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  • Porphyry copper, copper skarn, and volcanogenic massive sulfide occurrences in the Chandalar copper district, Alaska

    Nicholson, Lisa; Keskinen, Mary (1990-05)
    Metamorphosed porphyry copper, copper skarn, and volcanogenic massive sulfide (VMS) occurrences have been found in 5 key prospects within Devonian rocks of the Chandalar copper district, Alaska. The Venus, Victor, Eva, and Evelyn Lee prospects contain "proximal" porphyry copper/copper skarn mineralization, whereas the Luna prospect contains "distal" Cu-Zn skarn and Cu-Zn VMS mineralization. Porphyry copper mineralization is recognized by granodiorite composition meta-intrusives; zoned potassic, sericitic and propylitic alteration; and del34S values of -1.5 to -0.6 per mil. Skarns consist of andraditic garnet (Ad30-100) and diopsidic pyroxene (Hd9-46), and have del34S values of -4.7 to -1.1 per mil. Alteration types in intrusive rocks and adjacent skarn are generally compatible. VMS occurrences contain chloritic and silicic alteration, and massive sulfides have del34S values of -0.8 to 6.9 per mil, consistent with values from known Devonian VMS deposits.
  • The kinetics of glucose limited growth by a marine yeast

    McNab, Allen David (1969-05)
    The kinetics of glucose limited growth by a marine yeast, shown to be a Rhodotorula species, have been studied in a continuous culture apparatus. The saturation constant, in synthetic media, has been calculated to be 0.25 mg/l, on the assumption that saturation kinetics are followed, The maximum growth rate was determined in both synthetic media, and artificial sea water. On the basis of inhibition kinetics, the kinetic behavior of this yeast in the marine environment has been predicted. The effect of temperature on the maximum growth rate has been determined and, on the assumption of a similar effect on the saturation constant, the saturation constant has been postulated to be in agreement with similar values determined for other microorganisms.
  • Small spatial and fast temporal ionosphere -magnetosphere coupling processes

    Zhu, Hua; Otto, Antonius (2000)
    I have developed a two-dimensional, three-fluid model (electrons, ions and neutrals) to simulate small-scale magnetosphere-ionosphere coupling processes. The code includes ionization and recombination processes, the Hall term in Ohm's law, and various heat sources in the energy equations. The electro-dynamic response and the evolution of the collision frequencies are treated self-consistently in a height resolved ionosphere. The model allows for the propagation of Alfven waves. The simulation is particularly suited for fast temporal variations and small spatial scale ionospheric structures associated with filamentary aurora and ionospheric heating experiments (e.g. HAARP). I have investigated the evolution of field-aligned currents in the magnetosphere-ionosphere system and found several notable effects---ion heating due to plasma-neutral friction, electron heating resulting from energetic particle precipitation and ohmic dissipation by strong field-aligned currents. The simulation of plasma. heating in the ionosphere is motivated by a specific auroral event that was simultaneously observed with optical and radar instruments. The results indicate that a consistent explanation of this event requires ohmic heating of electrons in a strong field-aligned electric current layer. They suggest strongly that the observed sequence of events can be explained only if spatial structure is present in the ionosphere so that it requires at least a two-dimensional model. Electron heating in strong field-aligned currents also provides a mechanism to deposit energy in the F-region of ionosphere and thus can explain the formation of tall auroral arcs. The simulation of the formation of field-aligned currents shows a strong plasma density depletion in the region of downward field-aligned current layer. The depletion is due to the divergent flow of the plasma. Similarly, the plasma density increases in the region of upward field-aligned current because of the convergent plasma motion. A modification of the ionospheric conditions by localized particle precipitation has an interesting effect. At the edge of the precipitation region, a new field-aligned current filament is formed. Finally, the simulation code is not limited by steady state assumptions commonly used for the Hall model and Pedersen conductivities.
  • Modeling of Arctic stratus cloud formation and the maintenance of the cloudy Arctic boundary layer

