• Calcareous fen vegetation and ecology and the disjunct Betula glandulosa in Southeastern Alaska

      Johnson, Joni M. (2006-08)
      Calcareous fens are rare within southeastern Alaska due to their unique geochemical setting, as are the plant communities produced by these environs. On a global scale these wetland types have been identified as valuable for their biodiversity and have received special protection. The first objective of this research was to characterize the floristics and hydrogeochemistry of a subset of calcareous fens on Chichagof Island in the northern Alexander Archipelago through intensive sampling within each site. Multivariate analyses were used to describe these wetland systems. The second objective of this study included investigating whether or not the disjunct Betula glandulosa (dwarf birch) population was restricted to its current site. B. glandulosa is a habitat generalist in its known range; however, it is found in only one location within the Alexander Archipelago. Germination and seedling transplant experiments were conducted that tested for the effects of site, competition, and the interaction between site and competition. In this manner a subset of calcareous fens in the region was described and abiotic parameters associated with B. glandulosa evaluated. Obtaining baseline information and understanding mechanisms behind these sources of regional biodiversity are important for monitoring purposes and detecting disturbance effects
    • Calving ground habitat selection: Teshekpuk Lake and Western Arctic caribou herds

      Kelleyhouse, Rebecca A. (2001-12)
      Barren-ground caribou (Rangifer tarandus granti) exhibit relative fidelity to calving grounds each spring. The Western Arctic Herd (WAH) and Teshekpuk Lake Herd (TLH) calve separately on Alaska's north slope, each selective of the dominant vegetation type. The WAH consumed mostly sedges, though the TLH diet varied. Despite differing snow conditions between the calving grounds, both herds were selective of the lowest snow cover class. Rugged terrain was avoided by both herds. While the TLH selected a high rate of increase in biomass, the WAH selected high biomass at calving and at peak lactation. Climate trends (1985-2001) were variable. There was a warming trend on the WAH calving ground, though no significant trends were present on the TLH calving ground, as expressed by median NDVI on 21 June. These herds have similar winter ranges and population trends, yet they differ in respect to habitat composition, selection and climate patterns during calving.
    • Camera Trapping Grid Data in Nepal Hindu Kush-Himalaya for regions of Humla 2015 , Manang 2014-2015 and Manang 2016-2017

      Ganga, Regmi; Lama, Rinzin Phunjok; Ghale, Tashi Rapte; Lama, Tenzing; Puri , Ganesh; Huettmann, Falk (2020-04)
      This multi-year, multi-site and multi-species dataset describes Bushnell Camera Trap data from three locations in remote Nepal: Humla 2015, Manang 2014-2015 and Manang 2016-2017. The data from the Hindu Kush-Himalaya region comes from a geo-referenced survey grid and are stored in three MS Excel sheets, also combined and available in CSV consisting of 175658 records and 15 columns with a file size of 19MB. Species covered are Blue Sheep/Bharal (Pseudois nayaur Taxonomic Serial Number TSN 180596 ), Snow Leopard (Panthera unica, Uncia uncia TSN 183811), Beech Marten (Martes foina TSN 621941), Wolf (Canis lupus TSN 180596), birds (Aves Golden Eagle etc.),Pika (Ochotona), Red Fox (Vulpes vulpes TSN 180604), Mountain Weasel (Mustela altaica TSN 621947), Pallas�s Cat (Otocolobus manul, Felis manul TSN 183791), and Golden Jackal (Canis aureus TSN 183817)
    • Capacitance measurements of bulk salinity and brine movement in first-year sea ice

      Backstrom, Lars G. E. (2007-05)
      Sea ice is an important component of the global climate system, as it changes the properties of the ocean-atmosphere interface. Understanding sea ice requires detailed knowledge of its temperature and bulk salinity. To measure these attributes using non-destructive in-situ techniques, instruments were frozen into first-year sea ice, and analysed jointly with ice-core, mass balance and climate data. The bulk salinity of the ice is calculated from measurements of temperature and complex dielectric permittivity at 50 MHz in landfast ice in McMurdo Sound, Antarctica, the Chukchi Sea, Alaska, and in an outdoor tank experiment in Fairbanks, Alaska. A simple relation for estimating brine volume fraction and bulk salinity in columnar, bubble-free ice from the real part of the complex dielectric permittivity was derived. For relative brine volumes below 50-70 % the error in the derived bulk salinity was below 15%. The observed brine movement events are analyzed. The data clearly indicate the extent and impact of brine movement on ice temperature and salinity. The analysis of a drainage event recorded by both the temperature and dielectric permittivity probe provided insight into gravity drainage of brine driven by a large brine reservoir in the freeboard layer.
    • Carbon exchange and permafrost collapse: implications for a changing climate

