flow visualization and to study boundary layer formation on the various test surfaces. The knowledge gained during the experiments will help improve ice accretion codes by providing heat transfer coefficient validation data and by providing flow visualization data helping understand current and future experiments performed in the VIST.
Methods are disclosed that provide for structures and techniques for the fabrication of ordered arrangements of crystallographically determined nanometer scale steps on single crystal substrates, particularly Sic. The ordered nanometer scale step structures are produced on the top surfaces of mesas by a combination of growth and etching processes. These structures sometimes referred to herein as artifacts are to enable step-height calibration, particularly suitable for scanning probe microscopes and profilometers, from less than one nanometer (nm) to greater than 10 nm, with substantially no atomic scale roughness of the plateaus on either side of each step.
The unique solution of tidal wave propagation within the thermosphere depends on the boundary conditions of the model. It is shown that the radiation condition leads to such a unique solution. Any other boundary values give rise to deviations from the physical solution with unrealistic physical parameters in the environment of the boundaries. The thickness of these boundary layers with unrealistic solutions is a few scale heights below the upper boundary of the model and a few tens of scale heights above the lower boundary of the model.
The birthrate of galactic supernovae is estimated in three different ways. The three ranges overlap, and it is suggested that 70 + or - 35 yr represents a more realistic estimate of the rate than some that have previously been made. The galactic supernova remnants and their observed systematic brightness gradients perpendicular to the galactic plane imply a scale height of about 200 pc for the remnant progenitors and a galactic magnetic field scale height of about 300 pc. Long standing anomalies associated with the young remnant AD 1006, the galactic loops, and faint remnants, are accounted for by the brightness gradient effect. This provides firm, independent evidence for the validity of the remnant method of deducing the birthrate of galactic supernovae.
The latest results from an investigation to establish links between solar-wind and topside-ionospheric parameters will be presented including a case where high-latitude topside electron-density Ne(h) profiles indicated dramatic rapid changes in the scale height during the main phase of a large magnetic storm (Dst < -200 nT). These scale-height changes suggest a large heat input to the topside ionosphere at this time. The topside profiles were derived from ISIS-1 digital ionograms obtained from the NASA Space Physics Data Facility (SPDF) Coordinated Data Analysis Web (CDA Web). Solar-wind data obtained from the NASA OMNIWeb database indicated that the magnetic storm was due to a magnetic cloud. This event is one of several large magnetic storms being investigated during the interval from 1965 to 1984 when both solar-wind and digital topside ionograms, from either Alouette-2, ISIS-1, or ISIS-2, are potentially available.
Turbulence is known to possess structure on many scales. The largest or integral scale L is usually taken to be the largest relevant dimension of the system; for the nebula as a whole, it would be on the order of a vertical gas scale height H approximately 0.1R where R is the distance from the sun. Turbulent kinetic energy cascades towards smaller scales; for fully developed, homogeneous turbulence, the turbulent kinetic energy peaks at the integral scale and is distributed within its "inertial range" according to the Kolmogorov energy spectrum dE(k) = E(sub 0)(kL)(sup -5/3)dk where k is the wavenumber or inverse wavelength. The smallest scale in a turbulent regime is the Kolmogorov scale (n)(sometimes referred to as the inner scale). On this scale, molecular viscosity can dissipate turbulent kinetic energy . Turbulent flows are characterized by their Reynolds number Re = UL/v, where U is a characteristic velocity scale and v is molecular viscosity. More energetic (higher Re) flows drive turbulence to smaller Kolmogorov scales: n = LRe(sup -3/4). Two different turbulent regimes are likely to be of importance; early stage convective turbulence in a hot nebula probably extends over the entire nebula scale height, and probably has typical eddy frequency comparable to the orbit frequency. At a later stage, midplane shear layer turbulence can be driven by the presence of a differentially rotating, densely settled particle layer, with different length and time scales.
A large refined data sample is used to study the properties and origin of the disk system of globular clusters. A scale height for the disk cluster system of 800-1500 pc is found which is consistent with scale-height determinations for samples of field stars identified with the Galactic thick disk. A rotational velocity of 193 + or - 29 km/s and a line-of-sight velocity dispersion of 59 + or - 14 km/s have been found for the metal-rich clusters.
One of Titan's many characteristics is the presence of a haze that veils its surface. This haze is composed of heavy organic particles and determining the chemical composition of these particles is a primary objective for future probes that would conduct in situ analysis. Meanwhile, solar occultations provide constraints on the optical characteristics of the haze layer. This paper describes solar occultation observations obtained by the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft. These observations strongly constrain the optical characteristics of the haze layer. We detail the different steps involved in the processing of these data and apply them to two occultations that were observed at the South Pole and at the equator in order to investigate the latitudinal dependence of optical properties. The light curves obtained in seven atmospheric windows between 0.933-microns to 5-microns allow us to characterize atmospheric layers from 300 km to the surface. Very good fits of the light curves are obtained using a simple profile of number density of aerosols that is characterized by a scale height. The main difference between the South Pole and the equator is that the value of the scale height increases with altitude at the South Pole whereas it decreases at the equator. The vertically integrated amount of aerosols is similar at the two locations. The curve describing the cross-section versus wavelength is identical at the two locations suggesting that the aerosols have similar characteristics. Finally, we find that the two-way vertical transmission at 5-microns is as large as 80% at both locations.