    Zhang, Qiuqing; Stamnes, Knut; Harrington, Jerry; Sentman, Davis; Watkins, Brenton (1999)
    The formation of Arctic stratus clouds (ASCs) and the maintenance of the cloudy Arctic boundary layer are studied with two models: a one-dimensional radiative-convective model and a three-dimensional large eddy simulation (LES) model. The one-dimensional radiative-convective model consists of a comprehensive radiative module, a cloud parameterization with detailed microphysics and a convective adjustment scheme. The model is designed specifically for studying ASC formation. With this model, the roles of radiation and cloud microphysics in the formation of ASCs and multiple cloud layers are investigated. The simulations reproduce both single and multiple cloud layers that were observed with inversions of temperature and humidity occurring near the cloud top. The detailed cloud microstructure produced by the model also compares well with the observations. The physics of the formation of both single and multiple cloud layers is investigated. Radiative cooling plays a key role during the initial stage of cloud formation in a atmosphere. It leads to a continual temperature decrease promoting water vapor condensation on available cloud condensation nuclei. The vertical distribution of humidity and temperature determines the radiative cooling and eventually where and when the cloud forms. The observed temperature inversion may also be explained by radiative cooling. The three-dimensional LES model is adopted to evaluate the one-dimensional model, especially the convective adjustment scheme. The advantages and limitations of the one-dimensional model are discussed. The LES results suggest that the convective adjustment scheme is capable of capturing the main features of the vertical heat and moisture fluxes in the cloudy Arctic boundary layer. The LES model is also used to investigate the maintenance of the cloudy Arctic boundary layer. The turbulence in the cloudy Arctic boundary layer is primarily maintained by the buoyancy effect due to the cloud top cooling. It is found that weak large scale downward motion aids in cloud development and maintenance.
  • Single and multiple electromagnetic scattering by size -shape distributions of small nonspherical particles

    Schulz, Frank Michael (1998)
    A comprehensive model for light scattering by size-shape distributions of randomly oriented nonspherical particles is developed. The model uses spheroids as model particles. The vector Helmholtz equation is solved with a new separation of variables (SVM) approach that allows one to calculate the ensemble-averaged single scattering optical properties of ensembles of randomly oriented particles analytically. Since the use of the SVM in spheroidal coordinates properly accounts for the geometry of the particles, the method is applicable to a large range of shapes ranging from elongated prolate needles via spheres to flat oblate disks. The relation between geometric symmetries of particles and symmetry relations of the electromagnetic scattering solution is investigated systematically in the general framework of the theory of point groups. The results are exploited in the model for increasing the computational efficiency. A comprehensive vector radiative transfer model is in part developed in this work. This radiative transfer model takes the output of the single scattering model as input and computes the Stokes vector components in a vertically inhomogeneous, plane parallel medium as a function of polar and azimuth angle and as a function of optical depth. The single scattering model is applied to investigate the impact of particle shape on the optical properties of size-shape distributions of randomly oriented particles, such as aerosol layers or ice clouds in the atmosphere. The optical properties are found to be much more sensitive to a variation in the effective aspect ratio than to a variation in the effective variance of a shape-distribution. The results of this study are used as input to the vector radiative transfer model in order to study the shape-sensitivity of the radiation field in a macroscopic medium containing a size-shape distribution of randomly oriented particles. It is found that both the radiance, and the degree of linear polarization, and the degree of circular polarization are strongly shape-sensitive in most viewing directions.
  • Ice -wedge networks and "whale-hole" ponds in frozen ground