      Myers-Smith, Isla Heather (2005-05)
      With a warmer climate, the wetlands of Interior Alaska may experience more frequent or extensive stand-replacing fires and permafrost degradation. This, in turn may change the primary factors controlling carbon emissions. I measured carbon exchange along a moisture transect from the center of a sphagnum-dominated bog into a burned forest (2001 Survey Line Fire) on the Tanana River Floodplain. Both the bog and the surrounding burn were sinks for CO₂, and the bog was a CH₄ source in the abnormally dry summer of 2004. Thermokarst and subsiding soils were observed on the margin of the bog in the three years since the fire, increasing the anaerobic portion of the soil landscape. I observed the greatest variation in carbon fluxes in this portion of the transect. I conclude that permafrost collapse is altering the pattern of emissions from this landscape. I tracked historical changes in vegetation, hydrology and fire at this site through macrofossil, charcoal and diatom analysis of peat cores. The paleoecological record suggests that fire mediates permafrost collapse in this system. This study indicates that future changes in temperature and precipitation will alter carbon cycling and vegetation patterns across this boreal landscape.
    • Carbon Sequestration In Alaska's Boreal Forest: Planning For Resilience In A Changing Landscape

      Fresco, Nancy; Chapin, Stuart (2006)
      Northern ecosystems and those who rely upon them are facing a time of unprecedented rapid change. Global boreal forests will play an important role in the feedback loop between climate, ecosystems, and society. In this thesis, I examine forest carbon dynamics and the potential for carbon management in Interior boreal Alaska in three distinct frameworks, then analyze my results in the context of social-ecological resilience. In Chapter 1, I analyze comparative historical trends and current regulatory frameworks governing the use and management of boreal forests in Russia, Sweden, Canada, and Alaska, and assess indicators of socio-ecological sustainability in these regions. I conclude that low population density, limited fire suppression, and restricted economic expansion in Interior Alaska have resulted in a 21st-century landscape with less compromised human-ecosystem interactions than other regions. Relative wealth and a strong regulatory framework put Alaska in a position to manage for long-term objectives such as carbon sequestration. In Chapter 2, I model the landscape-level ecological possibilities for sequestration under three different climate scenarios and associated changes in fire and forest growth. My results indicate that Interior Alaska could act as either a weak carbon source or as a weak sink in the next hundred years, and that management for carbon credits via fire suppression would be inadvisable, given the associated uncertainty and risks. In Chapter 3, I perform a social, ecological, and economic analysis of the feasibility of switching from fossil fuels to wood energy in Interior Alaska villages. I demonstrate that this is a viable option with the potential benefits of providing lower-cost power, creating local employment, reducing the risk of catastrophic wildfire near human habitation, and earning marketable carbon credits. Finally, in Chapter 4, I assess how each of the above factors may impact social-ecological resilience. My results show some system characteristics that tend to bolster resilience and others that tend to increase vulnerability. I argue that in order to reduce vulnerability, management goals for Alaska's boreal forest must be long-term, flexible, cooperative, and locally integrated.
    • Carbonate facies and sequence stratigraphy of the carboniferous Lisburne group, Upper Nanushuk River Region, Central Brooks Range, Alaska

