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NASA NTRS2003

Enhanced Mixing in a Rectangular Duct

An experimental investigation of the mixing of non-reacting opposed rows of jets injected normal to a confined rectangular crossflow has been conducted. Planar Mie-scattering was used to measure the time-average concentration distribution of the jet fluid in planes perpendicular to the duct axis. Particular emphasis was placed on the study of closely spaced orifice configurations applicable to the mixing zone of an RQL combustor. Baseline studies were performed of mixing under "ideal" conditions, i.e., plenum fed jets injecting into a crossflow uniform in velocity and turbulence intensity. In addition, more practical ("non-ideal") issues encountered during hardware design were also studied. As in other studies, mixing effectiveness, determined using a spatial unmixedness parameter based on the variance of mean jet concentration distributions, was found to be optimum when the spacing-to-duct-height ratio was inversely proportional to the square root of the jet-to-mainstream momentum-flux ratio. This relationship is suitable for design under ideal flow conditions. Inlet flow boundary conditions of the jet and approach flow (mainstream) were found to strongly influence mixing performance, but no attempt was made to determine optimum performance under non-ideal conditions. The tests performed do offer some guidance as to expected mixing behavior for several common variables likely to be imposed by hardware constraints. Additionally, in this study it was found that for rows of orifices with opposite centerlines inline, mixing was similar for blockages up to 89 percent (previous crossflow mixing studies concerned with dilution zone configurations, blockages were typically less than 50 percent). Lower levels of unmixedness were obtained as a function of downstream location when axial injection length was minimized. Mixing may be enhanced if orifice centerlines of opposed rows are staggered, but blockage must be =50 percent in this configuration. Round hole and "square" orifice shapes had similar performance. Other variations in orifice shape did not substantially augment overall mixing performance. Furthermore an isothermal mixing data set was generated and used by CFDRC as input to a NO(x) inference code.

Liscinsky, D. S.↗
NASA NTRSDate not supplied

PM 2.5 Concentrations over Major Metropolitan Regions Inferred from Airborne High Spectral Resolution Lidar Measurements Using Machine Learning Regression

We use measurements of near-surface aerosol backscatter, extinction, and depolarization acquired by four NASA Langley Research Center airborne High Spectral Resolution Lidars (HSRLs) to develop a machine learning regression methodology to infer PM2.5 concentrations at the surface and aloft. These airborne HSRL measurements were acquired over major metropolitan regions in the United States and Asia during more than 170 flights since 2010. Hourly surface PM2.5 measurements from the EPA air quality system and similar networks in other countries acquired within 10 km and 15 minutes of these near-surface HSRL measurements are used to train models that compute PM2.5 concentrations from the HSRL measurements. We examine several regression methods and find that exponential Gaussian Process algorithms consistently give the best performance in terms of the lowest root-mean-square (RMS) errors and the highest correlations. Model performance varies significantly depending on various combinations of HSRL aerosol measurements (e.g., aerosol backscatter, extinction, depolarization, backscatter color ratios, lidar ratios, aerosol optical thickness) and retrievals (e.g., mixed layer height, aerosol type) used in the regressions. Models that use near-surface measurements of aerosol backscatter and aerosol intensive properties such as depolarization, backscatter color ratio, and lidar ratio typically give the best performance with RMS errors around 4 mg/m3 and correlation coefficients above 0.9. HSRL measurements were often acquired when the aircraft flew systematic “raster-scan” patterns for several hours over these cities. These flight patterns enabled measurements of the spatial, temporal, and vertical variabilities in the distributions of aerosol backscatter and aerosol intensive properties and allowed us to derive the corresponding variabilities in PM2.5 concentrations. We present examples of such variabilities over urban areas in the United States as well as Asia. We describe also how the distribution of surface PM2.5 varies with aerosol type and use these retrievals to examine model simulations of surface PM2.5 in these metropolitan regions. We also discuss how this methodology may be applied to measurements from satellite lidars such as CALIOP on CALIPSO and ATLID on EarthCARE.

lidar↗
NASA NTRS2001

Stratospheric Age Spectra and Mean Ages from In Situ Observations of Carbon Dioxide