    Plug, Lawrence J.; Hopkins, David M. (2000)
    The patterns of ice-wedge networks and of whale-hole ponds in frozen ground self-organize by strong interactions between pattern elements. Mechanisms for the consistent spacing (15--25 m) and orientation between ice wedges are examined in a model encapsulating the opening of fractures under a combination of thermally-induced tensile stress, stress reduction near open fractures, and heterogeneity of frozen ground and insulating snow. Modeled networks are similar to ice-wedge networks on the Espenberg coastal plain, Bering Land-Bridge National Park, Alaska, at the level of variation among Espenberg networks, as indicated by: (i) comparisons of distributions of relative orientation and spacing between wedges; and (ii) application of nonlinear spatial forecasting to modeled and Espenberg network patterns. Spacing in modeled networks is sensitive to fracture depth and weakly sensitive to thermally-induced tensile stress and substrate strength, consistent with the narrow range of spacing between natural ice wedges in different regions. In an extended model that includes recurring fractures over thousands of winters, networks similar to natural ice-wedge networks form. The annual pattern of fractures diverges from the ice-wedge pattern, with only ½--¾ of wedges fracturing in a single year at a steady-state reached after approximately 103 y. Short-lived sequences of extreme stress from cooling can permanently alter the spacing between and the fracture frequency of modeled ice wedges, suggesting that the existence and characteristics of existing and relic natural ice-wedge networks reflect extreme, not mean, climate conditions. Ponds on the Espenberg beach-ridge plain, approximately 2 m across and 1 m deep and surrounded by raised rings of ice-rich permafrost 2 m across and 0.5 m high, form through an interplay between localized bacterial decomposition of peat, thawing of frozen ground and frost heaving of peat in rings. Groups of hundreds of ponds at Espenberg assemble through time because new ponds are favored to form adjacent to raised rings around existing ponds. The nonlinear behavior that results from strong interactions in patterns of ice-wedge networks and in ponds suggests general limitations in the application of linear approaches to inferring the response of geomorphic systems to changes in forcing, such as climate change.
  • Seismic investigations of subsurface volcanic structures and processes at Mount Spurr, Alaska and Soufriere Hills Volcano, Montserrat, West Indies

    Power, John A.; Wyss, Max (1998)
    Seismological techniques are used to infer the subsurface structures and volcanic processes at two recently active volcanoes: Mount Spurr, Alaska, and Soufriere Hills Volcano, Montserrat, West Indies. The three-dimensional P-wave velocity structure of Mount Spurr is determined to depths of 10 km by tomographic inversion of 3,754 P-wave arrival times from local earthquakes. Results show a prominent low-velocity zone beneath the southeast flank of Crater Peak extending from the surface to 3--4 km below sea level, spatially coincident with an active geothermal system. Beneath Crater Peak an approximately 3-km-wide zone of relatively low velocities correlates with a near vertical band of seismicity, suggestive of a magma conduit. No large low-velocity zone indicative of a magma chamber occurs within the upper 10 km of the crust. In the three years bracketing the 1992 eruptions of Mount Spurr's Crater Peak vent, approximately 2,500 located events were classified as Volcano-Tectonic (VT) earthquakes, Long-Period (LP) events, or Hybrid events. An unusual mix of VT, LP, and hybrid events at 20 to 40 km depth began coincident with the onset of unrest and peaked shortly after eruptive activity ended. The classified seismic events are combined with geophysical and geological data to develop a simplified model of the magmatic plumbing system of Mount Spurr. The major components of this model are a deep magma source zone at 20--40 km depth, a smaller storage zone at about 10 km depth, and a pipe-like conduit that extends to the surface. The frequency-magnitude distribution of earthquakes measured by the b-value is determined as a function of space beneath Soufriere Hills Volcano, from data recorded between August 1, 1995 and March 31, 1996. A volume of high b-values (b > 3.0) with a 1.5 Ian radius is imaged between 0 and 1.5 Ian beneath English's Crater and Chance's Peak. This anomaly extends southwest to Gage's Soufriere. At depths greater than 2.5 km, volumes of comparatively low b-values ( b <math> <f> ~</f> </math> 1) are found beneath St. George's Hill, Windy Hill, and below 2.5 kin to the south of English's Crater.
  • Cloud and surface properties and the solar radiation budget derived from satellite data over the Arctic Ocean: Comparisons with surface measurements and in situ aircraft data