      White, Jesse Garnett (2007-12)
      This study documents the stratigraphy, facies, facies associations, depositional environment, sequence stratigraphy, and conodont biostratigraphy of the upper Nanushuk River section of the Lisburne Group. 1621 meters of Kayak Shale and Lisburne Group rocks were measured and studied for facies analysis. Sixteen lithofacies and eleven microfacies were identified composing six facies assemblages. Facies analysis, stacking patterns, and associations suggest that the Nansushuk River section represents a homoclinal carbonate ramp recording an intertidal (Kayak Shale) and open marine to basin transitional sequence. Facies associations, stacking patterns and marine flooding surfaces helped to delineate major sequence boundaries and maximum flooding surfaces. Six 3rd order stratigraphic sequences have been identified in the Nanushuk River section. The section ranges in age from Osagean to lower Morrowan based on conodont biostratigraphy. The reservoir rock potential of the Nanushuk River section resides primarily in the dolomite of the Wachsmuth Limestone. The remainder of the section is considered 'tight' from a microfacies standpoint. Regionally, this study is important for paleogeographic reconstruction of the Lisburne Group across northern Alaska and adds to the general geologic knowledge of the Lisburne Group by obtaining stratigraphic data from a relatively isolated area in the Brooks Range.
    • Carboniferous Lisburne Group Carbonates Of The Porcupine Lake Valley: Implications For Surface To Subsurface Sequence Stratigraphy, Paleogeography, And Paleoclimatology

      Mcgee, Michelle Marie; Whalen, Michael T. (2004)
      This study utilizes high-resolution stratigraphy and sequence stratigraphy to document the response of the Carboniferous Lisburne Group carbonate platform during a change from greenhouse to icehouse conditions. The Lisburne Group in northern Alaska represents a laterally extensive carbonate ramp deposited on a passive continental margin during a greenhouse to icehouse transition. The Lisburne Group is subdivided into the Mississippian Wachsmuth and Alapah Limestones and Mississippian to Pennsylvanian Wahoo Limestone. I have identified six depositional sequences and corresponding systems tracts within the Lisburne Group based on bounding surfaces, cycle stacking patterns, and lateral lithofacies relationships. The Wachsmuth Limestone (Sequences I and II) is comprised of relatively thick cycles that have a "layer cake" stacking pattern that records minor migration of facies. Cycles in the uppermost Wachsmuth Limestone and the Alapah Limestone (Sequences III and IV) are thick, less "layer cake"-like, have deep water tongues at the base, and record significant migration of facies. Cycles in the uppermost Alapah Limestone and the Wahoo Limestone (Sequences V and VI) are thin, juxtapose deep water over shallow water facies, and record significant migration of facies. An unconformity marked by paleosols and karst features has been documented near the Mississippian-Pennsylvanian boundary in the Wahoo Limestone. I interpret the distinct change in cycle stacking patterns between the Mississippian and Pennsylvanian Lisburne Group to be related to changes in Paleoclimate. I interpret Sequences I through IV to be deposited during a greenhouse and transitional climate; whereas, Sequences V and VI were deposited during an icehouse climate.
    • Causes and consequences of coupled crystallization and vesiculation in ascending mafic magmas

      Lindoo, Amanda N.; Larsen, Jessica F.; Freymueller, Jeffrey; Izbekov, Pavel; Trainor, Tom (2017-08)
      Transitions in eruptive style and eruption intensity in mafic magmas are poorly understood. While silicic systems are the most researched and publicized due to their explosive character, mafic volcanoes remain the dominant form of volcanism on the earth. Eruptions are typically effusive, but changes in flow behavior can result in explosive, ash generating episodes. The efficiency of volatiles to degas from an ascending magma greatly influences eruption style. It is well known that volatile exsolution in magmas is a primary driving force for volcanic eruptions, however the roles vesicles and syn-eruptive crystallization play in eruption dynamics are poorly understood. Permeability development, which occurs when gas bubbles within a rising magma form connected pathways, has been suspected to influence eruption style and intensity. Numerous investigations on natural eruptive products, experimental samples, and analog experiments have extended the understanding of permeability development and fragmentation processes. However, these studies have focused on silicic, high viscosity, crystal-poor magmas. Little progress has been made in understanding fragmentation mechanisms in mafic or alkali magmas. Mafic systems involve lower viscosity magmas that often form small crystals, also known as microlites, during ascent. Because the merging of bubbles in magma is mitigated by melt viscosity, it is predicted that permeability development in mafic magma will occur at lower bubble volume fractions than in silicic magma. However, no study has been performed on experimental samples to provide evidence for this hypothesis. Furthermore, it is unknown how microlites affect the degassing process in terms of facilitating or hindering permeability development. This thesis employs experimental petrology to: 1) experimentally observe how melt viscosity alone affects permeability development, 2) Understand the effects of syn-eruptive crystallization in vesiculating mafic magmas and synergizes these results to 3) relate experimental findings to the 2008 eruption of Kasatochi volcano.
    • Causes and consequences of geophagy in snowshoe hares (Lepus americanus), an important generalist herbivore of the boreal forest

