• Emergent impacts of rapidly changing climate extremes in Alaska

      Lader, Rick T.; Walsh, John E.; Bhatt, Uma S.; Rupp, T. S.; Zhang, Xiangdong (2018-08)
      The frequency and intensity of certain extreme weather events in Alaska are increasing, largely due to climate warming from greenhouse gas emissions. Future projections indicate that these trends will continue, potentially leading to billions of dollars in climate-related damages this century. Expected damages arise from increases in extreme precipitation, severe wildfire, altered ocean chemistry, land subsidence from permafrost thaw, and coastal erosion. This dissertation applies new downscaled reanalysis and climate model simulations from the fifth phase of the Coupled Model Intercomparison Project to enhance current understanding of climate extremes in Alaska. Model output is analyzed for a historical period (1981-2010) and three projected periods (2011-2040, 2041-2070, 2071-2100) using representative concentration pathway 8.5. Unprecedented heat and precipitation are expected to occur when compared to the historical period. Maximum 1-day and consecutive 5-day precipitation amounts are expected to increase by 53% and 50%, respectively, and the number of summer days per year (Tmax > 25°C) increases from a statewide average of 1.5 from 1981-2010 to 29.7 for 2071-2100. Major alterations to the landscape of Alaska are anticipated due to a decreasing frequency of freezing temperatures. Growing season length extends by 48-87 days by 2071-2100 with the largest changes in northern Alaska. In contrast, projections indicate a reduced snow season length statewide and many locations in southwest Alaska no longer have continuous winter snow cover. Changes to these metrics indicate that a climate-warming signal emerges from the historical inter-annual variability, meaning that future distributions are entirely outside of those previously observed. The largest changes to extremes may be avoided by following a lower emissions trajectory, which would reduce the impacts and associated costs to maintain infrastructure and human health.
    • An evaluation of reanalysis products for Alaska to facilitate climate impact studies

      Lader, Rick T.; Bhatt, Uma; Walsh, John E.; Polyakov, Igor V.; Rupp, T. Scott (2014-08)
      Alaska is experiencing effects of global climate change due, in large part, to the positive feedback mechanisms associated with polar amplification. The major risk factors include loss of sea ice, glaciers, thawing permafrost, increased wildfires, and ocean acidification. Reanalyses, which are weather forecast models that assimilate observations, are integral to understanding mechanisms of Alaska's past climate and to help calibrate future modeling efforts. This study evaluates five reanalyses using monthly gridded datasets of temperature, precipitation, and snowwater equivalent, as well as daily station data of maximum and minimum temperature, precipitation, and snow depth across six climate regions in Alaska, and at eight stations from 1979-2009. The reanalyses evaluated in this study include the: NCEP-NCAR Reanalysis (NCEP-R1), North American Regional Reanalysis (NARR), Climate Forecast System Reanalysis (CFSR), ERA-Interim, and Modern-Era Retrospective Analysis for Research and Applications (MERRA). MERRA was the top-performing reanalysis for the station-based assessment, has the lowest statewide precipitation bias, and is the most reliable model for snow-water equivalent. NARR and ERA-Interim have the lowest near-surface air temperature biases across Alaska. The quality of reanalysis data varies by region, season, and variable. This thesis provides guidance for reanalysis users to make informed decisions.
    • Evaluation of the hydro-thermodynamic soil-vegetation scheme on the basis of observations and a Galerkin type finite element numerical scheme

      Narapusetty, Balachandrudu (2005-08)
      The Hydro-Thermodynamic Soil- vegetation Scheme (HTSYS), coupled in a two-way mode with the PennState/National Center for Atmospheric Research (NCAR) Mesoscale Meteorological Model generation 5 (MM5), has been evaluated for a 5 day typical snow-melt period using the Baltic Sea experiment meteorological data center's soil temperature, snow depth, and precipitation datasets. The HTSVS-MM5 evaluation investigates the coupled system's sensitivity to two cloud models and two radiation models, with their cross effects presented along with skill scores for snow depth changes. The coupled model satisfactorily predicts the soil temperature diurnal course cycles, changes in the snow depths, and accumulated precipitation. HTSVS's soil model has been further tested and evaluated in an offline mode for the advanced numerical treatment for the Partial Differential Equations (PDEs) using soil temperature datasets from three sites at Council, Alaska. A Galerkin Weak Finite Element (GWFE) method was tested and evaluated for the numerical treatment of PDEs and the predictions were compared against the existing Crank-Nicholson finite differences scheme (CNFD). GWFE solutions exhibit a remarkable soil temperature predictability, better capture the temperature peaks, and yield non-diffuse and non-oscillatory solutions for relatively high convection dominated regimes, while CNFD performs comparably well in diffusion dominated regimes with a lower computational burden.
    • Exploration of mesospheric metal layers from Chatanika, Alaska