In situ observations of CO2 obtained from 1992 through 2000 using the NASA ER-2 aircraft and high-altitude balloons show that seasonal and interannual variations in CO2 mixing ratios propagate from the troposphere into the lower stratosphere via the tropical tropopause, along with the long-term trend due to fossil fuel combustion. These signals spread laterally and vertically, providing detailed quantitative information about the transport history of sampled air. We have used these data to derive age spectra and mean ages that can be compared with results from models of the stratospheric circulation. For an air parcel at a point in the stratosphere, the age spectrum is defined as the probability distribution function for transit times from the tropical tropopause for each fluid element comprising the parcel. The mean age is the average transit time, corresponding to the first moment of the age spectrum. Age spectra have been derived for altitudes below approximately 20 km for the tropics and for northern midlatitudes where there is sufficient data and where the amplitudes of the seasonal and interannual oscillations in CO2 mixing ratios are large enough to be detected. Tropical age spectra are narrow, with seasonal variation indicating faster ascent during northern winter, consistent with a circulation driven by breaking of extratropical waves. The midlatitude CO2 data are consistent with bimodal age spectra, which could result from a subtropical "barrier" to horizontal exchange over a substantial altitude region. Seasonally resolved mean ages are available with nearly pole-to-pole coverage below 20 km and in the tropics and at middle and high northern latitudes up to the maximum altitude reached by the balloons (approximately 30 km). At ER-2 altitudes, steep meridional gradients in mean age are observed in the subtropics. Between 20 and 30 km, midlatitude air is approximately 2 years older than tropical air at the same altitude. The oldest air sampled was in the Arctic polar vortex with a mean age of .5 plus or minus 0.5 years. This value is much younger than mean ages inferred from simultaneous and previous observations of SF6 in the Arctic vortex, providing evidence for a mesospheric sink for SF6. The mean age in the midlatitude middle stratosphere (approximately 25-32 km) is nearly constant with respect to altitude at 5 plus or minus 0.5 years. Comparison with earlier balloon observations of CO2 dating back to the 1970s shows that the mean age of air in this region has been relatively invariant over the last 25 years.

Andrews, Arlyn E.↗
NASA NTRS2015

Aerosol Correction for Improving OMPS/LP Ozone Retrieval

The Ozone Mapping and Profiler Suite Limb Profiler (OMPS-LP) on board the Suomi National Polar-orbiting Partnership (SNPP) satellite was launched on Oct. 28, 2011. Limb profilers measures the radiance scattered from the Earth's atmospheric in limb viewing mode from 290 to 1000 nm and infer ozone profiles from tropopause to 60 km. The recently released OMPS-LP Version 2 data product contains the first publicly released ozone profiles retrievals, and these are now available for the entire OMPS mission, which extends from April, 2012. The Version 2 data product retrievals incorporate several important improvements to the algorithm. One of the primary changes is to turn off the aerosol retrieval module. The aerosol profiles retrieved inside the ozone code was not helping the ozone retrieval and was adding noise and other artifacts. Aerosols including polar stratospheric cloud (PSC) and polar mesospheric clouds (PMC) have a detectable effect on OMPS-LP data. Our results show that ignoring the aerosol contribution would produce an ozone density bias of up to 10 percent in the region of maximum aerosol extinction. Therefore, aerosol correction is needed to improve the quality of the retrieved ozone concentration profile. We provide Aerosol Scattering Index (ASI) for detecting aerosols-PMC-PSC, defined as ln(Im-Ic) normalized at 45km, where Im is the measured radiance and Ic is the calculated radiance assuming no aerosols. Since ASI varies with wavelengths, latitude and altitude, we can start by assuming no aerosol profiles in calculating the ASIs and then use the aerosol profile to see if it significantly reduces the residuals. We also discuss the effect of aerosol size distribution on the ozone profile retrieval process. Finally, we present an aerosol-PMC-PSC correction scheme.

OMPS/LP↗
NASA NTRS2005

Atmospheric Soundings from AIRS/AMSU in Partial Cloud Cover

Simultaneous use of AIRS/AMSU-A observations allow for the determination of accurate atmospheric soundings under partial cloud cover conditions. The methodology involves the determination of the radiances AIRS would have seen if the AIRS fields of view were clear, called clear column radiances, and use of these radiances to infer the atmospheric and surface conditions giving rise to these clear column radiances. Susskind et al. demonstrate via simulation that accurate temperature soundings and clear column radiances can be derived from AIRS/AMSU-A observations in cases of up to 80% partial cloud cover, with only a small degradation in accuracy compared to that obtained in clear scenes. Susskind and Atlas show that these findings hold for real AIRS/AMSU-A soundings as well. For data assimilation purposes, this small degradation in accuracy is more than offset by a significant increase in spatial coverage (roughly 50% of global cases were accepted, compared to 3.6% of the global cases being diagnosed as clear), and assimilation of AIRS temperature soundings in partially cloudy conditions resulted in a larger improvement in forecast skill than when AIRS soundings were assimilated only under clear conditions. Alternatively, derived AIRS clear column radiances under partial cloud cover could also be used for data assimilation purposes. Further improvements in AIRS sounding methodology have been made since the results shown in Susskind and Atlas . A new version of the AIRS/AMSU-A retrieval algorithm, Version 4.0, was delivered to the Goddard DAAC in February 2005 for production of AIRS derived products, including clear column radiances. The major improvement in the Version 4.0 retrieval algorithm is with regard to a more flexible, parameter dependent, quality control. Results are shown of the accuracy and spatial distribution of temperature-moisture profiles and clear column radiances derived from AIRS/AMSU-A as a function of fractional cloud cover using the Version 4.0 algorithm. Use of the Version 4.0 AIRS temperature profiles increased the positive forecast impact arising from AIRS retrievals relative to what was shown in Susskind and Atlas .

