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Ground-based observations of Jupiter show that the planet's stratospheric and tropospheric thermal emission are anticorrelated. The observations can possibly be explained by latitudinal variations in cloud altitude. These variations cause differential stratospheric heating by sunlight which is reflected off the clouds and then absorbed within the stratosphere by visible and near-infrared bands of methane.
Magnetotransport measurements of Pr4Ni3O10 single crystals performed under externally applied pressures up to 73 GPa in diamond anvil cells with either KBr or Nujol oil as pressure media yield signatures of superconductivity with a maximum onset temperature of approximately 31 K. True zero resistance was not observed, consistent with a nonpercolating superconducting volume fraction. Magnetization measurements provided corroborating evidence of superconductivity, with a pressure-dependent diamagnetic signal occurring below the onset temperature, and an estimate from the absolute value of the susceptibility suggests a superconducting volume fraction on the order of 10%. We observe sample to sample variations in the magnitude and pressure dependence of 𝑇𝑐 as well as a dependence on the configuration of electrical contacts on a given sample. Possible causes of this behavior may be significant inhomogeneities in the pressure and/or damage to the samples induced by the pressure media as well as inhomogeneities in the crystals themselves. The results imply that our as-grown Pr4Ni3O10 single crystals are not bulk superconductors but that there is a minority structure present within the crystals that is indeed superconductin
Subsecond variations of hard X-ray emission from solar flares were first observed with a balloon-borne detector. With the launch of the Solar Maximum Mission (SMM), it is now well known that subsecond variations of hard X-ray emission occur quite frequently. Such rapid variations give constraints on the modeling of electron energization. Such rapid variations reported until now, however, were observed at relatively low energies. Fast mode data obtained by the Hard X-ray Burst Spectrometer (HXRBS) has time resolution of approximately 1 ms but has no energy resolution. Therefore, rapid fluctuations observed in the fast-mode HXRBS data are dominated by the low energy hard X-rays. It is of interest to know whether rapid fluctuations are observed in high-energy X-rays. The highest energy band at which subsecond variations were observed is 223 to 1057 keV. Subsecond variations observed with HXRBS at energies greater than 300 keV are reported, and the implications discussed.
Photoelectric filter photometry and spectrophotometry undertaken to establish homogeneous, quantitative data on chemical abundances in comets is discussed. Absolute column densities of a particular species were derived from a comparison of the absolute flux of an emission feature due to the species with a fluorescence calculation, and converted into species production rates by the use of a Haser model and the species lifetime. Observations of C2 and CN reveal a constant production rate ratio at heliocentric distances up to 1.5-2.0 AU, which implies a compositional homogeneity with depth and the formation of most comets from a homogeneous volume in the solar nebula. Observations of the trace species C3 indicate no apparent variation in relative abundances, while observations of low levels of NH2 and CH imply that NH3 and CH4 are not abundant species. H2O is considered to be the most abundant species based on detections of O, H and OH, while variations in CO or CO2 content may account for the very large differences in cometary gas-to-dust ratios and morphologies.
The Thermal InfraRed Sensor (TIRS) on the Perseverance rover has provided nearly two full Mars years of systematic monitoring of the total aerosol optical depth above Jezero Crater. These observations span a wide range of timescales, capturing seasonal patterns, diurnal variations, and minute-to-minute fluctuations in aerosol loading. By combining TIRS retrievals with orbital observations, the relative contributions of dust and water ice aerosols can be estimated, revealing their different seasonal and diurnal behaviors. The TIRS record shows distinct periods of dust storm activity, including strong regional storms during the perihelion season as well as short lived but intense dust events outside the typical dust storm season. Water ice clouds exhibit pronounced seasonal and diurnal variability, with peak activity occurring during the aphelion season but with a presence throughout the year. The diurnal variation of clouds differs significantly between the aphelion and perihelion seasons, with clouds persisting throughout the night during the aphelion season, while largely absent outside of specific periods after sunrise and sunset during the perihelion season. These results provide new insights into the complex behavior of aerosols at Jezero Crater and their connections to atmospheric dynamics and the Martian dust and water cycles.