      Martus, Cameron M.; Collins, Richard L.; Mölders, Nicole; Sassen, Kenneth (2013-08)
      Layers of free metal atoms exist in the mesopause region of the atmosphere, generally between 80 and 100 km altitude. Resonance fluorescence lidar provides the best way to measure the structure and dynamics of these metal layers. Resonance lidar observations using tunable dye lasers are conducted at the Lidar Research Laboratory (LRL) of Poker Flat Research Range (PFRR), Chatanika, Alaska (65°N, 147°W). In this thesis, we present three fundamental aspects of mesospheric resonance lidar studies: lidar system commissioning and operation, analysis of temporal variations in the metal layers based on observations, and observations of the nickel layer. An excimer-pumped dye laser system has been used in the past for observations at LRL-PFRR, and we report on the alignment and testing of this system as well as the deployment of a new Nd:YAG-pumped dye laser system. Both of these systems are tested with observations of the sodium layer at 589 nm. Through an analysis of simultaneous observations of the sodium and iron layers taken in the past at LRL-PFRR, we study the common motion of the two layers and suggest an external forcing mechanism for the motions. We find that the motion of the layers is, in most of the observations, consistent with downward propagating gravity waves. Based on elemental abundances in meteors, the most likely source of mesospheric metal layers, we expect to find a nickel layer, yet such a layer has not been reported. We attempt to detect the layer using resonance lidar at the 337 nm nickel absorption line. We make several likely detections of the layer and present an initial estimate of the nickel profile. Signals received in the nickel measurements are as expected from a simulation based on signals received in past observations of sodium and iron.
    • Global and local contributors to the historical and projected regional climate change on the North Slope of Alaska

      Cai, Lei; Alexeev, Vladimir A.; Arp, Christopher D.; Bhatt, Uma S.; Liljedahl, Anna K. (2018-05)
      This thesis includes four studies that explore and compare the impacts of four contributing factors resulting in regional climate change on the North Slope of Alaska based on a numerical simulation approach. These four contributing factors include global warming due to changes in radiative forcing, sea ice decline, earlier Arctic lake ice-off, and atmospheric circulation change over the Arctic. A set of dynamically downscaled regional climate products has been developed for the North Slope of Alaska over the period from 1950 up to 2100. A fine grid spacing (10 km) is employed to develop products that resolve detailed mesoscale features in the temperature and precipitation fields on the North Slope of Alaska. Processes resolved include the effects of topography on regional climate and extreme precipitation events. The Representative Concentration Pathway (RCP) 4.5 scenario projects lower rates of precipitation and temperature increase than RCP8.5 compared to the historical product. The increases of precipitation and temperature trends in the RCP8.5 projection are higher in fall and winter compared to the historical product and the RCP4.5 projection. The impacts of sea ice decline are addressed by conducting sensitivity experiments employing both an atmospheric model and a permafrost model. The sea ice decline impacts are most pronounced in late fall and early winter. The near surface atmospheric warming in late spring and early summer due to sea ice decline are projected to be stronger in the 21st century. Such a warming effect also reduces the total cloud cover on the North Slope of Alaska in summer by destabilizing the atmospheric boundary layer. The sea ice decline warms the atmosphere and the permafrost on the North Slope of Alaska less strongly than the global warming does, while it primarily results in higher seasonal variability of the positive temperature trend that is bigger in late fall and early winter than in other seasons. The ongoing and projected earlier melt of the Arctic lake ice also contributes to regional climate change on the Northern coast of Alaska, though only on a local and seasonal scale. Heat and moisture released from the opened lake surface primarily propagate downwind of the lakes. The impacts of the earlier lake ice-off on both the atmosphere and the permafrost underneath are comparable to those of the sea ice decline in late spring and early summer, while they are roughly six times weaker than those of sea ice decline in late fall and early winter. The permafrost warming resulted from the earlier lake ice-off is speculated to be stronger with more snowfall expected in the 21st century, while the overall atmospheric warming of global origin is speculated to continue growing. Two major Arctic summer-time climatic variability patterns, the Arctic Oscillation (AO) and the Arctic Dipole (AD), are evaluated in 12 global climate models in Coupled Model Intercomparison Program Phase 5 (CMIP5). A combined metric ranking approach ranks the models by the Pattern Correlation Coefficients (PCCs) and explained variances calculated from the model-produced summer AO and AD over the historical period. Higher-ranked models more consistently project a positive trend of the summer AO index and a negative trend of summer AD index in their RCP8.5 projections. Such long-term trends of large-scale climate patterns will inhibit the increase in air temperature while favoring the increase in precipitation on the North Slope of Alaska. In summary, this thesis bridges the gaps by quantifying the relative importance of multiple contributing factors to the regional climate change on the North Slope of Alaska. Global warming is the leading contributing factor, while other factors primarily contribute to the spatial and temporal asymmetries of the regional climate change. The results of this thesis lead to a better understanding of the physical mechanisms behind the climatic impacts to the hydrological and ecological changes of the North Slope of Alaska that have been become more severe and more frequent. They, together with the developed downscaling data products, serve as the climatic background information in such fields of study.
    • Hydroclimate in Eurasia from the Arctic to the Tropics

