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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Modifying magnetic properties of MnBi with carbon: an experimental and theoretical study

MnBi and MnBi-based materials have been investigated as prospective rare-earth-free permanent magnets with moderate energy product. One of the main issues with MnBi synthesis is the presence of residual Bi in the sample which reduces the net magnetization. Here, we have found that MnBi synthesized in the presence of carbon substantially reduces the amount of residual Bi, improving its saturation magnetization. We have synthesized Mn 55 Bi 45 and Mn 55 Bi 45 C x samples using arc melting and high-vacuum annealing. The room temperature x-ray diffraction patterns indicate that both Mn 55 Bi 45 and Mn 55 Bi 45 C x crystallize in the hexagonal NiAs-type structure. The Rietveld analysis of the x-ray patterns shows that the amount of residual Bi reduces from 16 wt.% for Mn 55 Bi 45 to 5 wt.% for Mn 55 Bi 45 C x . The high-field (3 T) magnetizations measured at room temperature are 61 emu g –1 and 66 emu g –1 for Mn 55 Bi 45 and Mn 55 Bi 45 C x , respectively. To understand the role of C in enhancing the magnetization of MnBi, we carried out the first-principles calculations of both stoichiometric and nonstoichiometric MnBi alloys, which suggests that the increase of magnetization in Mn 55 Bi 45 C x may be due to the coating of MnBi grains with C.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Facile diamond synthesis from lower diamondoids

Carbon-based nanomaterials have exceptional properties that make them attractive for a variety of technological applications. Here, we report on the use of diamondoids (diamond-like, saturated hydrocarbons) as promising precursors for laser-induced high-pressure, high-temperature diamond synthesis. The lowest pressure and temperature $(P-T)$ conditions that yielded diamond were 12 GPa (at ~2000 K) and 900 K (at ~20 GPa), respectively. This represents a substantially reduced transformation barrier compared with diamond synthesis from conventional (hydro)carbon allotropes, owing to the similarities in the structure and full sp 3 hybridization of diamondoids and bulk diamond. At 20 GPa, diamondoid-to-diamond conversion occurs rapidly within <19 μs. Molecular dynamics simulations indicate that once dehydrogenated, the remaining diamondoid carbon cages reconstruct themselves into diamond-like structures at high $P-T$. This study is the first successful mapping of the $P-T$ conditions and onset timing of the diamondoid-to-diamond conversion and elucidates the physical and chemical factors that facilitate diamond synthesis.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Star-spots and magnetism: testing the activity paradigm in the Pleiades and M67

We measure star-spot filling fractions for 240 stars in the Pleiades and M67 open star clusters using APOGEE high-resolution H-band spectra. For this work, we developed a modified spectroscopic pipeline which solves for star-spot filling fraction and star-spot temperature contrast. We exclude binary stars, finding that the large majority of binaries in these clusters (80 per cent) can be identified from Gaia DR3 and APOGEE criteria – important for field star applications. Our data agree well with independent activity proxies, indicating that this technique recovers real star-spot signals. In the Pleiades, filling fractions saturate at a mean level of 0.248 ± 0.005 for active stars with a decline at slower rotation; we present fitting functions as a function of Rossby number. In M67, we recover low mean filling fractions of 0.030 ± 0.008 and 0.003 ± 0.002 for main sequence GK stars and evolved red giants, respectively, confirming that the technique does not produce spurious spot signals in inactive stars. Star-spots also modify the derived spectroscopic effective temperatures and convective overturn time-scales. Effective temperatures for active stars are offset from inactive ones by −109 ± 11 K, in agreement with the Pecaut & Mamajek empirical scale. Star-spot filling fractions at the level measured in active stars changes their inferred overturn time-scale, which biases the derived threshold for saturation. Finally, we identify a population of stars statistically discrepant from mean activity–Rossby relations and present evidence that these are genuine departures from a Rossby scaling. Our technique is applicable to the full APOGEE catalogue, with broad applications to stellar, galactic, and exoplanetary astrophysics.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Environmental monitoring data from the 2022-2023 field experiment at Game Ridge, Missoula County, Montana, USA