Independent Bennett radio-frequency ion mass spectrometers on the Pioneer Venus bus and orbiter spacecraft obtained in situ measurements of the composition of the ionosphere of Venus. The spectrometer on the bus explored the dawn region while the spectrometer on the orbiter explored the duskside region. Information on the ion composition in the topside, the lower ionosphere, and the upper ionosphere is presented. Below the O(+) peak near 200 km, the ions are found to exhibit scale heights consistent with a neutral gas temperature of about 180 K near the terminator. In the upper ionosphere, scale heights of all species reflect the effects of plasma transport.
A 2.4-micron map of the northern Galactic plan is used to determine the 3D luminosity distribution of the Milky Way. The radial surface brightness profile of the disk is found to have an exponential scale length of 3.0 kpc. In the solar neighborhood, the scale height is about 247 pc, which is in agreement with star counts perpendicular to the Galactic plane. The scale height is not constant with the radius but decreases to about 165 pc. To the first order, the bulge can be represented by an oblate spheroid with an axis ratio of 0.61. The 2.2-micron/12-micron flux ratio for the bulge is typical of other dust-free spheroidal systems. Luminosity fluctuations along the Galactic plane are found to be caused chiefly by variations in the line-of-sight extinction.
Near-infrared spectra taken in a limb-viewing geometry by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on-board the Mars Reconnaissance Orbiter (MRO) provide a useful tool for probing atmospheric structure. Specifically, the observed radiance as a function of wavelength and height above the limb allows the vertical distribution of both dust and ice aerosols to be retrieved. These data serve as an important supplement to the aerosol profiling provided by the MRO/MCS instrument allowing independent validation and giving additional information on particle physical and scattering properties through multi-wavelength studies. A total of at least ten CRISM limb observations have been taken so far covering a full Martian year. Each set of limb observations nominally contains about four dozen scans across the limb giving pole-to-pole coverage for two orbits at roughly 100 and 290 W longitude over the Tharsis and Syrtis/Hellas regions, respectively. At each longitude, limb scans are spaced roughly 10 degrees apart in latitude, with a vertical spatial resolution on the limb of roughly 800 m. Radiative transfer modeling is used to model the observations. We compute synthetic CRISM limb spectra using a discrete-ordinates radiative transfer code that accounts for multiple scattering from aerosols and accounts for spherical geometry of the limb observations by integrating the source functions along curved paths in that coordinate system. Retrieved are 14-point vertical profiles for dust and water ice aerosols with resolution of 0.4 scale heights between one and six scale heights above the surface. After the aerosol retrieval is completed, the abundances of C02 (or surface pressure) and H20 gas are retrieved by matching the depth of absorption bands at 2000 nm for carbon dioxide and at 2600 run for water vapor. In addition to the column abundance of water vapor, limited information on its vertical structure can also be retrieved depending on the signal available from aerosol scattering.
On the dayside of Venus, the hot oxygen corona extending above the ionopause is the principal source of pickup oxygen ions. The ions are born here and picked up by the ionosheath plasma as it is deflected around the planet. These pickup ions have been observed by the Orbiter Plasma Analyzer (OPA) throughout the Pioneer Venus Orbiter (PVO) mission. They were observed over a region extending from their dayside source to great distances downstream (about 10 Venus radii), in the solar wind wake, as PVO passed through apoapsis. Finite gyroradius effects in the velocity distribution of the oxygen pickup ions are expected in the source region because the gyroradius is several times larger than the scale height of the hot oxygen source. Such effects are also expected in those regions of the ionosheath where the scale lengths of the magnetic field and the ambient plasma velocity field are less than the pickup ion gyroradius. While explicitly accounting for the spatial distribution of the hot oxygen source, an analytic expression for the pickup oxygen ion velocity distribution is developed to study how it is affected by finite gyroradii. The analysis demonstrates that as the gyroradius increases by factors of three to six above the hot oxygen scale height, the peak of the pickup oxygen ion flux distribution decreases 25 to 50% below the maximum allowed speed, which is twice the speed of the ambient plasma times the sine of the angle between the magnetic field and the flow velocity. The pickup oxygen ion flux distribution observed by OPA is shown to follow this behavior in the source region. It is also shown that this result is consistent with the pickup ion distributions observed in the wake, downstream of the source, where the flux peaks are usually well below the maximum allowed speed.
Thermodynamic arguments demonstrate that kinetic energy dissipation must occur in the convection zone. The dissipation rate depends on the temperature gradient, which is at a minimum in the hydrogen ionization zone. As a result, the kinetic energy dissipation rate per density scale height shows a maximum just below the photosphere and another maximum beneath the ionization zone. It is proposed that intensified convection at these two levels is the explanation for the two distinct phenomena of granulation and supergranulation. The values of the scale heights at these maxima are consistent with the length scales of the granulation and the supergranulation. A moderate amount of a radial diffusion of kinetic energy does not alter this result.