      Majhi, Ipshita; Bhatt, Uma S.; Zhang, Xiangdong; Molders, Nicole; Walsh, John; Krishnamurthy (2018-05)
      Hydrometeorology in Eurasia connects the Arctic with lower latitudes through exchanges in moisture and teleconnections influencing climate variability. This thesis investigates the role of dams on the Kolyma basin, of precipitation and temperature change on a pristine permafrost lined basin of the Yana, and of changing snow cover over Eurasia on the Indian Monsoon. These three pieces of work illustrate different aspects of a changing climate that impact Eurasian hydrometeorological variations. The Kolyma is one of the large rivers which flows into the Arctic Ocean where there has been a large winter increase and summer decrease in flow over the 1986-2000 period. Winter months are characterized by low flow while summer months by high flow. Reservoir regulation was identified as the main cause of changes in the discharge pattern, since water is released in winter for power generation and stored in summer for flood control. The overall discharge to the Arctic Ocean has decreased for Kolyma basin, despite the increase during winter. This study documents how human activities (particularly reservoirs) impact seasonal and regional hydrological variations. The Yana Basin is a small pristine basin that has experienced minimal human impact and is ideal for investigating the role of climate variability on discharge. The precipitation discharge and temperature discharge analysis for Ubileinaya suggests that increased precipitation and higher temperatures resulted in higher discharge, but other parameters also come into play since greater precipitation does not always yield higher discharge. Overall our analysis for this station has increased our understanding of natural basins and how the climate variables like precipitation and temperature play a role. Recent increases in May-June Indian monsoon rain fall were investigated in the context of Eurasian snow cover variations since the onset of the monsoon has long been linked to Himalayan snow cover. Himalayan snow cover and depth have decreased and this study argues that this is the driver of increased rainfall during May-June, the pre-monsoon and early monsoon period. In addition, there has been an increase in snow water equivalent in Northern part of Eurasia and decrease in Southern part, suggesting that the anomalies are large-scale. Storm track analysis reveals an increase in the number of storms in northern and a decrease in southern Eurasia. The large-scale Eurasian snow increases have been shown by other studies to be linked to Arctic sea ice decline. The direct linkage between fall Arctic sea ice decline and an increase in May-June Indian monsoon rainfall is proposed in this work but the exact climate mechanism is tenuous at this point. This study is focused on understanding changing Arctic rivers and the connection of the Arctic with the Indian monsoon. Our study has shed some light into the connection between the Arctic and the tropics. This study could benefit from modeling study where we could have case study with and without sea ice to understand better how that could impact the monsoon and the hydrological cycle in the present and the future. Better understanding of the mechanism would help us take steps towards better adaptation policies.
    • Ice clouds over Fairbanks, Alaska

