• 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.