This dataset contains sensor data from programmed loggers as well as handheld moisture probes, including weather data, air and soil temperature, and soil volumetric water content. Data files and data dictionary(ies) are uploaded as .csv files. The Users Guide is a .pdf file. Location data can be found in the Google Earth file GameRidge_SitePlotCoordinates.kmz.kml included here. These datasets were collected for Plant Carbohydrate Depletion, Mycorrhizal Networks, and Vulnerability to Drought: An Experimental Test in the Field. This experiment examined the interdependency between plant hydraulics and carbohydrate availability and sought to develop ways to incorporate interactions with below ground symbiotic organisms to better model and quantify forest response to drought. This environmental data was collected to provide context for the fungal community data and Pinus ponderosa physiological data.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Structural and magnetic properties of Pt/Co/Mn-based multilayers

Magnetic multilayers are a rich class of material systems with numerous highly tunable physical parameters that determine both their magnetic and electronic properties. Here, we present a comprehensive experimental study of the system Pt/Co/Mn, which extends the group of Pt / Co / X ( X = metal) multilayers that have been investigated thus far. We demonstrate that an increasing Co layer thickness changes the magnetic anisotropy from out of plane to in plane, whereas the deposition of thicker Mn layers leads to a decrease in the saturation magnetization. Temperature-dependent magnetometry measurements reinforce the hypothesis of antiferromagnetic coupling at the Co/Mn interfaces being responsible for the observed Mn thickness dependence of the magnetization reversal. Moreover, magneto-optical imaging experiments indicate systematic changes in magnetic domain patterns as a function of the Co and Mn layer thickness, suggesting the existence of bubblelike domains—potentially even magnetic skyrmions—in the case of sufficiently thick Mn layers, which are expected to contribute to a sizable Dzyaloshinskii-Moriya interaction in the multilayer stacks. As a result, we identify Pt/Co/Mn as a highly complex multilayer system with strong potential for further fundamental studies and possible applications.

36 MATERIALS SCIENCE↗
DOE OSTI2023

How does humidity data impact land surface modeling of hydrothermal regimes at a permafrost site in Utqia$\mathrm{\dot{g}}$vik, Alaska?

Humidity is a basic and crucial meteorological indicator commonly measured in several forms, including specific humidity, relative humidity, and absolute humidity. These different forms can be inter-derived based on the saturation vapor pressure (SVP). In past decades, dozens of formulae have been developed to calculate the SVP with respect to, and in equilibrium with, liquid water and solid ice surfaces, but many prior studies use a single function for all temperature ranges, without considering the distinction between over the liquid water and ice surfaces. These different approaches can result in humidity estimates that may impact our understanding of surface-subsurface thermal-hydrological dynamics in cold regions. In this study, we compared the relative humidity (RH) downloaded and calculated from four data sources in Alaska based on five commonly used SVP formulas. These RHs, along with other meteorological indicators, were then used to drive physics-rich land surface models at a permafrost-affected site. Here, we found that higher values of RH (up to 40%) were obtained if the SVP was calculated with the over-ice formulation when air temperatures were below freezing, which could lead to a 30% maximum difference in snow depths. The choice of whether to separately calculate the SVP over an ice surface in winter also produced a significant range (up to 0.2 m) in simulated annual maximum thaw depths. The sensitivity of seasonal thaw depth to the formulation of SVP increases with the rainfall rate and the height of above-ground ponded water, while it diminishes with warmer air temperatures. These results show that RH variations based on the calculation of SVP with or without over-ice calculation meaningfully impact physically-based predictions of snow depth, sublimation, soil temperature, and active layer thickness. Under particular conditions, when severe flooding (inundation) and cool air temperatures are present, care should be taken to evaluate how humidity data is estimated for land surface and earth system modeling.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Evaluation of Engineered Form MOFs CaSDB and HKUST-1

