516 research outputs found
A new regional climate model for POLAR-CORDEX : evaluation of a 30-year hindcast with COSMO-CLM2 over Antarctica
Continent-wide climate information over the Antarctic Ice Sheet (AIS) is important to obtain accurate information of present climate and reduce uncertainties of the ice sheet mass balance response and resulting global sea level rise to future climate change. In this study, the COSMO-CLM2 Regional Climate Model is applied over the AIS and adapted for the specific meteorological and climatological conditions of the region. A 30-year hindcast was performed and evaluated against observational records consisting of long-term ground-based meteorological observations, automatic weather stations, radiosoundings, satellite records, stake measurements and ice cores. Reasonable agreement regarding the surface and upper-air climate is achieved by the COSMO-CLM2 model, comparable to the performance of other state-of-the-art climate models over the AIS. Meteorological variability of the surface climate is adequately simulated, and biases in the radiation and surface mass balance are small. The presented model therefore contributes as a new member to the COordinated Regional Downscaling EXperiment project over the AIS (POLAR-CORDEX) and the CORDEX-CORE initiative
From vocational training to education: the development of a no-frontiers education policy for Europe?
This article focuses on developments towards an EU educational policy. Education was not included as one of the Community competencies in the Treaty of Rome. The first half of the article analyses the way that the European Court of Justice and the Commission of the European Communities between them managed to develop a series of substantial Community programmes out of Article 128 on vocational training. The second half of the article discusses educational developments in the community following the Treaty on European Union and the Treaty of Amsterdam. Whilst the legal competence of the community now includes education, the author's argument is that the inclusion of an educational competence will not result in further developments to mirror those in the years before the Treaty on Europe</p
Structural and functional identification of two human, tumor-derived monocyte chemotactic proteins (MCP-2 and MCP-3) belonging to the chemokine family.
Drifting snow measurements on the Greenland Ice Sheet and their application for model evaluation
This paper presents autonomous drifting snow observations performed on the
Greenland Ice Sheet in the fall of 2012. High-frequency snow particle counter
(SPC) observations at ~ 1 m above the surface provided drifting snow
number fluxes and size distributions; these were combined with meteorological
observations at six levels. We identify two types of drifting snow events:
katabatic events are relatively cold and dry, with prevalent winds from the
southeast, whereas synoptic events are short lived, warm and wet.
Precipitating snow during synoptic events disturbs the drifting snow
measurements. Output of the regional atmospheric climate model RACMO2, which
includes the drifting snow routine PIEKTUK-B, agrees well with the observed
near-surface climate at the site, as well as with the frequency and timing of
drifting snow events. Direct comparisons with the SPC observations at 1 m
reveal that the model overestimates the horizontal snow transport at this
level, which can be related to an overestimation of saltation and the typical
size of drifting snow particles
Structural and Luminescence Properties of Silica-Based Hybrids Containing New Silylated-Diketonato Europium(III) Complex
A new betadiketonate ligand displaying a trimethoxysilyl group as grafting function and a diketone moiety as complexing site (TTA-Si = 4,4,4-trifluoro-2-(3-trimethoxysilyl)propyl)-1-3-butanedione (C4H3S)COCH[(CH2)3Si(OCH3)3]COCF3) and its highly luminescent europium(III) complex [Eu(TTA-Si)3] have been synthesized and fully characterized. Luminescent silica-based hybrids have been prepared as well with this new complex grafted on the surface of dense silica nanoparticles (28 (+/-3 nm) or on mesoporous
silica particles. The covalent bonding of Eu(TTA-Si)3 inside the core of uniform silica
nanoparticles (40 (+/- 5 nm) was also achieved. Luminescence properties are discussed in relation to the europium chemical environment involved in each of the three hybrids. The general methodology proposed allowed high grafting ratios and overcame chelate release and tendency to agglomeration, and it could be applied to any silica matrix (in the core or at the surface, nanosized or not, dense or mesoporous) and therefore numerous applications such as luminescent markers and luminophors could be foreseen
Ice core evidence for a 20th century increase in surface mass balance in coastal Dronning Maud Land, East Antarctica
