Now showing items 21-40 of 494

    • 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.
    • Characterization and optimization of the magnetron directional amplifier

      Hatfield, Michael Craig; Hawkins, Joseph G. (1999)
      Many applications of microwave wireless power transmission (WPT) are dependent upon a high-powered electronically-steerable phased array composed of many radiating modules. The phase output from the high-gain amplifier in each module must be accurately controlled if the beam is to be properly steered. A highly reliable, rugged, and inexpensive design is essential for making WPT applications practical. A conventional microwave oven magnetron may be combined with a ferrite circulator and other external circuitry to create such a system. By converting it into a two-port amplifier, the magnetron is capable of delivering at least 30 dB of power gain while remaining phase-locked to the input signal over a wide frequency range. The use of the magnetron in this manner is referred to as a MDA (Magnetron Directional Amplifier). The MDA may be integrated with an inexpensive slotted waveguide array (SWA) antenna to form the Electronically-Steerable Phased Array Module (ESPAM). The ESPAM provides a building block approach to creating phased arrays for WPT. The size and shape of the phased array may be tailored to satisfy a diverse range of applications. This study provided an in depth examination into the capabilities of the MDA/ESPAM. The basic behavior of the MDA was already understood, as well as its potential applicability to WPT. The primary objective of this effort was to quantify how well the MDA could perform in this capacity. Subordinate tasks included characterizing the MDA behavior in terms of its system inputs, optimizing its performance, performing sensitivity analyses, and identifying operating limitations. A secondary portion of this study examined the suitability of the ESPAM in satisfying system requirements for the solar power satellite (SPS). Supporting tasks included an analysis of SPS requirements, modeling of the SWA antenna, and the demonstration of a simplified phased array constructed of ESPAM elements. The MDA/ESPAM is well suited for use as an amplifier or an element in a WPT phased array, providing over 75% efficiency and a fractional bandwidth exceeding 1.7% at 2.45 GHz. The results of this effort provide the WPT design engineer with tools to predict the MDA's optimum performance and limitations.
    • Studies of Bagley Icefield during surge and Black Rapids Glacier, Alaska, using spaceborne SAR interferometry

      Fatland, Dennis Robert; Lingle, Craig S. (1998)
      This thesis presents studies of two temperate valley glaciers---Bering Glacier in the Chugach-St.Elias Mountains, South Central Alaska, and Black Rapids Glacier in the Alaska Range, Interior Alaska---using differential spaceborne radar interferometry. The first study was centered on the 1993--95 surge of Bering Glacier and the resultant ice dynamics on its accumulation area, the Bagley Icefield. The second study site was chosen for purposes of comparison of the interferometry results with conventional field measurements, particularly camera survey data and airborne laser altimetry. A comprehensive suite of software was written to interferometrically process synthetic aperture radar (SAR) data in order to derive estimates of surface elevation and surface velocity on these subject glaciers. In addition to these results, the data revealed unexpected but fairly common concentric rings called 'phase bull's-eyes', image features typically 0.5 to 4 km in diameter located over the central part of various glaciers. These bull's-eyes led to a hypothetical model in which they were interpreted to indicate transitory instances of high subglacial water pressure that locally lift the glacier from its bed by several centimeters. This model is associated with previous findings about the nature of glacier bed hydrology and glacier surging. In addition to the dynamical analysis presented herein, this work is submitted as a contribution to the ongoing development of spaceborne radar interferometry as a glaciological tool.
    • Advancements in seismic tomography with application to tunnel detection and volcano imaging