This paper describes approaches to measuring small- and medium-scale spatial rate of vertical TEC from GNSS observations. The horizontal scale size measured by small-scale TEC spatial rate (STSR, in TECU/km), including its latitude and longitude components, ranges from about 1.8 km to 15 km at 450 km altitude. The medium-scale TEC gradient components can be derived from global ionospheric map (GIM) based TEC gradient (GBTG) over about 110 km horizontally at low and middle latitudes, with smaller scale lengths in the longitude component in the polar region. Our analyses of GPS data show that the latitude component of STSR and GBTG is much larger than the longitude component. The spatial rates in most regions of the globe are relatively small, and their absolute mean values are mostly under 0.03 TECU/km. However, STSR is substantially larger, often greater than 0.05 TECU/km, in the equatorial ionospheric anomaly (EIA) region than in other regions, or when ionospheric disturbances occur. The disturbances include ionospheric irregularities, significant changes of regional ionospheric state during space weather events, and traveling ionospheric disturbances. Combined global TEC gradient (CGTG) with STSR and GBTG is also shown in this paper as snapshots using data from networks of more than three thousand GNSS receivers. The comparisons between STSR and GBTG indicate that their regional variation patterns are consistent though STSR is often larger than GBTG in the equatorial anomaly region or during ionospheric disturbances particularly during space weather events. The difference is attributed to the fact that the global TEC mapping technique may smooth the gradient in regions where spatial variations are large at small- and medium scales.
Abstract This paper reviews current observations regarding processing conditions for oxide dispersion-strengthened steels consolidated through additive manufacturing techniques. Variations in ODS steels observed across process parameters include changes in grain size, grain texture, oxide size, density of oxides, porosity, melt pool characteristics, and mechanical properties. These properties were then compared across techniques to understand which techniques and processing conditions lead to the highest strength, ductility, and oxide density. Current literature suggests that a mix of grain types, in the form of either morphology or phase, can significantly increase the strength of printed ODS steels. Meanwhile, the most ductile samples, regardless of consolidation technique or matrix material, were made from feedstock with oxide additions located on the powder surface. Reported grain and oxide sizes were plotted against the ratio of laser power to scan speed, volumetric energy density, and normalized enthalpy. No strong correlation between these values and microstructural features was observed. The plots that were made suggest that a larger data set, more in-depth representative equations, and more defined material properties as a function of specific feedstock used are necessary to determine a value that can be correlated to the printed ODS steel microstructure.
As moderately volatile elements, isotopes of Rb and K can trace volatilization processes in planetary bodies. Rubidium isotopic data are however very scarce, especially for non-carbonaceous meteorites. Here, in this study, we report combined Rb and K isotopic data (δ 87/85 Rb and δ 41/39 Κ) for 7 ordinary, 6 enstatite, and 4 Martian meteorite falls to understand the causes for the variations in volatile abundances and isotopic compositions. Bulk Rb and K isotopic compositions of planetary bodies are estimated to be (Table 1): Mars +0.10 ± 0.03 ‰ for Rb and -0.26 ± 0.05 ‰ for K, bulk OCs $-0.12^{+0.15}_{-0.24}$ ‰ for Rb and $-0.72^{+0.28}_{-0.41}$ ‰ for K, bulk ECs $-0.02^{+0.29}_{-0.26}$ ‰ for Rb and $-0.33^{+0.37}_{-0.23}$ ‰ for K. The bulk K isotopic compositions of subgroup OCs are estimated to be $-0.72^{+0.26}_{-0.55}$ ‰ for H chondrites, $-0.71^{+0.23}_{-0.39}$ ‰ for L chondrites, and $-0.77^{+0.63}_{-0.30}$ ‰ for LL chondrites. A broad correlation between the Rb and K isotopic compositions of planetary bodies is observed. The correlation follows a slope that is consistent with kinetic evaporation and condensation processes, suggesting volatility-controlled mass-dependent isotope fractionation (as opposed to nucleosynthetic anomalies). Individual