1,053 research outputs found
Recommended from our members
Airmass analysis of the processes driving the progression of the Indian summer monsoon
The Indian summer monsoon is a vital source of water and a cause of severe impacts for more than a billion people in the Indian subcontinent. The INCOMPASS project investigates the mechanisms driving its onset and progression through an observational field campaign supplemented by highâresolution numerical simulations for the 2016 season using UK Met Office models. A 4.4âkm resolution convectionâpermitting limitedâarea model simulation (driven at its boundaries by a dailyâinitialised global model) is used in this study, and verified against observations, along with shortâleadâtime operational global forecasts. These data show that the monsoon progression towards northwest India in June 2016 is a nonâsteady process, modulated by the interaction between moist lowâlevel southwesterly flow from the Arabian Sea and a northwesterly incursion of descending dry air from western and central Asia. The location and extent of these two flows are closely linked to midlatitude dynamics, through the southward propagation of potential vorticity streamers and the associated formation of cyclonic circulations in the region where the two airmasses interact. Particular focus is devoted to the use of Lagrangian trajectories to characterise the evolution of the airstreams and complement the Eulerian monsoon progression analysis. The trajectories confirm that the interaction of the two airstreams is a primary driver of the general moistening of the troposphere associated with monsoon progression. They also indicate the occurrence of local diabatic processes along the airstreams, such as turbulent mixing and local evaporation from the Arabian Sea, in addition to moisture transport from remote sources. In summary, this combined EulerianâLagrangian analysis reveals the nonâsteady nature of monsoon progression towards northwest India. This process is driven by the interaction of different airmasses and influenced by a synergy of factors on a variety of scales, such as midlatitude dynamics, transient weather systems and local diabatic processes
Improved understanding of groundwater flow in complex superficial deposits using three-dimensional geological-framework and groundwater models: an example from Glasgow, Scotland (UK)
Groundwater models are useful in improving knowledge of groundwater flow processes, both for testing existing hypotheses of how specific systems behave and predicting the response to various environmental stresses. The recent advent of highly detailed three-dimensional (3D) geological-framework models provides the most accurate representation of the subsurface. This type of modelling has been used to develop conceptual understanding of groundwater in the complex Quaternary deposits of Glasgow, Scotland (UK). Delineating the 3D geometry of the lithostratigraphical units has allowed the most detailed conceptualisation of the likely groundwater flow regime yet attempted for these superficial deposits. Recharge and groundwater flow models have been developed in order to test this conceptual understanding. Results indicate that the direction of groundwater flow is predominantly convergent through the permeable, relatively thick Quaternary deposits of the Clyde valley towards the River Clyde, which runs through Glasgow, with some indication of down-valley flow. A separate nearby system with thick and potentially permeable Quaternary deposits, the Proto-Kelvin Valley, may also be a significant conveyor of groundwater towards the River Clyde, although the absence of local data makes any conclusions conjectural. To improve the robustness of the current model there is a need for an overall increase in good quality groundwater-level data, particularly outside central Glasgow. A prototype groundwater-monitoring network for part of Glasgow is an encouraging development in this regard. This would allow the development of a time-variant groundwater model which could be used to study future modelling scenarios
Friends or Foes? Emerging Impacts of Biological Toxins
Toxins are substances produced from biological sources (e.g., animal, plants, microorganisms) that have deleterious effects on a living organism. Despite the obvious health concerns of being exposed to toxins, they are having substantial positive impacts in a number of industrial sectors. Several toxin-derived products are approved for clinical, veterinary, or agrochemical uses. This review sets out the case for toxins as âfriendsâ that are providing the basis of novel medicines, insecticides, and even nucleic acid sequencing technologies. We also discuss emerging toxins (âfoesâ) that are becoming increasingly prevalent in a range of contexts through climate change and the globalisation of food supply chains and that ultimately pose a risk to health
Phenomenology of -CDM model: a possibility of accelerating Universe with positive pressure
Among various phenomenological models, a time-dependent model is selected here to investigate the -CDM cosmology.
Using this model the expressions for the time-dependent equation of state
parameter and other physical parameters are derived. It is shown that
in model accelerated expansion of the Universe takes place at negative
energy density, but with a positive pressure. It has also been possible to
obtain the change of sign of the deceleration parameter during cosmic
evolution.Comment: 16 Latex pages, 11 figures, Considerable modifications in the text;
Accepted in IJT
Supernovae as a probe of particle physics and cosmology
It has very recently been demonstrated by Csaki, Kaloper and Terning (CKT)
that the faintness of supernovae at high redshift can be accommodated by mixing
of a light axion with the photon in the presence of an intergalactic magnetic
field, as opposed to the usual explanation of an accelerating universe by a
dark energy component. In this paper we analyze further aspects of the CKT
mechanism and its generalizations. The CKT mechanism also passes various
cosmological constraints from the fluctuations of the CMB and the formation of
structure at large scales, without requiring an accelerating phase in the
expansion of the Universe. We investigate the statistical significance of
current supernova data for pinning down the different components of the
cosmological energy-momentum tensor and for probing physics beyond the standard
models.Comment: 17 pages, LaTeX, 4 figures; v2: typos corrected, minor changes,
references added; v3: updated figures, details regarding fits include
Dark Energy and the quietness of the Local Hubble Flow
The linearity and quietness of the Local () Hubble Flow (LHF) in
view of the very clumpy local universe is a long standing puzzle in standard
and in open CDM cosmogony. The question addressed in this paper is whether the
antigravity component of the recently discovered dark energy can cool the
velocity flow enough to provide a solution to this puzzle. We calculate the
growth of matter fluctuations in a flat universe containing a fraction
of dark energy obeying the time independent equation of state
. We find that dark energy can indeed cool the LHF. However the
dark energy parameter values required to make the predicted velocity dispersion
consistent with the observed value have been ruled out
by other observational tests constraining the dark energy parameters and
. Therefore despite the claims of recent qualitative studies dark
energy with time independent equation of state can not by itself explain the
quietness and linearity of the Local Hubble Flow.Comment: 4 pages, 3 figures, accepted in Phys. Rev. D. Minor corrections, one
figure adde
Model- and calibration-independent test of cosmic acceleration
We present a calibration-independent test of the accelerated expansion of the
universe using supernova type Ia data. The test is also model-independent in
the sense that no assumptions about the content of the universe or about the
parameterization of the deceleration parameter are made and that it does not
assume any dynamical equations of motion. Yet, the test assumes the universe
and the distribution of supernovae to be statistically homogeneous and
isotropic. A significant reduction of systematic effects, as compared to our
previous, calibration-dependent test, is achieved. Accelerated expansion is
detected at significant level (4.3 sigma in the 2007 Gold sample, 7.2 sigma in
the 2008 Union sample) if the universe is spatially flat. This result depends,
however, crucially on supernovae with a redshift smaller than 0.1, for which
the assumption of statistical isotropy and homogeneity is less well
established.Comment: 13 pages, 2 figures, major change
A model of the Universe including Dark Energy accounted for by both a Quintessence Field and a (negative) Cosmological Constant
In this work we present a model of the universe in which dark energy is
modelled explicitely with both a dynamical quintessence field and a
cosmological constant. Our results confirm the possibility of a future
collapsing universe (for a given region of the parameter space), which is
necessary for a consistent formulation of string theory and quantum field
theory. We have also reproduced the measurements of modulus distance from
supernovae with good accuracy.Comment: 11 pages, 4 figures, only the results for the single exponential
potential are preserved. One author added. Some changes in the reference
section. Submitted to Physical Review
- âŠ