      Clippard, James Doyle; Christensen, Douglas H.; Pulpan, Hans; Barry, Ronald P.; Harisen, Roger A.; Eichelberger, John C. (1998)
      Practical geotomography is an inverse problem with no unique solution. A priori information must be imposed for a stable solution to exist. Commonly used types of a priori information smooth and attenuate anomalies, resulting in 'blurred' tomographic images. Small or discrete anomalies, such as tunnels, magma conduits, or buried channels are extremely difficult imaging objectives. Composite distribution inversion (CDI) is introduced as a theory seeking physically simple, rather than distributionally simple, solutions of non-unique problems. Parameters are assumed to be members of a composite population, including both well-known and anomalous components. Discrete and large amplitude anomalies are allowed, while a well-conditioned inverse is maintained. Tunnel detection is demonstrated using CDI tomography and data collected near the northern border of South Korea. Accurate source and receiver location information is necessary. Borehole deviation corrections are estimated by minimizing the difference between empirical distributions of apparent parameter values as a function of location correction. Improved images result. Traveltime computation and raytracing are the most computationally intensive components of seismic tomography when imaging structurally complex media. Efficient, accurate, and robust raytracing is possible by first recovering approximate raypaths from traveltime fields, and then refining the raypaths to a desired accuracy level. Dynamically binned queuing is introduced. The approach optimizes graph-theoretic traveltime computation costs. Pseudo-bending is modified to efficiently refine raypaths in general media. Hypocentral location density functions and relative phase arrival population analysis are used to investigate the Spring, 1996, earthquake swarm at Akutan Volcano, Alaska. The main swarm is postulated to have been associated with a 0.2 km$\sp3$ intrusion at a depth of less than four kilometers. Decay sequence seismicity is postulated to be a passive response to the stress transient caused by the intrusion. Tomograms are computed for Mt. Spurr, Augustine, and Redoubt Volcanoes, Alaska. Relatively large amplitude, shallow anomalies explain most of the traveltime residual. No large amplitude anomalies are found at depth, and no magma storage areas are imaged. A large amplitude low-velocity anomaly is coincident with a previously proposed geothermal region on the southeast flank of Mt. Spurr. Mt. St. Augustine is found to have a high velocity core.
    • Systems approach for applying remote video technology and the Internet to real time weather and runway condition reporting for aviation use: Case study at rural airports in interior Alaska

      Buckingham, James Miller; Perkins, Robert; Ra, Jang (2000)
      Aviation is critical to the infrastructure of Alaska. However, systems that provide runway and weather condition information about rural airstrips are not meeting the needs of the aviation community. Accordingly, aviation safety is compromised, efficiency of operations is reduced and service to clients is mediocre. Research was conducted to determine methods of improving the accuracy and reliability of runway and weather condition reporting Systems in Interior Alaska. A thorough background study of current reporting systems was conducted. A statistical study of aviation accidents in Interior Alaska was completed to document the premise that runway condition and weather reporting systems contribute to the problem. Current reporting systems were analyzed to isolate root causes of system degradation. An analysis of primary stakeholders associated with aviation reporting systems was completed. An hypothesis was formed which favored the use of remote video camera technology to provide near real-time weather information directly to end users A $114 K grant was obtained to conduct a test of the capabilities and benefits that would accrue from transmitting images of distant runway and sky conditions onto the Internet. For nine months, images of the sky and runway from three distant airstrips in Ruby, Kaltag and Anaktuvuk Pass, Alaska were transferred every thirty minutes to a publicly accessible website for use by the aviation community in assessing current conditions for preflight planning. Technical feasibility was confirmed. It was clearly determined that the system exceeded the expectations of the aviation community and provided greatly improved weather information to pilots. The aviation community in Interior Alaska has embraced the concept, used it operationally and declared it to be a critical enhancement to current systems. The project was an overwhelming success as confirmed by surveys, national and international media releases, and intense interest in the project by both private and governmental agencies. Aspects of the system are now patent pending. The research concluded that the remote video concept should be expanded throughout Alaska under the auspices of the Federal Aviation Administration (FAA) and/or the National Weather Service (NWS). Strong evidence was obtained to support potential expansion throughout the United States and internationally.
    • An investigation of small-scale relationships between optical and HF radar aurora