Susskind, Joel↗
NASA NTRS2004

Chondrites and the Protoplanetary Disk, Part 1

The papers discussed the following: The Formation Process of Adhering and Consorting Compound Chondrules Inferred Their Petrology and Major-Element Composition. The Prospect of High-Precision Pb Isotopic Dating of Meteorites. Evolution of UV-Irradiated Protoplanetary Disks. A Model for the Formation of E Chondrites. Oxygen Isotopic Diffusion and Exchange Experiments on Olivine and Chondrule Melts: Preliminary Results. Shock Heating: Origin of Shock Waves in the Protoplanetary Disk. Thermal Structures of Protoplanetary Disks. Meteoritical Astrophysics: A New Subdiscipline. Origin and Thermal History of FeNi-Metal in Primitive Chondrites. The Collisions of Chondrules Behind Shock Waves. Primary Signatures of the Nebular Dust Preserved in Accretionary Rims and Matrices of CV Chondrites. History of Thermally Processed Solids in the Protoplanetary Disk: Reconciling Theoretical Models and Meteoritical. Evidence Evaporation and Condensation During CAI and Chondrule Formation. Shock Heating: Effects on Chondritic Material. Rhounite-bearing Inclusions E201 and E202 from Efremovka: Constraints from Trace. Element Measurements Element Mapping in Anhydrous IDPs: Identification of the Host Phases of Major/Minor Elements as a Test of Nebula Condensation Models. Theoretical Studies of Disk Evolution Around Solar Mass Stars. Chemical Effects of High-Temperature Processing of Silicates. I-Xe and the Chronology of the Early Solar System. The Effects of X-Rays on the Gas and Dust in Young Stellar Objects. Origin of Short-lived Radionuclides in the Early Solar System. On Early Solar System Chronology: Implications of an Initially Heterogeneous Distribution of Short-lived Radionuclides. The Origin of Short-lived Radionuclides and Early Solar System Irradiation. Disequilibrium Melting and Oxygen Isotope Exchange of CAIs and Chondrules in the Solar Nebula. Mineralogy and Chemistry of Fine-grained Matrices, Rims, and Dark Inclusions in the CR Carbonaceous Chondrites Acfer/El Djouf 001 and the Ungrouped Carbonaceous Chondrites Acfer 094 and Adelaide. Oxygen Isotopes of Aluminum-rich Chondrules from Unequilibrated Enstatite Chondrites.

Source record↗
NASA NTRS2011

Comment on "'Elevated Heat Pump' Hypothesis for the Aerosol-Monsoon Hydroclimate Link: 'Grounded' in Observations?" by S. Nigam and M. Bollasina

In their recent paper, Nigam and Bollasina [2010] (hereinafter NB) claimed to have found observational evidences that are at variance with the elevated heat pump (EHP) hypothesis regarding the possible impacts of absorbing aerosols on the South Asian summer monsoon [Lau et al., 2006; Lau and Kim, 2006]. We found NB's arguments and inferences against the EHP hypothesis flawed, stemming from their own out of context interpretation of the hypothesis. NB argued that the simultaneous negative correlation of aerosol with rainfall, and correlations with other quantities in May, are evidence against the EHP hypothesis. Their argument cannot be justified. First, Lau and Kim [2006] (hereinafter LK06) never stated that the main rainfall response to EHP is in May. Second, the EHP is about responses of the entire Indian monsoon system that are nonlocal in space and time with respect to the aerosol forcing. As shown in Figure 4 of LK06, while the aerosol anomalies are strongest in April-May, the strongest rainfall response is in June-July, with the enhanced rainfall fed by an induced thermally driven circulation which brings additional moisture from the ocean to the Indian subcontinent. Third, the increased rainfall over the Bay of Bengal as shown in Figure 1a of NB and the increased low-level convergence in Figure 1f of NB do not necessarily reflect responses associated with EHP but rather the large ]scale circulation that provides the buildup of the aerosols before the onset of the monsoon rainfall over India. Because aerosol can only accumulate where there is little or no washout by rain, the negative correlation is a necessary condition for increased atmospheric loading of aerosols. For the same reason, the spatial distributions of rainfall and aerosol generally are offset with each other, i.e., high aerosol in regions of low rainfall. This is evident in Figure 1, which shows the climatological mean of the MODIS aerosol optical depth (AOD), and TRMM rainfall over India in May. The maximum AOD is found over the Indo-Gangetic Plain and the desert regions of northwest India and Pakistan

Lau, K. M.↗
NASA NTRS2000

BOREAS TE-9 In Situ Understory Spectral Reflectance Within the NSA

The Boreal Ecosystem-Atmospheric Study (BOREAS) TE-9 (Terrestrial Ecology) team collected several data sets related to chemical and photosynthetic properties of leaves in boreal forest tree species. Spectral reflection coefficients of the forest understory at the ground level, in three boreal forest sites of Northern Manitoba (56 N latitude and 98 W longitude), were obtained and analyzed in 1994. In particular, angular variation of the reflection coefficients in the old jack pine and young jack pine forests, as well as nadir reflection coefficient in the young aspen forest, were investigated. The complexity of understory composition and the light patterns limited quantitative conclusions; however, a number of interesting trends in the behavior of the measured values can be inferred. In particular, the unique spectral profiles of lichens show very strongly in the old jack pine understory, yet are definitely less conspicuous for young jack pine, and virtually absent in the aspen forest. The angular variation of the reflection coefficient by the young pine understory seems to be significantly toned down by fine-structured branches and their shadows. Our study also indicates how difficult the ground reflection coefficient problem in a forest is, compared to certain previously investigated areas that have a more uniform appearance, such as prairie grassland, bare soil, or agricultural crops. This is due to several factors, generally typical of a forest environment, that may influence the overall understory reflection coefficient, including: (1) a strong diversity of the forest floor due to the presence of dead tree trunks, holes in the ground, patches of different types of vegetation or litter, etc.; (2) pronounced 3-D structures at the ground level, such as shrubs, bushes, and young trees; and (3) an irregular shadow mosaic, which not only varies with the time of the day, causing intensity variations, but likely also effectively modifies the spectrum of the illuminating light and hence the reflection coefficient signal as well The data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

