Numerical Modeling Of Seasonally Freezing Ground And Permafrost

Thesis (Ph.D.) University of Alaska Fairbanks, 2007This thesis represents a collection of papers on numerical modeling of permafrost and seasonally freezing ground dynamics. An important problem in numerical modeling of temperature dynamics in permafrost and seasonally freezing ground is related to parametrization of already existing models. In this thesis, a variation data assimilation technique is presented to find soil properties by minimizing the discrepancy between in-situ measured temperatures and those computed by the models. The iterative minimization starts from an initial approximation of the soil properties that are found by solving a sequence of simple subproblems. In order to compute the discrepancy, the temperature dynamics is simulated by a new implementation of the finite element method applied to the heat equation with phase change. Despite simplifications in soil physics, the presented technique was successfully applied to recover soil properties, such as thermal conductivity, soil porosity, and the unfrozen water content, at several sites in Alaska. The recovered properties are used in discussion on soil freezing/thawing and permafrost dynamics in other parts of this thesis. Another part of this thesis concerns development of a numerical thermo-mechanical model of seasonal soil freezing on the lateral scale of several meters. The presented model explains observed differential frost heave occurring in non-sorted circle ecosystems north of the Brooks Range in the Alaskan tundra. The model takes into account conservation principles for energy, linear momentum and mass of three constituents: liquid water, ice and solid particles. The conservation principles are reduced to a computationally convenient system of coupled equations for temperature, liquid water pressure, porosity, and the velocity of soil particles in a three-dimensional domain with cylindrical symmetry. Despite a simplified rheology, the model simulates the ground surface motion, temperature, and water dynamics in soil and explains dependence of the frost heave on specific environmental properties of the ecosystem. In the final part, simulation of the soil temperature dynamics on the global scale is addressed. General Circulation Models are used to understand and predict future climate change, but most of them do not simulate permafrost dynamics and its potentially critical feedback on climate. In this part, a widely used climate model is evaluated and the simulated temperatures are compared against observations. Based on this comparison, several modifications to the Global Circulation Models are identified to improve the fidelity of permafrost and soil temperature simulations. These modifications include increasing the total soil depth by adding new layers, incorporating a surface organic layer, and modifying the numerical scheme to include unfrozen water dynamics

Propagation of tsunami-induced acoustic-gravity waves in the atmosphere

A dynamical core of an atmospheric GCM is utilized for assessing the qualitative picture of propagation of atmospheric acoustic-gravity waves in response to perturbations generated by tsunami waves at the surface. Both resting isothermal atmosphere and model- generated atmosphere with realistic stratification and circulation features were considered. Shallow water tsunami model was run in two different configurations: ocean of equal depth of 4 km and ocean with realistic continents and bottom topography. Amplitude and timing of atmospheric response is analyzed as a function of vertical stratification and configuration of atmospheric jets. This approach has a potential for early tsunami detection by measuring changes in electric properties of the upper atmosphere in response to acoustic-gravity waves generated by tsunami.DJN was supported in part by Cooperative Institute for Alaska Research with funds from NOAA under cooperative agreement NA08OAR4320751 with the University of Alaska

PHYSICAL OBJECT-ORIENTED MODELING IN DEVELOPMENT OF INDIVIDUALIZED TEACHING AND ORGANIZATION OF MINI-RESEARCH IN MECHANICS COURSES

Subject of Research. The paper presents a relatively simple method to develop interactive computer models of physical systems without computer programming skills or automatic generation of the numerical computer code for the complex physical systems. Developed computer models are available over the Internet for educational purposes and can be edited by users in an unlimited number of possibilities. An applicability of computer simulations for the massive open individualized teaching and an organization of undergraduate research are also discussed. Method. The presented approach employs an original physical object-oriented modeling method, which is an extension of object-oriented programming ideas to tasks of developing simulations of the complex physical systems. In this framework, a computer model of the physical system is constructed as a set of interconnected computer objects simulating the system components: particles and fields. Interactions between the system components are described by self-adapting algorithms that are specified during the model initiation stage and are set according to either the classical or relativistic approach. The utilized technique requires neither a priori knowledge regarding an evolution of the physical system nor a formulation of differential equations describing the physical system. Main Results. Testing of the numerical implementation and an accuracy of the algorithms was performed with the use of benchmarks with the known analytical solutions. The developed method - a physical reality constructor - has provided an opportunity to assemble a series of computer models to demonstrate physical phenomena studied in the high school and university mechanic courses. More than 150 original interactive models were included into the collections of multi-level multimedia resources to support teaching of the mechanics. The physical reality constructor was successfully tested to serve as a test bed for the independent research by students on physical properties of complex mechanical systems, the analysis of which is beyond the scope of the standard physics and mathematics curriculum. The heuristic capabilities of models created by the physical reality constructor were also demonstrated. The capability to investigate dynamics of the complex systems, an a priori analysis of which is not evident or with a difficult or impossible-to-calculate evolution, was also demonstrated. Practical Relevance. The developed computer program for automated development of interactive educational simulations provides a solution to standing problems in accompanying massive open individualized learning multi-level courses in physics as well as an opportunity to develop creative forms of training in physics with elements of research