    Xiong, Xiaozhen; Stamnes, Knut (2000)
    Use of satellite data to study the surface and cloud properties and the solar radiation budget (SRB) is very important for improving our understanding of cloud and sea-ice albedo feedback in the Arctic. Based on an accurate and comprehensive Radiative Transfer Model (RTM), algorithms were developed for using the National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) data for the discrimination of cloud from snow/ice surfaces, retrieval of snow surface properties and surface albedo, and retrieval of cloud optical depth (tau) and effective droplet size ( re). Through the improved estimation of solar reflectance in AVHRR channel 3 (3.75 mum) and atmospheric anisotropic correction, a threshold function was found and used for developing an automatic cloud discrimination algorithm over snow/ice surfaces. Thin cirrus was discriminated using the brightness temperature difference between AVHRR channels 4 and 5 and brightness temperature in channel 4. Retrieval of snow grain size and mass-fraction of soot from AVHRR is difficult because of the effects of aerosol in channel 1 and the strong water vapor absorption in channel 2. Retrieval of surface albedo is more promising, but, with the melt of snow/ice, different narrow-to-broadband conversion relations should be used to derive broadband albedo. AVHRR channels 2, 3 and 4 are used to retrieve tau, r e and cloud top temperature simultaneously. Validation of these algorithms with in-situ aircraft measurements by the NCAR C-130 and the NASA ER-2 and with surface measurements obtained during the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment indicates that the retrieved re is close to the "true" value of re, but the retrieved tau tends to be overestimated. Uncertainties of cloud retrievals with regard to cloud cover fraction, vertical inhomogeneity, multi-layer stratification and cloud phase were examined. Inter comparison of different satellite data demonstrates that NOAA-14 AVHRR data for SHEBA is overestimated by 10--20% using the calibration by Rao and Chen (1996). Finally, seasonal variation of surface albedo, cloud properties and SRB over SHEBA was derived based on 1 or 2 AVHRR overpasses per day from April to August, 1998.
  • Till deformation beneath Black Rapids Glacier, Alaska, and its implication on glacier motion

    Truffer, Martin; Harrison, W. D. (1999)
    The motion of a glacier is largely determined by the nature of its bed. The basal morphology and its reaction to the overlying ice mass have been subject to much speculation, because the glacier bed is usually difficult to access, and good field data are sparse. In spring 1997 a commercial wireline drill rig was set up on Black Rapids Glacier, Alaska, to extract cores of basal ice, subglacial till, and underlying bedrock. One of the boreholes was equipped with three tiltmeters to monitor till deformation, and a piezometer to record pore water pressure. The surface velocity and ice deformation in a borehole were also measured. The drill successfully reached bedrock twice after penetrating a till layer, some 5 to 7 m in thickness, confirming an earlier seismic interpretation. The till consisted of a sandy matrix containing clasts up to boulder size. Bedrock and till lithology indicated that all the drill holes were located to the north of the Denali Fault, a major tectonic boundary along which the glacier flows. The mean annual surface velocity of the glacier was 60 ma-1 , of which 20 to 30 ma-1 were ice deformation, leaving 30 to 40 ma-1 of basal motion. The majority of this basal motion occurred at a depth of more than 2 m in the till, contradicting previously held ideas about till deformation. Basal motion could occur as sliding of till over the underlying bedrock, or on a series of shear layers within the till. This finding has implications for the interpretation of the geologic record of former ice sheets, for geomorphology, and for glacier dynamics. The effect of a thick till layer on ice flow and on quantities observable at the glacier surface was calculated. These include velocity changes on secular, seasonal, and shorter time scales. A mechanism for uplift events and dye tracing responses was suggested. An easy surface observation that could serve to clearly distinguish a glacier underlain by till from the more traditional view of a glacier underlain by bedrock could not be identified.
  • Geology and timing of zinc-lead-silver mineralization, northern Brooks Range, Alaska