      Besser, Veronika; Smith, Roger (2000)
      An investigation is undertaken of the relationship between visual aurora and the occurrence of radar-detectable irregularities in the nightside ionosphere. Understanding how auroral signatures appear in HF radar backscatter could combine the advantages of detailed information about auroral fluxes in optical measurements with extended coverage of HF radars. Auroral particle precipitation ionizes the ionosphere and creates localized plasma density enhancements. Irregularities with various smaller sizes are generated from larger density structures through instability-induced cascading. HF waves are coherently scattered by decameter structures within the ionospheric plasma. Hence aurorally induced irregularities can be seen by the radar in the form of "HF radar aurora." A statistical treatment of the occurrence of optical and HF radar aurora reveals a high degree of variability in backscatter patterns even under seemingly similar auroral displays. The small-scale correspondence between visual aurora and HF backscatter thus represents a more differentiated picture than the spatially and temporally averaged data of earlier studies. The relationship between the occurrence or the characteristics of aurora and the occurrence of HF echoes can therefore not be quantified. An analysis of single events isolates processes that lead to the observed variety of backscatter patterns in the presence of aurorally induced irregularities. They involve the ambient ionospheric density and localized enhanced densities at different altitude regimes and locations in the path of the radar signal. Conditions for HF wave propagation are partly determined by the aurora itself, partly they are imposed by ambient ionospheric density levels. It is found that low or high ambient densities have a dominating effect on the success of ionospheric probing. Low densities hamper the return of radar signals despite the presence of irregularities. High ambient densities can overcome some of the adverse effects on HF wave propagation associated with sporadic E. The information contained in the diversity of the relationships between optical and HF backscatter improves thus our knowledge about the nighttime ionosphere. A more detailed specification of ionospheric parameters is necessary to gain better insight into these relationships.
    • Relationship between the aerosol number distribution and the cloud condensation nuclei supersaturation spectrum

      Cantrell, Will Hart, Ii; Shaw, Glenn E. (1999)
      Though Cloud Condensation Nuclei (CCN) are a subset of atmospheric aerosol, relatively little is known of what links the two. A recently developed instrument called the CCN Remover, which directly relates the CCN supersaturation spectrum to the aerosol number distribution, is described. Instrumental errors are quantified and laboratory tests used to verify the instrument's accuracy are also presented. We made measurements with the CCN Remover in the Aerosol Characterization Experiment 2 (ACE 2) and the INdian Ocean EXperiment (INDOEX). These two multinational field campaigns shared the objective of investigating aerosol particles' ability to modulate cloud albedo by activating as CCN. In both instances, we found that aerosol particles were not activating with the characteristics of pure ammonium sulfate, which is generally regarded as the major component of the majority of aerosol particles which act as CCN. Either a substantial fraction of the aerosol was not participating in the activation process or the presence of a hydrophobic surface film inhibited water vapor transport. Measurements of the aerosol's chemical composition and hygroscopic growth factors are used to examine these possibilities. Anthropogenic activity is modifying the properties of natural aerosol particles in a way which could affect their ability to act as CCN. We discuss evidence for aerosol particles coated with sulfuric acid in an Arctic air mass in support of this claim. In some instances, the connection between aerosol and CCN can be inferred directly from the aerosol number distribution. Clouds segregate aerosol into two populations---those that act as CCN and those that do not, and when the cloud evaporates, the aerosol number distribution bears the signature of the cloud through which it has cycled---a minimum in the aerosol number distribution. The diameter at which this minimum occurs can be related to the maximum supersaturation in the cloud, and the number of particles larger than the minimum is the population of particles that acted as CCN. Over 1,000 bimodal aerosol number distributions from five widely separated locations have been analyzed for maximum supersaturation and cloud droplet (or CCN) et (or CCN) concentrations.
    • Development of a spatially distributed model of Arctic thermal and hydrologic processes (MATH)

      Zhang, Ziya; Kane, Douglas L. (1998)
      A process based, spatially distributed hydrologic model with the acronym MATH (Model of Arctic Thermal and Hydrologic Processes) is constructed to quantitatively simulate the energy and mass transfer processes and their interactions within arctic regions. The impetus for development of this model was the need to have spatially distributed soil moisture data for use in models of trace gas fluxes (carbon dioxide and methane) generated from the carbon-rich soils of this region. The model is applied against the data from the Imnavait watershed (2.2 $\rm km\sp2)$ and the Upper Kuparuk River basin (146 $\rm km\sp2)$ located on the North Slope of Alaska. Both point and spatially distributed data such as precipitation, radiation, air temperature, and other meteorological data have been used as model inputs. Based on the digital elevation data, one component of the model determines drainage area, channel networks, and the flow directions in a watershed that is divided into many triangular elements. Simulated physical processes include hydraulic routing of subsurface flow, overland flow and channel flow, evapotranspiration (ET), snow ablation, and active layer thawing and freezing. This hydrologic model simulates the dynamic interactions of each of these processes and can predict spatially distributed snowmelt, soil moisture, and ET over a watershed at each time step as well as discharge at any point(s) of interest along a channel. Modeled results of spatially distributed soil moisture content, discharge at gauging stations and other results yield very good agreement, both spatially and temporally, with independently derived data sets, such as Synthetic Aperture Radar (SAR) generated soil moisture data, field measurements of snow ablation, measured discharge data and water balance computations. The timing of simulated discharge results do not compare well to the measured data during snowmelt periods because the effect of snow damming on runoff generation is not considered in the model. It is concluded that this model can be used to simulate spatially distributed hydrologic processes within the arctic regions provided that suitable data sets for input are available. This physically based model also has the potential to be coupled with atmospheric and biochemical models.
    • Wild-type and mutant 2,2-dialkylglycine decarboxylases: The catalytic role of active site glutamine 52 investigated by site-directed mutagenesis and computer analysis