Hall, Forrest G.↗
NASA NTRS1999

"Electrostructural Phase Changes" In Charged Particulate Clouds: Planetary and Astrophysical Implications

There is empirical evidence that freely-suspended triboelectrostatically charged particulate clouds of dielectric materials undergo rapid conversion from (nominally) monodispersed "aerosols" to a system of well-defined grain aggregates after grain motion or fluid turbulence ceases within the cloud. In United States Microgravity Laboratory Space Shuttle experiments USML-1 and USML-2, it was found that ballistically-energized grain dispersions would rapidly convert into populations of filamentary aggregates after natural fluid (air) damping of grain motion. Unless continuously disrupted mechanically, it was impossible to maintain a non-aggregated state for the grain clouds of sand-size materials. Similarly, ground- based experiments with very fine dust-size material produced the same results: rapid, impulsive "collapse" of the dispersed grains into well-defined filamentary structures. In both ground-based and microgravity experiments, the chains or filaments were created by long-range dipole electrostatic forces and dipole-induced dielectric interactions, not by monopole interactions. Maintenance of the structures was assisted by short-range static boundary adhesion forces and van der Waals interactions. When the aggregate containers in the USML experiments were disturbed after aggregate formation, the quiescently disposed filaments would rearrange themselves into fractal bundles and tighter clusters as a result of enforced encounters with one another. The long-range dipole interactions that bring the grains together into aggregates are a product of randomly-distributed monopole charges on the grain surfaces. In computer simulations, it has been shown that when the force vectors of all the random charges (of both sign) on a grain are resolved mathematically by assuming Coulombic interaction between them, the net result is a dipole moment on individual grains, even though the grains are electrically neutral insofar as there is no predominance, on their surface, of one charge sign over another. The random charges of both sign derive from natural grain-to-grain interactions that produce triboelectrification via charge exchange every time grain surfaces make contact with one another. The conversion from a random distribution of grains (upon which there are randomly distributed charges) into an organization of electrostatically-ordered aggregates, can be regarded (within the framework of granular-material science) as an "electrical or Coulombic phase change" of the particulate cloud. It is not totally dissimilar from the more normal phase-change concept in which, for example, a gas with long free-path-molecules suddenly becomes a solid as a result of structural ordering of the molecules (notably, also the result of electronic forces, albeit at a different scale). In both the gas-to-solid case, and the aerosol-to-aggregate case, the same materials and charges are present before and after the phase change, but their arrangement now has a higher degree of order and a lower-energy configuration. An input of energy into the system is required to reverse the situation. The aggregates in the USML experiments were observed to undergo at least two phase changes as noted above. The point about phase changes, and by implication, the "electrostructural" reorganizations in particulate clouds, is the following: (a) they can occur very rapidly, almost spontaneously, above a critical cloud density, (b) in going from a higher energy state to a lower energy state, they convert to a denser system, (c) energy must be required to reverse the situation, implying that energy is released during the high-to-low energy phase change. In applying this information to natural particulate clouds, some inferences can be made (it is stressed that reference is still to dielectric materials attracted by dipole forces). There are several natural settings to which the USML observations apply, and to which the phase-change implications likewise apply. Dense clouds of triboelectrically-charged, kinetically-energized grains are to be found in volcanic eruptions (particularly on earth), aeolian dust storms (particularly on Mars), meteorite impact ejecta curtains (on all planets), in "immature" debris rings around planets (e.g., that from which our own Moon may have condensed), and in gravitationally collapsing protoplanetary dust/planetesimal debris disks where dielectric granules are being increasingly brought into collisional relationships with one another (increasing both charge exchange and physical proximity). It is noted that in many of these cases, the degree of electrical charging on the grains is likely to be much higher than that in the USML experiments where charging was not enhanced above the "normal", naturally encountered level for the particular materials (quartz, glass, and various silicate minerals). Application of the phase-change concept suggests that volcanic, aeolian, and impact debris clouds may, under certain circumstances, undergo rapid, impulsive, or even catastrophic collapse into a denser state that will lead to rapid precipitation or fall-out of suspended particulates. Although this idea has been suggested previously by the author , the phase change concept possibly permits some new insights into cloud-system behavior. For example, in a protoplanetary debris disk, the work of gravity may suddenly be enhanced by electrostatically driven collapse of the system when materials reach a critical intergranular spacing or grain number density. This might reduce the rate of planet formation by orders of magnitude (considering the ratio of g-forces to electrostatic ones for very small grains in close proximity), and indeed, it might drive the collapse into a system configuration that would perhaps not be created by gravity alone. Additional information is contained in the original.

