482 research outputs found
Modelling the mid-Pliocene Warm Period climate with the IPSL coupled model and its atmospheric component LMDZ5A
This paper describes the experimental design and model results of the climate simulations of the mid-Pliocene Warm Period (mPWP, ca. 3.3–3 Ma) using the Institut Pierre Simon Laplace model (IPSLCM5A), in the framework of the Pliocene Model Intercomparison Project (PlioMIP). We use the IPSL atmosphere ocean general circulation model (AOGCM), and its atmospheric component alone (AGCM), to simulate the climate of the mPWP. Boundary conditions such as sea surface temperatures (SSTs), topography, ice-sheet extent and vegetation are derived from the ones imposed by the Pliocene Model Intercomparison Project (PlioMIP), described in Haywood et al. (2010, 2011). We first describe the IPSL model main features, and then give a full description of the boundary conditions used for atmospheric model and coupled model experiments. The climatic outputs of the mPWP simulations are detailed and compared to the corresponding control simulations. The simulated warming relative to the control simulation is 1.94 °C in the atmospheric and 2.07 °C in the coupled model experiments. In both experiments, warming is larger at high latitudes. Mechanisms governing the simulated precipitation patterns are different in the coupled model than in the atmospheric model alone, because of the reduced gradients in imposed SSTs, which impacts the Hadley and Walker circulations. In addition, a sensitivity test to the change of land-sea mask in the atmospheric model, representing a sea-level change from present-day to 25 m higher during the mid-Pliocene, is described. We find that surface temperature differences can be large (several degrees Celsius) but are restricted to the areas that were changed from ocean to land or vice versa. In terms of precipitation, impact on polar regions is minor although the change in land-sea mask is significant in these areas
In-medium effects on K-0 mesons in relativistic heavy-ion collisions
We present the transverse momentum spectra and rapidity distributions of pi(-) and K-S(0) in Ar + KCl reactions at a beam kinetic energy of 1.756 A GeV measured with the High Acceptance Di-Electron Spectrometer (HADES). The reconstructed K-S(0) sample is characterized by good event statistics for a wide range in momentum and rapidity. We compare the experimental pi(-) and K-S(0) distributions to predictions by the Isospin Quantum Molecular Dynamics (IQMD) model. The model calculations show that K-S(0) at low transverse momenta constitute a particularly well-suited tool to investigate the kaon in-medium potential. Our K-S(0) data suggest a strong repulsive in-medium K-0 potential of about 40 MeV strength.We gratefully acknowledge the useful discussions
with J. Aichelin and H. Oeschler.
The HADES collaboration gratefully acknowledges
the support by BMBF grants 06TM970I, 06GI146I,
06FY171, and 06DR135 (Germany), by GSI (TMFR1,
GI/ME3, OF/STR), by Excellence Cluster
of Universe (Germany), by grants GA AS CR
IAA100480803 and MSMT LC 07050 (Czech Republic),
by grant KBN 5P03B 140 20 (Poland), by
INFN (Italy), by CNRS/IN2P3 (France), by grants
MCYT FPA2000-2041-C02-02 and XUGA PGID
T02PXIC20605PN (Spain), by grant UCY-10.3.11.12
(Cyprus), by INTAS grant 06-1000012-8861 and EU
contract RII3-CT-2004-506078.Peer reviewe
Comparison of spatial downscaling methods of general circulation model results to study climate variability during the last glacial maximum
The extent to which climate conditions influenced the spatial
distribution of hominin populations in the past is highly debated.
