• Atmospheric forcing of wave states in the southeast Chukchi Sea

      Francis, Oceana Puananilei; Atkinson, David; Bhatt, Uma; Metzger, Andrew; Walsh, John; Weingartner, Thomas (2012-05)
      The objective of this study was to assess the impact that the ocean state, particularly ocean waves, have on coastal communities and operations in the Western Alaska region. In situ measurements and one-dimensional spectra models, were used to link observed wave activity – wind-sea and swells – to their synoptic drivers. Bottommounted Recording Doppler Current Profilers (RDCPs) were placed at offshore and nearshore locations in the southeast Chukchi Sea, Alaska, during 2007 and 2009-2010. The highest significant wave height (SWH) “events” were defined as wave heights above 2m and 3m for a duration of 6h or more. Results show that SWH events appeared to be driven by three types of systems, 1) cyclonic systems that moved into the eastern Bering Sea and then stalled there, 2) cyclonic systems that moved into the eastern Chukchi Sea and then loitered there, and 3) a cyclonic system over the Brooks Range, a less common occurrence. Results also show the offshore region having highest SWHs with an east wind and wave direction, and classified as a wind-sea state. For the nearshore region, highest SWHs with south and west wind and wave directions, generally showed a swell state. Agreement between one-dimensional spectral models and in situ measurements was greatest for the higher wind-sea state in the offshore region, while discrepancies arose for the lower swell state in the nearshore region. Cross-validation of in situ measurements with satellite altimeter radar measurements were also conducted. Good correlation was found for the offshore regions iv but not for the nearshore regions. Satellite observations were also used to assess wave conditions in the Arctic during the years 1993-2011. A 0.020m/year increase of SWH for the SE Chukchi Sea and a 0.025m/year increase for the Pacific-Arctic, was found which correlates well with diminishing sea ice and the heighted wind speed, also shown in this study.
    • Atmospheric moisture transport and its impact on the water cycle over Alaska and Hawaii: the roles of the Pacific Decadal Oscillation and El Nino

      Borries, Cecilia J.; Zhang, Xiangdong; Bhatt, Uma; Mölders, Nicole (2014-05)
      Precipitation over the North Pacific can fluctuate under climate patterns such as the Pacific Decadal Oscillation (PDO) and El Niño-Southern Oscillation (ENSO). In order to better understand the role which these climatic patterns play in the North Pacific water budgets and pathways, we employed the Community Atmosphere Model 5.0 (CAM) and conducted sensitivity experiments to examine how atmospheric moisture convergence and moisture transport respond to sea surface temperature (SST) anomalies associated with the PDO and ENSO phase transitions. We have found that changes in transient moisture transport, as the PDO phase shifts from cool to warm, are due to increases in specific humidity and decreases in wind speeds over Alaska and the North Pacific. Additionally, increases in moisture convergence, specific humidity, and wind speeds and decreases in transient moisture transport are seen over the North Pacific during El Niño events compared to La Niña events.
    • Atp-Dependent Chromatin Remodeling Complexes In Xenopus Development

      Brown, Elvin E.; Krebs, Jocelyn E.; Drew, Kelly (2010)
      A central question in the study of vertebrate development is how to account for the exquisite interplay of genes within differentiating cells and of groups of cells as they create the organs of the vertebrate embryo. Recently it has become clear that gene regulation by epigenetic processes adds a formerly unappreciated level of complexity to the regulatory network of development. One form of epigenetic gene regulation is embodied in ATP-dependent chromatin remodeling complexes, which use the energy of ATP hydrolysis to alter the interactions of DNA and histones. Chromatin remodeling complexes can both promote and repress expression of a gene at the appropriate time and place in vertebrate development. The list of their known roles in development is long and growing. Here I have studied the developmental role of CHRAC17, a subunit of the CHRAC and ATAC complexes, by visualizing its expression and by ablating CHRAC17 function in Xenopus laevis embryos. Whole mount in situ hybridization localized CHRAC17 expression to the neural tube, cranial placodes, and myotomes. Loss of CHRAC17 function following injection of embryos with CHRAC17-specific morpholino oligonucleotides resulted in abnormal development in the neural tube, eyes, notochord, and pharyngeal pouches, underlining the critical importance of CHRAC17 function in Xenopus development. Similarly, ablating the function of CHD4, the ATPase motor of the NuRD chromatin remodeling complex, resulted in severe developmental abnormalities in early Xenopus development.
    • Attenuation of the herbicide glyphosate along railroad corridors in Alaska