Marshall, J. R.↗
NASA NTRS1993

On the High- and Low- Altitude Limits of the Auroral Electric Field Region

Using measurements from the High Altitude Plasma Instrument (HAPI) on the Dynamics-Explorer 1 (DE-1) spacecraft and the Low Altitude Plasma Instrument (LAPI) on Dynamics Explorer 2 (DE 2), we investigate both die high altitude and low altitude extents of the auroral acceleration region. To infer the high altitude limit, we searched the HAPI data base for evidence of upward-directed auroral electric fields located above the spacecraft when the HAPI spacecraft is above 9000 km altitude. We find that such acceleration is common when DE-1 flies through die auroral oval at an altitude of 9,000-11,000 km. At altitudes above 11,000 km, the fraction of the orbits with evidence of at least a 1000 V potential drop above the spacecraft falls, becoming essentially zero above an altitude of 15,000 km. Above that altitude, small (100 V) potential drops are frequently observed, but only rarely are approx. 1 kV potentials observed, typically associated with polar cap or 'theta' arcs or westward traveling surges. To investigate the low-altitude limit of the auroral acceleration region, we use conjunctions of DE 1 and DE 2 along auroral field lines and match the upgoing fluxes of ionospheric ions observed by DE 2 with the flux of accelerated upgoing ions observed at DE 1. Calculating the ionospheric scale height from the ion and electron temperatures and assuming that the parallel flow velocity is independent of height above 800 km, we calculate the altitude at which the upwelling ionospheric ions are effectively completely lost to upward acceleration. The initial lowest-altitude acceleration process could be either a perpendicular acceleration or a parallel electric field, but it must be sufficient to give the entire distribution escape energy. We find that in the two cases studied, near the region of peak auroral potential drop the altitude of this acceleration was around 1700 km (near the O/H neutral crossover altitude), but was significantly higher (approx. 2000 km) near the edges of the arc, where the potential was lower. The composition of the upgoing ion beam was consistent with these heights, being predominately H(+) near the edges and O(+) near the peak.

Reiff, P. H.↗
NASA NTRSDate not supplied

Using Secondary Craters to Assess Strength Differences Between Neighboring Surface Units

Introduction: An issue with Martian remote sensing studies is the difficulty directly inferring surface and crustal material properties. For direct measurements we currently rely on the instruments of landed missions, like InSight. However, these are limited to specific locations (i.e., Elysium Planitia for InSight). To understand how results from in situ missions apply to other parts of Mars’ crust, we would like to apply a methodology that uses remote sensing. We are exploring using secondary craters, which are often thought of as nuisances when finding accurate relative ages, to get at these properties. An upside of secondary craters is that they form by ejecta blocks moving at relatively slow speeds (compared to primary impacts), which lets them reside in a different crater scaling regime [1], one that is more sensitive to the crust’s effective strength (Yeff) and its porosity. Secondary Crater Scaling: There are multiple parameters that influence the size of secondary craters, but we can measure craters in ways that isolate the dependence of crater size to just Yeff. We focus on secondary clusters that have impacted into distinct but bordering geological units. These secondaries can be used to determine Yeff thanks to one important fact: all the secondaries in this cluster are from the same distant primary, and as a result, the ejecta velocity, median block sizes, and densities are expected to be the same (at least to first order). Thus, variations between crater size on the two units are due to material property differences (i.e. Yeff). Thanks to the steep size frequency distributions (SFD) of secondaries [2], observable secondary crater sizes are tightly clustered, and we can simply use differences in median secondary sizes between two geologic units to constrain the ratio of Yeff. We are also able to use the SFD of our counting areas to check if our counted craters are secondaries (i.e. have a steep distribution), and if the two crater counting areas are from the same source (and thus have the same power law slope), but are offset from each other at around the same factor as the median difference.

Mars; Craters; Crustal Strength↗
NASA NTRS1996

The Interstellar Polarization Feature Associated with the 2175 Angstrom Extinction Bump

The most successful model at fitting the wavelength dependence of interstellar extinction consists of two populations of bare silicate and graphite grains (Mathis, Rumpl & Nordsieck, (MRN)). The graphite grains are needed to fit the strong 2175 A extinction bump, with the silicates providing most of the smooth extinction seen at other wavelengths. From observations of the IR silicate absorption features, it was inferred that the silicate grains, non-spherical and aligned to the Galactic magnetic field, were responsible for the interstellar polarization. Aligned silicate grains make a very good fit to the smooth featureless UV polarization curves that comprise most of the observed sample. The lines of sight showing a UV polarization feature require something different, perhaps a second population of grains as do the fits to the extinction curve. The polarization wavelength dependence of HD 197770 can be fit by a MRN-like mixture of aligned bare silicate and graphite grains. However, none of the popular grain models including MRN envisaged an aligned bump grain population. It has been suggested that the extinction bump is not due to graphite but rather to a population of polycyclic aromatic hydrocarbons (PAHs). If the observed UV polarization features could be associated with the 2175 A bump then it would strengthen the argument that the bump must be due to grains rather than PAHs which are not likely to be aligned to the Galactic Magnetic field. The reality of ultraviolet polarization features has been confirmed by observations with ASTRO-2. The original detection toward HD 197770 has been confirmed and a new feature has been detected toward HD 147933-4. Both features have centroids lying close to 2175 A the location of the UV extinction bump. Two possibilities are considered for the source of the polarization bump, alignment of graphite grains responsible for the extinction bump or changes in the size distribution of the aligned silicate grains responsible for the continuum polarization. It seems the graphite grains are a more likely source of the polarization.