    Werdon, Melanie Beth; Newberry, Rainer J. (1999)
    The north-central and northwestern Brooks Range of Alaska hosts widespread Carboniferous Zn-Pb-Ag +/- Ba shale-hosted massive sulfide (Sedex) deposits, and Zn-Pb-Ag +/- Cu vein-breccia and disseminated sulfide occurrences. The Sedex deposits are hosted by black carbonaceous shale and siliceous mudstone of the Mississippian to Pennsylvanian Kuna Formation and are spatially associated with minor (e.g. Red Dog) to locally abundant (e.g. Drenchwater) volcanic and hypabyssal intrusive rocks. The vein-breccia and disseminated sulfide occurrences show no obvious igneous association and are hosted by a deformed but only weakly metamorphosed package of Upper Devonian to Lower Mississippian mixed continental and marine elastic rocks (the Endicott Group). Textural, mineralogical, isotopic, chemical, and fluid inclusion data indicate that sulfides, quartz, and lesser carbonates in the Kady vein-breccia and disseminated sulfide prospect were deposited from slightly acidic, low salinity, carbon-destructive, relatively oxidized, low temperature (<250�C) hydrothermal fluids, under evolving chemical conditions (i.e. decreasing temperature and pressure, and increasing pH, fo2, fs2). The lack of known Sedex mineralization in the north-central Brooks Range and the presence of sulfide mineralization within the Endicott Group suggests that Kady represents the hydrothermal fluid pathway below a failed or non-existent Sedex system. Trace element analyses of volcanic rocks and 40Ar/ 39Ar laser step-heating ages indicate the following geologic history for the north-central and northwestern Brooks Range: within-plate alkaline volcanic rocks at Red Dog and Drenchwater were emplaced from approximately 344 Ma to 336 Ma in a continental extensional environment. This presumably set up an elevated geothermal gradient, which heated basinal fluids. Sedex mineralization is estimated to have formed between 337 and ~314 Ma by basinal dewatering. 40Ar/39Ar ages of recrystallized white mica in Upper Devonian sandstone adjacent to large sulfide-bearing vein-breccia zones fall within the independently estimated time frame for Sedex mineralization. Tholeiitic gabbro magmatic activity occurred around 276 +/- 15 Ma. The transition with time from within plate alkaline to tholeiitic magmatism suggests progressive episodic extension in a continental basin.
  • Returning: Twentieth century performances of the King Island Wolf Dance

    Kingston, Deanna Marie; Morrow, Phyllis (1999)
    In 1982 and again in 1991, the King Island (Alaska) Native Community revived the Wolf Dance, which is a complex ritual involving songs, dances, feasts, competitive games and an exchange of goods. The object of this dissertation is to discover why they chose to revive the Wolf Dance, rather than the Polar Bear Dance which was their most significant ritual in the early twentieth century. Archival sources and other literature pertaining to Inupiaq and Yup'ik ceremonialism were consulted in order to interpret the meaning and purpose of the Wolf Dance. In addition, contemporary King Island community members were interviewed in order to obtain their interpretations. Videotapes of both the 1982 and 1991 performances were viewed in order to gain information not obtained in either written or oral sources. Finally, archival sources were again searched to understand the interactions between King Islanders and members of Western society, including missionaries, tourists, public folklorists, and agents of the Bureau of Indian Affairs. This dissertation concludes that the Wolf Dance was revived for reasons that served both individuals and the community. Organizers of Wolf Dance performances desired to enact either their own or a family member's return to the community. The King Island community performed the Wolf Dance either to create peace or to encourage youth to return to traditional activities. Although particular meanings of the Wolf Dance changed through time, the basic themes of the Wolf Dance (returning, reciprocity, friendship/enmity, and danger) were maintained in contemporary performances. Finally, because the Wolf Dance embodied the cultural value placed on balancing, rather than resolving, tensions and contradictions, this ritual mirrors their perceived need to balance traditions with new influences of Western society. Catholicism was balanced with traditional beliefs, the use of Western resources (such as funding) was balanced with the need to counteract Western forces, and the need to be interdependent with mainland Natives was balanced with their need to be separate from them. Thus, the Wolf Dance reflects not only basic themes of their social order, but also their history of interaction with Western society.
  • Mid -Cretaceous plutonic -related gold deposits of interior Alaska: Characteristics, metallogenesis, gold-associative mineralogy and geochronology