      Ballou, Nellie B. (2011-05)
      Following the application of glyphosate in the formulation of AquaMaster® at two contrasting sub-arctic zones along the railroad corridor in Alaska, attenuation of the herbicide glyphosate was investigated. Study sites were established in continental and coastal zones. Glyphosate soil attenuation was similar to temperate regions during the growing season but exhibited an extended persistence during the winter months. Although glyphosate microbial degradation likely slowed during winter, both sites showed evidence of slight glyphosate degradation during the winter months. The coastal site attenuated more rapidly than the continental site which is presumably due to increased rainfall relative to the continental site. Glyphosate attenuation at the coastal site was likely driven by dispersion while microbial degradation was responsible for the attenuation of glyphosate at the continental site. Movement to subsurface soils (10-25 cm) at low concentrations was observed at both sites with slightly more transport at the coastal site than the continental site. Glyphosate transport to groundwater along railroad corridors was not conclusive. Vegetation cover reduction was reduced at the continental site but could not be determined at the coastal site.
    • Attenuation of the LG phase in Interior Alaska

      Marriott, Duncan A. (2002-12)
      A simultaneous inversion of a large dataset produced robust estimates of regional attenuation for the Lg phase in interior Alaska. Data were collected from summer 1999 through summer 2001 from the Broadband Experiment Across the Alaska Range (BEAAR). Spectra calculated from this dataset were used in a nonlinear simultaneous least squares inversion to determine source factors, path effects and site amplification terms. The average regional attenuation of the Lg phase in interior Alaska was found to be: LgQ(f)=166f⁰·⁵⁸ Variation in regional attenuation has two main characteristics: variation on small spatial scales caused by small crustal heterogeneities, and increased excitation of the Lg phase along raypaths perpendicular to the strike of subduction from shallow subduction events due to the effect of the subduction zone geometry. This study also estimated stress drops, site factors, and developed a robust method of estimating seismic moment (Mo) for small events.
    • Attitude determination for small satellites using gps signal-to-noise ratio

      Peters, Daniel; Raskovic, Dejan; Hawkins, Joseph; Thorsen, Denise (2014-05)
      An embedded system for GPS-based attitude determination (AD) using signal-to-noise (SNR) measurements was developed for CubeSat applications. The design serves as an evaluation testbed for conducting ground based experiments using various computational methods and antenna types to determine the optimum AD accuracy. Raw GPS data is also stored to non-volatile memory for downloading and post analysis. Two low-power microcontrollers are used for processing and to display information on a graphic screen for real-time performance evaluations. A new parallel inter-processor communication protocol was developed that is faster and uses less power than existing standard protocols. A shorted annular patch (SAP) antenna was fabricated for the initial ground-based AD experiments with the testbed. Static AD estimations with RMS errors in the range of 2.5° to 4.8° were achieved over a range of off-zenith attitudes.
    • Attributions of blame and social reactions to scenarios of sexual assault of adult women