      Woon, See-Tarn (1998)
      The ability of pyridoxal 5$\sp\prime$-phosphate (PLP)-dependent 2,2-dialkylglycine decarboxylase (DGD) to catalyze decarboxylation and transamination of amino acids at a single active site depends on the subsite within the active site that cleaves $\alpha$-H and $\alpha$-COO$\sp-$ bonds. As observed in the crystal structure, the strategic position of glutamine 52 at the active site suggests a role in enhancing decarboxylation via formation of a hydrogen bond to the substrate carboxyl group. Supporting evidence for this hypothesis is provided by studies with glutamine 52 active site mutants, computer modeling and protein sequence analyses. Ten mutant DGDs containing alanine, asparagine, aspartate, arginine, glutamate, glycine, histidine, leucine, lysine, and tryptophan at position 52 were produced. All, except the histidine mutant, exhibited decreased rates of decarboxylation compared to wild-type. Histidine and asparagine mutants showed measurable decarboxylation rates. These results and that of wild-type DGD suggest that hydrogen bonding with the substrate is required for decarboxylation. Mutants incapable of hydrogen bonding to the substrate, such as alanine, leucine and tryptophan mutants, showed negligible decarboxylation reactions. Transamination rates increased for some mutants and decreased for others. These data imply that the DGD subsite is influenced by the presence of glutamine 52. Furthermore, there is evidence showing that the subsite environment of wild-type DGD, the histidine and the glutamate mutants are different; the three DGD forms exhibited different chromophores at around $\rm\lambda\sb{max}$ of 500 nm when treated with 2-methylalanine or L-alanine in the presence of 3% glycerol. These results have important implications for other PLP-dependent enzymes, such as ornithine aminotransferase and $\gamma$-aminobutyrate aminotransferase. Since protein sequence alignment indicates DGD is homologous to the two aminotransferases, mutations at amino acid position corresponding to glutamine 52 of DGD at the active sites of these aminotransferases could disrupt the functionality of the enzymes. Protein sequence alignment showed that all but one of the PLP-dependent aminotransferases lack residues at position 52 capable of hydrogen bonding with the substrate carboxyl group, further re-affirming the role of glutamine 52 in decarboxylation.
    • An investigation of cusp latitude magnetosphere-ionosphere physics: A time series analysis approach

      Szuberla, Curt A. L.; Olson, John V. (1997)
      The shocked solar wind plasma of the magnetosheath has direct access to the Earth's high-latitude ionosphere and upper atmosphere only through the magnetospheric cusps. The interaction of solar and terrestrial plasmas and fields in these regions has made them an obvious choice for the study of coupling processes in the geospace environment. Some of the information regarding these processes is manifest in the transmission and generation of wave energy, a portion of which can be detected by ground-based magnetometers. In the present day, records of the magnetic field are stored in a digital format; therefore, some form of signal processing is required to extract meaningful physical information from them. This thesis is aimed at the physical characterization of the cusp region through the careful application of digital time series analysis techniques to ground-based magnetometer records. It is demonstrated that judicious application of signal processing techniques can yield new, physically meaningful results from ground-based magnetometer records, and aid in the understanding of disparate reports from groups using different analysis techniques on like data. Characterization of the cusp region is couched in terms of three specific, open problems of the physics of magnetic perturbations in the cusp: (1) the coherence of localized pulsations, (2) the spatiotemporal nature of the cusp magnetic spectrum, and (3) the ground-based magnetic determination of the separatrix. The first problem is addressed by assuming that localized pulsations are coherent only over some finite spatial extent. A statistical measure of interstation coherence is developed to estimate an upper bound of ${\cal O}$(200 km) for the coherence length of this class of pulsations. The second problem is addressed by examining the ultra low frequency polarization spectrum. An information theoretic measure is established as a quantitative means of discriminating the spatial passage of the cusp by ground-based magnetic means. This procedure replaces previous determinations which were made "by-eye." Finally, separatrix identification is addressed by applying the statistical interstation coherence measure to pulsations presumably representative of a magnetic field line resonance. The analysis indicates that a determination is not possible to a resolution better than ${\cal O}$3(300 km).
    • The mass balance and the flow of a polythermal glacier, McCall Glacier, Brooks Range, Alaska