ordinary and enstatite chondrites show large Rb and K isotopic variations (-1.02 to +0.29 ‰ for Rb and -0.91 to -0.15 ‰ for K). Samples of lower metamorphic grades display correlated elemental and isotopic fractionations between Rb and K, while samples of higher metamorphic grades show great scatter, suggesting that chondrite parent-body processes have decoupled the two elements and their isotopes at the sample scale. Several processes could have contributed to the observed isotopic variations of Rb and K, including (i) chondrule “nugget effect”, (ii) volatilization during parent-body thermal metamorphism (heat-induced vaporization and gas transport within parent bodies), (iii) thermal diffusion during parent-body metamorphism, and (iv) impact/shock heating. Quantitative modeling of the first two processes suggests that neither of them could produce isotopic variations large enough to explain the observed isotopic variations. Volatilization during parent-body thermal metamorphism [the scenario (ii)], which has been commonly invoked to explain the isotopic variations of volatile elements, is gas transport-limited and its effect on isotopic fractionations of moderately volatile elements should be negligible. Modeling of diffusion processes suggests that (iii) could produce K isotopic variation comparable to the observed variation. The large isotopic variations in non-carbonaceous meteorites are thus most likely due to diffusive redistribution of K and Rb during metamorphism and/or shock-induced heating and vaporization.
Variation in crystal size and physical temperature of snowfield observations from space give large variations in the microwave brightness temperature. Since the brightness temperature is a function of wavelength, the microwave brightness temperature can be used to extract the snow temperature and mean crystal radius profiles. The Scanning Multichannel Microwave Radiometer (SMMR), to be launched on board the Nimbus-G and Seasat-A spacecraft, will make observations in wavelengths of 0.8, 1.4, 1.7, 2.8, and 4.6 cm. A statistical retrieval method was developed to determine the snowfield temperature profile and mean crystal size by using the scanning multifrequency microwave radiometer on board a spacecraft. The estimated errors for retrieval are approximately 1.5 K for temperature and 0.001 for crystal radius in the presence of 1 K rms noise for each SMMR channel.
The additional cooling mechanism responsible for the unexpectedly cold dayside Venus thermosphere is isolated. Consideration is given not only to the condition that the calculated temperatures must be reduced to the observed dayside temperatures but also that the theoretical temperature variations must be in accord with the observed low amplitude of temperature variations associated with the 27-d variations of the sun. It is found that the low amplitude of the 27-d oscillations, combined with the cooling necessary for observed 300-K dayside temperatures, cannot be explained by eddy conduction cooling and can only be explained by very strong 15-micron cooling. Implications of the decrease in amplitude of the 11-yr Venus thermospheric variability due to the 15-micron thermostat effect are examined.
An analysis of long baseline NIMBUS 7 SBUV (Solar Backscatter UV Spectrometer) observations of the latitudinal variation of the noontime vertical Mg' content above approx. 70 km have revealed seasonal, solar activity and magnetic activity dependencies in the Mg+ content. The distributions were categorized in terms of magnetic coordinates partially because transport processes lifting metallic ions from the main meteor ionization layer below 100 km up into the F- region and down again are controlled by electrodynamical processes. Alternatively, the Nimbus Mg+ distributions may simply be a result of ion/neutral chemistry changes resulting from atmospheric changes and not dynamics. In such a case magnetic control would not dominate the distributions. Using in situ satellite measurements of metal ions from the Atmosphere Explorer satellites in the region above the main meteor layer and published sounding rocket measurements of the main metallic ion layers, the effects of the dynamics on the vertical content are delineated. The consequences of atmospheric changes on the vertical content are explored by separating the Nimbus measurements in a geodetic frame of reference.