      Worker, Suzanne; Kielland, Knut; Barboza, Perry; Ruess, Roger (2013-12)
      Geophagy, the consumption of mineral soil, is believed to have several benefits for herbivores. Soils high in clay are often implicated in the detoxification of plant secondary metabolites. High mineral concentrations in soils may also provide nutrients that are poorly available from plants. Local observers report that snowshoe hares (Lepus americanus) use a lick in the foothills of the Brooks Range, Alaska. Using soil from this lick and other mineral supplements, I conducted a series of feeding trials on captive snowshoe hares fed felt-leaf willow (Salix alaxensis) or a formulated ration to determine whether geophagy resulted in a physiological benefit and, if so, which soil constituents are therapeutic. When fed willow leaves, hares ate more and lost less weight when they had access to soil. Access to soil increased sodium intake and dietary ratios of sodium to potassium in hares fed willow. Soil consumption resulted in higher calcium to phosphorous ratios for both diets. Across diets, higher sodium to potassium and lower calcium to phosphorus ratios corresponded to reduced weight loss. Access to pure calcium carbonate resulted in reduced weight loss in hares fed winter dormant willow twigs, suggesting that carbonates may also be an important component of this lick.
    • Causes and consequences of variable extrafloral nectar secretions in quaking aspen (Populous tremuloides Michx.)

      Newman, Jonathon R.; Wagner, Diane; Doak, Patricia; Green, Thomas (2014-05)
      Extrafloral (EF) nectaries mediate a defensive mutualism in many plant populations, wherein plants attract predatory arthropods by providing nectar rewards. The primary objectives of this study were to identify abiotic and biotic factors that may affect secretion by EF nectaries in quaking aspen (Populus tremuloides Michx.) and to determine how variation in secretion rate affects attractiveness of P. tremuloides ramets to predatory arthropods such as ants. I investigated the effects of water stress, defoliation, and genotype on extrafloral sugar secretions in P. tremuloides and tested how variations in EF sugar quantity affect ant visitation to P. tremuloides ramets in interior Alaska. Additionally, I analyzed P. tremuloides sugar composition from three genotypes. Extrafloral sugar secretions were inducible by defoliation, and the induction response was not inhibited by water stress. Irrespective of defoliation, water stress had a variable effect on sugar secretion rates between genotypes, with one out of four genotypes exhibiting a reduction in secretion rate in response to low water availability. Genotypes differed in secretion rates overall, which could potentially influence defensive levels among clonal stands. Ant visitation to ramets with experimentally increased sugar availability was increased for one of three genotypes in early summer, though in mid-summer ants did not respond to nectar supplementation. There was no effect of nectar reduction on ant visitation in either early or mid-summer trials. Genotypes attracted different average numbers of ants, which may have been a result of intrinsic variation in volatile organic compound emission, EF nectar secretion rates, or nectar composition. Analysis of EF sugar secretions of P. tremuloides using nuclear magnetic resonance spectroscopy revealed that EF nectar tends to be dominated by sucrose over glucose and fructose. This composition may increase attractiveness to mutualistic ant species, which tend to favor sucrose dominated nectar blends. This study expands our knowledge of the sources of variation in EF nectar secretion and their impact in a widespread, ecologically important tree species.
    • Cenozoic tectono-thermal history of the southern Talkeetna Mountains, Alaska: multiple topographic development drivers through time

