Ion observations from geosynchronous orbit as a proxy for ion cyclotron wave growth during storm times

[1] There is still much to be understood about the processes contributing to relativistic electron enhancements and losses in the radiation belts. Wave particle interactions with both whistler and electromagnetic ion cyclotron (EMIC) waves may precipitate or accelerate these electrons. This study examines the relation between EMIC waves and resulting relativistic electron flux levels after geomagnetic storms. A proxy for enhanced EMIC waves is developed using Los Alamos National Laboratory Magnetospheric Plasma Analyzer plasma data from geosynchronous orbit in conjunction with linear theory. In a statistical study using superposed epoch analysis, it is found that for storms resulting in net relativistic electron losses, there is a greater occurrence of enhanced EMIC waves. This is consistent with the hypothesis that EMIC waves are a primary mechanism for the scattering of relativistic electrons and thus cause losses of such particles from the magnetosphere

The phonon dispersion of graphite by inelastic x-ray scattering

We present the full in-plane phonon dispersion of graphite obtained from inelastic x-ray scattering, including the optical and acoustic branches, as well as the mid-frequency range between the $K$ and $M$ points in the Brillouin zone, where experimental data have been unavailable so far. The existence of a Kohn anomaly at the $K$ point is further supported. We fit a fifth-nearest neighbour force-constants model to the experimental data, making improved force-constants calculations of the phonon dispersion in both graphite and carbon nanotubes available.Comment: 7 pages; submitted to Phys. Rev.

Exciton binding energies in carbon nanotubes from two-photon photoluminescence

One- and two-photon luminescence excitation spectroscopy showed a series of distinct excitonic states in single-walled carbon nanotubes. The energy splitting between one- and two-photon-active exciton states of different wavefunction symmetry is the fingerprint of excitonic interactions in carbon nanotubes. We determine exciton binding energies of 0.3-0.4 eV for different nanotubes with diameters between 0.7 and 0.9 nm. Our results, which are supported by ab-initio calculations of the linear and non-linear optical spectra, prove that the elementary optical excitations of carbon nanotubes are strongly Coulomb-correlated, quasi-one dimensionally confined electron-hole pairs, stable even at room temperature. This alters our microscopic understanding of both the electronic structure and the Coulomb interactions in carbon nanotubes, and has direct impact on the optical and transport properties of novel nanotube devices.Comment: 5 pages, 4 figure

Submesoscale CO2 variability across an upwelling front off Peru

As a major source for atmospheric CO2, the Peruvian upwelling region exhibits strong variability in surface fCO2 on short spatial and temporal scales. Understanding the physical processes driving the strong variability is of fundamental importance for constraining the effect of marine emissions from upwelling regions on the global CO2 budget. In this study, a frontal decay on length scales of (10 km) was observed off the Peruvian coast following a pronounced decrease in down-frontal (equatorward) wind speed with a time lag of 9 h. Simultaneously, the sea-to-air flux of CO2 on the inshore (cold) side of the front dropped from up to 80 to 10 mmol m−2 day−1, while the offshore (warm) side of the front was constantly outgassing at a rate of 10–20 mmol m−2 day−1. Based on repeated ship transects the decay of the front was observed to occur in two phases. The first phase was characterized by a development of coherent surface temperature anomalies which gained in amplitude over 6–9 h. The second phase was characterized by a disappearance of the surface temperature front within 6 h. Submesoscale mixed-layer instabilities were present but seem too slow to completely remove the temperature gradient in this short time period. Dynamics such as a pressure-driven gravity current appear to be a likely mechanism behind the evolution of the front

The Vulnerability and Resilience of Seagrass Ecosystems to Marine Heatwaves in New Zealand: A Remote Sensing Analysis of Seascape Metrics Using PlanetScope Imagery

Seagrasses are foundation species that provide ecosystem functions and services, including increased biodiversity, sediment retention, carbon sequestration, and fish nursery habitat. However, anthropogenic stressors that reduce water quality, impose large-scale climate changes, and amplify weather patterns, such as marine heatwaves, are altering seagrass meadow configurations. Quantifying large-scale trends in seagrass distributions will help evaluate the impacts of climate drivers on their functions and services. Here, we quantified spatiotemporal dynamics in abundances and configurations of intertidal and shallow subtidal seagrass (Zostera muelleri) meadows in 20 New Zealand (NZ) estuaries that span a 5-year period (mid/late 2016–early 2022) just before, during and after the Tasman Sea 2017/18 marine heatwave, the warmest summer ever recorded in NZ. We used high-resolution PlanetScope satellite imagery to map interseasonal seagrass extent and quantify seascape metrics across 20 estuaries along a latitudinal gradient spanning 12° in NZ. We also explored the association of changes in seagrass metrics with satellite-derived predictors such as sea surface temperature (SST), SST anomaly (SSTa), water column turbidity, and nutrient concentration. Our analyses revealed that NZ seagrass meadows varied in areal extent between years and seasons, but with no clear patterns over the 5-year period, implying resilience to large-scale stressors like the 2017/18 marine heatwave. Small-scale patterns were also dynamic, for example, patch sizes and patch configurations differed across estuaries, seasons, and years. Furthermore, seagrass patches expanded in some estuaries with increasing SST and SSTa. These results highlight dynamic seagrass patterns that likely affect local processes such as biodiversity and carbon sequestration. Our analyses demonstrate that a combination of high-resolution satellite remote sensing and seascape metrics is an efficient and novel approach to detect impacts from anthropogenic stressors, like eutrophication and climate changes, and climate extremes like cyclones and heatwaves