      Kayetha, Vinay Kumar; Sassen, Kenneth; Mölders, Nicole; Collins, Richard (2014-05)
      Arctic clouds have been recognized long ago as one of the key elements modulating the global climate system. They have gained much interest in recent years because the availability of new continuous datasets is opening doors to explore cloud and aerosol properties as never before. This is particularly important in the light of current climate change studies that predict changing weather scenarios around the world. This research investigates the occurrence and properties of a few types of ice clouds over the Arctic region with datasets available through the Arctic Facility for Atmospheric Remote Sensing (AFARS; 64.86° N, 147.84° W). This study exclusively focuses on ice clouds that form in the upper (cirrus clouds) and midlevels of the troposphere, and that are transparent to laser pulses (visible optical depth τ< 3.0 - 4.0). Cirrus clouds are icedominated clouds that are formed in the upper levels of the troposphere and are relatively thin such that their visual appearances range from bluish to gray in color. Mid-level ice clouds are those clouds primarily composed of ice crystals forming in the midlevels of the troposphere. It is hypothesized that unlike the basic midlevel cloud type (altostratus), other varieties of midlevel ice clouds exist at times over the Arctic region. The midlevel ice clouds studied here are also transparent to laser pulses and sometimes appear as a family of cirrus clouds to a surface observer. Because of their intermediate heights of occurrence in the troposphere, these could have microphysical properties and radiative effects that are distinct from those associated with upper level ice clouds in the troposphere. A ground-based lidar dataset with visual observations for identifying cloud types collected at AFARS over eight years is used to investigate this hypothesis. Cloud types over AFARS have been identified by a surface observer (Professor Kenneth Sassen) using established characteristics traits. Essential macrophysical properties of the clouds are derived from the lidar data, which serves as a climatological representation for the visually identified cirrus and mid-level ice clouds over a typical sub-Arctic location. Synoptic-scale weather patterns conducive for such cloud type formations are derived using a clustering technique applied to a re-analysis dataset. The cloud properties derived from ground-based lidar over AFARS are used to assess the cloud observations from the CALIPSO satellite.
    • Impacts of storm on sea ice: from case study to climate scale analysis

      Peng, Liran; Zhang, Xiangdong; Collins, Richard; Fochesatto, Javier; Polyakov, Igor (2019-12)
      Recent studies have shown that intense and long-lasting storms potentially facilitate sea ice melting. Under the background of extratropical storm tracks poleward shift, significant reductions of Arctic sea ice coverage, and thinning of sea ice thickness over the last several decades, a better understanding on how storms impact sea ice mass balance is obviously of great importance to better predict future sea ice and the Arctic climate changes. This thesis presents a multi-scale study on how storms impact sea ice, consisting of three different parts of the effort. In the first part, we examined the impacts of the 2016 summer intense storm on sea ice changes over the Chukchi Sea using ship-borne observations. The results show that the intense storm can accelerate ice melt through enhanced upper-ocean mixing and upward heat transport. The satellite-observed long-term sea ice variations potentially can be impacted by many factors. In the second part, we first explore key physical processes controlling sea ice changes under no-storm condition. We examined and compared results from 25 sensitivity experiments using the NCAR's Community Earth System Model (CESM). We found that sea ice volume, velocity, and thickness are highly sensitive to perturbed air-ice momentum flux and sea ice strength. Increased sea ice strength or decreased air-ice momentum flux causes counter-clockwise rotation of the transpolar drift, resulting in an increase in sea ice export through Fram Strait and therefore reduction of the pan-Arctic sea ice thickness. Following four tracers released over the Arctic, we found the sea ice thickness distributions following those tracers are broader over the western Arctic and becomes narrower over the eastern Arctic. Additionally, thermodynamic processes are more dominant controlling sea ice thickness variations, especially over periphery seas. Over the eastern Arctic, dynamic processes play a more important role in controlling sea ice thickness variation. Previous studies show that thin ice responds to external perturbations much faster than the thick ice. Therefore, the impacts of storms on sea ice are expected to be different compared with the western/eastern Arctic and the entral/periphery seas. In the third part, we conduct a new composite analysis to investigate the storm impact on sea ice over seven regions for all storms spanning from 1979 to 2018. We focused on sea ice and storm changes over seven regions and found storms tend to have different short-term (two days before and after storm passage), mid-term (one-two weeks after storm passage), and long-term (from 1979 to 2018) impact on sea ice area over those regions. Over periphery seas (Chukchi, East Siberian, Laptev, Kara, and Barents Seas), storms lead to a short-term sea ice area decrease below the climatology, and a mid-term sea ice increase above the climatology. This behavior causes sea ice area to have a small correlation with the storm counts from 1979 to 2018, which suggest that storms have a limited long-term impact on sea ice area over periphery seas. Both the short term and mid-term storm impacts on sea ice area are confined within a 400 km radius circle with maximum impacts shown within a 200 km radius circle. Storms over the western Arctic (Chukchi, East Siberian, and Laptev Seas) have a stronger short-term and mid-term impact on sea ice area compared with the Eastern Arctic (Barents and Kara Seas). Storms over both Atlantic and Pacific entrance regions have a small impact on sea ice area, and storms over the Norwegian, Iceland, and Greenland Seas have the smallest impact on the sea ice area. Compared to the periphery seas, storms tend to have a stronger long-term impact on sea ice area over the central Arctic. The correlation coefficients between the storm count and sea ice area exceed 0.75.
    • An improved method of ice nucleus measurement