      Rabus, Bernhard Theodor; Echelmeyer, Keith (1997)
      Studies of surface motion and geometry, ice thickness, and mass balance were carried out on the arctic McCall Glacier. They revealed characteristic processes of glacier flow and mass balance that independently reflect the polythermal temperature regime of the glacier, which consists of cold ice except for a discontinuous layer of temperate ice at the base. Analysis of the present flow of McCall Glacier showed the longitudinal stress coupling length to be significantly larger than on temperate glaciers. This is a consequence of the smaller mass balance gradients and associated lower strain rates of arctic glaciers. Furthermore, flow analysis suggests year-round basal sliding beneath a section of the lower glacier, which accounts for more than 70% of the total motion. This sliding anomaly is reflected in corresponding anomalies of the observed ice thickness and surface profiles. Changes in surface velocity, both on a decadal and on a seasonal scale, were also studied. Velocities during the short summer season increase by up to 75% above winter values as a result of enhanced basal sliding at the temperate glacier bed. The zone affected by this speed-up extends upglacier of any obvious sources of meltwater input to the bed. The mass balance of McCall Glacier exhibits a trend towards increasingly negative values. This is shown by both annual measurements during 1969-72 and 1993-96 and by comparing long-term values for two periods, 1957-71 and 1972-93. The contribution of refreezing surface water in the cold surface layers of firn and ice (internal accumulation) to the net accumulation was found to increase from about 40% in the 1970s to more than 90% in the 1990s. Comparative studies of long-term volume changes of neighboring glaciers showed that the McCall Glacier mass balance is regionally representative. Existing good correlations of the mass balance with meteorological parameters recorded by a weather station more than 400 km to the east furthermore suggest that McCall Glacier is representative on a synoptic scale and thus is a valuable indicator of climate change in the Arctic.
    • Natural disturbance at the site and landscape levels in temperate rainforests of southeast Alaska

      Ott, Robert A.; Juday, Glenn Patrick (1997)
      Wind disturbance in forests of southeast Alaska is poorly understood. Dynamics of canopy gaps, formed primarily by wind, were investigated in the western hemlock (Tsuga heterophylla)/blueberry (Vaccinium spp.)/shield fern (Dryopteris austriaca) plant association in northern southeast Alaska; twenty gaps were sampled at each of 3 sites. Gaps comprised about 9% of the forest area. The majority of gaps were $<$50 m$\sp2$ in area, had a diameter-to-height (D/H) $<$0.50, were created from the death of 1 or 2 gapmakers, and had experienced gap expansion. Emulating the small-scale natural disturbance regime would be best achieved if single tree selection and small group selection cuts were administered within a stand. Diffuse light levels were greatest and most variable at both the shrub and herb layers in canopy gaps, and lowest and least variable under closed canopy forest. Shrub layer light levels were positively associated with mean and median canopy gap areas. Herb layer light levels, however, were determined by the amount of light interception at the shrub layer and not by canopy gap size. Most species were robust in terms of their light requirements compared to the range of light conditions present in the understory. Sorenson Index values indicated that gaps and closed canopy forest generally were very similar in species composition. Seedling heights suggest that western hemlock and Sitka spruce seedlings benefit from the presence of canopy gaps. However, the ability of Sitka spruce to maintain itself through gap-phase replacement is limited. Techniques are needed that allow forest managers to interpret wind patterns in remote locations, at both site- and landscape-levels, and across complex topography. I demonstrated the use of circular data analysis of treefall directions as a technique to investigate wind flows at the site-level. I also demonstrated the feasibility of mapping wind flows across a large landscape of complex terrain in southeast Alaska using flagged trees, treefall directions of large-scale natural blowdowns, and treefall directions of blowdowns associated with clearcuts.
    • Seismic array processing and computational infrastructure for improved monitoring of Alaskan and Aleutian seismicity and volcanoes

