89 research outputs found
Managing groundwater supplies subject to drought: perspectives on current status and future priorities from England (UK)
Effective management of groundwater resources during drought is essential. How is groundwater currently managed during droughts, and in the face of environmental change, what should be the future priorities? Four themes are explored, from the perspective of groundwater management in England (UK): (1) integration of drought definitions; (2) enhanced fundamental monitoring; (3) integrated modelling of groundwater in the water cycle; and (4) better information sharing. Whilst these themes are considered in the context of England, globally, they are relevant wherever groundwater is affected by drought
Integrating geospatial information into fire risk assessment
Fire risk assessment should take into account the most relevant components associated to fire occurrence. To estimate when and where the fire will produce undesired effects, we need to model both (a) fire ignition and propagation potential and (b) fire vulnerability. Following these ideas, a comprehensive fire risk assessment system is proposed in this paper, which makes extensive use of geographic information technologies to offer a spatially explicit evaluation of fire risk conditions. The paper first describes the conceptual model, then the methods to generate the different input variables, the approaches to merge those variables into synthetic risk indices and finally the validation of the outputs. The model has been applied at a national level for the whole Spanish Iberian territory at 1-km2 spatial resolution. Fire danger included human factors, lightning probability, fuel moisture content of both dead and live fuels and propagation potential. Fire vulnerability was assessed by analysing values-at-risk and landscape resilience. Each input variable included a particular accuracy assessment, whereas the synthetic indices were validated using the most recent fire statistics available. Significant relations (P < 0.001) with fire occurrence were found for the main synthetic danger indices, particularly for those associated to fuel moisture content conditions.Peer reviewe
Searches for Ultra-High-Energy Photons at the Pierre Auger Observatory
The Pierre Auger Observatory, being the largest air-shower experiment in the
world, offers an unprecedented exposure to neutral particles at the highest
energies. Since the start of data taking more than 18 years ago, various
searches for ultra-high-energy (UHE, ) photons have
been performed: either for a diffuse flux of UHE photons, for point sources of
UHE photons or for UHE photons associated with transient events like
gravitational wave events. In the present paper, we summarize these searches
and review the current results obtained using the wealth of data collected by
the Pierre Auger Observatory.Comment: Review article accepted for publication in Universe (special issue on
ultra-high energy photons
A Catalog of the Highest-energy Cosmic Rays Recorded during Phase I of Operation of the Pierre Auger Observatory
A catalog containing details of the highest-energy cosmic rays recorded through the detection of extensive air-showers at the Pierre Auger Observatory is presented with the aim of opening the data to detailed examination. Descriptions of the 100 showers created by the highest-energy particles recorded between 1 January 2004 and 31 December 2020 are given for cosmic rays that have energies in the range 78 EeV to 166 EeV. Details are also given of a further nine very-energetic events that have been used in the calibration procedure adopted to determine the energy of each primary. A sky plot of the arrival directions of the most energetic particles is shown. No interpretations of the data are offered
Constraining the sources of ultra-high-energy cosmic rays across and above the ankle with the spectrum and composition data measured at the Pierre Auger Observatory
In this work we present the interpretation of the energy spectrum and mass
composition data as measured by the Pierre Auger Collaboration above eV. We use an astrophysical model with two extragalactic source
populations to model the hardening of the cosmic-ray flux at around eV (the so-called "ankle" feature) as a transition between these two
components. We find our data to be well reproduced if sources above the ankle
emit a mixed composition with a hard spectrum and a low rigidity cutoff. The
component below the ankle is required to have a very soft spectrum and a mix of
protons and intermediate-mass nuclei. The origin of this intermediate-mass
component is not well constrained and it could originate from either Galactic
or extragalactic sources. To the aim of evaluating our capability to constrain
astrophysical models, we discuss the impact on the fit results of the main
experimental systematic uncertainties and of the assumptions about quantities
affecting the air shower development as well as the propagation and redshift
distribution of injected ultra-high-energy cosmic rays (UHECRs).Comment: Submitted to JCA
Cosmological implications of photon-flux upper limits at ultra-high energies in scenarios of Planckian-interacting massive particles for dark matter
We present a thorough search for signatures that would be suggestive of
super-heavy particles decaying in the Galactic halo, in the data of the
Pierre Auger Observatory. From the lack of signal, we derive upper limits for
different energy thresholds above \,GeV on the expected
secondary by-product fluxes from -particle decay. Assuming that the energy
density of these super-heavy particles matches that of dark matter observed
today, we translate the upper bounds on the particle fluxes into tight
constraints on the couplings governing the decay process as a function of the
particle mass. We show that instanton-induced decay processes allow us to
derive a bound on the reduced coupling constant of gauge interactions in the
dark sector: \alpha_X \alt 0.09, for 10^{9} \alt M_X/\text{GeV} < 10^{19}.
This upper limit on is complementary to the non-observation of
tensor modes in the cosmic microwave background in the context of
Planckian-interacting massive particles for dark matter produced during the
reheating epoch. Viable regions for this scenario to explain dark matter are
delineated in several planes of the multidimensional parameter space that
involves, in addition to and , the Hubble rate at the end of
inflation, the reheating efficiency, and the non-minimal coupling of the Higgs
with curvature.Comment: 15 pages, 8 figures, Accompanying paper of arXiv:2203.0885
Constraining the sources of ultra-high-energy cosmic rays across and above the ankle with the spectrum and composition data measured at the Pierre Auger Observatory
In this work we present the interpretation of the energy spectrum and mass composition data as measured by the Pierre Auger Collaboration above 6 Ă— 1017 eV. We use an astrophysical model with two extragalactic source populations to model the hardening of the cosmic-ray flux at around 5 Ă— 1018 eV (the so-called "ankle"feature) as a transition between these two components. We find our data to be well reproduced if sources above the ankle emit a mixed composition with a hard spectrum and a low rigidity cutoff. The component below the ankle is required to have a very soft spectrum and a mix of protons and intermediate-mass nuclei. The origin of this intermediate-mass component is not well constrained and it could originate from either Galactic or extragalactic sources. To the aim of evaluating our capability to constrain astrophysical models, we discuss the impact on the fit results of the main experimental systematic uncertainties and of the assumptions about quantities affecting the air shower development as well as the propagation and redshift distribution of injected ultra-high-energy cosmic rays (UHECRs)
A Catalog of the Highest-energy Cosmic Rays Recorded during Phase I of Operation of the Pierre Auger Observatory
A catalog containing details of the highest-energy cosmic rays recorded through the detection of extensive air
showers at the Pierre Auger Observatory is presented with the aim of opening the data to detailed examination.
Descriptions of the 100 showers created by the highest-energy particles recorded between 2004 January 1 and 2020
December 31 are given for cosmic rays that have energies in the range 78–166 EeV. Details are also given on a
further nine very energetic events that have been used in the calibration procedure adopted to determine the energy
of each primary. A sky plot of the arrival directions of the most energetic particles is shown. No interpretations of
the data are offered
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