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Stefanescu E.R.,State University of New York at Buffalo | Patra A.K.,State University of New York at Buffalo | Madankan R.,State University of New York at Buffalo | Jones M.,New York University | And 6 more authors.
Journal of Advances in Modeling Earth Systems | Year: 2014

Uncertainty in predictions from a model of volcanic ash transport in the atmosphere arises from uncertainty in both eruption source parameters and the model wind field. In a previous contribution, we analyzed the probability of ash cloud presence using weighted samples of volcanic ash transport and dispersal model runs and a reanalysis wind field to propagate uncertainty in eruption source parameters alone. In this contribution, the probabilistic modeling is extended by using ensemble forecast wind fields as well as uncertain source parameters. The impact on ash transport of variability in wind fields due to unresolved scales of motion as well as model physics uncertainty is also explored. We have therefore generated a weighted, probabilistic forecast of volcanic ash transport with only a priori information, exploring uncertainty in both the wind field and the volcanic source. © 2014. The Authors. Source

Johnstone J.F.,University of Saskatchewan | Johnstone J.F.,University of Alaska Fairbanks | Chapin III F.S.,University of Alaska Fairbanks | Hollingsworth T.N.,University of AlaskaFairbanks | And 3 more authors.
Canadian Journal of Forest Research | Year: 2010

In the boreal forests of interior Alaska, feedbacks that link forest soils, fire characteristics, and plant traits havesupported stable cycles of forest succession for the past 6000 years. This high resilience of forest stands to fire disturbanceis supported by two interrelated feedback cycles: (i) interactions among disturbance regime and plant-soil-microbial feedbacks that regulate soil organic layer thickness and the cycling of energy and materials, and (ii) interactions among soil conditions, plant regeneration traits, and plant effects on the environment that maintain stable cycles of forest community composition. Unusual fire events can disrupt these cycles and trigger a regime shift of forest stands from one stability domain to another (e.g., from conifer to deciduous forest dominance). This may lead to abrupt shifts in forest cover in response to changing climate and fire regime, particularly at sites with intermediate levels of moisture availability where stand-scale feedback cycles are only weakly constrained by environmental conditions. However, the loss of resilience in individual stands may foster resilience at the landscape scale, if changes in the landscape configuration of forest cover types feedback to stabilize regional patterns of fire behavior and climate conditions. Source

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