Photodetachment Cross Section of H- in Crossed Electric and Magnetic Fields. I. Closed-Orbit Theory

In this, the first of two papers, we obtain a simple analytic formula for the photodetachment cross section of H− in crossed electric and magnetic fields. The three-dimensional semiclassical approximation predicts oscillations in the spectrum and these oscillations are correlated with closed classical orbits. In the following paper [A. D. Peters and J. B. Delos, Phys. Rev. A 47, 3036 (1993)] we derive fully-quantum-mechanical formulas for the cross section in perpendicular electric and magnetic fields and show how these results can be reduced to the semiclassical results of this paper

Photodetachment Cross Section of H- in Crossed Electric and Magnetic Fields. II. Quantum Formulas and Their Reduction to the Result of the Closed-Orbit Theory

In this, the second of two papers, we derive general quantum formulas for the photodetachment cross section for H− in perpendicular electric and magnetic fields. The results are valid for any polarization and can be reduced to the semiclassical results of the first paper [A. D. Peters and J. B. Delos, Phys. Rev. A 47, 3020 (1993)]: a smooth background plus oscillatory terms. This connection between the quantum and semiclassical results is made using a stationary-phase approximation and it is shown that each stationary-phase point corresponds to a closed orbit

Quantum Manifestations of Bifurcations of Classical Orbits: An Exactly Solvable Mode

We examine photodetachment of H− in parallel electric and magnetic fields, hν+H−→H+e− using semiclassical approximations. The fields cause the electron to return to the atom, producing recurrences that are visible as interference oscillations in the photodetachment cross section. As the energy is varied, new returning orbits are created through bifurcations. Each such new recurrence increases the complexity of the absorption spectrum, and each bifurcation causes a local failure of the semiclassical approximation. The failure is repaired by a Fresnel diffraction integral

Closed-orbit Theory and the Photodetachment Cross Section of H- in Parallel Electric and Magnetic Fields

In this paper we obtain a simple analytic formula for the photodetachment cross section of H− in parallel electric and magnetic fields. The three-dimensional semiclassical approximation predicts oscillations in the spectrum and correlates these oscillations with closed classical orbits. The cylindrical symmetry of the Hamiltonian produces some interesting effects. In particular, at boundary energies the semiclassical approximation fails as a focused cusp approaches the origin

Diagnosing the Nature of Land-Atmosphere Coupling: A Case Study of Dry/Wet Extremes

Land-atmosphere (L-A) interactions play a critical role in determining the diurnal evolution of land surface and planetary boundary layer (PBL) temperature and moisture states and fluxes. In turn, these interactions regulate the strength of the connection between surface moisture and precipitation in a coupled system. To address deficiencies in numerical weather prediction and climate models due to improper treatment of L-A interactions, recent studies have focused on development of diagnostics to quantify the strength and accuracy of the land-PBL coupling at the process-level. In this study, a diagnosis of the nature and impacts oflocalland-atmosphere coupling (LoCo) during dry and wet extreme conditions is presented using a combination of models and observations during the summers of2006-7 in the U.S. Southern Great Plains. Specifically, the Weather Research and Forecasting (WRF) model has been coupled to NASA's Land Information System (LIS), which provides a flexible and high-resolution representation and initialization of land surface physics and states. A range of diagnostics exploring the links and feedbacks between soil moisture and precipitation are examined for the dry/wet regimes of this region, along with the behavior and accuracy of different land-PBL scheme couplings under these conditions. In addition, we examine the impact of improved specification ofland surface states, anomalies, and fluxes that are obtained through the use of a hew optimization and uncertainty module in LIS, on the L-A coupling in WRF forecasts. Results demonstrate how LoCo diagnostics can be applied to coupled model components in the context of their integrated impacts on the process-chain connecting the land surface to the PBL and support of hydrological anomalies

Quantum Manifestations of Bifurcations of Closed Orbits in the Photodetachment Cross Section of H- in Parallel Fields