      Shih, Chi-Fan G. (1982-09)
      Ice nuclei, which initiate the ice nucleation process at a higher temperature than the homogeneous nucleation temperature, are essential for the initiation of the ice phase in clouds. Unfortunately, no standard method has been established for the measurement of ice nucleus concentration. The filter technique is a promising candidate if the tendency for ice nucleus concentrations to decreases as the volume sampled increases can be explained. For this study, an improved ventilation method for the development of exposed filters was developed and tested. The results were compared with results obtained in a static diffusion chamber. The volume effect was observed to be less with the new dynamic system. Further work needs to be done to find the optimum flow rate in order to reduce the vapor depletion problem to a minimum. The ratio of total counts of dynamic and static system appears to be a promising evaluation index.
    • Investigation of North Pacific sea ice anomalies in the context of atmospheric and oceanic variability

      Tivy, Adrienne (2001-08)
      This study investigates the main mode of variability in North Pacific sea ice and examines the relationship between sea ice concentration and northern hemispheric climate variability for the period 1968-1997. Through empirical orthogonal function (EOF) analysis, correlations, and composite analysis, it was found that the seesaw pattern (first EOF of wintertime sea ice concentrations) between ice concentrations in the Bering Sea and the Sea of Okhotsk, generally used to characterize North Pacific sea ice, does not adequately address variability in the Sea of Okhotsk. Relationships between the sea ice dipole and the large-scale circulation were investigated and were found to change with the 1977 and 1989 regime shifts in the North Pacific climate. Before 1977 the sea ice dipole is strongly related to tropical variability while after 1977 the dipole is more strongly related to mid-latitude variability.
    • Investigation of thin midlevel ice clouds in the Arctic using calipso data and radiative transfer modeling

      Kayetha, Vinay Kumar; Collins, Richard; Meyer, Franz; Prakash, Anupma; Bhatt, Uma (2015-08)
      In this research we investigate the global occurrence and properties of optically thin midlevel ice clouds. These clouds are difficult to detect with passive radiometric techniques and are under-represented in current studies. We use the Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data set to identify thin midlevel ice clouds and determine their global occurrence and distribution. For the first time, we find that the global mean occurrence of these clouds is at least 4.5%, being at least 7.3% of all the tropospheric clouds detected at a horizontal scale of 10 km. Seasonally, these clouds are found most commonly in the polar regions. These clouds occur most commonly in the Arctic in winter and least commonly in the summer. In winter these clouds can occur up to 19% of the time. The occurrence of these clouds decreases with increasing spatial scale and are most commonly found at spatial scales of 25 km or less. We found five large distinct clouds over the Arctic and investigated them for their meteorological conditions and radiative effects. These thin midlevel ice clouds are formed along the frontal zones in weakly ascending air masses. Our model simulations show that thin midlevel ice clouds have a net warming effect on the surface of 23-48 W/m². We conclude that these clouds have a significant impact on the radiation budget in Arctic winters. Our study highlights the importance of active satellite-based remote sensing in globally detecting and characterizing optically thin clouds. Our estimates of occurrence and fraction of clouds represents a lower bound, as these clouds can be obscured by optically thicker clouds. The volume of measurements provided by the satellite allowed us to identify a small but consistent set of large clouds with which we could conduct a contemporary radiative analysis. These findings can be used to improve the representation of clouds and their impacts in regional and global climate models.
    • Investigation On Cirrus Clouds By The Cloud-Aerosol Lidar And Infrared Pathfinder Satellite Observation Data

      Zhu, Jiang; Sassen, Kenneth (2011)
      Understanding and describing the role of clouds in the climate system need intensive and extensive research on cloud properties. The albedo and greenhouse effects of clouds and their relations with the physical properties of clouds are analyzed. Cloud-top height and ice water content are key factors in impacting the longwave and shortwave radiation, respectively. Lidar and infrared radiometer measurement technologies are introduced. Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) level 1 Lidar profile, level 2 cloud layer, and level 2 Lidar/IIR track products are briefly reviewed. The algorithms for identification of cirrus clouds, Linear Depolarization Ratio (LDR), and effective diameter are presented. An average LDR profile is calculated by using the sum of total attenuated backscattering profiles and the sum of perpendicular attenuated backscattering profiles. A weight-average method is applied to calculate the average LDR. A split-window method is applied to estimate the effective diameters of clouds. A set of bulk ice crystal models and a radiative transfer model are applied to produce a look-up table that includes the radiative transfer simulation results. The macro-physical properties of cirrus clouds are analyzed. The frequency of occurrence of cirrus clouds varies with latitude, and strongly relates to the atmospheric circulation. Cirrus clouds are few in high-pressure zones and abundant where seasonal monsoonal circulation occurs. Cloud-top height decreases with increasing latitude. Cloud-top temperature is lower in the tropical regions than in the midlatutude and the polar regions. The measured cloud thickness shows a great diurnal variation.
    • Investigation on the impacts of low-sulfur fuel used in residential heating and oil-fired power plants on PM₂.₅₋ concentrations and its composition in Fairbanks, Alaska