General circulation models (GCMs) and archaeological data have been
used to address this issue. Most GCMs are not currently capable of
simulating past surface climate conditions with sufficiently
detailed spatial resolution to distinguish areas of potential
hominin habitat, however. In this paper, we propose a statistical
downscaling method (SDM) for increasing the resolution of climate
model outputs in a computationally efficient way. Our method uses a
generalised additive model (GAM), calibrated over present-day
climatology data, to statistically downscale temperature and
precipitation time series from the outputs of a GCM simulating the
climate of the Last Glacial Maximum (19 000–23 000 BP) over western
Europe. Once the SDM is calibrated, we first interpolate the
coarse-scale GCM outputs to the final resolution and then use the
GAM to compute surface air temperature and precipitation levels
using these interpolated GCM outputs and fine-resolution
geographical variables such as topography and distance from an
ocean. The GAM acts as a transfer function, capturing non-linear
relationships between variables at different spatial scales and
correcting for the GCM biases. We tested three different techniques
for the first interpolation of GCM output: bilinear, bicubic and
kriging. The resulting SDMs were evaluated by comparing downscaled
temperature and precipitation at local sites with paleoclimate
reconstructions based on paleoclimate archives (archaeozoological
and palynological data) and the impact of the interpolation
technique on patterns of variability was explored. The SDM based on
kriging interpolation, providing the best accuracy, was then
validated on present-day data outside of the calibration period. Our
results show that the downscaled temperature and precipitation
values are in good agreement with paleoclimate reconstructions at
local sites, and that our method for producing fine-grained
paleoclimate simulations is therefore suitable for conducting
paleo-anthropological research. It is nonetheless important to
calibrate the GAM on a range of data encompassing the data to be
downscaled. Otherwise, the SDM is likely to overcorrect the
coarse-grain data. In addition, the bilinear and bicubic
interpolation techniques were shown to distort either the temporal
variability or the values of the response variables, while the
kriging method offered the best compromise. Since climate
variability is an aspect of the environment to which human
populations may have responded in the past, the choice of
interpolation technique is therefore an important consideration.</p
Response of methane emissions from wetlands to the Last Glacial Maximum and an idealized Dansgaard-Oeschger climate event: insights from two models of different complexity
The role of different sources and sinks of CH<sub>4</sub> in changes in atmospheric methane ([CH<sub>4</sub>]) concentration during the last 100 000 yr is still not fully understood. In particular, the magnitude of the change in wetland CH<sub>4</sub> emissions at the Last Glacial Maximum (LGM) relative to the pre-industrial period (PI), as well as during abrupt climatic warming or Dansgaard–Oeschger (D–O) events of the last glacial period, is largely unconstrained. In the present study, we aim to understand the uncertainties related to the parameterization of the wetland CH<sub>4</sub> emission models relevant to these time periods by using two wetland models of different complexity (SDGVM and ORCHIDEE). These models have been forced by identical climate fields from low-resolution coupled atmosphere–ocean general circulation model (FAMOUS) simulations of these time periods. Both emission models simulate a large decrease in emissions during LGM in comparison to PI consistent with ice core observations and previous modelling studies. The global reduction is much larger in ORCHIDEE than in SDGVM (respectively −67 and −46%), and whilst the differences can be partially explained by different model sensitivities to temperature, the major reason for spatial differences between the models is the inclusion of freezing of soil water in ORCHIDEE and the resultant impact on methanogenesis substrate availability in boreal regions. Besides, a sensitivity test performed with ORCHIDEE in which the methanogenesis substrate sensitivity to the precipitations is modified to be more realistic gives a LGM reduction of −36%. The range of the global LGM decrease is still prone to uncertainty, and here we underline its sensitivity to different process parameterizations. Over the course of an idealized D–O warming, the magnitude of the change in wetland CH<sub>4</sub> emissions simulated by the two models at global scale is very similar at around 15 Tg yr<sup>−1</sup>, but this is only around 25% of the ice-core measured changes in [CH<sub>4</sub>]. The two models do show regional differences in emission sensitivity to climate with much larger magnitudes of northern and southern tropical anomalies in ORCHIDEE. However, the simulated northern and southern tropical anomalies partially compensate each other in both models limiting the net flux change. Future work may need to consider the inclusion of more detailed wetland processes (e.g. linked to permafrost or tropical floodplains), other non-wetland CH<sub>4</sub> sources or different patterns of D–O climate change in order to be able to reconcile emission estimates with the ice-core data for rapid CH<sub>4</sub> events
Investigating the evolution of major Northern Hemisphere ice sheets during the last glacial-interglacial cycle