Idaho National Laboratory (INL) and Pacific Northwest National Laboratory (PNNL) have studied different sorbents for the purpose of separating krypton (Kr) and xenon (Xe). PNNL has researched various metal-organic frameworks (MOFs) that have characteristics theoretically suitable for the separation. Based on computational analysis, PNNL chose Calcium–4,4’–sulfonyl dibenzoate (CaSDB) and Hong Kong University of Science and Technology MOF1 (HKUST–1). The raw MOFs are supplied in a powder form and must be incorporated into a robust engineered form to be viable for gas separation. In 2016, PNNL produced an engineered form of CaSDB by compressing and grinding the raw MOF material. This form was sent to INL for adsorption testing. Gentle mechanical agitation of the compressed form produced a large amount of powder, resulting in the conclusion that the form was not viable for the application. In 2019, INL successfully produced two engineered forms, CaSDB–EF1 and HKUST–EF2, by incorporating the active MOF powders into a polyacrylonitrile (PAN) binder. PNNL also produced two engineered forms, CaSDB–10pmma and HKUST–10pmma, by using polymethyl methacrylate (PMMA) as a binder. Surface area analysis indicated that the forms could be viable for separations in which the CaSDB–EF1 retained 84% of the raw CaSDB surface area and CaSDB–10pmma retained 48%. HKUST–EF2 retained all the raw HKUST–1 surface area, whereas HKUST–10pmma retained only 28%. Mechanical stability testing demonstrated that the PMMA forms formed a fine powder whereas, the PAN forms did not. In general, adsorption testing showed that CaSDB–10pmma had a lower Xe breakthrough capacity than CaSDB–EF1, but a higher saturation capacity at both room temperature and at 253 K. The CaSDB MOF was intended to be used as a room temperature sorbent to capture Xe. However, both CaSDB engineered forms displayed relatively short initial break through times. Reduced temperature increased the Xe capacity of both engineered forms. HKUST–1 was expected to be effective only at sub-zero temperatures. At 195 K, HKUST–10pmma had an initial Xe breakthrough capacity of 119 mmol/ kg, compared to HKUST–EF2 at 339 mmol/ kg. The saturation capacities were 275 and 383 mmol/ kg, respectively. HKUST–10ppm also had a lower Kr capacity of 1.7 mmol/kg, whereas the HKUST–EF had a Kr capacity of 3 mmol/ kg. Test results indicate that the PAN engineered forms are a more suitable choice for the complete separation of Xe and Kr, due to the increase in initial breakthrough capacity. CaSDB allows rapid breakthrough of Kr and Xe regardless of the type of engineered form. At 253 K, it is more viable, but is still not the most effective sorbent. HKUST–EF2 demonstrated viability for Xe capture at 195 K, which may merit further study, however it may be cost prohibitive.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

Disruption of acyl-acyl carrier protein (acyl-ACP) synthetase in cyanobacteria impairs lipid remodeling as revealed by acyl-ACP measurements

Free fatty acid (FFA) production in bacteria is a key target for metabolic engineering. The knockout of the acyl-ACP synthetase (AAS) prevents reincorporation of FFA into the fatty acid biosynthetic cycle and is widely used to enhance their secretion. However, the role of AAS in membrane lipid remodeling under environmental stress, such as altered temperature, remains poorly understood. In cyanobacteria, temperature shifts are known to affect fatty acid desaturation and membrane fluidity, yet it is unclear whether AAS contributes to these adaptive responses through re-esterification of membrane-released acyl chains. We elucidated unique aspects of fatty acid metabolism in response to temperature changes in biotechnologically relevant microbes with the development of an efficient method for quantifying acyl-ACP intermediates using anion exchange chromatography (AEX). In Escherichia coli, which performs desaturation during fatty acid biosynthesis, we detected saturated and unsaturated acyl-ACPs that confirm biosynthetic pathway operation. In the cyanobacteria, Picosynechococcus sp. PCC 7002 and the Δaas strain, changes between two temperatures were interpreted with support from proteomic and lipidomic analyses and indicated that the AAS is tied to membrane lipid remodeling. Further, polyunsaturated acyl-ACPs were detected in the Δaas strain, which was unexpected because fatty acid synthesis does not produce polyunsaturates in cyanobacteria, suggesting the presence of alternative acyl-activating enzymes or unknown acyl-ACP desaturases. This study highlights the possible link between acyl chain recycling and lipid remodeling in cyanobacteria and demonstrates the utility of AEX-based acyl-ACP profiling in dissecting fatty acid metabolism.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS2002