      Terhune, Patrick J.; Benowitz, Jeffrey; Freymueller, Jeffrey; Gillis, Robert (2018-08)
      Intraplate mountain ranges can have polyphase topographic development histories reflecting diverse plate boundary conditions. We apply ⁴⁰Ar/³⁹Ar, apatite fission track (AFT) and apatite (U-Th)/He (AHe) geochronology-thermochronology to plutonic and volcanic rocks in the southern Talkeetna Mountains of Alaska to document regional magmatism, rock cooling and inferred exhumation patterns as proxies for the deformation history of this long-lived intraplate mountain range. High-temperature ⁴⁰Ar/³⁹Ar geochronology on muscovite, biotite and K-feldspar from Jurassic granitoids indicates post-emplacement (~158-125 Ma) cooling and Paleocene (~61 Ma) thermal resetting. ⁴⁰Ar/³⁹Ar whole rock volcanic ages and AFT cooling ages in the southern Talkeetna Mountains are predominantly Paleocene-Eocene, suggesting that the Range is partially paleotopography that formed during an earlier tectonic setting. Miocene AHe cooling ages within ~10 km of the Castle Mountain Fault suggest ~2-3 km of vertical displacement that also contributed to mountain building, likely in response to the inboard progression of the subducted Yakutat microplate. Paleocene-Eocene volcanic and exhumation ages across interior southern Alaska north of the Border Ranges Fault System are similar and show no N-S or W-E progressions, suggesting a broadly synchronous and widespread volcanic and exhumation event that conflicts with the proposed diachronous subduction of an active west-east sweeping spreading ridge beneath south-central Alaska. To reconcile this, we propose a new model for the Cenozoic tectonic evolution of southern Alaska. We infer that slab breakoff sub-parallel to the trench and subsequent mantle upwelling drove magmatism, exhumation and rock cooling synchronously across south-central Alaska and played a primary role in the development of the southern Talkeetna Mountains.
    • Central CO2 chemosensitivity in tadpoles: impairment and the role of serotonin

      Audie, Spencer D.; Taylor, Barbara E.; Harris, Michael B.; Duffy, Lawrence K. (2012-05)
      Nicotine and ethanol are known neuroteratogens and prenatal exposure correlates with Sudden Infant Death Syndrome (SIDS), which is thought to result from failure to maintain pH homeostasis through respiratory adjustments. This failed homeostatic control is believed to be serotonergic in origin. In previous studies nicotine or ethanol exposure ablated the robust hypercapnic response of early-stage tadpoles. These findings lead us to question if the ablation occurred through a serotonindependent mechanism. This study investigated the role of serotonin (5- HT) in the nicotine- or ethanol-induced abolishment of the hypercapnic response. We found that toxin-exposed animals were insensitive to hypercapnia and also failed to respond to concomitant exposure to hypercapnia and 8-OH-DPAT, supporting our hypothesis that toxininduced abolishment of the hypercapnic response is mediated by 5-HTia receptors. Immunofluorescence data from brainstem slices of ethanolexposed animals showed a decrease in 5-HTia receptors and the serotonin-synthesizing enzyme tryptophan hydroxylase. In contrast, 3- wk nicotine-exposed animals displayed no significant difference in immunofluorescence for either protein. Taken together the electrophysiological and immunofluorescence data suggest the effects of ethanol or nicotine exposure, which impair the hypercapnic response, include a failure of serotonergic signaling and that this failure is not simply the reflection of a global reduction in serotonin levels.
    • Central Nervous System Regulation Of Metabolic Suppression In Arctic Ground Squirrels