A 2.5-dimensional climate model of intermediate complexity, CLIMBER-2, fully coupled with the GREMLINS 3-D thermo-mechanical ice sheet model is used to simulate the evolution of major Northern Hemisphere ice sheets during the last glacial-interglacial cycle and to investigate the ice sheets responses to both insolation and atmospheric CO<sub>2</sub> concentration. This model reproduces the main phases of advance and retreat of Northern Hemisphere ice sheets during the last glacial cycle, although the amplitude of these variations is less pronounced than those based on sea level reconstructions. At the last glacial maximum, the simulated ice volume is 52.5&times;10<sup>15</sup> m<sup>3</sup> and the spatial distribution of both the American and Eurasian ice complexes is in reasonable agreement with observations, with the exception of the marine parts of these former ice sheets. <br> A set of sensitivity studies has also been performed to assess the sensitivity of the Northern Hemisphere ice sheets to both insolation and atmospheric CO<sub>2</sub>. Our results suggest that the decrease of summer insolation is the main factor responsible for the early build up of the North American ice sheet around 120 kyr BP, in agreement with benthic foraminifera &delta;<sup>18</sup>O signals. In contrast, low insolation and low atmospheric CO<sub>2</sub> concentration are both necessary to trigger a long-lasting glaciation over Eurasia
Pluto: a Monte Carlo simulation tool for hadronic physics
Pluto is a Monte-Carlo event generator designed for hadronic interactions from Pion production threshold to intermediate energies of a few GeV per nucleon, as well as for studies of heavy ion reactions. The package is entirely based on ROOT, without the need of additional packages, and uses the embedded C++ interpreter of ROOT to control the event production. The generation of events based on a single reaction chain and the storage of the resulting particle objects can be done with a few lines of a ROOT-macro. However, the complete control of the package can be taken over by the steering macro and user-defined models may be added without a recompilation of the framework. Multi-reaction cocktails can be facilitated as well using either mass-dependent or user-defined static branching ratios. The included physics uses resonance production with mass-dependent Breit-Wigner sampling. The calculation of partial and total widths for resonances producing unstable particles is performed recursively in a coupled-channel approach. Here, particular attention is paid to the electromagnetic decays, motivated by the physics program of HADES. The thermal model supports 2-component thermal distributions, longitudinal broadening, radial blast, direct and elliptic flow, and impact-parameter sampled multiplicities. The interface allows angular distribution models (e.g. for the primary meson emission) to be attached by the user as well as descriptions of multi-particle correlations using decay chain templates. The exchange of mass sampling or momentum generation models is also possible. The first feature allows for consistent coupled-channel calculations, needed for a correct description of hadronic interactions. For elementary reactions, angular distribution models for selected channels are already part of the framework, based on parameterizations of existing data. This report gives an overview of the design of the package, the included models and the user interface
Pluto: A Monte Carlo Simulation Tool for Hadronic Physics
Pluto is a Monte-Carlo event generator designed for hadronic interactions
from Pion production threshold to intermediate energies of a few GeV per
nucleon, as well as for studies of heavy ion reactions. This report gives an
overview of the design of the package, the included models and the user
interface.Comment: XI International Workshop on Advanced Computing and Analysis
Techniques in Physics Research, April 23-27 2007, Amsterdam, the Netherland
Design of the Pluto Event Generator
We present the design of the simulation package Pluto, aimed at the study of
hadronic interactions at SIS and FAIR energies. Its main mission is to offer a
modular framework with an object-oriented structure, thereby making additions
such as new particles, decays of resonances, new models up to modules for
entire changes easily applicable. Overall consistency is ensured by a plugin-
and distribution manager. Particular features are the support of a modular
structure for physics process descriptions, and the possibility to access the
particle stream for on-line modifications. Additional configuration and
self-made classes can be attached by the user without re-compiling the package,
which makes Pluto extremely configurable.Comment: Presented at the 17th International Conference on Computing in High
Energy and Nuclear Physic
Design of the Pluto Event Generator
We present the design of the simulation package Pluto, aimed at the study of
hadronic interactions at SIS and FAIR energies. Its main mission is to offer a
modular framework with an object-oriented structure, thereby making additions
such as new particles, decays of resonances, new models up to modules for
entire changes easily applicable. Overall consistency is ensured by a plugin-
and distribution manager. Particular features are the support of a modular
structure for physics process descriptions, and the possibility to access the
particle stream for on-line modifications. Additional configuration and
self-made classes can be attached by the user without re-compiling the package,
which makes Pluto extremely configurable.Comment: Presented at the 17th International Conference on Computing in High
Energy and Nuclear Physic
Design of the Pluto Event Generator
We present the design of the simulation package Pluto, aimed at the study of
hadronic interactions at SIS and FAIR energies. Its main mission is to offer a
modular framework with an object-oriented structure, thereby making additions
such as new particles, decays of resonances, new models up to modules for
entire changes easily applicable. Overall consistency is ensured by a plugin-
and distribution manager. Particular features are the support of a modular
structure for physics process descriptions, and the possibility to access the
particle stream for on-line modifications. Additional configuration and
self-made classes can be attached by the user without re-compiling the package,
which makes Pluto extremely configurable.Comment: Presented at the 17th International Conference on Computing in High
Energy and Nuclear Physic
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