Non-stationary frequency analysis of extreme precipitation in South Korea using peaks-over-threshold and annual maxima

The conventional approach to the frequency analysis of extreme precipitation is complicated by non-stationarity resulting from climate variability and change. This study utilized a non-stationary frequency analysis to better understand the time-varying behavior of short-duration (1-, 6-, 12-, and 24-h) precipitation extremes at 65 weather stations scattered across South Korea. Trends in precipitation extremes were diagnosed with respect to both annual maximum precipitation (AMP) and peaks-over-threshold (POT) extremes. Non-stationary generalized extreme value (GEV) and generalized Pareto distribution (GPD) models with model parameters made a linear function of time were applied to AMP and POT respectively. Trends detected using the Mann–Kendall test revealed that the stations showing an increasing trend in AMP extremes were concentrated in the mountainous areas (the northeast and southwest regions) of South Korea. Trend tests on POT extremes provided fairly different results, with a significantly reduced number of stations showing an increasing trend and with some stations showing a decreasing trend. For most of stations showing a statistically significant trend, non-stationary GEV and GPD models significantly outperformed their stationary counterparts, particularly for precipitation extremes with shorter durations. Due to a significant-increasing trend in the POT frequency found at a considerable number of stations (about 10 stations for each rainfall duration), the performance of modeling POT extremes was further improved with a non-homogeneous Poisson model. The large differences in design storm estimates between stationary and non-stationary models (design storm estimates from stationary models were significantly lower than the estimates of non-stationary models) demonstrated the challenges in relying on the stationary assumption when planning the design and management of water facilities. This study also highlighted the need of caution when quantifying design storms from POT and AMP extremes by showing a large discrepancy between the estimates from those two approaches.     

RAGLAND,AN LL3.4 CHONDRITE FIND FROM NEW MEXICO

The Ragland, New Mexico chondrite was found in 1978, and consists of a single stone of 12.16 kg that broke into three pieces. The stone is moderately weathered and has a pronounced chondritic texture. Bulk composition favors an LL classification, and modal analysis and oxygen isotopic composition are consistent with this. The thermoluminescence sensitivity of 0.056 ± 0.020 normalized to Dhajala, compositional variability of olivine (mean Fa 18.3, σ = 10.1) and low-Ca pyroxene (mean Fs 14.6, σ = 6.7), and Ca concentrations in olivine indicate metamorphic subtype 3.4 ± 0.1. The isotopically heavy oxygen composition, which is characteristic of subtypes 3.0–3.1, may be a primary characteristic and not a result of weathering. Low concentrations of radiogenic ⁴⁰Ar and planetary ³⁶Ar suggest noble gas loss.     

Oscillations in radiation-driven outflows

In this paper we investigate the dynamical behaviour of radiation-driven winds, specifically winds that arise when Compton scattering transfers momentum from the radiation field to the gas flow. Such winds occur during strong X-ray bursts from slowly accreting neutron stars, and also may be driven from the inner regions of a black hole or neutron star accretion disc when the mass transfer rate is very high. By linearizing the radiation hydrodynamic equations around steady spherical outflow, we evaluate the time-dependent response of these winds to perturbations introduced at their inner boundaries. We find that although radiation-driven winds are generally stable, they act as mechanical filters that should produce quasi-periodic oscillations or peaked noise in their radiation output when perturbations force them stochastically. This behaviour may underlie the photospheric oscillations observed in some strong Type I X-ray bursts.     

Cosmic-ray positrons: are there primary sources?

Galactic cosmic rays consist of primary and secondary particles. Primary cosmic rays are thought to be energized by first order Fermi acceleration processes at supernova shock fronts within our Galaxy. The cosmic rays that eventually reach the Earth from this source are mainly protons and atomic nuclei, but also include electrons. Secondary cosmic rays are created in collisions of primary particles with the diffuse interstellar gas. They are relatively rare but carry important information on the Galactic propagation of the primary particles. The secondary component includes a small fraction of antimatter particles, positrons and antiprotons. In addition, positrons and antiprotons may also come from unusual sources and possibly provide insight into new physics. For instance, the annihilation of heavy supersymmetric dark matter particles within the Galactic halo could lead to positrons or antiprotons with distinctive energy signatures. With the High-Energy Antimatter Telescope (HEAT) balloon-borne instrument, we have measured the abundances of positrons and electrons at energies between 1 and 50 GeV. The data suggest that indeed a small additional antimatter component may be present that cannot be explained by a purely secondary production mechanism. Here we describe the signature of the effect and discuss its possible origin.     

Uy phoenicis: RR lyrae variable,not dwarf nova

Stellar and atomic systems obey analogous angular momentum/mass relationships and analogous angular momentum/magnetic dipole moment relationships. The dimensional constants in both pairs of angular momentum laws appear to be related by a simple set of self-similar scaling equations, suggesting that atomic and stellar systems may be self-similar.     

