• Particle dynamics in the plasma sheet

      Wagner, John S. (1978-08)
      Trajectories of charged particles in the tail region of the earth's magnetosphere are studied using a model magnetic field. The particles form a thin sheet-like structure in the magnetotail called the plasma sheet. It is shown that most trajectories are categorized by two dimensionless parameters. One of them is equal to the ratio of the cross-tail electric force to the magnetic force in the midplane and determines the maximum particle energization. The other parameter is the ratio of the plasma sheet thickness to the particle gyroradius in the midplane and determines the degree to which the particle motion is adiabatic. All previous attempts at studying trajectories in the magnetotail are shown to be applicable only over limited ranges of the two parameters. Hence those studies are combined into a common framework, and those trajectories which have not been studied previously are added for completeness.
    • Radar studies of turbulence and lidar studies of the nickel layer in the Arctic mesosphere

      Li, Jintai; Collins, Richard L.; Simpson, William R.; Newman, David E. (2016-05)
      This thesis presents studies of the Arctic middle atmosphere using Incoherent Scatter Radar (ISR) and resonance lidar at Poker Flat Research Range (PFRR), Chatanika, Alaska. The Poker Flat Incoherent Scatter Radar (PFISR) provides measurements of mesospheric turbulence and the resonance lidar provides measurements of mesospheric nickel layer. We develop retrieval and analysis techniques to determine the characteristics of the turbulence and the nickel layer. We present measurements of mesospheric turbulence with PFISR on 23 April 2008 and 18 February 2013. We characterize mesospheric turbulence in terms of the energy dissipation rate as a function of altitude and time on these days. We present an extensive analysis of the radar measurements to show that the use of high quality PFISR data and an accurate characterization of the geophysical conditions are essential to achieve accurate turbulent measurements. We find that the retrieved values of the energy dissipation rate vary significantly based on how the data is selected. We present measurements of mesospheric nickel layer with resonance lidar on the night of 27-28 November 2012 and 20-21 December 2012. We characterize the mesospheric nickel layer in terms of the nickel concentration as a function of altitude on these days. We find that our nickel concentrations are significantly higher than expected from studies of meteors. We present an extensive analysis of the lidar measurements to show that these measurements of unexpectedly high values of the nickel concentrations are accurate and not biased by the lidar measurements.
    • Rayleigh lidar studies of mesospheric inversion layers at Poker Flat Research Range, Chatanika, Alaska

      Irving, Brita K. (2012-08)
      Rayleigh lidar observations at Poker Flat Research Range, Chatanika, Alaska (65°N, 213°E), have yielded density and temperature measurements from 40-80 km. These measurements have been made under clear nighttime skies since November 1997. This thesis presents a study of Mesospheric Inversion Layers (MILs) and lidar performance at Chatanika. MILs are identified and characterized in the 40-70 km altitude region on 55 of the 149 wintertime observations over two periods, November 1997-April 2005 and November 2007-March 2009, using a new detection algorithm. Investigation of the MILs compared with planetary wave activity as observed by satellite finds a strong correlation between the presence of MILs and the structure of the planetary waves. These two periods are marked by strong planetary wave activity and sudden stratospheric warming events. MILs are found to occur more frequently than previously reported at Arctic sites, but less frequently than at lower latitudes. In spring 2012 the existing lidar system was extended by incorporating a larger aperture telescope and higher power laser and field trials were conducted. The results from these field trails are presented and the ability of the new lidar system to extend the scope of future studies at Chatanika is assessed.
    • The relation of spring pollen release to weather in Fairbanks, Alaska

      Fathauer, Theodore F.; Mölders, Nicole; Bhat, Uma; Wendler, Gerd (2012-08)
      Twenty-three years of pollen data for Fairbanks have been analyzed and related to meteorological data (temperature, wind, relative humidity and precipitation). The purpose of this research is to develop quantitative statistical relationships between weather parameters and the timing and magnitude of pollen release for four taxa native to the Fairbanks area (birch, alder spruce and grass). During the spring and early summer in Fairbanks, dry, sunny and breezy days are common. These conditions are ideal for establishing an unstable boundary layer and its accompanying convective circulation, which can loft large quantities of pollen into the atmosphere. The timing of pollen release varies from season to season by as many as 24 days. Growing degree days based upon daily maximum temperatures and daily minimum relative humidity are the parameters which best define the timing of the onset of significant pollen release. The day-to-day concentration of pollen and the seasonal totals of pollen released can vary by more than an order of magnitude. Weather plays an important part in this because the release of pollen is a result of a drying process accompanied by turbulent circulation, which disperses the pollen.
    • Response of major modes of eastern Arctic Ocean variability to climate change

