Testing predictors of eruptivity using parametric flux emergence simulations

Solar flares and coronal mass ejections (CMEs) are among the most energetic events in the solar system, impacting the near-Earth environment. Flare productivity is empirically known to be correlated with the size and complexity of active regions. Several indicators, based on magnetic-field data from active regions, have been tested for flare forecasting in recent years. None of these indicators, or combinations thereof, have yet demonstrated an unambiguous eruption or flare criterion. Furthermore, numerical simulations have been only barely used to test the predictability of these parameters. In this context, we used the 3D parametric MHD numerical simulations of the self-consistent formation of the flux emergence of a twisted flux tube, inducing the formation of stable and unstable magnetic flux ropes of Leake (2013, 2014). We use these numerical simulations to investigate the eruptive signatures observable in various magnetic scalar parameters and provide highlights on data analysis processing. Time series of 2D photospheric-like magnetograms are used from parametric simulations of stable and unstable flux emergence, to compute a list of about 100 different indicators. This list includes parameters previously used for operational forecasting, physical parameters used for the first time, as well as new quantities specifically developed for this purpose. Our results indicate that only parameters measuring the total non-potentiality of active regions associated with magnetic inversion line properties, such as the Falconer parameters $L_{ss}$, $WL_{ss}$, $L_{sg}$ and $WL_{sg}$, as well as the new current integral $WL_{sc}$ and length $L_{sc}$ parameters, present a significant ability to distinguish the eruptive cases of the model from the non-eruptive cases, possibly indicating that they are promising flare and eruption predictors.Comment: 46 pages, 16 figures, accepted for publication in Space Weather and Space Climate on June, 8t

Sink or ecological trap for tree swallows in Central Minnesota?

Background: An ecological trap is typically defined as a low-quality habitat, incapable of sustaining a population, which is preferred over a high quality habitat. Ecological traps may lead to species extinction in populations with 1) strict habitat requirements 2) minimal information about the habitat, and 3) low population size. Tree Swallows (Tachycineta bicolor) meet the former two of these criteria. Methods: We monitored Tree Swallow (TS) nest boxes (n=90) at two ecologically similar sites A and B with similar occupancy rates. Site B has lower reproductive fitness —suggestive of an ecological trap. Binary logistic regression was used to identify whether TS in better condition preferred site A or B and what environmental characteristics predicted nest box occupancy. Results: Site A’s Tree Swallows were in significantly better condition and laid eggs earlier than site B’s TS. Significant predictors of nest box occupancy include distance from nearest box (p=0.000), DBH of largest stem in adjacent wooded area (p=0.026). Conclusion: Tree Swallows seemingly recognized site A to be a superior breeding habitat over site B, suggesting that site B is a sink rather than an ecological trap. Distance from an adjacent box was an important predictor of occupancy, possibly to reduce extra-pair mating or depredation. TS favored nest boxes adjacent to an edge with smaller stems which may lessen competition by birds a nesting in naturally occurring cavities along hardwood edges. Although not a significant predictor of occupation, the average distance from the edge was greater at Site A (p = 0.012). It is possible that distance from the edge is a habitat cue utilized by Tree Swallows, independent of whether hetero- or conspecifics might be nesting in nearby natural cavities

Local interactions in active matter are reinforced by spatial structure

The flocking of self-propelled particles in heterogeneous environments is relevant to both natural and artificial systems. The Vicsek model is a canonical choice to investigate such systems due to the minimal number of parameters required to define flocking. Prior research on the Vicsek model has investigated the effects of interaction rules, particle speed, and obstacle packing on the flocking behavior, but the effect of interaction radius remains an open question. Unlike obstacle-free domains, the locality of interactions not only affects how quickly the system can become polarized, but also how well the flocks can align or realign after colliding with obstacles. In this letter, we delve into this subtle relationship that exists in the scale of the perception of Vicsek particles in the presence of obstacles. We demonstrate that the presence of obstacles impacts group density, which provides the basis to identify distinct phases for collective behavior. This leads to the counter-intuitive result that obstacles, while generally confounding for macroscopic order, may enable global order even as noise in the system increases

Do assumptions about the central density of subhaloes affect dark matter annihilation and lensing calculations?

A growing body of evidence suggests that the central density of cuspy dark matter subhaloes is conserved in minor mergers. However, empirical models of subhalo evolution, calibrated from simulations, often assume a drop in the central density. Since empirical models of subhaloes are used in galaxy-galaxy lensing studies and dark matter annihilation calculations, we explore the consequences of assuming different subhalo models. We find that dark matter annihilation calculations are very sensitive to the assumed subhalo mass profile, and different models can give more than a magnitude difference in the J-factor and boost factor in individual haloes. On the other hand, the shear and convergence profiles used in galaxy-galaxy lensing are sensitive to the initial profile assumed (e.g., NFW versus Einato) but are otherwise well-approximated by a simple model in which the original profile is sharply truncated. We conclude that since the innermost parts of haloes are difficult to resolve in simulations, it is important to have a theoretical understanding of how subhaloes evolve to make accurate predictions of the dark matter annihilation signal.Comment: 15 pages, 13 figures. Submitted to MNRA

Rolling covenants to protect coastal ecosystems in the face of sea-level rise

This article considers how “rolling covenants” (i.e., covenants on land title that can operate in a “rolling” geographic area to keep pace with sea-level rise) can be used to permit productive use of land in the short term, while ensuring land use can shift over time to allow for coastal ecosystem migration in the medium to long term. We use Australia as a case study, and through analysis of legislation and a series of semistructured interviews, we demonstrate how land title-based covenants can be used to give legal effect to “rolling covenant” arrangements where land is subject to existing use and occupation. We then consider practical issues associated with drafting a rolling covenant arrangement, including an analysis of the types of events or scenarios that could be used as a basis for land use changing (e.g., projected sea-level rise, actual ecosystem migration), and the advantages and disadvantages of each. We conclude that rolling covenants are a viable option for land management in the coastal zone, especially in circumstances where funding sources are available to incentivize uptake. Rolling covenants may provide opportunities for coastal wetlands to be maintained and even enhanced in cover, thereby delivering important ecosystem services (e.g., blue carbon) into the future