      Skanis, Marie L.; Lopez, Ellen; Rivkin, Inna; Gifford, Valerie; Worrall, John (2019-08)
      Alaska consistently has the highest rate of sexual assault in the nation, yet research within the state has focused on stranger rape or assaults which were reported to medical or law enforcement professionals. National research suggests these characteristics are not representative of most victims. The current study fills a gap in research by examining the attitudes and reactions towards victims of stranger and acquaintance rape who have disclosed their assault to friends rather than authorities. Attribution theory was hypothesized to underlie relationships between attributions, emotional reactions, and social behaviors that victims encounter. Using an experimental design, participants were randomly assigned to read either a scenario of realistic acquaintance (common) or stereotypical (rare) stranger rape. The stereotypical assault scenario depicted a victim who was attacked outdoors by a stranger in a physically violent manner. The acquaintance rape scenario, in which a woman experiences assault inside her home by a known acquaintance who uses coercive verbal tactics, reflects characteristics of sexual assault that are experienced by most victims. The influences of type of rape, modern sexism, rape myth acceptance, expected peer rape myth acceptance, gender, training, or experience responding to disclosures of sexual assault on participant reactions were explored. It was hypothesized that participants reading the acquaintance rape scenario, participants with higher acceptance of negative attitudes (rape myths and modern sexism) and expectations that peers accept high levels of rape myths, male participants, and those who lack training or experience responding to disclosures would report more negative attributions (high fault and blame), emotional reactions (low empathy and high anger), and social reactions to the victim and positive reactions towards the perpetrator (low attributions of fault and blame, high empathy and low anger). Results revealed that acceptance of modern sexism, rape myths, and expecting that friends accept rape myths were associated with higher attributions of fault and blame to the victim, more anger towards the victim, more empathy felt for the perpetrator, and increased likelihood of offering the victim negative social responses. When asked what would improve response to sexual assault at UAF, participants indicated that changes in training, the UAF community, Title IX processes, awareness, resources, and demonstrating trustworthiness are important. Given these results, recommendations for stakeholders include communicating that most students do not accept modern sexism or rape myths to combat pluralistic ignorance and targeting the most prevalent rape myths in training. Changes to education and awareness efforts are recommended, including conducting sessions in-person, over several sessions, within single-gender groups, and utilization of pre- and post-training outcomes assessments to measure a variety of biases (such as rape myths). Stakeholders are encouraged to use existing research as a framework for teaching students about different types of reactions to disclosures of sexual assault, emphasizing which reactions victims experience as helpful and hurtful. Limitations and strengths of the study are also discussed.
    • Auroral Thermospheric Temperatures

      Cole, Marjorie Althea (1980)
    • Auroral Zone Thermospheric Dynamics Using Fabry-Perot Interferometric Measurements Of The Neutral Oxygen 15867K Emission (Solar Maximum, Electrojets, Temperature)

      Sica, Robert Joseph (1984)
      Forty-four nights of thermospheric neutral wind and temperature measurements were obtained from College, Alaska (65(DEGREES) invariant latitude) during solar maximum using a ground-based Fabry-Perot interferometer. When averaged by increasing geomagnetic activity, the wind exhibits two main features. First, the general flow pattern, poleward and westward in the evening, changing to southward and eastward in the morning, persists with increasing activity. The flow velocity increases and the change in direction occurs earlier in magnetic local time as the geomagnetic activity increases. Second, as the activity increases, the meridional wind pattern shifts equatorward with the auroral oval. Consequently, the low geomagnetic activity average wind pattern in the north is similar to the moderate activity average pattern in the south. The average thermospheric temperature is governed by the geomagnetic activity and by the previous day's 10.7cm solar flux. The increase in temperature with solar flux is about the same as with auroral activity ((DBLTURN) 225(DEGREES)K). The dynamical behavior on individual nights highlights the importance of local auroral substorms, which can cause large deviations from both global models and the observed averages. Coupling between the E and F regions is inferred by comparing the bulk motion of the optical aurora and the observed wind. Westward-drifting auroral forms accompany the westward evening zonal wind. The arrival of the westward electroject heralds the change from westward to eastward zonal flow, with time delays from less than fifteen minutes to over two hours. Increasing electrojet strength results in higher zonal wind speeds. Around magnetic midnight, as the aurora moves east, the equatorward meridional wind decreases in velocity. Vertical winds are commonly observed and can be quite large and variable, particularly during pulsating aurora. Type-A red aurorae are associated with large (>300(DEGREES)K) temperature increases, consistent with atmospheric heating due to precipitating electrons.
    • Austin Powers meets Robin Hood: exploring texts through drama