      Baumann, Till M.; Polyakov, Igor V.; Bhatt, Uma S.; Walsh, John E.; Weingartner, Thomas J. (2019-12)
      The Arctic Ocean plays a central role in ongoing climate change, with sea ice loss being the most prominent indicator. Recent observations showed that Atlantic inflows play an increasingly important role in the demise of sea ice. This encroaching atlantification of the eastern Arctic Ocean impacts the mean state and the variability of hydrography and current dynamics throughout the basin. Among the most energetic modes of variability are the seasonal cycle and high frequency semidiurnal (∼12-hourly) dynamics in the tidal and inertial frequency band. Limited observations indicated a substantial increase of both, hydrographic seasonal cycles as well as semidiurnal current dynamics in the eastern Arctic over the last decade. Using a uniquely comprehensive data set from an array of six moorings deployed across the eastern Eurasian Basin (EB) continental slope along the 125°E meridian between 2013 and 2015 within the NABOS project, we assess the state of hydrographic seasonal cycles in the eastern EB. Results show a complex pattern of seasonality with a remarkably strong (∆T=1.4°C), deep reaching (∼600 m) temperature signal over the continental slope and large-scale seasonal displacements of isopycnal interfaces. Seasonally changing background conditions are also the main source of variability of semidiurnal frequency band currents: During winter, vigorous baroclinic tidal currents whose amplitudes by far exceed predictions follow the vertical evolution of the pycnocline. During summer, extensive open-water periods additionally lead to strong wind-driven inertial currents in the upper ocean, routinely exceeding 30 cm/s far offshore in the deep basin. In order to obtain an Arctic-wide perspective on the impact of baroclinic tidal currents, a pan-Arctic tidal current atlas has been developed that synthesizes all available observations from the last 20 years. This atlas allows for in-depth studies of regional baroclinic tidal current variability as well as for validation of ocean and climate models, an essential step towards more accurate projections of the future Arctic Ocean state. Our findings from the eastern EB region already indicate a new, more dynamic state of the eastern Arctic Ocean with direct implications for the ecosystem and further sea-ice reduction.
    • Rocket and lidar studies of waves and turbulence in the Arctic middle atmosphere

      Triplett, Colin Charles; Collins, Richard L.; Weingartner, Thomas; Newman, David; Lehmacher, Gerald; Bhatt, Uma S. (2016-08)
      This dissertation presents new studies of waves and turbulence in the Arctic middle atmosphere. The study has a primary focus on wintertime conditions when the largescale circulation of the middle atmosphere is disrupted by the breaking of planetary waves associated with sudden stratospheric warming (SSW) events. We used ongoing Rayleigh lidar measurements of density and temperature to conduct a multi-year study of gravity waves in the upper stratosphere-lower mesosphere (USLM) over Poker Flat Research Range (PFRR) at Chatanika, Alaska. We analyzed the night-to-night gravity wave activity in terms of the wind structure and the ageostrophy. We find that the weak winds during disturbed conditions block the vertical propagation of gravity waves into the mesosphere. The gravity wave activity is correlated with the altitudes where the winds are weakest. During periods of weak winds we find little correlation with ageostrophy. However, during periods of stronger winds we find the USLM gravity wave activity is correlated with the ageostrophy in the upper troposphere indicating that ageostrophy in this region is a source of the gravity waves. Inter-annually we find the wintertime gravity wave activity is correlated with the level of disturbance of the middle atmosphere, being reduced in those winters with a higher level of disturbance and weaker winds. We used rocket-borne ion gauges to measure turbulence in the wintertime middle atmosphere while documenting the larger meteorological context from Rayleigh lidar and satellites. This investigation of turbulence was called the Mesosphere-Lower Thermosphere Turbulence Experiment (MTeX). During MTeX we found a highly disturbed atmosphere associated with an SSW where winds were weak and gravity wave activity was low. We found low levels of turbulence in the upper mesosphere. The turbulence was primarily found in regions of convective instability in the topside of mesospheric inversion layers (MILs). The strongest and most persist turbulence was found in a MIL that is associated with the breaking of a monochromatic gravity wave. These MTeX observations indicate that turbulence is generated by gravity wave breaking as opposed to gravity wave saturation. These MTeX findings of low levels of turbulence are consistent with recent model studies of vertical transport during SSWs and support the view that eddy transport is not a dominant transport mechanism during SSWs.
    • Role of Arctic Sea Ice Variability in Climate Models