Ice Cloud Formation and Dehydration in the Tropical Tropopause Layer

Stratospheric water vapor is important not only for its greenhouse forcing, but also because it plays a significant role in stratospheric chemistry. Several recent studies have focused on the potential for dehydration due to ice cloud formation in air rising slowly through the tropical tropopause layer (TTL). Holton and Gettelman showed that temperature variations associated with horizontal transport of air in the TTL can drive ice cloud formation and dehydration, and Gettelman et al. recently examined the cloud formation and dehydration along kinematic trajectories using simple assumptions about the cloud properties. In this study, a Lagrangian, one-dimensional cloud model has been used to further investigate cloud formation and dehydration as air is transported horizontally and vertically through the TTL. Time-height curtains of temperature are extracted from meteorological analyses. The model tracks the growth, advection, and sedimentation of individual cloud particles. The regional distribution of clouds simulated in the model is comparable to the subvisible cirrus distribution indicated by SAGE II. The simulated cloud properties and cloud frequencies depend strongly on the assumed supersaturation threshold for ice nucleation. The clouds typically do not dehydrate the air along trajectories down to the temperature minimum saturation mixing ratio. Rather the water vapor mixing ratio crossing the tropopause along trajectories is 10-50% larger than the saturation mixing ratio. I will also discuss the impacts of Kelvin waves and gravity waves on cloud properties and dehydration efficiency. These simulations can be used to determine whether observed lower stratospheric water vapor mixing ratios can be explained by dehydration associated with in situ TTL cloud formation alone.

Jensen, Eric↗
NASA NTRS1990

Pressure-driven sound turbulence in a high-beta plasma

LF turbulence is investigated experimentally in a 2-m-long 1-m-diameter magnetized electron fluid with beta(e) = about 0.5 and unmagnetized ions, generated in a double-pulsed linear dc discharge under a uniform external magnetic field of 15 G. The results of measurements with Langmuir probes, electric probes, and a directional particle analyzer are presented in graphs and characterized in detail. It is shown that the strong cross-field sound turbulence observed near the lower hybrid frequency is caused by the electron pressure gradient rather than E x B drift, with (1) temperature-gradient wave refraction as the dominant saturation mechanism, (2) wave-enhanced ion mass flow, and (3) only negligible ion-tail formation. The relevance of the present findings for studies of magnetic shock propagation is indicated.

Stenzel, R. L.↗
NASA NTRSDate not supplied

Calcium and Magnesium Distribution Between Sulfide and Silicate Melts: Thermodynamic Modeling and Insights into Mercury's Mantle-Crust Differentiation

Mercury stands out as the terrestrial planet with the lowest degree of oxidation among all planets of our solar system. It is characterized by a high abundance of sulfur, which is expected to replace oxygen in silicate melts. This sulfur enrichment could lead to sulfide saturation in its mantle, potentially resulting in the formation of sulfides rich in calcium and magnesium. Utilizing experimental data from the literature, we constructed a thermodynamic model to explore the partitioning of calcium and magnesium between sulfide and silicate melts. This model aims to improve our comprehension of the chemical equilibria driving the process of mantle-crust differentiation on Mercury. Our models indicate that increased temperature, decreased pressure, and low concentrations of iron, oxygen, and carbon within the sulfide phase, along with low sulfur concentrations in the silicate phase, favor calcium’s partitioning into the sulfide. Additionally, magnesium partitioning into the sulfide melt is favored with decreased pressure, decreased temperature, low concentrations of iron and calcium within the sulfide, and low concentrations of sulfur within the silicate. Our results suggest that up 9.4% and 5.6% Ca and Mg, respectively, can be present in sulfides equilibrated with sulfide-saturated silicate melts during mantle-crust differentiation. Further investigation will focus on the distribution of sulfide phases within the mantle and crust to better constrain Mercury’s internal structure.