Clayton, Geoffrey C.↗
NASA NTRS1999

The MSP 2001 Mars Environmental Compatibility Assessment (MECA)

A chemical analysis of soil-water mixtures and the first microscopic images of martian soil will be among the results to be returned by the Mars Environmental Compatibility Assessment (MECA) payload on the Mars Surveyor Program 2001 Lander. Sponsored by the Human Exploration and Development of Space (HEDS) enterprise, MECA's primary goal is to evaluate potential geochemical and environmental hazards that may confront future martian explorers, and to guide HEDS scientists in the development of high fidelity Mars soil simulants. As a survey of soil properties, the MECA data set will also be rich in information relevant to basic geology, paleoclimate, and exobiology. The integrated MECA payload contains a wet-chemistry laboratory, a microscopy station, an electrometer to characterize the electrostatics of the soil and its environment, and arrays of material patches to study the abrasive and adhesive properties of soil grains. MECA is allocated a mass of 10 kg and a peak power usage of 15 W within an enclosure of 35 x 25 x 15 cm. The Wet Chemistry Laboratory (WCL) consists of four identical cells that will accept samples from surface and subsurface regions accessible to the Lander's robotic arm, mix them with water, and perform extensive analysis of the solution. Ion-selective electrodes and related sensors will evaluate total dissolved solids, redox potential, pH, and the concentration of many soluble ions and gases. Cyclic voltammetry will address oxidants, and anodic stripping voltammetry will probe potentially hazardous trace metals. MECA's microscopy station combines optical and atomic-force microscopy (AFM) in a controlled illumination environment to image dust and soil particles from millimeters to nanometers in size. Careful selection of substrates and an abrasion tool allows experimental study of size distribution, adhesion, abrasion, hardness, color, shape, aggregation, magnetic and other properties. Mounted on the end of the robot arm, MECA's electrometer consists of four types of sensors: an electric field meter, several triboelectricity monitors, an ion gauge, and a thermometer. Tempered only by ultra-violet- light-induced ions and a low-voltage break-down threshold, the dry, cold, dusty martian environment presents an imposing electrostatic hazard to both robots and humans. In addition, the electrostatic environment is key to transport of dust and, consequently, martian meteorology. MECA will also observe natural dust accumulation on engineering materials. Viewed with the robot arm camera, the abrasion and adhesion plates are strategically placed to allow direct observation of the inter-action between materials and soils on a macroscopic scale. Materials of graded hardness are placed directly under the robot arm scoop to sense wear and soil hardness. A second array, placed on the lander deck, is deployed after the dust plume of landing has settled. It can be manipulated in a primitive fashion by the arm, first having dirt deposited on it from the scoop and subsequently shaken clean. Dust accumulation as a function of conductivity, magnetic field strength, and other parameters will be explored. The MECA instruments described above will assess potential hazards that the Martian soil might present to human explorers and their equipment. In addition, MECA will provide information on the composition of ancient surface water environments, observing microscopic evidence of geological (and biological?) processes, inferring soil and dust transport, comminution and weathering mechanisms, and characterizing soil horizons that might be encountered during excavation. Additional information is contained in the original extended abstract.

Hecht, M. H.↗
NASA NTRS1997

Parameterizing Grid-Averaged Longwave Fluxes for Inhomogeneous Marine Boundary Layer Clouds

This paper examines the relative impacts on grid-averaged longwave flux transmittance (emittance) for Marine Boundary Layer (MBL) cloud fields arising from horizontal variability of optical depth tau and cloud sides, First, using fields of Landsat-inferred tau and a Monte Carlo photon transport algorithm, it is demonstrated that mean all-sky transmittances for 3D variable MBL clouds can be computed accurately by the conventional method of linearly weighting clear and cloudy transmittances by their respective sky fractions. Then, the approximations of decoupling cloud and radiative properties and assuming independent columns are shown to be adequate for computation of mean flux transmittance. Since real clouds have nonzero geometric thicknesses, cloud fractions A'(sub c) presented to isotropic beams usually exceed the more familiar vertically projected cloud fractions A(sub c). It is shown, however, that when A(sub c)less than or equal to 0.9, biases for all-sky transmittance stemming from use of A(sub c) as opposed to A'(sub c) are roughly 2-5 times smaller than, and opposite in sign to, biases due to neglect of horizontal variability of tau. By neglecting variable tau, all-sky transmittances are underestimated often by more than 0.1 for A(sub c) near 0.75 and this translates into relative errors that can exceed 40% (corresponding errors for all-sky emittance are about 20% for most values of A(sub c). Thus, priority should be given to development of General Circulation Model (GCM) parameterizations that account for the effects of horizontal variations in unresolved tau, effects of cloud sides are of secondary importance. On this note, an efficient stochastic model for computing grid-averaged cloudy-sky flux transmittances is furnished that assumes that distributions of tau, for regions comparable in size to GCM grid cells, can be described adequately by gamma distribution functions. While the plane-parallel, homogeneous model underestimates cloud transmittance by about an order of magnitude when 3D variable cloud transmittances are less than or equal to 0.2 and by approx. 20% to 100% otherwise, the stochastic model reduces these biases often by more than 80%.