      Dammann, Dyre O.; Bhatt, Uma; Polyakov, Igor; Zhang, Xiang (2011-08)
      Arctic sea ice plays an important role in climate by influencing surface heat fluxes and albedo, so must be accurately represented in climate models. This study finds that the fully coupled ice-ocean-atmosphere-land Community Climate System Model (CCSM3.0) underestimates day-to-day ice variability compared to observations and employs the Community Atmosphere Model (CAM3.0) to investigate the atmospheric sensitivity to sea ice variability. Three 100-ensemble experiments are forced with climatological, daily-varying, and smoothly-varying sea ice conditions from an anomalously low ice period (September 2006-February 2007). Daily ice variability has a large local impact on the atmosphere when ice undergoes rapid changes, leading to local cooling and subsequent circulation changes. The most notable example of a large-scale atmospheric response occurs over Northern Europe during fall where daily ice variability forces reductions in the number and strength of cyclones, leading to positive sea level pressure anomalies, surface warming, and reduced cloud cover.
    • Role Of Waves On The Circulation Of The Arctic Middle Atmosphere: Rayleigh Lidar Measurements And Analysis

      Thurairajah, Brentha (2009)
      Rayleigh lidar measurements of the upper stratosphere and mesosphere are made on a routine basis over Poker Flat Research Range (PFRR), Chatanika, Alaska, (65�N, 147�W). Rayleigh lidar measurements have yielded high resolution temperature and density profiles in the 40-80 km altitude. These measurements are used to calculate gravity wave activity in the 40-50 km altitude. The thermal structure of the stratosphere and mesosphere is documented using an eight year data set, and the role of small scale gravity waves on the large scale meridional circulation is analyzed in terms of the synoptic structure of the Arctic stratospheric vortex, Aleutian anticyclone, and planetary wave activity. The monthly mean temperature indicates colder January temperatures that appear to be due to the increase in frequency of occurrence of stratospheric warming events from 1997-2004. The gravity wave potential energy density is analyzed during stratospheric warming events in two experimental time periods. From the first study consisting of three winters, 2002-2003, 2003-2004, and 2004-2005, the first direct measurement of suppression of gravity wave activity during the formation of an elevated stratopause following the 2003-2004 stratospheric warming event is presented. The gravity wave potential energy density at Chatanika is positively correlated with horizontal wind speeds in the stratosphere, and indicates that the wave activity in the 4050 km altitude is partially modulated by the background flow. In the second study with more recent winters of 2007-2008 and 2008-2009, no systematic difference in the magnitude of potential energy density between the vortex displacement warming event during the 2007-2008 winter and vortex split warming event during the 2008-2009 winter is found. However, the low correlation between gravity wave potential energy and horizontal wind speed after the first warming in January 2008, and a higher correlation after the January 2009 warming suggests that while the gravity wave activity after the 2009 warming is modulated by the background flow, other wave sources modulate the gravity wave activity after the 2008 warming.
    • Single-column model simulations of Arctic cloudiness and surface radiative fluxes during the surface heat budget of Arctic (SHEBA) experiment

      Hannay, Cécile (2001-08)
      We evaluate the ability of a typical cloud parameterization from a global model (CCM3 from NCAR) to simulate the Arctic cloudiness and longwave radiative fluxes during wintertime. Simulations are conducted with a Single-Column model (SCM) forced with observations and reanalysis data from the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment. Typically, the SCM overestimates the Arctic cloud fraction and the downwelling longwave flux. Moreover, the SCM does not capture accurately the temperature and moisture profiles, and the surface flux fields. Relaxing temperature and moisture profiles to observed values dramatically improves the simulations. This suggests that the cloud parameterization of CCM3 is suitable for Arctic clouds, as long as the temperature and moisture fields are captured correctly. Sensitivities studies show that the cloud fraction is not very sensitive to cloud type, ice effective radius, ice liquid ratio amount and uncertainty of the advective forcing.
    • Theoretical investigations on strategies for sampling meteorological and chemical field quantities in smoke plumes using UAVs

      Butwin, Mary K.; Mölders, Nicole; Collins, Richard L.; Bhatt, Uma S. (2015-08)
      Wildfires emit large quantities of pollutants that decrease the air quality in the atmospheric boundary layer. Understanding the chemical makeup of a fire plume is beneficial for air quality studies and for air quality forecasting in communities. To be able to understand the chemical composition, Unmanned Aerial Vehicles (UAVs) should be flown into plumes with an air quality instrumental payload. Before such flights can be completed it is crucial that the flight paths will allow for a complete understanding of the chemical concentration distributions within the plume. To develop such a flight path, with respect to flight altitude, direction and speed the UAV should travel at for examining a wildfire plume in Interior Alaska, output from the Weather Research and Forecasting model coupled with Chemistry (WRF/Chem) was used and was considered to be the true atmospheric conditions over the UAV measurement domain. For this thesis simulations were for 3-10 August 2009 of the Alaska fire season, centered in Interior Alaska. Focus for the UAV study was on the smoke plumes from the Crazy Mountain Complex fires near Circle, AK. Based on the results from the comparison of different flight altitudes, sampling patterns, and speeds of the simulated UAV flights, recommendations can be made for the use of UAVs in a field campaign into a wildfire plume in Interior Alaska.
    • Theoretical, experimental and numerical simulation study of a radially injected barium disk

