125 research outputs found
The Environment of Warm-Season Elevated Thunderstorms Associated with Heavy Rainfall Over the Central United States
Twenty-one warm-season heavy-rainfall events in the central United States produced by mesoscale convective systems (MCSs) that developed above and north of a surface boundary are examined to define the environmental conditions and physical processes associated with these phenomena. Storm-relative composites of numerous kinematic and thermodynamic fields are computed by centering on the heavy-rain-producing region of the parent elevated MCS. Results reveal that the heavy-rain region of elevated MCSs is located on average about 160 km north of a quasi-stationary frontal zone, in a region of low-level moisture convergence that is elongated westward on the cool side of the boundary. The MCS is located within the left-exit region of a south-southwesterly lowlevel jet (LLJ) and the right-entrance region of an upper-level jet positioned well north of the MCS site. The LLJ is directed toward a divergence maximum at 250 hPa that is coincident with the MCS site. Near-surface winds are light and from the southeast within a boundary layer that is statically stable and cool. Winds veer considerably with height (about 1408) from 850 to 250 hPa, a layer associated with warm-air advection. The MCS is located in a maximum of positive equivalent potential temperature ue advection, moisture convergence, and positive thermal advection at 850 hPa. Composite fields at 500 hPa show that the MCS forms in a region of weak anticyclonic curvature in the height field with marginal positive vorticity advection. Even though surfacebased stability fields indicate stable low-level air, there is a layer of convectively unstable air with maximumu e CAPE values of more than 1000 J kg21 in the vicinity of the MCS site and higher values upstream. Maximumu e convective inhibition (CIN) values over the MCS centroid site are small (less than 40 J kg21) while to the south convection is limited by large values of CIN (greater than 60 J kg21). Surface-to-500-hPa composite average relative humidity values are about 70%, and composite precipitable water values average about 3.18 cm (1.25 in.). The representativeness of the composite analysis is also examined. Last, a schematic conceptual model based upon the composite fields is presented that depicts the typical environment favorable for the development of elevated thunderstorms that lead to heavy rainfall
Electrodes for Solid Oxide Electrolysis (SOE) and Natural-Gas Assisted Steam Electrolysis (NGASE)
V838 Mon: light echo evolution and distance estimate
Following its 2002 February eruption, V838 Mon developed a light echo that
continues to expand and evolve as light from the outburst scatters off
progressively more distant circumstellar and/or interstellar material.
Multi-filter images of the light echo, obtained with the South African
Astronomical Observatory (SAAO) 1.0-m telescope between 2002 May and 2004
December, are analysed and made available electronically. The expansion of the
light echo is measured from the images and the data compared with models for
scattering by a thin sheet and a thin shell of dust. From these model results
we infer that the dust is likely in the form of a thin sheet distant from the
star, suggesting that the material is of interstellar origin, rather than being
from earlier stages in the star's evolution. Although the fit is uncertain, we
derive a stellar distance of ~ 9 kpc and a star-dust distance of ~ 5 pc, in
good agreement with recent results reported from other methods. We also present
JHKL and Cousins UBVRI photometry obtained at the SAAO during the star's
second, third and fourth observing seasons post-outburst. These data show
complex infrared colour behaviour while V838 Mon is slowly brightening in the
optical.Comment: 9 pages, 6 figures - accepted for publication in MNRA
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Synthesis and Assessment Product
This Synthesis and Assessment Product (SAP), Uses and Limitations of Observations, Data, Forecasts, and Other Projections in Decision Support for Selected Sectors and Regions. This is part of a series of 21 SAPs produced by the CCSP aimed at providing current assessments of climate change science to inform public debate, policy, and operational decisions. This SAP focuses on the use of climate observations, data, forecasts, and other projections in decision support
Measurement of the cosmic ray spectrum above eV using inclined events detected with the Pierre Auger Observatory
A measurement of the cosmic-ray spectrum for energies exceeding
eV is presented, which is based on the analysis of showers
with zenith angles greater than detected with the Pierre Auger
Observatory between 1 January 2004 and 31 December 2013. The measured spectrum
confirms a flux suppression at the highest energies. Above
eV, the "ankle", the flux can be described by a power law with
index followed by
a smooth suppression region. For the energy () at which the
spectral flux has fallen to one-half of its extrapolated value in the absence
of suppression, we find
eV.Comment: Replaced with published version. Added journal reference and DO
Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger Observatory
The Auger Engineering Radio Array (AERA) is part of the Pierre Auger
Observatory and is used to detect the radio emission of cosmic-ray air showers.
These observations are compared to the data of the surface detector stations of
the Observatory, which provide well-calibrated information on the cosmic-ray
energies and arrival directions. The response of the radio stations in the 30
to 80 MHz regime has been thoroughly calibrated to enable the reconstruction of
the incoming electric field. For the latter, the energy deposit per area is
determined from the radio pulses at each observer position and is interpolated
using a two-dimensional function that takes into account signal asymmetries due
to interference between the geomagnetic and charge-excess emission components.