Barker, Howard W.↗
NASA NTRS2000

Investigation of the Transport of Solar Ions Through the Earth's Magnetosphere

The objective of this study has been to infer, by statistical means, the most probable mode of entry of solar wind plasma into Earth's magnetotail, using a particular set of archived data from the Lockheed Plasma Composition Experiment on the International Sun-Earth Explorer One (ISEE-1) satellite, jointly sponsored by the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) in the 1970's and 80's. Despite their considerable age, the Lockheed ISEE-1 data are still, at the time of this report, the only substantial ion composition data in the sub-keV to keV energy range available from the magnetotail beyond 9 R(sub E), because of various technical problems with ion mass spectrometers on later missions, and are therefore a unique source of information about the mixing of solar and terrestrial origin plasmas in the tail, within the ISEE-1 apogee of almost 23 R(sub E). The entire set of archived data used in this study, covering the 4.5 years of operation of the instrument and comprising not only tail measurements but also data from the inner magnetosphere as well as data from outside the magnetopause, is now available to the public via the WorldWideWeb at the address: http://cis.spasci.com/ISEE_ions The fundamental assumption of this and other studies of magnetosphere ion composition is that He++ and O+ ions are virtually certain "tags" of solar and terrestrial origins, respectively. This is an assumption with strong theoretical basis and it is corroborated by observational evidence, including the often substantial differences between the velocity distribution functions of those two species. The H+ ions can have a dual origin, in principle, but the close resemblance in the ISEE-1 data between the dynamics of H+ and He++ ions indicates a predominantly solar origin of the H+ ions in the tail, at least. By the same token, the usually minor He+ ions are probably almost entirely of terrestrial origin, because of their similarity to the O+ ions.

Lennartsson, O. W.↗
NASA NTRS2023

Mineralogical, Elemental, and Tomographic Reconnaissance Investigation for CLPS (METRIC)

METRIC is a robotic science laboratory that can determine the mineralogy, elemental chemistry, micromorphology, and thermophysical properties of planetary regolith. The METRIC suite comprises METRIC XRD/F, an X-ray diffraction/X-ray fluorescence instrument that can determine the mineralogy and elemental chemistry of regolith samples; METRIC XCT, a micro X-ray computed tomography instrument that can be used to evaluate grain/crystallite sizes and textures; METRIC IRS, an imaging spectrometer mounted on a rover that can determine mineralogy and thermophysical properties at the landing site; and a pneumatic sample collection, processing, distribution system developed by Honeybee Robotics. The payload elements could be deployed on a static lander or a rover. Data returned from the METRIC payload would inform origin, formation, and evolution of rocky planetary bodies. METRIC XRD/F draws on heritage from the CheMin instrument on the Mars Science Laboratory (MSL) Curiosity rover [1], with a few important improvements. Like CheMin, METRIC XRD/F operates in transmission geometry and uses piezoelectric actuators on sample cells in a tuning fork geometry to induce convective grain motion of the regolith to create a randomly oriented powder. MSL CheMin uses an energy-sensitive CCD to collect XRD patterns and XRF spectra simultaneously from the same sample cell, resulting in qualitative XRF data. METRIC XRD/F uses two different sample cells, one optimized for XRD and one optimized for XRF, and a silicon drift detector to detect fluoresced X-rays. This improvement to the XRF capabilities provides quantitative geochemical data of major elements down to Z = 11 and allows for the detection of minor and trace elements that are critical for evaluating geologic evolution of the Moon (e.g., P and Th). Modest improvements to the XRD geometry and hardware allow for better angular resolution and the ability to distinguish between members of the pyroxene group. METRIC XCT uses the same geometry and much of the same hardware as METRIC XRD/F, where a CCD would capture images of a regolith sample in a 3 mm diameter sample tube that is rotated 360° in steps <1°. Image brightness can be used to infer compositional data, where brighter materials indicate a higher Z, much like scanning electron microscopy. Data from METRIC XCT complement those from METRIC XRD/F. Particle size, shape, and texture can provide petrologic and provenance information, whereas vesicle size and morphology in volcanic or impact melt lithologies can inform cooling rates. METRIC IRS is a hyperspectral thermal imager that can be mounted to a lander or rover to provide mineralogical data from the broader landing site and help determine whether the samples analyzed by METRIC XRD/F and XCT are representative. The METRIC IRS spectral range (8–14 μm) and resolution (10.8 cm-1) allow for quantitative mineralogy from modelling Reststrahlen bands of major rock-forming minerals (e.g., silicates, phosphates). Radiance cubes can be processed and modelled with an onboard high-performance computer to determine mineral abundances of plagioclase, high-Ca pyroxene, pigeonite, orthopyroxene, olivine, and glass. Regolith samples can be acquired, processed, and delivered to the X-ray instruments via multiple sample handling systems, but the pneumatic sampling systems developed by Honeybee Robotics [e.g., 2] are best suited for relatively low-cost missions that are being competed for the Moon (e.g., NASA’s Payloads and Research Investigations for the Surface of the Moon program). There are pneumatic sampling systems that collect surface material and other systems that pneumatically drill up to ~1 m below the surface, providing material that has not been space weathered and has not been affected by the lander’s exhaust. [1] Blake, D. F., Vaniman, D., Achilles, C., Anderson, R., Bish, D., et al. (2012). Space Sci. Rev. 170, 341-478. https://doi.org/10.1007/s11214-012-9905-1. [2] Zacny, K., Betts, B., Hedlund, M., Long, P., Gramlich, M., Tura, K., Chu, P., Jacob, A., Garcia, A. (2014). IEEE Aerospace Conference, 3-7 March 2014, Big Sky, MT, U.S.A.