      Ragan, Barbara S. (2006-05)
      This research project followed an ethnically and culturally diverse, sixth-grade classroom as they shared and constructed meaning from a selected text through a variety of drama activities. Unlike most studies on drama in the classroom, this research project examined the relationship between social construction of meaning through multiple literacies and the influence this has on student engagement. This study is centered in sociocultural theory, the central premise of which describes human thought as constituted by and originating from language-based social interactions with others. This research project also addressed the concept of multiple literacies and how it applied to the extension of communication choices beyond that of just language. It included drama, film, video, computer technology, visual arts, and music. As traditional forms of reading, writing, and communicating take on new literary forms, students need to be prepared and encouraged to critically think about the information they are exploring, especially in the area of media literacy. Through participant observation, field notes, fieldwork journal entries, audio and video recording, and interviews, I analyzed the students' social learning experiences, and their use of a variety of literacies to enhance and extend the traditional methods of reading, writing, speaking, and listening.
    • Authentic Assessment For Yuuyaraq Middle School Students Based On The Yuuyaraq Curriculum

      Nicholai, Rachel Cikigaq; Cole-Ritchie, Marilee (2010)
      This study examines how the Yuuyaraq curriculum is being applied in the context of a middle school classroom in a small Yup'ik village in Alaska, specifically focusing on how to better assess the outcomes of the curriculum. In the early 1980s, the Yuuyaraq curriculum (YC) was revised to include the seasonal activities of the region, but lacked alignment with the assessments. By using the Participatory Action Research methodology, the researcher identified a problem, observed the situation, analyzed and interpreted the data, and developed an action plan. Data revealed that authentic assessments used in the Yuuyaraq curriculum can be assess Indigenous knowledge, how teachers' indigenous knowledge contributed to a classroom, and how rubrics are in need in a classroom to monitor student progress. The conclusions include various forms of authentic assessments used in the YC, how teacher's knowledge and practice contributed to a classroom that focused on her students' culture and identity and engaged them in a culturally relevant curriculum through the frameworks of sociocultural theory and Indigenous knowledge systems.
    • Authentic Assessment In Action: The Challenges, Success, And Discoveries Made In A 5Th Grade Classroom

      Hendrickson, Kristen I.; Coles-Ritchie, Marilee (2010)
      This research study focuses on the success, challenges, and the discoveries I made implementing authentic assessment in my 5th grade classroom of Alaska Native, English Language Learners (ELLS). The primary goals of this study are to provide students, parents, and education professionals with a more accurate picture of students' academic and language knowledge and skills; and to share my own experience implementing authentic assessments into my classroom. Standardized assessment scores, authentic assessment results, interviews, observations, and my research journal provided the bulk of the data that was analyzed. Two learner profiles were constructed for each participant. The first profile was constructed based on the student's standardized test scores. The second learner profile was constructed from the information obtained about the learner through authentic assessments. This study concludes with my reflections and recommendations regarding the feasibility of implementing authentic assessments in a classroom.
    • Author as ethnographer: The merging of genres in Raymond Carver's and Thomas Pynchon's texts