      Leelasakultum, Ketsiri; Mölders, Nicole; Bhatt, Uma; Collins, Richard (2013-08)
      The effects of using low-sulfur fuel for oil-heating and oil-burning facilities on the PM₂.₅-concentrations at breathing level in an Alaska city surrounded by vast forested areas were examined with the Weather Research and Forecasting model coupled with chemistry packages that were modified for the subarctic. Simulations were performed in forecast mode for a cold season using the National Emission Inventory 2008 and alternatively emissions that represent the use of low-sulfur fuel for oil-heating and oil-burning facilities while keeping the emissions of other sources the same as in the reference simulation. The simulations suggest that introducing low-sulfur fuel would decrease the monthly mean 24h-averaged PM₂.₅-concentrations over the city's PM₂.₅-nonattainment area by 4%, 9%, 8%, 6%, 5% and 7% in October, November, December, January, February and March, respectively. The quarterly mean relative response factors for PM₂.₅ of 0.96 indicate that with a design value of 44.7 µg/m³ introducing low-sulfur fuel would lead to a new design value of 42 .9µg/m³ that still exceeds the US National Ambient Air Quality Standard of 35µg/m³ . The magnitude of the relation between the relative response of sulfate and nitrate changes differs with temperature. The simulations suggest that in the city, PM₂.₅-concentrations would decrease more on days with low atmospheric boundary layer heights, low hydrometeor mixing ratio, low downward shortwave radiation and low temperatures. Furthermore, a literature review of other emission control measure studies is given, and recommendations for future studies are made based on the findings.
    • Investigations On The Impacts Of Land-Cover Changes And/Or Increased Carbon Dioxide Concentrations On Four Regional Water Cycles And Their Interactions With The Global Water Cycle

      Li, Zhao; Molders, Nicole (2007)
      A suite of simulations that combine reference (355ppmv), doubled and tripled CO2 concentrations alternatively without and with land-cover changes in four similar-sized study regions, the Yukon, Ob, St. Lawrence and Colorado basin and adjacent land, are performed with the fully coupled Community Climate System Model to investigate the impact on global and regional water cycles and the interaction of these regional water cycles with the global water cycle. The relative changes in water-cycle quantities caused by increased CO 2 enhance with latitude and CO2 concentrations. Regional and global water cycles interactions are more pronounced in a warmer climate, but regional precipitation and evapotranspiration is affected differently in high-latitudes (Yukon, Ob) than mid-latitudes (Colorado, St. Lawrence). Land-cover changes can have comparable impacts on regional water cycles than increased CO2 concentrations do. Land-cover changes substantially alter the high-latitude water cycles through enhanced snow-albedo feedback and mid-latitude water cycles through vegetation activity in the warm season. The land-cover changes in different regions interact with each other through heat and moisture advections and secondary effects. This interaction enhances with increasing CO2 concentrations. Interactions between land-cover changes and increasing CO2 concentrations enhance with increasing CO2 due to the high sensitivity of regional water cycles to temperature changes.
    • Ion dynamics in auroral potential structures and formation of ion conic distribution

      Yang, Wei-hong (1981-12)
      This thesis is concerned with the problem of how the positive ions are energized by the two-dimensional potential structures along auroral field lines; these auroral potential structures are known to be responsible for accelerating electrons into the ionosphere to produce discrete auroras. A systematic numerical study of the test ion dynamics in auroral potential structures, either V-shaped or S-shaped, has been carried out. Transverse ion accelerations occur if the width of the auroral potential structure (Lx ≤ ρi). This result shows that the conic distribution of upstreaming ions observed on auroral field lines can be generated by the same potential structures which produce the thin auroral arcs (Lx ≤ ρi). This transverse acceleration mechanism operates more effectively on heavier ions, resulting in O+ ions more energetic than H+ ions as indicated by observations.
    • Late quaternary and future biome simulations for Alaska and eastern Russia