X-ray diffraction↗
NASA NTRS2004

Large Alluvial Fans on Mars

Several dozen distinct alluvial fans, 10 to greater than 40 km long downslope are observed exclusively in highlands craters. Within a search region between 0 deg. and 30 deg. S, alluvial fan-containing craters were only found between 18 and 29 S, and they all occur at around plus or minus 1 km of the MOLA-defined Martian datum. Within the study area they are not randomly distributed but instead form three distinct clusters. Fans typically descend greater than 1 km from where they disgorge from their alcoves. Longitudinal profiles show that their surfaces are very slightly concave with a mean slope of 2 degrees. Many fans exhibit very long, narrow low-relief ridges radially oriented down-slope, often branching at their distal ends, suggestive of distributaries. Morphometric data for 31 fans was derived from MOLA data and compared with terrestrial fans with high-relief source areas, terrestrial low gradient alluvial ramps in inactive tectonic settings, and older Martian alluvial ramps along crater floors. The Martian alluvial fans generally fall on the same trends as the terrestrial alluvial fans, whereas the gentler Martian crater floor ramps are similar in gradient to the low relief terrestrial alluvial surfaces. For a given fan gradient, Martian alluvial fans generally have greater source basin relief than terrestrial fans in active tectonic settings. This suggests that the terrestrial source basins either yield coarser debris or have higher sediment concentrations than their Martian counterpoints. Martian fans and Basin and Range fans have steeper gradients than the older Martian alluvial ramps and terrestrial low relief alluvial surfaces, which is consistent with a supply of coarse sediment. Martian fans are relatively large and of low gradient, similar to terrestrial fluvial fans rather than debris flow fans. However, gravity scaling uncertainties make the flow regime forming Martian fans uncertain. Martian fans, at least those in Holden crater, apparently formed around the time of the Noachian-Hesperian boundary. We infer that these fans formed during an episode of enhanced precipitation (probably snow) and runoff, which exhibited both sudden onset and termination.

Moore, Jeffrey M.↗
NASA NTRS2007

Comparisons of Instantaneous TRMM Ground Validation and Satellite Rain Rate Estimates at Different Spatial Scales

This study provides a comprehensive inter-comparison of instantaneous rain estimates from the two rain sensors aboard the TRMM satellite with ground data from thee designated Ground Validation Sites: Kwajalein Atoll, Melbourne, Florida and Houston, Texas. The satellite rain retrievals utilize rain observations collected by the TRMM microwave imager (TMI) and the Precipitation Radar (PR) aboard the TRMM satellite. Three standard instantaneous rain products are the generated from the rain information retrieved from the satellite using the TMI, PR and Combined (COM) rain algorithms. The validation data set used in this study was obtained from instantaneous rain rates inferred from ground radars at each GV site. The first comparison used 0.5(sup 0) x 0.5(sup 0) gridded data obtained from the TRMM 3668 product, and similarly gridded GV data obtained from ground-based radars. The comparisons were made at the same spatial and temporal scales in order to eliminate sampling biases in our comparisons. An additional comparison was made by averaging rain rates for the PR, COM and GV estimates within each TMI footprint (approx. 150 square kilometers). For this analysis, unconditional mean rain rates from PR, COM and GV estimates were calculated within each TMI footprint that was observed within 100 km from the respective GV site (and also observed by the PR). This analysis used all the available matching data from the period 1999-2004, representing a sample size of over 50,000 footprints for each site. In the first analysis our results showed that all of the respective rain rate estimates agree well, with some exceptions. The more salient differences were associated with heavy rain events in which one or more of the algorithms failed to properly retrieve these extreme events. Also, it appears that there is a preferred mode of precipitation for TMI rain rates at or near 2 mm per hour over the ocean. This mode was noted over ocean areas of Melbourne, Florida and Kwajalein, Republic of the Marshall Islands, and is shown to exist in TRMM tropical-global ocean areas as well. Further research by algorithm developers is needed to explain or justify the seemingly errant observed probability distributions.

Wolff, David B.↗