Taylor McCombs↗
DOE OSTI2021

Time-dependent experimental identification of inter-ELM microtearing modes in the tokamak edge on DIII-D

In a series of discharges on the DIII-D tokamak, fast vertical plasma jogs are used to induce current perturbations in the steep gradient region of the H-mode edge. These current perturbations directly influence the edge q profile, decoupling the resonant location and instability drive of pedestal-localized microtearing modes (MTMs.) By exploiting this effect, we develop and apply a new experimental technique to track the dynamical frequency evolution of MTMs in the pedestal region, providing a compelling validation of the MTM model. The frequency of potential MTMs is calculated as the Doppler-shifted electron diamagnetic frequency at rational q=m/n surfaces, showing remarkable agreement with chirped frequency behavior of n=3, 4 and 5 modes detected with fast magnetics. Data is collected throughout multiple ELM cycles in order to build robust statistics describing the time-dependent frequency evolution of MTMs, which can be explained by examining the recovery of pedestal gradients after an ELM event. MTMs have a dominant transport contribution in the electron thermal channel, so the presented results indicate that reduced models of pedestal transport must be electromagnetic in nature and constructed with accurate calculations of MTM stability; inclusion of this physics is essential for accurate predictions of the electron temperature pedestal profile. Supporting measurements of mode saturation, propagation direction and transport fingerprints are made to support the dynamic frequency determination, unambiguously and experimentally identifying MTMs in the pedestal region of DIII-D.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1994

Associations of Methanotrophs With the Roots and Rhizomes of Aquatic Vegetation

Results of an in vitro assay revealed that root-associated methane consumption was a common attribute or diverse emergent wetland macrophytes from a variety of habitats. Maximum potential uptake rates (V(sub maxp)) varied between about 1 and 10 micro mol g/ (dry weight) h, with no obvious correlation between rate and gross morphological characteristics of the plants. The V(sub maxp) corresponded to about 2 x 10(exp 18) to 2 x 10(exp 9) methanotrophs g/ (dry weight), assuming that root-associated methanotrophs have cell-specific activities comparable to those of known isolates. V(sub maxp) varied seasonally for an aquatic grass, Calamogrostis canadensis, and for the cattail, Typha latifolia, with highest rates in late summer. V(sub maxp) was well correlated with ambient temperature for C. canadensis but weakly correlated for T. Wifolia. The seasonal changes in V(sub maxp), as well as inferences from apparent half-saturation constants for methane uptake (K(sub app); generally 3 to 6 micro M), indicated that oxygen availability might be more important than methane as a rate determinant. In addition, roots incubated under anoxic conditions showed little or no postanoxia aerobic methane consumption, indicating that root-associated metbanotrophic populations might not tolerate variable oxygen availability. Hybridization of oligodeoxynucleotide probes specific for group 1 or group 2 methylotrophs also varied seasonally. The group 2-specific probe consistently hybridized to a greater extent than the group 1 probe, and the relative amount of group 2 probe hybridization to C. canadensis root extracts was positively correlated with V(sub maxp).

King, Gary M.↗
NASA NTRS2000

Interpreting Assemblages with Titanite (Sphene): It Does not have to be Greek to You.