In this fourth paper in a series, we present a model of the remarkable temporal and azimuthal variability of the Io plasma torus observed during the Cassini encounter with Jupiter. Over a period of three months, the Cassini Ultraviolet Imaging Spectrograph (UVIS) observed a dramatic variaton in the average torus composition. Superimposed on this long-term variation, is a 10.07-hour periodicity caused by azimuthal variation in plasma composition subcorotating relative to System III longitude. Quite surprisingly, the amplitude of the azimuthal variation appears to be modulated at the beat frequency between the System III period and the observed 10.07-hour period. Previously, we have successfully modeled the months-long compositional change by supposing a factor of three increase in the amount of material supplied to Io's extended neutral clouds. Here, we extend our torus chemistry model to include an azimuthal dimension. We postulate the existence of two azimuthal variations in the number of superthermal electrons in the torus: a primary variation that subcorotates with a period of 10.07 hours and a secondary variation that remains fixed in System III longitude. Using these two hot electron variations, our model can reproduce the observed temporal and azimuthal variations observed by Cassini UVIS.
Using energetic-particle data taken in the near-earth tail by the AMPTE/Charge Composition Explorer (CCE) satellite, 167 ion injection events, that were essentially dispersionless over a 25-285 keV energy range, were identified, and the variations in the total magnetic field strength over the course of these events were examined in order to determine the dependence of the magnetic field strength on dipole latitude. Results indicate that, during periods of substorm activity, the latitudinal position of the current sheet varied significantly within the 32-deg wedge centered on the dipole equator traversed by CCE. Results also suggest that, even in the near-earth magnetotail out to 8.8 R(E) (CCE apogee), the local field measurements are a better guide to the determination of satellite's position relative to the current shield during a substorm, than is the magnetic latitude.
We report a wide-ranging study of Titan's surface temperatures by analysis of the Moon's outgoing radiance through a spectral window in the thermal infrared at 19 mm (530/cm) characterized by lower atmospheric opacity. We begin by modeling Cassini Composite Infrared Spectrometer (CIRS) far infrared spectra collected in the period 2004-2010, using a radiative transfer forward model combined with a non-linear optimal estimation inversion method. At low-latitudes, we agree with the HASI near-surface temperature of about 94 K at 101S (Fulchignoni et al., 2005). We find a systematic decrease from the equator toward the poles, hemispherically asymmetric, of approx. 1 K at 60 deg. south and approx. 3 K at 60 deg. north, in general agreement with a previous analysis of CIRS data and with Voyager results from the previous northern winter. Subdividing the available database, corresponding to about one Titan season, into 3 consecutive periods, small seasonal changes of up to 2 K at 60 deg N became noticeable in the results. In addition, clear evidence of diurnal variations of the surface temperatures near the equator are observed for the first time: we find a trend of slowly increasing temperature from the morning to the early afternoon and a faster decrease during the night. The diurnal change is approx. 1.5 K, in agreement with model predictions for a surface with a thermal inertia between 300 and 600 J/ sq. m s (exp -1/2) / K. These results provide important constraints on coupled surface-atmosphere models of Titan's meteorology and atmospheric dynamic.
Transient ULF pulsations associated with variations in solar wind plasma density observed by the IMP 8 satellite are presently studied in light of observations obtained during a fortuitous alignment of the AMPTE and Viking satellites with respect to the EISCAT Magnetometer Cross. It is found that the isolated 10-min oscillation in solar wind plasma density produced magnetic field compression oscillations within the magnetosphere at the same frequency, thereby enhancing resonant oscillations at approximately twice the frequency which were already present. Support is seen for the periodic solar wind density variation's exciting of a tailward-traveling large-scale magnetosphere wave train which excites local field line resonant oscillations.
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The mean monthly hemispheric total ozone values as determined from between the two sets of data indicates that the mean difference between the calculated total ozone amount as determined for the entire period from all the satellite data and that derived from the satellite data restricted to location of ground based stations is 1.3 m atm cm for the Northern Hemisphere and 0.7 m atm cm for the Southern Hemisphere (0.3 and 0.2 percent respectively of the average total ozone in each hemisphere).
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