    Mccoy, Daniel Thomas; Newberry, Rainer J. (2000)
    Mid-Cretaccous gold deposits in interior Alaska are hosted in or near apices of low magnetite plutons that formed in a broad continental arc. Ore is hosted in (1) anastomosing quartz veins with potassic or albitic envelopes, (2) planar veins and shear zones with sericitic alteration, and (3) pyroxene-rich skarn deposits. This study was undertaken to constrain the fluid and metal source and composition, formation conditions, gold associative mineralogy, age relationships, and areal extent of this mineralizing event Techniques included reflected light petrographic, 40Ar/39Ar step-heating, stable isotope, fire assay, Mossbauer spectroscopy, electron microprobe, and scanning ion mass spectroscopy analysis. Results suggest ages between 85 Ma and 107 Ma with a 0 to 2 million-year differential between magmatic biotite and hydrothermal veins in the same deposits. Deposits are 10 to 20 million years younger than local metamorphism. Fluid calculated stable isotopic ratios (delta13C = -9 to -10 per mil; delta18O = 5--10 per mil; deltaD = -47 to -100; delta34S = -5 to +5 per mil) suggest gold precipitated from magmatic fluids. Fluid inclusions in ore-bearing quartz contain high CO2 with trapping temperatures and pressures of 270� to 570�C and 0.5 to 2 kb respectively. The Fort Knox and Pogo deposits have a strong Au-Bi association and high relative amounts of potassic; and albitic alteration with mineralogical evidence for the original existence of maldonite (Au2Bi) or Au-Bi melt subsequently overprinted by native gold + bismuthinite. The True North deposit has a strong Au-As association and no Au-Bi association. It lacks potassic or albitic alteration and contains only sub-micron gold, approximately half chemically bound to arsenopyrite or arsenian pyrite. The Dolphin and Ryan Lode deposits are intermediate in Au-Bi association, gold-associative mineralogy and alteration features. Arsenopyrite geothermometry yield temperatures between 300� and 630�C for albitic and potassic alteration and between 250� and 420�C for sericitic alteration. 40Ar/39Ar dating and metal ratios suggest that gold mineralization is (1) solely mid-Cretaceous in the Fairbanks mining district, (2) mid-Cretaceous and late Cretaceous in the Kantishna mining district, and (3) mid-Cretaceous and early Tertiary in the Livengood, district.
  • Subsurface structure of the volcanoes in Katmai National Park, Alaska

    Jolly, Arthur D.; McNutt, Steve; Wyss, Max; Eichelberger, John; Stone, David (2000)
    The three-dimensional velocity, attenuation and b-value structure is mapped beneath the Katmai group volcanoes, located in south-central Alaska. Data for these studies include 4320 earthquakes recorded in the period July 26, 1995 to November 30, 1999 on a 5--18 station short-period seismograph array. The velocity structure is determined by inversion of P-wave travel-times for 8041 rays from 815 earthquakes. The inversion revealed the lowest velocities (3.6--5.0 km/s) centered beneath Novarupta, Trident and Mageik volcanoes between the surface and 4 km below sea level and moderately lower velocities at 0--6 km depth between Martin volcano and Katmai caldera (4.5--6.0 km/s). Higher relative velocities (5.0--6.5 km/s) prevail outboard of the volcanic axis and at Griggs volcano. The attenuation structure is determined by inversion of the amplitude spectra roll off to obtain t* for 1301 rays from 230 earthquakes in the magnitude range (0.8 < ML < 1.8). The inversion, which is well constrained in the depth range 0--6 km, reveals higher attenuation along the volcanic axis 1/Q = 0.008-0.018 (55 < Q < 125) and lower attenuation in non-volcanic regions of the study area 1/Q = 0.01--0.000 (100 < Q < infinity). The attenuation is greatest beneath Mageik, Trident and Novarupta (1/Q = 0.018; Q = 55) between the surface and 6 km below sea level. Frequency-magnitude distributions are determined by mapping b-values for ~1300 earthquakes larger than the magnitude of completeness (0.7 ML). The analysis reveals high b -values at Mageik volcano (1.2--2.2), intermediate b-values at Martin (1.0--1.6) and Katmai caldera (1.2--1.4) and low b-values at Trident (0.6--1.2). Results point to the existence of a large region of partially molten rock centered beneath Mageik, Novarupta and Trident volcanoes at 0--4 km depth. The localized nature of the high b-value zone at Mageik volcano suggests that the magma is discontinuous, occurring as several distinct bodies. The deeper high attenuation anomaly might mark the now solidified but highly fractured plumbing system associated with the 1912 Novarupta eruption.
  • Evaluating interpretive programs