      Hendricks, Amy S.; Walsh, John; Saito, Kazuyuki; Bigelow, Nancy; Bhatt, Uma (2016-05)
      Arctic biomes across a region including Alaska and Eastern Russia were investigated using the BIOME4 biogeochemical and biogeography vegetation model. This study investigated past (the last 21,000 years), present, and future vegetation distributions in the study area, using climate forcing from five CMIP5 models (CCSM4, GISS-E2-R, MIROC-ESM, MPI-ESM, and MRI-CGCM3). The present-day BIOME4 simulations were generally consistent with current vegetation observations in the study region characterized by evergreen and deciduous taiga and shrub tundras. Paleoclimatological simulations were compared with pollen data samples collected in the study region. Pre-industrial biome simulations are generally similar to the modern reconstruction but differ by having more shrub tundra in both Russia and Alaska to the north, as well as less deciduous taiga in Alaska. Pre-industrial simulations were in good agreement with the pollen data. Mid-Holocene simulations place shrub tundras along the Arctic coast, and in some cases along the eastern coast of Russia. Simulations for the Mid-Holocene are in good agreement with pollen-based distributions of biomes. Simulations for the Last Glacial Maximum (LGM) show that the Bering Land Bridge was covered almost entirely by cushion forb, lichen and moss tundra, shrub tundra, and graminoid tundra. Three out of the five models’ climate data produce evergreen and deciduous taiga in what is now southwestern Alaska, however the pollen data does not support this. The distributions of cushion forb, lichen, and moss tundra and graminoid tundra differ noticeably between models, while shrub tundra distributions are generally similar. Future simulations of BIOME4 based on the RCP8.5 climate scenario indicate a northward shift of the treeline and a significant areal decrease of shrub tundra and graminoid tundra regions in the 21st century. Intrusions of cool mixed, deciduous, and conifer forests above 60°N, especially in southwest Alaska, were notable. Across eastern Russia, deciduous taiga begins to overtake evergreen taiga, except along the coastal regions where evergreen taiga remains the favored biome.
    • Lidar and radar studies of turbulence, instabilities, and waves in the Arctic middle atmosphere

      Li, Jintai; Collins, Richard L.; Newman, David E.; Simpson, William R.; Thorsen, Denise L.; Williams, Bifford P. (2019-08)
      This dissertation presents new studies of gravity waves and turbulence in the Arctic middle atmosphere. The studies employ lidars and radar to characterize wave activity, instability and turbulence. In the lidar-based studies, we analyze turbulence and wave activity in the MLT based on lidar measurements of atmospheric temperature, density and sodium density, temperature and wind. This combination of measurements provides simultaneous characterization of both the atmospheric stability as well as material transport that allow us to estimate the eddy diffusion coefficient associated with turbulence. We extend the scope of previous studies by developing retrievals of potential temperature and sodium mixing ratio from the Rayleigh density temperature lidar and sodium resonance density lidar measurements. We find that the estimated values of turbulent eddy diffusion coefficients, K, of 400-2800 m²/s, are larger than typically reported (1-1000 m²/s) while the values of the energy dissipation rates, ε, of 5-20 mW/kg, are more typical (0.1-1000 mW/kg). We find that upwardly propagating gravity waves accompany the instabilities. In the presence of instabilities, we find that the gravity waves are dissipating as they propagate upward. We estimate the energy available for turbulence generation from the wave activities and estimate the possible turbulent energy dissipation rate, εGW. We find that the values of εGW are comparable to the values of ε. We find that the estimate of the depth of the layer of turbulence are critical to the estimate of the values of both ε and εGW. We find that our method tends to overestimate the depth, and thus overestimate the value of ε, and underestimate the value of εGW. In the radar-based study, we conduct a retrieval of turbulent parameters in the mesosphere based on a hypothesis test. We distinguish between the presence and absence of turbulence based on fitting Voigt-based and Lorentzian-based line shapes to the radar spectra. We also allow for the presence and absence of meteoric smoke particles (MSPs) in the radar spectra. We find examples of Poker Flat Incoherent Scatter Radar (PFISR) spectra showing both the presence and absence of turbulence and the presence and absence of MSPs in the upper mesosphere. Based on the analysis, we find that relatively few of the radar measurements yield significant measurements of turbulence. The significant estimates of turbulence have a strength that is over a factor of two larger than the average of the estimates from all of the radar measurements. The probability of true positives increases with the quality factor of the spectrum. The method yields significant measurements of turbulence with probabilities of true positives of greater than 30% and false positives less than 0.01%.
    • Lidar and satellite studies of noctilucent clouds over Alaska