      Jinka, Tulasi Ram; Drew, Kelly L. (2010)
      The main focus of this dissertation is central nervous system regulation of metabolic suppression in hibernating mammals in general, and the Arctic ground squirrel (Urocitellus parryii) as a model for seasonal hibernation. Hibernation is a unique physiological, morphological, and behavioral adaptation to overcome the periods of resource limitation. Metabolic suppression seen in torpor during hibernation has several biomedical applications. A multitude of studies have revealed the role of the central nervous system in regulating hibernation, including a role for neurotransmitters and neuromodulators. Previous studies have shown that the neuromodulator adenosine mediates altered thermoregulation during induction of torpor in facultative hibernators, but it is not clear how adenosine influences torpor in seasonal hibernators. The main focus of the current project was to test the hypothesis that a seasonal change in purinergic signaling is necessary for the onset of spontaneous torpor in the Arctic ground squirrel. My dissertation reports that adenosine meets all of the necessary requirements for an endogenous mediator of torpor in the hibernating Arctic ground squirrel. A progressive increase in sensitivity to adenosine A 1 receptors mediated signaling defines the seasonal transition into the hibernation phenotype. I show that adenosine A1 receptor activation is necessary and sufficient to induce torpor in the Arctic ground squirrel. Glutamate is an excitatory neurotransmitter which is widely studied in hibernation research. My dissertation demonstrates that N-methyl-D-aspartate type glutamate receptors, located in the periphery or circumventricular organs, are involved in inducing arousal from torpor in the hibernating Arctic ground squirrel. This dissertation also presents evidence that dietary restriction sensitizes adenosine A1receptors in rats through an increase in surface expression in thermoregulatory regions of the brain (hypothalamus). This contributes to the decline in body temperature and respiratory rate in animals subjected to a restricted diet, which mimics a torpor-like effect.
    • Ceramide Metabolism Regulates A Neuronal Nadph Oxidase Influencing Neuron Survival During Inflammation

      Barth, Brian M. (2009)
      Inflammation is a major component of acute and chronic pathologies of the central nervous system, including psychiatric disorders. Microglia respond to pathogens, injury, and toxins by secreting inflammatory mediators including pro-inflammatory cytokines in an event known as neuroinflammation. This thesis research investigated a link between neuroinflammation and oxidative stress, and ultimately neurodegeneration. The cytokine tumor necrosis factor alpha was shown to stimulate a neuronal NADPH oxidase (NOX), specifically by stimulating the production of ceramide and ceramide-1-phosphate via Mg 2+-neutral sphingomyelinase (Mg2+-nSMase) and ceramide kinase. Intriguingly, glucosylceramide blocked NOX activation, linking ceramide neutralization directly to a decline in oxidative stress. Most importantly, NOX activity interfered with actin and sphingosine kinase-1 via oxidation, demonstrating a positive and detrimental feedback mechanism that impedes neuronal survival pathways. Interestingly, crude extracts from wild Alaskan bog blueberries showed the ability to interfere with Mg2+-nSMase, demonstrating a specific neuroprotective property of the berry. Altogether, this thesis research defined a key neuronal pathway linking inflammation to oxidative stress via ceramide metabolism, potentially allowing for future therapeutic development to improve neuronal function and survival.
    • Characteristic behavior of the dayside aurora in the minutes leading up to substorm onset: evidence for external triggering of substorms by the interplanetary magnetic field

      Andersen, Carl Stephen (2005-12)
      Two meridian scanning photometers, one located in Alaska and one in Svalbard, are used to examine the behavior of the dayside aurora just before the onset of the expansion phase of 61 substorms. In a strong majority of cases (80%), a poleward movement of the dayside aurora is seen in the minutes preceding sub storm onset. For the cases examined where a poleward movement of the dayside aurora is seen, a northward turning of the (generally southward) IMF is usually, but not always, seen. This suggests that for a majority of substorms, the 'trigger' is, or is related to, a northward turning of the IMF which can be seen by the motions of the dayside aurora. The observed movements of the dayside aurora and supposed onset triggers begin, on average, 12 minutes before substorm onset, which is the period before on-set during which nightside 'auroral fading' is known to happen. Two opposite but not necessarily exclusive behaviors of ionospheric convection have also been reported to occur during this period before onset, namely a decrease and/or an increase in polar cap convection velocities. Radar measurements of ionospheric convection are examined for these events but do not show an easily identifiable characteristic behavior.
    • Characteristics And Variability Of Storm Tracks In The North Pacific, Bering Sea And Alaska