    Pendergrast, Donald Cameron (1998)
    In the face of budgetary shortfalls there needs to be more, not less interpretive program evaluation. Direct evaluation includes the visitor in the evaluation process. Focus groups were tested to achieve direct evaluation for three types of evaluation: front-end, formative, and summative. These tests led to a simplified focus group technique that combines the evaluation objectives, questioning schedule, data recording, analysis, and reporting into one working document resulting in a more efficient and effective method. The Synthesized Model for integrating evaluation and the program development process is presented. The model links the three types of evaluation to appropriate program development stages. It is suggested that direct evaluation with focus groups would fit the model well.
  • Time-dependent electron transport and optical emissions in the aurora

    Peticolas, Laura Marie; Lummerzheim, Dirk (2000)
    This thesis presents the first time-dependent transport model of auroral electrons. The evolution of the spherical electron intensity in phase space is studied for a variety of incident electron intensities. It is shown that the secondary electrons with energies <10 eV and at altitudes >150 km can take over 300 ms to reach steady state in phase space. Since there are bright optical emissions in this region, such a time dependence in the auroral electrons is important. The emissions of N2(2PG) 3371 A and <math> <f> <rm>N<sup>+</sup><inf>2</inf></rm></f> </math> (1NG) 4278 A are studied for time-varying electron pulses to show for the first time that this ratio will change until the secondary electrons reach steady state in the ionosphere. The way in which the 3371A/4278A ratio changes with time-varying precipitation depends on the precipitating electron spectra. The changes in the emission ratio can be used to learn more about the auroral acceleration region and the role of the ionosphere in auroral emissions. Field-aligned bursts (FABs), often observed in electron spectra of instruments flying over flickering aurora, are modeled with the time-dependent transport model. How the ionosphere modifies these electrons is shown. The 3371 and 4278 A emissions of flickering FABs are modeled to study the optical effects of modulated electron intensities in time. A study of 4278 A emissions for electron source regions from 630 to 4,000 km are studied along with frequency variations from 5 to 100 Hz. This study shows that the percent variation of the maximum to the minimum column brightness is less for higher frequencies and more distant source regions. It is shown that with an accurate time-dependent transport calculation and 4278 A emission observations of flickering aurora it should be possible to deduce the source altitude of the modulated electrons creating the optical flickering.
  • Benzene and toluene mixing ratios in indoor air of homes with attached garages and measurement of respective biomarkers of exposure and ventilation effects

    Isbell, Maggie Ann; Duffy, Larry (2000)
    Benzene and toluene mixing ratios were measured in the indoor air of homes with attached garages for several seasons using a thermal desorption GC-FID sampling and analysis protocol (EPA T0-17). Benzene in the living area of these homes ranged from 1--72 ppbv and toluene ranged 3--111 ppbv. The garage levels of benzene ranged from 8--304 pbbv and the toluene levels ranged from 14--591 ppbv. Numerous experiments and a model support the hypothesis of a single source of toluene and benzene. Source strength estimate calculations supported the hypothesis that gasoline in the attached garage is the primary source of these compounds in living area air. They also showed that the home with the air-to-air heat exchangers and forced ventilation had less transport of aromatics than an unventilated home. Perturbation experiments showed that a metal gas can filled with gasoline in the garage and an indoor window open were important factors for benzene and toluene levels in the living areas of the homes. For most experiments, weighted regression analyses of toluene and benzene mixing ratios were consistent with a sole source. Finally, no correlation was observed between the levels of benzene and toluene measured in living areas and their respective urinary biomarkers: t,t-MA and hippuric acid.
  • Electromagnetic scattering by spheroidal particles: Applications to the atmosphere