      Alspach, Jennifer H.; Collins, Richard; Bossert, Katrina; Thorsen, Denise; Fochesatto, Javier (2020-05)
      This thesis presents studies of noctilucent clouds (NLCs) occurring in the summer polar mesosphere over Alaska. Lidar observations of NLCs conducted at Poker Flat Research Range in Chatanika, Alaska (65° N, 147° W) from 1998-2019 are analyzed. The NLCs detected by lidar are characterized in terms of their brightness properties and duration. NLCs were detected on ~51% of the nights when lidar observations have been conducted during NLC season. The brighter NLCs are found to exist at lower altitudes, indicating a growth-sedimentation mechanism. Cloud Imaging and Particle Size (CIPS) data from the Aeronomy of Ice in the Mesosphere (AIM) satellite is used to examine NLC occurrence and brightness over the Alaska region (60-70° N, 130-170° W). In general, high frequency and brightness in the CIPS data corresponds to positive detections of NLCs by the lidar. Microwave Limb Sounder (MLS) temperature and water vapor data from the Aura satellite is used to investigate the meteorological environment of the NLCs observed by lidar at Chatanika. The occurrence of NLCs at Chatanika is found to be driven by the temperature relative to the frost point. Low temperatures relative to the frost point (> 4 K below) correspond to observations when NLCs were present. High temperatures relative to the frost point (> 8 K above) correspond to observations when NLCs were absent. The MLS data is also used to investigate the stability of an ice cloud at different latitudes (64.7°-70.3° N) relative to the equilibrium water vapor mixing ratio. The stability study suggests that the weakest NLCs detected by lidar at Chatanika were in subsaturated conditions, and it is likely that the NLCs formed over several hundred kilometers to the north of Chatanika. The Rayleigh three-channel receiver system was used to conduct NLC measurements during 2019. A technical overview of the three-channel system and the density and temperature retrieval methods is presented at the end of the thesis using observations from the winter of 2018 and the summer of 2019.
    • Micropulse lidar observations of aerosols over the atmospheric radiation measurement site at Barrow

      Tiruchirapalli, Ramaswamy A.S.R. (2006-12)
      Micropulse lidar (MPL) is a ground-based optical remote sensing system designed to determine the vertical structure of clouds and aerosols in the atmosphere. An MPL has operated at Barrow, Alaska since November 2002. From these data, we seek to determine the altitude of aerosol layers in the free troposphere from lidar backscatter profiles. Layer heights are then fed into the HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory Model) model, a back-trajectory model developed by NOAA (National Oceanic and Atmospheric Administration) to compute isentropic back-trajectories. The model is run interactively using the READY interface and can calculate trajectories from multiple heights within a layer. Case analyses are done correlating dates and trajectory coordinates, synoptic weather charts and events reported from satellites and other remote sensing instruments to determine aerosol sources (e.g. forest fire, volcano eruption or dust storm). All the aerosol events detected by the MPL were categorized into five common atmospheric flow patterns identified from the NCEP (National Centers for Environmental Prediction) / NCAR (National Center for Atmospheric Research) reanalysis charts. We conclude that most of the MPL-identified free-tropospheric aerosol layers could be attributed to Siberian/Alaskan forest fires and Asian dust storms.
    • Midlatitude Cirrus Cloud Structural Properties Analyzed From The Extended Facility For Atmospheric Remote Sensing Dataset

      Wang, Likun; Sassen, Kenneth; Cahill, Cathy; Mölders, Nicole; Shaw, Glen; Starr, David O'C (2004)
      The knowledge on cirrus inhomogeneous structural properties is important not only in radiation calculations, but also in deeply understanding the dynamics mechanism including the formation, development, and dissipation of cirrus clouds. The midlatitude cirrus inhomogeneous structural properties have been evaluated by analyzing the 10-year high cloud datasets obtained at the University of Utah, Facility for Atmospheric Remote Sensing in Salt Lake City, UT. Three goals have been reached in this research. First, the means to analyze lidar data using wavelet analysis, an advanced approach to obtain information on the structure of cirrus clouds, has been successfully developed. And then, typical cirrus structures including Kelvin-Helmholtz instabilities, cirrus mammata, and the uncinus cells have been analyzed by case studies and statistical survey. Their dynamical mechanisms, environmental characteristics, and vertical and horizontal length scale have been studied. Thirdly, using the method based on the wavelet transform and other methods, a climatology of midlatitude cirrus horizontal inhomogeneous properties is developed from the FARS lidar backscattered power data, the proxies of real cirrus clouds.