In the preceding paper, we showed that the semiclassical approximation diverges at a bifurcation, and that this divergence coincides with the passage of a focused cusp through the origin. Here we obtain a wave function in the vicinity of this cusp, and we use that wave function to eliminate the divergences in the photodetachment cross section. To describe the focused cusp, we first discuss the wave function of an ordinary two-dimensional (nonfocused) cusp. This wave function is known as a Pearcey function, and it has been studied extensively. Then we show how the formulas that lead to the Pearcey function have to be modified to describe a cylindrically focused cusp. The resulting wave function turns out to be given by an integral of Fresnel type containing within it a cylindrical Bessel function. This wave function is used to derive a formula for the photodetachment cross section near a bifurcation. That formula is a simple closed-form expression containing a Fresnel integral. Comparison with exact quantum calculations shows that this corrected-semiclassical formula is quite accurate

Diagnosing the Nature of Land-Atmosphere Coupling During the 2006-7 Dry/Wet Extremes in the U. S. Southern Great Plains

The degree of coupling between the land surface and PBL in NWP models remains largely undiagnosed due to the complex interactions and feedbacks present across a range of scales. In this study, a framework for diagnosing local land-atmosphere coupling (LoCo) is presented using a coupled mesoscale model with observations during the summers of 2006/7 in the U.S. Southern Great Plains. Specifically, the Weather Research and Forecasting (WRF) model has been coupled to NASA's Land Information System (LIS), which enables a suite of PBL and land surface model (LSM) options along provides a flexible and high-resolution representation and initialization of land surface physics and states. This coupling is one component of a larger project to develop a NASA-Unified WRF (NU-WRF) system. A range of diagnostics exploring the feedbacks between soil moisture and precipitation are examined for the dry/wet extremes, along with the sensitivity of PBL-LSM coupling to perturbations in soil moisture

Genetic diversity of Ectocarpus (Ectocarpales, Phaeophyceae) in Peru and northern Chile, the area of origin of the genome-sequenced strain

International audienceThe origin of the Ectocarpus strain used for genome sequencing (the ‘genome strain’) was Peru, where no Ectocarpus had been reported previously. To study the genetic diversity in the region and to increase the number of individuals from this area available for genetic experiments, 119 new Ectocarpus strains were isolated from eight localities along the 3000 km of coastline from central Peru to central Chile.Internal transcribed spacer 1 (ITS1) genotyping revealed nine different genotypes, five of which were endemic to the area studied and three of which were previously unknown.Individuals of the same genotype as the genome strain occurred from Peru to northernmost Chile, representing 61% of the samples in this area, from which five more genotypes were isolated. Further south, down to central Chile, most individuals belonged to Ectocarpus siliculosus, Ectocarpus fasciculatus and Ectocarpus crouaniorum. In sexual crosses, the genome strain and the new isolates of the same genotype were fully compatible.Sequences from four nuclear and cytoplasmic genetic markers (ITS1, ITS2, Rubisco spacer and Cytochrome‐c oxidase subunit 3 (cox3)) separated the genome strain from the known species of Ectocarpus. It may in future be recognized as a separate species

Analysis of Abrupt Transitions in Ecological Systems

The occurrence and causes of abrupt transitions, thresholds, or regime shifts between ecosystem states are of great concern and the likelihood of such transitions is increasing for many ecological systems. General understanding of abrupt transitions has been advanced by theory, but hindered by the lack of a common, accessible, and data-driven approach to characterizing them. We apply such an approach to 30–60 years of data on environmental drivers, biological responses, and associated evidence from pelagic ocean, coastal benthic, polar marine, and semi-arid grassland ecosystems. Our analyses revealed one case in which the response (krill abundance) linearly tracked abrupt changes in the driver (Pacific Decadal Oscillation), but abrupt transitions detected in the three other cases (sea cucumber abundance, penguin abundance, and black grama grass production) exhibited hysteretic relationships with drivers (wave intensity, sea-ice duration, and amounts of monsoonal rainfall, respectively) through a variety of response mechanisms. The use of a common approach across these case studies illustrates that: the utility of leading indicators is often limited and can depend on the abruptness of a transition relative to the lifespan of responsive organisms and observation intervals; information on spatiotemporal context is useful for comparing transitions; and ancillary information from associated experiments and observations aids interpretation of response-driver relationships. The understanding of abrupt transitions offered by this approach provides information that can be used to manage state changes and underscores the utility of long-term observations in multiple sentinel sites across a variety of ecosystems.Organismic and Evolutionary Biolog