Continent-Wide Patterns of Climate and Mast Seeding Entrain Boreal Bird Irruptions.

Avian irruptions are facultative, often periodic, migrations of thousands of birds outside of their resident range. Irruptive movements produce regional anomalies of abundance that oscillate over time, forming ecological dipoles (geographically disjunct regions of low and high abundance) at continental scales. Potential drivers of irruptions include climate and food variability, but these relationships are rarely tested over broad geographic scales.

Multiscale mushy layer model for Arctic marginal ice zone dynamics.

Perhaps the most dynamic component of the Arctic sea ice cover is the marginal ice zone (MIZ), the transitional region between dense pack ice to the north and open ocean to the south. It widens by a factor of four while seasonally migrating more than 1600 km poleward in the Bering-Chukchi Sea sector, impacting climate dynamics, ecological processes, and human accessibility to the Arctic. Here we showcase a transformative mathematical modeling approach to understanding changes in MIZ location and width, focusing on their seasonal cycles as observed by satellites.

A North American climate-masting-irruption teleconnection and its change under future climate.

Atmospheric variability can impact biological populations by triggering facultative migrations, but the stability of these atmosphere-biosphere connections may be vulnerable to climate change. As an example, we consider the leading mode of continental-scale facultative migration of Pine Siskins, where the associated ecological mechanism is changes in resource availability, with a mechanistic pathway of climate conditions affecting mast seeding patterns in trees which in turn drive bird migration. The three summers prior to pine siskin irruption feature an alternating west-east mast-seeding dipole in conifer trees with opposite anomalies over western and eastern North America.

Poleward shifts and altered periodicity in boreal bird irruptions over six decades.

Range boundaries are long-term biogeographic features of species distributions and abundance. However, many species demonstrate dynamic range boundaries, reflecting strong seasonal and annual variability in migratory behaviour. As a form of facultative migration, irruptions involve the movement of many individuals outside of their resident range in response to climate variability, resource availability, and demographic processes.

Climate Dipoles as Continental Drivers of Plant and Animal Populations.

Ecological processes, such as migration and phenology, are strongly influenced by climate variability. Studying these processes often relies on associating observations of animals and plants with climate indices, such as the El Niño-Southern Oscillation (ENSO). A common characteristic of climate indices is the simultaneous emergence of opposite extremes of temperature and precipitation across continental scales, known as climate dipoles.

Midwinter Arctic leads form and dissipate low clouds.

Leads are a key feature of the Arctic ice pack during the winter owing to their substantial contribution to the surface energy balance. According to the present understanding, enhanced heat and moisture fluxes from high lead concentrations tend to produce more boundary layer clouds. However, described here in our composite analyses of diverse surface- and satellite-based observations, we find that abundant boundary layer clouds are associated with low lead flux periods, while fewer boundary layer clouds are observed for high lead flux periods.

Long-term urban carbon dioxide observations reveal spatial and temporal dynamics related to urban characteristics and growth.

Cities are concentrated areas of CO emissions and have become the foci of policies for mitigation actions. However, atmospheric measurement networks suitable for evaluating urban emissions over time are scarce. Here we present a unique long-term (decadal) record of CO mole fractions from five sites across Utah's metropolitan Salt Lake Valley.

A Laplacian characterization of phytoplankton shape.

Phytoplankton exhibit pronounced morphological diversity, impacting a range of processes. Because these impacts are challenging to quantify, however, phytoplankton are often approximated as spheres, and when effects of non-sphericity are studied it is usually experimentally or via geometrical approximations. New methods for quantifying phytoplankton size and shape generally, so all phytoplankton are analyzable by the same procedure, can complement advances in microscopic imagery and automated classification to study the influence of shape in phytoplankton.

Observed variations in U.S. frost timing linked to atmospheric circulation patterns.

Several studies document lengthening of the frost-free season within the conterminous United States (U.S.) over the past century, and report trends in spring and fall frost timing that could stem from hemispheric warming.

Climatic dipoles drive two principal modes of North American boreal bird irruption.

Pine Siskins exemplify normally boreal seed-eating birds that can be sparse or absent across entire regions of North America in one year and then appear in large numbers the next. These dramatic avian "irruptions" are thought to stem from intermittent but broadly synchronous seed production (masting) in one year and meager seed crops in the next. A prevalent hypothesis is that widespread masting in the boreal forest at high latitudes is driven primarily by favorable climate during the two to three consecutive years required to initiate and mature seed crops in most conifers.

Vapor hydrogen and oxygen isotopes reflect water of combustion in the urban atmosphere.

Anthropogenic modification of the water cycle involves a diversity of processes, many of which have been studied intensively using models and observations. Effective tools for measuring the contribution and fate of combustion-derived water vapor in the atmosphere are lacking, however, and this flux has received relatively little attention. We provide theoretical estimates and a first set of measurements demonstrating that water of combustion is characterized by a distinctive combination of H and O isotope ratios.