On the interannual variability of arctic sea‐level pressure and sea ice

Abstract

Monthly mean sea‐level pressure (SLP) data from the Northern Hemisphere for the period January 1952‐December 1987 are analysed. Fluctuations in this field over the Arctic on interannual time‐scales and their statistical association with fluctuations farther south are determined. The standard deviation of the interannual variability is largest compared with that of the annual cycle along the seaboards of the major land masses. The SLP anomalies are generally in phase over the entire Arctic Basin and extend south over the northern Russia and Canada, but tend to be out of phase with fluctuations at mid‐latitudes. The anomalies are most closely associated with fluctuations over the North Atlantic and Europe except near the Chukchi Sea to the north of Bering Strait. The associations with the North Pacific fluctuations become increasingly more prominent at most Arctic sites (e.g. the Canadian Arctic Archipelago) as the time‐scale increases.

Associations between the SLP fluctuations and atmospheric indices that represent processes affecting sea‐ice drift (wind stress and wind stress curl) are determined. In every case local associations dominate, but some remote ones are also evident. For example, changes in the magnitude of the wind stress curl over the Beaufort Sea are increased if the atmospheric circulation over the North Pacific is intensified; wind stress over the region where sea ice is exchanged between the Beaufort Gyre and the Transpolar Drift Stream is modulated by both the Southern and North Atlantic Oscillations.

Severe sea‐ice conditions in the Greenland Sea (as measured by the Koch Ice Index) coincide with a weakened atmospheric circulation over the North Atlantic.     

Amphipod predation by the infaunal polychaete,Nephtys incisa

Survival of the tubicolous amphipodAmpelisca abdita in a sediment toxicity test was negatively correlated with the presence of indigenousNephtys incisa. The gut contents ofN. incisa held in uncontaminated sediment included identifiable portions of the amphipods.A. abdita andMicrodeutopus gryllotalpa. Although most nephtyid polychaete worms are active predators,Nephtys incisa has been considered a nonselective deposit-feeder. We coclude thatN. incisa will prey upon amphipods under laboratory conditions. This predation may be a factor in the exclusion of surface-dwelling amphipods from theNephtys-Nucula community common in southern New England.     

Depositional history of the Main Tuff Interval of the Wittenoom Formation, late Archean—early Proterozoic Hamersley Group, Western Australia

The Main Tuff Interval (MTI) is a 3.5 to 16.4 m thick sequence of pyroclastic turbidites in the Wittenoom Formation of the late Archean to early Proterozoic Hamersley Group, Western Australia. The Hamersley Group accumulated in a basin located on the Archean Pilbara Craton, Western Australia. MTI pyroclasts formed via hydrovolcanic eruption processes from a magma that was likely intermediate in composition. Eruption took place in a shallow subaqueous setting. The MTI was deposited by high- and low- concentration turbidity currents in four overlapping regional depositional packages. Paleocurrent and stratigraphic data indicate the MTI source lay to the north of the present exposure limits of the Hamersley Group on the Pilbara Craton, and was likely to have been a single volcano. Reflection of turbidity currents in the southeastern part of the study area and westward travel of the reflected flows indicate that the Hamersley Group depositional basin shallowed to the east and south at the time of MTI deposition. The presence of the MTI source volcano on the northern Pilbara Craton indicates that the subsidence and marine deposition recorded by the Hamersley Group may be limited to the southern portion of the craton, and that volcanism may have continued on the northern Pilbara Craton.     

Volcanic lithogeochemistry and alteration at the Delbridge massive sulfide deposit, Noranda, Quebec

The Delbridge orebody occurs within a thick sequence (> 1 km) of porphyritic to aphyric massive rhyolite and rhyolite breccia of the Archean Blake River Group. The orebody produced ≈ 370,000 tonnes grading 0.61% Cu, 9.6% Zn, 110 g/t Ag and 2.1 g/t Au (1969–1971). The footwall consists of massive quartz porphyritic rhyolite mantled by proximal rhyolite breccias. An irregular chloritic alteration pipe with mineralization is subvertical to the ore lens. The orebody occurs at a thick cherty horizon within rhyolite breccia, and is overlain by a succession of mafic debris flows, porphyritic to aphyric massive rhyolite flows, and finally andesite. The main alteration assemblage in the rhyolite units is quartz-albite-sericite-chlorite-carbonate. Immobile element plots and rare-earth element data indicate that the footwall rhyolite flows and proximal breccias are tholeiitic to transitional (Zr/Y = 3.5–5.5; La_N/Yb_N = 1.7–2.6), whereas hangingwall rhyolite flows are mildly calc-alkaline (Zr/Y = 6.5–7.5; La_N/Yb_N = 2.8–3.8). These two rhyolite types also have separate alteration lines in Ti-Zr space and in various immobile element plots. The identification of chemically different rhyolites above and below the orebody provides markers that can be identified and traced even where strongly altered. An intrusive rhyolite mass in the footwall is chemically identical to the hangingwall aphyric rhyolite flows, and is interpreted as the feeder to these flows. Calculated mass changes in the footwall rhyolite commonly are large, and result from major silica change (±30%), significant loss of Na₂O + CaO, and important additions of K₂O and FeO + MgO. The margins of the pipe show net mass gain, whereas the interior of the pipe shows net mass loss. Hangingwall rhyolite shows mass changes that generally are much smaller than in the footwall. Felsic rocks in the silica-sericite alteration zone up to ≈ 200 m from the orebody have high δ¹⁸O values of 10–12‰, reflecting low-temperature alteration. The orebody occurs near the contact between a mainly tholeiitic rhyolite footwall and an overlying sequence of mildly calc-alkaline rhyolite then andesite.