    Eide, Hans Arthur; Stamnes, Knut (2000)
    An efficient and reliable method is presented for computing the expansion coefficients in the eigenfunction series representing the prolate and oblate spheroidal functions. While the traditional method is based on recurrence relations, infinite continued fractions, and a variational procedure, the new method is based on reformulating the computational task as an eigenvalue problem. In contrast with the traditional method, the new method requires no initial estimates of the eigenvalues, and the computations can be performed using readily available computer library routines. The new method is shown to produce accurate expansion coefficients for the spheroidal functions required to study scattering by particles with a wide range of shapes, sizes, and complex refractive indices [1]. In a previous study in which the scattering characteristics of Polar Stratospheric Clouds (PSCs) were calculated using randomly oriented monodispersions of prolate spheroids [2], the scattering signature of the main types of PSC particles was related to particles of a certain shape and size range. Here these results are used as a reference for testing a new method for calculating the scattering characteristics of PSC like clouds. The method is based on finding the single scattering solution for spheroids using the rigorous Separation of Variables Method (SVM), and then from it obtain the so called T-matrix The following question is addressed: Can the backscatter depolarization returns be used together with other remote sensing techniques to determine either basic shape (degree of needle- or disc-like asphericity) or size information of ice cloud particles? To this end the SVM is again utilized to obtain the T-matrix for a variety of size, shape, and size-shape distributions of ensembles of randomly oriented spheroidal particles. The results indicate that single-wavelength depolarization lidar returns are insufficient to uniquely determine both the size and the shape of the particles in an ice cloud. However, a combination of an NIR depolarization lidar and additional information obtained by complementing instruments---from which either size or shape can be estimated---has the potential for determining the mean size and shape of particles in an ice cloud.
  • Optical spectroscopic observations of sprites, blue jets, and elves: Inferred microphysical processes and their macrophysical implications

    Heavner, Matthew James; Sentman, Davis D. (2000)
    During the past decade, several new upper atmospheric phenomena associated with thunderstorms have been discovered. The four main types of optical emissions are now called sprites, blue jets, lves, and halos. Sprites are primarily red and appear between 40--95 km altitude and last between 1--100 ms. The dominant sprite emission is the molecular nitrogen first positive band, a relatively low energy emission also observed in the red lower borders of aurorae. The total optical energy output of a bright sprite is on the order of 50 kJ. Based on spectral observations, the total vibrational and electronic energy deposited in molecular nitrogen and oxygen in the upper atmosphere is 250 MJ-1 GJ. Blue jets last hundreds of milliseconds and span altitudes 15--40 km. Spectral observations of blue jets have not been obtained to date. Elves, the third type of observed optical emissions above thunderstorms, are red emissions at altitudes 75--95 km, lasting one millisecond or less. Elves and halos are similar phenomena, but are distinct based on altitude and duration. Halos typically last 3--6 ms and occur at lower altitudes than elves. This dissertation describes the optical spectrum of sprites obtained by the University of Alaska Fairbanks during summer campaigns of 1995, 1996, and 1998, and its implication to the understanding of the electrodynamics of the middle atmosphere. The single most significant result is the determination that a typical sprite deposits up to one gigajoule into the mesosphere. These forms of electrical energy coupling from tropospheric thunderstorms into the stratosphere, mesosphere, and thermosphere/ionosphere may have critical implications for the global chemistry and energy budgets in these regions.

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