      Lindquist, Kent Gordon; Hansen, Roger; Wyss, Max; Christensen, Douglas; McNutt, Stephen (1998)
      We constructed a near-real-time system, called Iceworm, to automate seismic data collection, processing, storage, and distribution at the Alaska Earthquake Information Center (AEIC). Phase-picking, phase association, and interprocess communication components come from Earthworm (U.S. Geological Survey). A new generic, internal format for digital data supports unified handling of data from diverse sources. A new infrastructure for applying processing algorithms to near-real-time data streams supports automated information extraction from seismic wavefields. Integration of Datascope (U. of Colorado) provides relational database management of all automated measurements, parametric information for located hypocenters, and waveform data from Iceworm. Data from 1997 yield 329 earthquakes located by both Iceworm and the AEIC. Of these, 203 have location residuals under 22 km, sufficient for hazard response. Regionalized inversions for local magnitude in Alaska yield $\rm M\sb{L}$ calibration curves $\rm (logA\sb0)$ that differ from the Californian Richter magnitude. The new curve is $\rm 0.2\ M\sb{L}$ units more attenuative than the Californian curve at 400 km for earthquakes north of the Denali fault. South of the fault, and for a region north of Cook Inlet, the difference is $\rm 0.4\ M\sb{L}.$ A curve for deep events differs by $\rm 0.6\ M\sb{L}$ at 650 km. We expand geographic coverage of Alaskan regional seismic monitoring to the Aleutians, the Bering Sea, and the entire Arctic by initiating the processing of four short-period, Alaskan seismic arrays. To show the array stations' sensitivity, we detect and locate two microearthquakes that were missed by the AEIC. An empirical study of the location sensitivity of the arrays predicts improvements over the Alaskan regional network that are shown as map-view contour plots. We verify these predictions by detecting an $\rm M\sb{L}$ 3.2 event near Unimak Island with one array. The detection and location of four representative earthquakes illustrates the expansion of geographic coverage from array processing. Measurements at the arrays of systematic azimuth residuals, between $5\sp\circ$ and $50\sp\circ$ from 203 Aleutian events, reveal significant effects of heterogeneous structure on wavefields. Finally, algorithms to automatically detect earthquakes in continuous array data are demonstrated with the detection of an Aleutian earthquake.
    • Microbial ecology and long-term persistence of crude oil in a taiga spruce forest

      Lindstrom, Jon Eric; Braddock, Joan F. (1997)
      The microbial ecology of a 1976 experimental crude oil spill in an Alaskan taiga black spruce forest was investigated in this study. Substantial oil residue remained in the soil, and several microbial parameters showed evidence of long-term oiling effects. Overall, the data suggest that the surviving community in the oiled plot has shifted toward using oil C for growth. Numbers of hydrocarbon degrading microbes, and specific hydrocarbon mineralization potentials, were significantly elevated in the oiled (OIL) plot compared to an adjacent oil-free, reference (REF) plot. Glutamate mineralization potentials and soil C mineralization, on the other hand, were not different between treatments, suggesting that OIL plot heterotrophs were well-acclimated to the oil. Despite little difference between OTL and REF soils in total C mineralized in vitro, net N mineralized was lower and net nitrification was absent in OIL soils. Analysis of the residual oil indicated minimal amounts of N were added with the spilled oil. Biomasses of total fungi and bacteria, and numbers of protozoa, showed no consistent effects due to oiling, but metabolically active fungal and bacterial biomasses were uniformally lower in OTL samples. Community-level multiple substrate metabolism (Biolog) was assessed using a new technique for extracting kinetic data from the microplates. This analysis suggested that the microbial population diversity in the OIL soils was lower than in REF soils. Further, these data indicated that the surviving populations in the OIL plot may be considered metabolic generalists. Some evidence of crude oil biodegradation was seen in the chemistry data, but enrichment of the oil residue in higher molecular weight components, duration of contact with soil organic material, and slow rates of C mineralization indicate the crude oil will persist at this site for decades. Contamination of Alaskan taiga soil at this site has yielded observable long-term microbial community effects with larger-scale consequences for ecosystem function.
    • Plant-herbivore interactions on the Yukon-Kuskokwim Delta: The effect of goose herbivory on arrowgrass