Assemblages with titanite, pyroxene(s), olivine, ilmenite, magnetite, and quartz can be used to constrain the intensive and compositional variables that operate during crystallization. Such assemblages are relatively rare in metamorphic rocks, but they are more common in igneous rocks and more frequently reported in plutonic than volcanic rocks. We used the program QUILF, enhanced with thermodynamic data for titanite, to compute stable reactions among titanite (CaTiOSiO4), Fe-Mg-Ti ilmenite and magnetite (hereafter ilmenite and magnetite), Ca-Mg-Fe pyroxenes and olivine, and quartz, and to evaluate some of the factors that control titanite stability. Calculations at 1, 3, and 6 Kbar and 650, 850, 1100 0 C, in the system CaO - MgO - FeO Fe2O3 - TiO2 - SiO2, suggest that the reactions: Augitc + Ilmenite = Titanite + Magnetite + Quartz and Augite + Ilmenite + Quartz = Titanite + Orthopyroxene, impose well defined fugacity of O2, alpha(sub SiO2), , and compositional restrictions to the assemblages: (1) Titanite + Magnetite + Quartz, (2) Titanite + Orthopyroxene, (3) Augite + Ilmenite, and consequently titanite stability. From our calculations in this system we can draw the following general conclusions: (1) The assemblage Titanite + Magnetite + Quartz is always a good indicator of relatively high fugacity of O2, and it is likely more common in relatively iron-rich bulk compositions and for decreasing temperature and pressure conditions. (2) At high temperatures (>= 650 C) titanite is not stable in quartz-saturated rocks that contain the assemblage Orthopyroxene + Augite + Ilmenite + Magnetite. (3) In quartz-saturated rocks the coexistence of titanite and magnetite with either orthopyroxene or olivine requires a confluence of conditions relating bulk composition, fugacity of O2, and slow cooling. Thus, such assemblages must be rare. (4) Regardless of T and fugacity of O2 conditions, and bulk-composition, titanite is not stable in quartz-absent rocks that contain Olivine + Orthopyroxene + Augite + Ilmenite + Magnetite. Decreasing temperature and pressure conditions appear to favor titanite crystallization, thus, it is not unsurprising that titanite is frequently observed in slowly cooled rocks, albeit, in association with amphibole. We argue that the titanite + amphibole association is likely favored by high water activity, regardless of oxygen fugacity. Because water activity increases during crystallization of a pluton, the association titanite + amphibole, and consequently titanite, is likely to be more common in plutonic rocks than in volcanic rocks.

Xirouchakis, Dimitrios M.↗
DOE OSTI2022

Small-moment antiferromagnetic ordering in single-crystalline La 2 Ni 7

Single crystals of La 2 Ni 7 have been grown out of a binary, La-Ni melt. Temperature dependent, zero magnetic field, specific heat, electrical resistivity, and low field magnetization measurements indicate that there is a series of antiferromagnetic phase transitions at T 1 = 61.0 ± 0.2 K, T 2 = 56.5 ± 0.2 K and T 3 = 42.2 ± 0.2 K. The three specific heat anomalies found at these temperatures qualitatively have very small entropy changes associated with them and the anisotropic M(H) data saturate at ~ 0.12 μ B /Ni; both observations strongly suggesting the AFM order is associated with very small, itinerant, moments. Anisotropic, H ||c and H ⟂c , ρ(H) and M(H) isotherms as well as constant field, ρ(T) and M(T) sweeps manifest signatures of multiple phase lines and result in HT phase diagrams that are clearly anisotropic. Analysis of M(T) and M(H) data allow for the identification of the two lower temperature magnetically ordered states as antiferromagnetically ordered, with the moments aligned along the crystallographic c-axis, and the higher temperature, T 2 < T < T 1 , state as having a finite ferromagnetic component. In addition, the metamagnetic transition at low temperatures, for H applied along the crystallographic c-axis (H ||c ) appears to be a near classic example of a spin-flop transition, resulting in a field stabilized antiferromagnetic state with the moments ordered perpendicular to the c-axis. Finally, although the small moment ordering, and existence of multiple phase transitions in field and temperature, suggesting an energetic proximity of these states, could foretell a degree of pressure sensitivity, our measurements of R(T) for applied pressures up to 2.0 GPa indicate that there is very little pressure dependence of T 1 , T 2 and T 3 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2003

Carbon Dioxide Convection in the Martian Polar Night and Its Implications for Polar Processes