      Snyder, Megan Dawn; Bird, Roy K. (1999)
      Several of Raymond Carver's short stories and two of Thomas Pynchon's novels are analyzed for their ability to function as ethnography, through which they reveal the dominant and dominated codes in American culture. These texts were approached from an interdisciplinary stance, using theories and concepts from literary criticism, cultural anthropology, and sociology in order to interpret them with a greater degree of accuracy; because the text is treated as an ethnographic representation of a culture, it is possible to turn to it as the sole illustration of cultural elements and, in doing so, to be more open to addressing themes that the text explicates, rather than approaching the it with a preconceived agenda of what necessarily constructs American culture. By focusing in this manner on Carver's and Pynchon's texts as accounts of what is to be "American," it is possible to remain closer to what the texts portray and to avoid misreadings as well as misinterpretations of culture. Through these authors' representations of characters who defy mainstream cultural codes, the reader encounters in these authors' works what mainstream America finds most unsettling: characters who are not only alienated, but also aware of their status as outsiders and, more frequently than not, choose to embrace deviance in their self-definitions. Carver and Pynchon, when taken together, afford the reader with a vision of our culture that explores the dissociation and alienation that cuts through our society regardless of class or background. In their varying presentations of reality, they offer complementary views of distinct American subcultures that feature characters who are isolated and who generally denounce mainstream ideals. Conformist society is merely hinted at within the texts; its presence appears through its absence, characters' recognition of what they are denying, and what characters are denied. Both authors feature characters who identify aberrant behavior, for which rule-breaking individuals are labeled. Characters, once labeled, adopt secondary deviance and instigate a deviant career, from which the authors rarely permit a reprieve. The effect of labeling is the creation of a schism in the social fabric of American culture, which is characterized by the societal exclusion of individuals who do not uphold the dominant beliefs. American culture is also characterized by assimilation; as characters in Carvers and Pynchon's texts resist this process, they pose a threat to the social order, which is the prime factor in their labeling.
    • Automated processing system for tidal analysis of MF radar winds

      Vemula, Sreenivas (2005-12)
      The medium frequency (MF) radar at Platteville, Colorado (40.18° N, 104.7° W) is used to estimate the zonal and meridional wind motions in the middle atmosphere. This radar has been in operation since January 2000. We currently have four years of wind estimates sampled every five minutes. An automated processing system has been developed in IDL to process these estimates and obtain the monthly mean winds and tidal parameters. The automated processing currently processes the wind estimates in time domain analysis using a least square fitting technique. The criteria for determining when the estimated tidal parameters are valid have been studied along with the error analysis of the data and processing. The diurnal and semidiurnal parameters are obtained using this least square fitting method and these tidal parameters are assumed to be valid only when the condition number is less than 10. In the spectral domain, the fast Fourier transform and Lomb-Scargle periodogram methods have been studied. A test signal is generated and its performance using both FFT and Lomb-Scargle methods are discussed for three different cases which are equivalent to our actual data. The results of the wind estimates from 2000-2003 collected using the MF radar have been processed using the automated processing system. This automated processing system can be used to generate the wind parameters on a 24 hour, 7 day a week basis for an elaborate study. Our data are compared with MF radar data from Saskatoon, Canada and Urbana, lllinois. Most of the time our data are similar to the behavior of GSWM-02 model.
    • Automated remote security scoring engine (ARSSE): gamification of cyber security education

      Chauhan, Arsh; Lawlor, Orion S.; Hartman, Christopher M.; Metzgar, Jonathan B. (2020-12)
      The goal of this project is to create an easy to use, extensible, and engaging method to compute scores interactively during a practical cyber security education. Gamification has been shown to be an effective teaching tool and has been used in the offensive cybersecurity education space (via Capture The Flag competitions and challenges such as hackthebox.eu) but there has not been an open-source effort to bring this idea to the defensive side (blue team) aspect of cybersecurity. The Automated Remote Security Scoring Engine (ARSSE, pronounced "Arsh") uses a combination of well maintained open-source tools and custom connectors to facilitate an easy to use, scalable, and secure system to check the state of a computer system against a desired state and award points based on passed checks. ARSSE has been released to the public with the hope that it will fill a gap in training the next generation of information security professionals.
    • Automatic classification of volcanic earthquakes using multi-station waveforms and dynamic neural networks