      Mulder, Christa Pauliene Hilda (1996)
      I examined effects of herbivory by black brant geese (Branta bernicla nigricans) on the small herbaceous perennial Triglochin palustris (arrowgrass) in a subarctic saltmarsh in SW Alaska. I investigated effects of biomass removal, and indirect effects of geese (changes in resource availability and competition) to compare the role of selective herbivory in this mixed-species environment with that of herbivory in monospecific saltmarsh communities. I manipulated nutrient availability, light availability, and salinity in a transplant experiment, and manipulated size of arrowgrass, and neighbor size and feces deposition in exclosure experiments. Additional experiments examined relationships between size, biomass allocation, survival and reproduction, and explanations for low rates of sexual reproduction in arrowgrass. A cellular automata model was used to investigate potential long-term effects of changes in grazing intensity. Direct effects of geese were smaller than indirect effects: biomass removal had little effect on rates of population growth or plant size, and resulting changes in biomass allocation did not affect survival or reproduction. For unclipped arrowgrass, feces deposition resulted in increased competition for light, which was ameliorated by consumption of neighboring plants, but some species may provide protection from grazing. Expansion into neighboring communities is limited by physical factors on the sea-side end of the distribution, and by competition for light and high selectivity on the inland end. Overall effects of changes in grazing pressure will depend on changes in goose foraging behavior and selectivity. Trade-offs exist between sexual reproduction and all other functions, and sexual reproduction may increase risk of herbivory. Goose effects occur at several spatial and temporal scales: immediately (through biomass removal), within a growing season (through changes in competition and resource availability), over several growing seasons (through feedbacks to foraging behavior), and over long periods (through changes in reproduction). Model results suggest increased grazing intensity may not decrease arrowgrass populations under some conditions, and that spatial distribution of geese affects population dynamics of arrowgrass. There is no evidence that feces deposition results in greater productivity of preferred species. More detailed knowledge of goose foraging behavior at several spatial and temporal scales is needed in order to understand the dynamics of this system.
    • Seismic detection of transient changes beneath Black Rapids Glacier, Alaska

      Nolan, Matthew Allen (1998)
      To gain new insight into the mechanisms of basal motion, I have demonstrated the feasibility of an active seismic technique to measure temporal changes in basal conditions on sub-hourly time-scales. Using changes observed in the summer of 1993 on Black Rapids Glacier, I have determined part of the basal morphology and the mechanisms of seismic change there. One region of the glacier's bed was monitored daily using seismic reflections, for a period of 45 days. The majority of these reflections were nearly identical. However, the englacial drainage of two ice-marginal lakes and one supra-glacial pothole upglacier of the study site each caused significant anomalies in the daily reflections, as well as dramatic increases in basal motion. Two of these seismic anomalies were nearly identical despite the fact that their drainage events occurred at different locations. Further, these two seismic anomalies were followed by records identical to the non-anomalous state, showing that the changes were seismically reversible. In one of these events, two records taken 36 minutes apart revealed that the transition between the anomalous and normal states occurred completely within this short interval. Reflection arrival times during the anomalies require that a basal layer at least 5 m thick was either created or changed in situ. Reflection amplitudes indicate that such a layer could be either water or a basal till, but water layers of such thickness are not physically reasonable. Published values of wave speeds and densities of till are then compared to those constrained by the observed reflection coefficients. Only a decrease in till saturation can produce the observed changes in reflection amplitudes in the time required. Because the transition from anomalous to normal states can occur in as little as 36 minutes, any mechanisms involving the diffusion of water through a thick till layer are ruled out, such as a change in porosity or pore-water (or effective) pressure. We therefore interpret the cause of the seismic anomalies as due to a temporary decrease in saturation, and propose that such a change may occur quickly and reversibly following a lake drainage by a redistribution of the overburden pressure.