      Dos Santos Mesquita, Michel (2009)
      Storm activity in the North Pacific, Bering Sea and Alaska regions is investigated using various automated storm tracking and parameter extraction algorithms. Specific, novel details of storm activity throughout the year are presented. The influence of major climatic drivers is considered, including the Pacific/North American Index and sea ice variability. Details of synoptic-scale forcing on a specific, severe storm event are considered in the context of how different tracking algorithms are able to depict the event. New storm climatology results show that the inter-seasonal variability is not as large during spring and autumn as it is in winter. Most storm variables exhibited a maxima pattern that was oriented along a zonal axis. From season to season this axis underwent a north-south shift and, in some cases, a rotation to the northeast. Barotropic processes have an influence in shaping the downstream end of storm tracks and, together with the blocking influence of the coastal orography of northwest North America, result in high lysis concentrations, effectively making the Gulf of Alaska the "graveyard" of Pacific storms. Summer storms tended to be longest in duration. Temporal trends tended to be weak over the study area. Sea surface temperature did not emerge as a major cyclogenesis control in the Gulf of Alaska. Positive sea-ice anomalies in the Sea of Okhotsk were found to decrease secondary cyclogenesis, shift cyclolysis locations westward, and alter the North Pacific subtropical jet. In the Atlantic, a negative North-Atlantic-Oscillation-like pattern is observed; these results were confirmed by experiments on the ECHAM5 Atmospheric Global Circulation Model driven with sea-ice anomalies in the Sea of Okhotsk. The destructive west Alaska storm of autumn 1992, which flooded Nome, was investigated using two storm tracking algorithms: NOAA's (National Oceanic and Atmospheric Administration) current operational algorithm and the Melbourne algorithm. Manual tracking was performed as a control. The main storm location features were captured by both algorithms, but differed in the genesis and lysis location. The NOAA algorithm broke the event into two. This storm was shown to have been affected by a blocking high that influenced how the tracking algorithms handled the event.
    • Characteristics of Arctic storms and their influence on surface climate

      Yang, Yang; Zhang, Xiangdong; Danielson, Seth; Fochesatto, Javier; Hock, Regine (2020-05)
      Impacts of intense synoptic storms on Chukchi Sea and Beaufort Sea surface environmental conditions are examined, focusing on storms moving into the regions with northward and eastward pathways. Both storms alter the prevailing northeasterly wind to southerly and southwesterly wind. The storms moving from the East Siberian Sea that follow a west to east route are most active in summer and have the longest duration. Increasing southwesterly wind plays a key role in the decline of thin sea ice within the warm season. Storms traveling from the relatively warm Pacific Ocean into the Arctic over the Bering Strait are more common in winter, and are typically more intense than the summer storms that propagate west to east. Downward longwave radiation increases considerably with the passage of intense winter storms over the ice-covered Chukchi Sea; the sea ice concentration decreases accordingly. The impact of different sea ice conditions on Arctic synoptic storm systems in autumn are investigated in the North Pacific and Atlantic sectors, based on the ten ensembles of hindcast simulations from coupled regional climate model HIRHAM-NAOSIM. In both the Pacific and Atlantic sectors, greater transfers of heat and moisture fluxes from the open ocean to the atmosphere occur in low sea ice years than in high sea ice years. The largest increase of upward heat fluxes and baroclinicity occurs over the Laptev, southern Chukchi and Beaufort Seas in the Pacific sector, and over the southern Greenland and Barents Seas in the Atlantic sector. Enhanced baroclinity plays a dominant role in the development of intense storm systems. Therefore, storms in reduced sea ice years are more intense than in enhanced sea ice years in both Atlantic and Pacific sectors. The storm count also increases over locations exhibiting high baroclinicity. Sea ice volume anomalies are significantly correlated with synoptic storm counts based on maximum covariance analysis (MCA) leading modes of covariance between sea ice volume and storm count over Pacific and Atlantic sectors are identified respectively. The results are consistent with our findings in the composite analysis. In the Pacific sector, the first pattern of the MCA demonstrates that increasing storm counts over the Laptev Sea corresponds to decreasing sea ice volume over that region. In the Atlantic sector, the decrease of sea ice volume is highly correlated with decreasing storm counts over the northern Greenland Sea. Connection of storm activity over the North Pacific Ocean with the tropical stratosphere quasi-biennial oscillation (QBO) is investigated following a composite analysis of intense storm vertical cross sections. An observed stronger potential vorticity anomaly of intense storms is associated with the QBO west phase and results in enhanced warm air advection near the surface. A warm core structure forms over the east or northeast direction relative to the surface low center, which bows the isentropes downward. Upward motion following the isentropes reduces the surface low pressure, which in turn, facilitate storms to keep propagating in east and northeast directions. Under the QBO east phase, a weak surface warm core forms to the southeast of the storm center, resulting in a slow development of the storms, and these storms tend to move southeastward.
    • Characteristics of dayside auroral displays in relation to magnetospheric processes