Future Transitions From a Conifer to a Deciduous-Dominated Landscape are Accelerated by Greater Wildfire Activity and Climate Change in Interior Alaska

Context In interior Alaska, increasing wildfire activity associated with climate change is projected to continue, potentially altering regional forest composition. Conifers are emblematic of boreal forest; however, greater frequency and severity of wildfires has been found to favor broadleaf-deciduous species in numerous studies. Objectives This study examines potential shifts in forest type in interior Alaska and how shifts may be impacted by recurring wildfires under future climate change. Methods A spatially-explicit forest landscape model, LANDIS-II, was used to simulate forest succession and wildfire over a 380,400-hectare landscape under historic and future (RCP 8.5) climate. Wildfire was modeled using the SCRPPLE fire extension and vegetation growth, belowground carbon, hydrologic, and permafrost dynamics were modeled with the DGS succession extension. The relative importance of drivers of forest type change away from black spruce was quantified using random forest models for areas on the landscape experiencing different numbers of wildfires. Results Greater frequencies of fire activity were associated with shifts in conifer-dominant areas to broadleaf-deciduous, which climate change accelerated. Vegetation transitions were most strongly influenced by percent tree mortality from the most recent wildfire. Starting deciduous fraction and proximity of mature black spruce to a site pre-fire were also influential, indicating pre-fire composition and context modified the effect of vegetation shifts. Conclusions These results underscore how shifts in forest type may occur in a nonlinear manner in this region as the landscape experiences pressure from climate change and forests are subject to complex interactions between wildfire, climate, belowground processes, and the arrangement of forest communities

Climate change damages to Alaska public infrastructure and the economics of proactive adaptation

Climate change in the circumpolar region is causing dramatic environmental change that is increasing the vulnerability of infrastructure. We quantified the economic impacts of climate change on Alaska public infrastructure under relatively high and low climate forcing scenarios [representative concentration pathway 8.5 (RCP8.5) and RCP4.5] using an infrastructure model modified to account for unique climate impacts at northern latitudes, including near-surface permafrost thaw. Additionally, we evaluated how proactive adaptation influenced economic impacts on select infrastructure types and developed first-order estimates of potential land losses associated with coastal erosion and lengthening of the coastal ice-free season for 12 communities. Cumulative estimated expenses from climate-related damage to infrastructure without adaptation measures (hereafter damages) from 2015 to 2099 totaled $5.5 billion (2015 dollars, 3$4.2 billion for RCP4.5, suggesting that reducing greenhouse gas emissions could lessen damages by $1.3 billion this century. The distribution of damages varied across the state, with the largest damages projected for the interior and southcentral Alaska. The largest source of damages was road flooding caused by increased precipitation followed by damages to buildings associated with near-surface permafrost thaw. Smaller damages were observed for airports, railroads, and pipelines. Proactive adaptation reduced total projected cumulative expenditures to$2.9 billion for RCP8.5 and $2.3 billion for RCP4.5. For road flooding, adaptation provided an annual savings of 80–100% across four study eras. For nearly all infrastructure types and time periods evaluated, damages and adaptation costs were larger for RCP8.5 than RCP4.5. Estimated coastal erosion losses were also larger for RCP8.5.United States. Environmental Protection Agency. Climate Change Division (Contract EP-D-14-031

Validation and inter-comparison of models for landslide tsunami generation

10.1016/j.ocemod.2021.101943OCEAN MODELLING17

Dependence of the evolution of carbon dynamics in the northern permafrost region on the trajectory of climate change.

We conducted a model-based assessment of changes in permafrost area and carbon storage for simulations driven by RCP4.5 and RCP8.5 projections between 2010 and 2299 for the northern permafrost region. All models simulating carbon represented soil with depth, a critical structural feature needed to represent the permafrost carbon-climate feedback, but that is not a universal feature of all climate models. Between 2010 and 2299, simulations indicated losses of permafrost between 3 and 5 million km2 for the RCP4.5 climate and between 6 and 16 million km2 for the RCP8.5 climate. For the RCP4.5 projection, cumulative change in soil carbon varied between 66-Pg C (1015-g carbon) loss to 70-Pg C gain. For the RCP8.5 projection, losses in soil carbon varied between 74 and 652 Pg C (mean loss, 341 Pg C). For the RCP4.5 projection, gains in vegetation carbon were largely responsible for the overall projected net gains in ecosystem carbon by 2299 (8- to 244-Pg C gains). In contrast, for the RCP8.5 projection, gains in vegetation carbon were not great enough to compensate for the losses of carbon projected by four of the five models; changes in ecosystem carbon ranged from a 641-Pg C loss to a 167-Pg C gain (mean, 208-Pg C loss). The models indicate that substantial net losses of ecosystem carbon would not occur until after 2100. This assessment suggests that effective mitigation efforts during the remainder of this century could attenuate the negative consequences of the permafrost carbon-climate feedback