The spatial integral over the signal distribution gives a direct measurement of
the energy transferred from the primary cosmic ray into radio emission in the
AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air
shower arriving perpendicularly to the geomagnetic field. This radiation energy
-- corrected for geometrical effects -- is used as a cosmic-ray energy
estimator. Performing an absolute energy calibration against the
surface-detector information, we observe that this radio-energy estimator
scales quadratically with the cosmic-ray energy as expected for coherent
emission. We find an energy resolution of the radio reconstruction of 22% for
the data set and 17% for a high-quality subset containing only events with at
least five radio stations with signal.Comment: Replaced with published version. Added journal reference and DO
Measurement of the Radiation Energy in the Radio Signal of Extensive Air Showers as a Universal Estimator of Cosmic-Ray Energy
We measure the energy emitted by extensive air showers in the form of radio
emission in the frequency range from 30 to 80 MHz. Exploiting the accurate
energy scale of the Pierre Auger Observatory, we obtain a radiation energy of
15.8 \pm 0.7 (stat) \pm 6.7 (sys) MeV for cosmic rays with an energy of 1 EeV
arriving perpendicularly to a geomagnetic field of 0.24 G, scaling
quadratically with the cosmic-ray energy. A comparison with predictions from
state-of-the-art first-principle calculations shows agreement with our
measurement. The radiation energy provides direct access to the calorimetric
energy in the electromagnetic cascade of extensive air showers. Comparison with
our result thus allows the direct calibration of any cosmic-ray radio detector
against the well-established energy scale of the Pierre Auger Observatory.Comment: Replaced with published version. Added journal reference and DOI.
Supplemental material in the ancillary file
Recurrent dust formation by WR 48a on a 30-year timescale
We present infrared photometry of the WC8 Wolf-Rayet system WR 48a observed
with telescopes at ESO, the SAAO and the AAT between 1982 and 2011 which show a
slow decline in dust emission from the previously reported outburst in 1978--79
until about 1997, when significant dust emission was still evident. This was
followed by a slow rise, accelerating to reach and overtake the first (1978)
photometry, demonstrating that the outburst observed in 1978--79 was not an
isolated event, but that they recur at intervals of 32+ years. This suggests
that WR 48a is a long-period dust maker and colliding-wind binary (CWB). The
locus of WR 48a in the (H-L), K colour-magnitude diagram implies that the rate
of dust formation fell between 1979 and about 1997 and then increased steadily
until 2011. Superimposed on the long-term variation are secondary (`mini')
eruptions in (at least) 1990, 1994, 1997, 1999 and 2004, characteristic of
relatively brief episodes of additional dust formation. Spectra show evidence
for an Oe or Be companion to the WC8 star, supporting the suggestion that WR
48a is a binary system and indicating a system luminosity consistent with the
association of WR 48a and the young star clusters Danks 1 and Danks 2. The
range of dust formation suggests that these stars are in an elliptical orbit
having e ~ 0.6. The size of the orbit implied by the minimum period, together
with the WC wind velocity and likely mass-loss rate, implies that the
post-shock WC wind is adiabatic throughout the orbit -- at odds with the
observed dust formation. A similar conflict is observed in the `pinwheel'
dust-maker WR 112.Comment: 15 pages, 8 figures, accepted for publication in MNRA
Cadophora margaritata sp. nov. and other fungi associated with the longhorn beetles Anoplophora glabripennis and Saperda carcharias in Finland
Symbiosis with microbes is crucial for survival and development of wood-inhabiting longhorn beetles (Coleoptera: Cerambycidae). Thus, knowledge of the endemic fungal associates of insects would facilitate risk assessment in cases where a new invasive pest occupies the same ecological niche. However, the diversity of fungi associated with insects remains poorly understood. The aim of this study was to investigate fungi associated with the native large poplar longhorn beetle (Saperda carcharias) and the recently introduced Asian longhorn beetle (Anoplophora glabripennis) infesting hardwood trees in Finland. We studied the cultivable fungal associates obtained from Populus tremula colonised by S. carcharias, and Betula pendula and Salix caprea infested by A. glabripennis, and compared these to the samples collected from intact wood material. This study detected a number of plant pathogenic and saprotrophic fungi, and species with known potential for enzymatic degradation of wood components. Phylogenetic analyses of the most commonly encountered fungi isolated from the longhorn beetles revealed an association with fungi residing in the Cadophora-Mollisia species complex. A commonly encountered fungus was Cadophora spadicis, a recently described fungus associated with wood-decay. In addition, a novel species of Cadophora, for which the name Cadophora margaritata sp. nov. is provided, was isolated from the colonised wood.Peer reviewe
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