Each Martian year nearly 30% of the atmosphere is exchanged with the polar ice caps. This exchange occurs through a combination of direct surface condensation and atmospheric precipitation of carbon dioxide. It has long been thought the amount of condensation within the polar night is maintained by a balance between diabatic processes such as radiative cooling and latent heating from condensing CO2. This assumption manifests itself in Mars General Circulation Models (GCM) in such a way as to never allow the atmospheric temperature to dip below the saturation temperature of CO2. However, observations from Mars Global Surveyor (MGS) Radio Science (RS) and the Thermal Emission Spectrometer (TES) have demonstrated this assumption to be, at best, approximate. Both RS and TES observations within the polar nights of both poles indicate substantial supersaturated regions with respect to CO2. The observed temperature profiles suggest conditionally unstable regions containing planetary significant amounts of potential convective energy. Presented here are estimates of the total planetary inventory of convective available potential energy (CAPE) and the potential convective energy flux (PCEF). The values for CAPE and PCEF are derived from RS temperature profiles and compared to Mars GCM results using a new convective CO2 cloud model that allows for the formation of CAPE.

Colaprete, A.↗
NASA NTRS1979

The Moho as a magnetic boundary

Magnetism in the crust and the upper mantle and magnetic results indicating that the seismic Moho is a magnetic boundary are considered. Mantle derived rocks - peridotites from St. Pauls rocks, dunite xenoliths from the Kaupulehu flow, and peridotite, dunite, and eclogite xenoliths from Roberts Victor and San Carlos diatremes - are weakly magnetic with saturation magnetization values from 0.013 emu/gm to less than 0.001 emu/gm which is equivalent to 0.01 to 0.001 wt% Fe304. Literature on the minerals in mantle xenoliths shows that metals and primary Fe304 are absent, and that complex Cr, Mg, Al, and Fe spinels are dominant. These spinels are non-magnetic at mantle temperatures, and the crust/mantle boundary can be specified as a magnetic mineralogy discontinuity. The new magnetic results indicate that the seismic Moho is a magnetic boundary, the source of magnetization is in the crust, and the maximum Curie isotherm depends on magnetic mineralogy and is located at depths which vary with the regional geothermal gradient.

Wasilewski, P. J.↗
NASA NTRS2012

Mars Atmospheric CO2 Condensation Above the North and South Poles as Revealed by Radio Occultation, Climate Sounder, and Laser Ranging Observations

We study the condensation of CO2 in Mars atmosphere using temperature profilesretrieved from radio occultation measurements from Mars Global Surveyor (MGS) as wellas the climate sounding instrument onboard the Mars Reconnaissance Orbiter (MRO),and detection of reflective clouds by the MGS Mars Orbiter Laser Altimeter (MOLA). Wefind 11 events in 1999 where MGS temperature profiles indicate CO2 condensation andMOLA simultaneously detects reflective clouds. We thus provide causal evidence thatMOLA non-ground returns are associated with CO2 condensation, which strongly indicatestheir nature being CO2 clouds. The MGS and MRO temperature profiles together revealthe seasonal expansion and shrinking of the area and the vertical extent of atmosphericsaturation. The occurrence rate of atmospheric saturation is maximized at high latitudes inthe middle of winter. The atmospheric saturation in the northern polar region exhibits moreintense seasonal variation than in the southern polar region. In particular, a shrinking ofsaturation area and thickness from LS 270 to 300 in 2007 is found; this is probablyrelated to a planet-encircling dust storm. Furthermore, we integrate the condensation areaand the condensation occurrence rate to estimate cumulative masses of CO2 condensatesdeposited onto the northern and southern seasonal polar caps. The precipitation flux isapproximated by the particle settling flux which is estimated using the impulse responses ofMOLA filter channels. With our approach, the total atmospheric condensation mass canbe estimated from these observational data sets with average particle size as the onlyfree parameter. By comparison with the seasonal polar cap masses inferred from thetime-varying gravity of Mars, our estimates indicate that the average condensate particleradius is 822 mm in the northern hemisphere and 413 mm in the southern hemisphere.Our multi-instrument data analysis provides new constraints on modeling the global climateof Mars.

MOLA↗