      Sydora, Richard D. (1981-05)
      An Investigation of the dynamics and stability of a high-altitude radial barium plasma injection is performed using theoretical and numerical simulation methods. The barium plasma cloud, injection experiment was conducted on March 16, 1980 and produced several interesting phenomena: (1) Three distinct rings of barium containing irregularities exhibiting collective motion; (2) A region of plasma depletion at the location of injection; (3) A structure of approximately eighteen distinct barium ion rays emanating from the injection location. A collisionless, electrostatic particle simulation model is used to understand the behavior of the plasma, indicating that the initial plasma deformation develops due to an E x B azimuthal velocity shear instability. A theoretical model used for a stability analysis of the plasma is formulated based on the number density distributions of the electrons and ions obtained from the numerical simulation results. The linear stability analysis shows that the number of unstable azimuthal modes created by the velocity shear instability is dependent upon the amount of charge separation occurring in the expanding plasma.
    • Using self-organizing maps to detail synoptic connections between climate indices and Alaska weather

      Winnan, Reynir C.; Bhatt, Uma S.; Collins, Richard L.; Walsh, John E.; Wackerbauer, Renate A. (2015-12)
      Seasonal forecasts for Alaska strongly depend on the phases of Pacific Decadal Oscillation (PDO), El Niño-Southern Oscillation (ENSO), and warm water in the North Pacific called the North Pacific Mode or more popularly the "Pacific blob." The canonical descriptions of these climate indices are based on seasonal averages, and anomalies that are based on a long-term mean. The patterns highlight general geographical placement and display a sharp contrast between opposing phases, but this may be misleading since seasonal averages hide much of the synoptic variability. Self-organizing maps (SOMs) are a way of grouping daily sea level pressure (SLP) patterns, over many time realizations into a specified set of maps (e.g. 35 maps) that describe commonly occurring patterns. This study uses the SOMs in the context of climate indices to describe the range of synoptic patterns that are relevant for Alaska. This study found that the patterns common during a given phase of the PDO include subtle differences that would result in Alaska weather that is very different from what is expected from the canonical PDO description, thus providing some explanation for recent studies that find the PDO link to Alaska climate is weakening. SOMs analysis is consistent with recent studies suggesting that the pattern responsible for the 2014 Pacific warm blob is linked to tropical sea-surface temperature (SST) forcing. An analysis of the summer SLP SOMs in the context of Alaska wildland fires was also conducted. This analysis identified several commonly occurring patterns during summers with large areas burned. These patterns are characterized by low pressure in the Bering Sea, which would be consistent with increased storm activity and thus an ignition source for the fires. Identifying synoptic patterns that occur during a particular phase of a teleconnection index contributes towards understanding the mechanisms of how these indices influence the weather and climate of Alaska.
    • Using WRF/Chem, in-situ observations, and Calipso data to simulate smoke plume signatures on high-latitude pixels

      Madden, James Michael; Mölders, Nicole; Sassen, Kenneth; Prakash, Anupma; Grell, Georg (2014-05)
      The transport of wildfire aerosols provides concerns to people at or near downwind propagation. Concerns include the health effects of inhalation by inhabitants of surrounding communities and fire crews, the environmental effects of the wet and dry deposition of acids and particles, and the effects on the atmosphere through the scattering and absorption of solar radiation. Therefore, as the population density increases in Arctic and sub-Arctic areas, improving wildfire detection increasingly becomes necessary. Efforts to improve wildfire detection and forecasting would be helped if additional focus was directed toward the distortion of pixel geometry that occurs near the boundaries of a geostationary satellite's field of view. At higher latitudes, resolution becomes coarse due to the curvature of the Earth, and pixels toward the boundaries of the field of view become difficult to analyze. To assess whether it is possible to detect smoke plumes in pixels at the edge of a geostationary satellite's field of view, several analyses were performed. First, a realistic, fourdimensional dataset was created from Weather Research and Forecasting model coupled with Chemistry (WRF/Chem) output. WRF/Chem output was statistically compared to ground observations through the use of skill scores. Output was also qualitatively compared to vertical backscatter and depolarization products from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite. After the quantitative and qualitative examinations deemed the model output to be realistic, synthetic pixels were constructed, appropriately sized, and used with the realistic dataset to examine the characteristic signatures of a wildfire plume. After establishing a threshold value, the synthetic pixels could distinguish between clean and smoke-polluted areas. Thus, specialized retrieval algorithms could be developed for smoke detection in strongly distorted pixels at the edge of a geostationary satellite's field of view.