      Minow, Joseph I.; Smith, Roger W. (1997)
      The use of dayside aurorae as a ground based monitor of magnetopause activity is explored in this thesis. The origin of diffuse (OI) 630.0 nm emissions in the midday auroral oval is considered first. Analysis of low altitude satellite records of precipitating charged particles within the cusp show an unstructured electron component that will produce a 0.5-1 kR 630.0 nm emission throughout the cusp. Distribution of the electrons is controlled by the requirement of charge neutrality in the cusp, predicting a diffuse 630.0 nm background even if the magnetosheath plasma is introduced into the magnetosphere in discrete merging events. Cusp electron fluxes also contain a structured component characterized by enhancements in the electron energy and energy flux over background values in narrow regions a few 10's of kilometers in width. These structured features are identified as the source of the transient midday arcs. An auroral model is developed to study the morphology of (OI) 630.0 nm auroral emissions produced by the transient arcs. The model demonstrates that a diffuse 630.0 nm background emission is produced by transient arcs due to the long lifetime of the O$(\sp1D)$ state. Two sources of diffuse 630.0 nm background emissions exist in the cusp which may originate in discrete merging events. The conclusion is that persistent 630.0 nm emissions cannot be interpreted as prima facie evidence for continuous particle transport from the magnetosheath across the magnetopause boundary and into the polar cusp. The second subject that is considered is the analysis of temporal and spatial variations of the diffuse 557.7 nm pulsating aurora in relation to the 630.0 nm dominated transient aurora. Temporal variations at the poleward boundary of the diffuse 557.7 nm aurora correlate with the formation of the 630.0 nm transient aurorae suggesting that the two events are related. The character of the auroral variations is consistent with the behavior of particle populations reported during satellite observations of flux transfer events near the dayside magnetopause. An interpretation of the events in terms of impulsive magnetic reconnection yields a new observation that relates the poleward moving transient auroral arcs in the midday sector to the flux transfer events.
    • Characterization and diagnostic methods for geomagnetic auroral infrasound waves

      Oldham, Justin J.; Szuberla, Curt A. (2015-12)
      Infrasonic perturbations resulting from auroral activity have been observed since the 1950's. In the last decade advances in infrasonic microphone sensitivity, high latitude sensor coverage, time series analysis methods and computational efficiency have elucidated new types of auroral infrasound. Persistent periods of infrasonic activity associated with geomagnetic sub-storms have been termed geomagnetic auroral infrasound waves [GAIW]. We consider 63 GAIW events recorded by the Fairbanks, AK infrasonic array I53US ranging from 2003 to 2014 and encompassing a complete solar cycle. We make observations of the acoustic features of these events alongside magnetometer, riometer, and all-sky camera data in an effort to quantify the ionospheric conditions suitable for infrasound generation. We find that, on average, the generation mechanism for GAIW is confined to a region centered about ~60° longitude east of the anti-Sun-Earth line and at ~77° North latitude. We note furthermore that in all cases considered wherein imaging riometer data are available, that dynamic regions of heightened ionospheric conductivity periodically cross the overhead zenith. Consistent features in concurrent magnetometer conditions are also noted, with irregular oscillations in the horizontal component of the field ubiquitous in all cases. In an effort to produce ionosphere based infrasound free from the clutter and unknowns typical of geophysical observations, an experiment was undertaken at the High Frequency Active Auroral Research Program [HAARP] facility in 2012. Infrasonic signals appearing to originate from a source region overhead were observed briefly on 9 August 2012. The signals were observed during a period when an electrojet current was presumed to have passed overhead and while the facilities radio transmitter was periodically heating the lower ionosphere. Our results suggest dynamic auroral electrojet currents as primary sources of much of the observed infrasound, with modulation of the electrojets due to energetic particle precipitation, dispersion due to coupling with gravity waves, and reflection and refraction effects in the intervening atmosphere all potential factors in the shaping of the waveforms observed.