      Bruton, Christopher Patrick; West, Michael; Tape, Carl; Freymueller, Jeffrey (2014-05)
      Earthquakes and seismicity have long been used to monitor volcanoes. In addition to the time, location, and magnitude of an earthquake, the characteristics of the waveform itself are important. For example, low-frequency or hybrid type events could be generated by magma rising toward the surface. A rockfall event could indicate a growing lava dome. Classification of earthquake waveforms is thus a useful tool in volcano monitoring. A procedure to perform such classification automatically could flag certain event types immediately, instead of waiting for a human analyst's review. Inspired by speech recognition techniques, we have developed a procedure to classify earthquake waveforms using artificial neural networks. A neural network can be "trained" with an existing set of input and desired output data; in this case, we use a set of earthquake waveforms (input) that has been classified by a human analyst (desired output). After training the neural network, new sets of waveforms can be classified automatically as they are presented. Our procedure uses waveforms from multiple stations, making it robust to seismic network changes and outages. The use of a dynamic time-delay neural network allows waveforms to be presented without precise alignment in time, and thus could be applied to continuous data or to seismic events without clear start and end times. We have evaluated several different training algorithms and neural network structures to determine their effects on classification performance. We apply this procedure to earthquakes recorded at Mount Spurr and Katmai in Alaska, and Uturuncu Volcano in Bolivia. The procedure can successfully distinguish between slab and volcanic events at Uturuncu, between events from four different volcanoes in the Katmai region, and between volcano-tectonic and long-period events at Spurr. Average recall and overall accuracy were greater than 80% in all three cases.
    • Automatic detection of changes in volcanic activity using ground based near-infrared cameras to monitor thermal incandescence

      Harrild, Martin C.; Webley, Peter; Dehn, Jonathan; Meyer, Franz (2017-05)
      An increase in thermal activity is a common precursor of volcanic eruptions and, if identified, can be used to advise local observatories to disseminate the appropriate advanced warnings. As continuously operating near-infrared (NIR) cameras are becoming more readily available at active volcanoes around the world, this investigation explores the use of identifying changes in pixel brightness in webcam imagery resulting from increased thermal incandescence. A fast, efficient, and fully automated Python algorithm has been developed with a primary focus on effective volcano monitoring and reducing overall financial costs. The algorithm includes three important tests (statistical analysis, edge detection, and Gaussian mixture model) to identify changes in activity in near-real time. The developed algorithm can be installed locally with a webcam or at a central location, with no need for additional costs. This algorithm approach was preliminarily tested on data from a permanently installed thermal infrared camera at Stromboli volcano, with a successful detection rate of 75.34%. The algorithm based methodology was further developed and applied to freely available online webcam imagery from Shiveluch volcano, with an overall accuracy of 96.0%, and a critical success index (CSI) of 76.7%. Further refinements to the algorithm were made to reduce the false alarm rate (FAR) and number of missed events, and applied to four additional image datasets at Shiveluch, Fuego, Popocatepetl, and Stromboli. The algorithm successfully identified two large eruptions at Shiveluch, between 40 minutes and 2.5 hours prior to other satellite remote sensing methods, correctly identified the beginning of a large eruption at Fuego, which corresponded with local seismic data, and successfully identified a 90-minutes window of increased activity leading to a large paroxysm event at Popocatepetl, which was describe by the local observatory as having 'little to no warning'. The algorithm underperformed at Stromboli as the images here were capture in the thermal infrared (TIR) instead of the NIR, identifying the need for further improvements to ensure the algorithm performs correctly across multiple datasets. Overall, the algorithm developed here identifies thermally incandescent activity from increases in image pixel brightness remarkably well, and would complement existing volcano observatory monitoring tools, especially in remote or financially restricted locations as the equipment and coding language used here are extremely cheap compared to many other monitoring methods.
    • Automatic detection of sensor calibration errors in mining industry

      Pothina, Rambabu; Ganguli, Rajive; Ghosh, Tathagata; Lawlor, Orion; Barry, Ronald (2017-12)
      Sensor errors cost the mining industry millions of dollars in losses each year. Unlike gross errors, "calibration errors" are subtle, develop over time, and are difficult to identify. Economic losses start accumulating even when errors are small. Therefore, the aim of this research was to develop methods to identify calibration errors well before they become obvious. The goal in this research was to detect errors at a bias as low as 2% in magnitude. The innovative strategy developed relied on relationships between a variety of sensors to detect when a given sensor started to stray. Sensors in a carbon stripping circuit at a gold processing facility (Pogo Mine) in Alaska were chosen for the study. The results from the initial application of classical statistical methods like correlation, aggregation and principal component analysis (PCA), and the signal processing methods (FFT), to find bias (±10%) in "feed" sensor data from a semi-autogenous (SAG) grinding mill operation (Fort Knox mine, Alaska) were not promising due to the non-linear and non-stationary nature of the process characteristics. Therefore, those techniques were replaced with some innovative data mining techniques when the focus shifted to Pogo Mine, where the task was to detect calibration errors in strip vessel temperature sensors in the carbon stripping circuit. The new techniques used data from two strip vessel temperature sensors (S1 and S2), four heat exchanger related temperature sensors (H1 through H4), barren flow sensor (BARNFL) and a glycol flow sensor (GLYFL). These eight sensors were deemed to be part of the same process. To detect when the calibration of one of the strip vessel temperature sensors, S1, started to stray, tests were designed to detect changes in relationship between the eight temperature sensors. Data was filtered ("threshold") based on process characteristics prior to being used in tests. The tests combined basic concepts such as moving windows of time, ratios (ratio of one sensor data to data from a set of sensors), tracking of maximum values, etc. Error was triggered when certain rules were violated. A 2% error was randomly introduced into one of the two strip vessel temperature data streams to simulate calibration errors. Some tests were less effective than others at detecting the simulated errors. The tests that used GLYFL and BARNFL were not very effective. On the other hand, the tests that used total "Heat" of all the heat exchanger sensors were very effective. When the tests were administered together ("Combined test"), they have a high success rate (95%) in terms of True alarms, i.e., tests detecting bias after it is introduced. In those True alarms, for 75% of the cases, the introduction of the error was detected within 39.5 days. A -2% random error was detected with a similar success rate.
    • Autonomous Full-Time Lidar Measurements Of Polar Stratospheric Clouds At The South Pole

      Campbell, James R.; Sassen, Kenneth (2006)
      Polar stratospheric clouds (PSC) are an artifact of extremely low temperatures in the lower-stratosphere caused by a lack of sunlight during winter. Their presence induces increased concentrations of chlorine and bromine radicals that drive catalytic ozone destruction upon the return of sunlight in spring. An eye-safe micropulse lidar (MPL; 0.23 mum) was installed at the Scott-Amundsen South Pole Station, Antarctica in December 1999 to collect continuous long-term measurements of polar clouds. A four-year data subset for analyzing PSC is derived from measurements for austral winters 2000 and 2003--2005. A statistical algorithm based on MPL signal uncertainties is designed to retrieve PSC boundary heights, attenuated scattering ratios and demonstrate instrument performance for low signal-to-noise measurements. The MPL measurements consist mostly of Type II PSC (i.e., ice). The likelihood for Type I measurements are described for specific conditions. Seasonal PSC macrophysical properties are examined relative to thermodynamic and chemical characteristics. The potential for dehumidification and denitrification of the lower Antarctic stratosphere is examined by comparing PSC observations to theoretical predictions for cloud based on common scenarios for water vapor and nitric acid concentrations. Conceptual models for seasonal PSC occurrence, denitrification and dehumidification and ozone loss are described. A linear relationship is established between total integrated PSC scattering and ozone loss, with high correlation. Polar vortex dynamics are investigated in relation to PSC occurrence, including synoptic-scale geopotential height anomalies, isentropic airmass trajectories and local-scale gravity waves. Moisture overrunning, from quasi-adiabatic cooling and transport along isentropic boundaries, is considered a primary mechanism for PSC occurrence. Middle and late-season PSC are found to be the result of mixing of moist air from the outer edges of the vortex that coots upon reaching South Pole. Gravity waves are considered to be only a secondary influence on PSC nucleation and growth.