Ice cores provide temporal records of surface mass balance (SMB). Coastal areas of Antarctica have relatively high and variable SMB, but are under-represented in records spanning more than 100 years. Here we present SMB reconstruction from a 120 m-long ice core drilled in 2012 on the Derwael Ice Rise, coastal Dronning Maud Land, East Antarctica. Water stable isotope (δ18O and δD) stratigraphy is supplemented by discontinuous major ion profiles and continuous electrical conductivity measurements. The base of the ice core is dated to AD 1759 ± 16, providing a climate proxy for the past  ∼ 250 years. The core's annual layer thickness history is combined with its gravimetric density profile to reconstruct the site's SMB history, corrected for the influence of ice deformation. The mean SMB for the core's entire history is 0.47 ± 0.02 m water equivalent (w.e.) a−1. The time series of reconstructed annual SMB shows high variability, but a general increase beginning in the 20th century. This increase is particularly marked during the last 50 years (1962–2011), which yields mean SMB of 0.61 ± 0.01 m w.e. a−1. This trend is compared with other reported SMB data in Antarctica, generally showing a high spatial variability. Output of the fully coupled Community Earth System Model (CESM) suggests that, although atmospheric circulation is the main factor influencing SMB, variability in sea surface temperatures and sea ice cover in the precipitation source region also explain part of the variability in SMB. Local snow redistribution can also influence interannual variability but is unlikely to influence long-term trends significantly. This is the first record from a coastal ice core in East Antarctica to show an increase in SMB beginning in the early 20th century and particularly marked during the last 50 years
Meltwater produced by wind–albedo interaction stored in an East Antarctic ice shelf
Surface melt and subsequent firn air depletion can ultimately
lead to disintegration of Antarctic ice shelves1,2 causing
grounded glaciers to accelerate3 and sea level to rise. In
the Antarctic Peninsula, foehn winds enhance melting near
the grounding line4, which in the recent past has led to the
disintegration of the most northerly ice shelves5,6. Here, we
provide observational and model evidence that this process
also occurs over an East Antarctic ice shelf, where meltwaterinduced
firn air depletion is found in the grounding zone.
Unlike the Antarctic Peninsula, where foehn events originate
from episodic interaction of the circumpolar westerlies with
the topography, in coastal East Antarctica high temperatures
are caused by persistent katabatic winds originating from the
ice sheet’s interior. Katabatic winds warm and mix the air
as it flows downward and cause widespread snow erosion,
explaining >3 K higher near-surface temperatures in summer
and surface melt doubling in the grounding zone compared with
its surroundings. Additionally, these winds expose blue ice and
firn with lower surface albedo, further enhancing melt. The
in situ observation of supraglacial flow and englacial storage
of meltwater suggests that ice-shelf grounding zones in East
Antarctica, like their Antarctic Peninsula counterparts, are
vulnerable to hydrofracturing7
The European Court of Human Rights and the Hague Child Abduction Convention:prioritising return or reflection?
Constraining the recent mass balance of Pine Island and Thwaites glaciers, West Antarctica, with airborne observations of snow accumulation
In Antarctica, uncertainties in mass input and output translate directly into uncertainty in glacier mass balance and thus in sea level impact. While remotely sensed observations of ice velocity and thickness over the major outlet glaciers have improved our understanding of ice loss to the ocean, snow accumulation over the vast Antarctic interior remains largely unmeasured. Here, we show that an airborne radar system, combined with ice-core glaciochemical analysis, provide the means necessary to measure the accumulation rate at the catchment-scale along the Amundsen Sea coast of West Antarctica. We used along-track radar-derived accumulation to generate a 1985–2009 average accumulation grid that resolves moderate- to large-scale features (>25 km) over the Pine Island–Thwaites glacier drainage system. Comparisons with estimates from atmospheric models and gridded climatologies generally show our results as having less accumulation in the lower-elevation coastal zone but greater accumulation in the interior. Ice discharge, measured over discrete time intervals between 1994 and 2012, combined with our catchment-wide accumulation rates provide an 18-year mass balance history for the sector. While Thwaites Glacier lost the most ice in the mid-1990s, Pine Island Glacier's losses increased substantially by 2006, overtaking Thwaites as the largest regional contributor to sea-level rise. The trend of increasing discharge for both glaciers, however, appears to have leveled off since 2008
Evaluating the impact of enhanced horizontal resolution over the Antarctic domain using a variable-resolution Earth system model
Earth system models are essential tools for understanding
the impacts of a warming world, particularly on the contribution of polar
ice sheets to sea level change. However, current models lack full coupling
of the ice sheets to the ocean and are typically run at a coarse resolution
(1∘ grid spacing or coarser). Coarse spatial resolution is
particularly a problem over Antarctica, where sub-grid-scale orography is
well-known to influence precipitation fields, and glacier models require
high-resolution atmospheric inputs. This resolution limitation has been
partially addressed by regional climate models (RCMs), which must be forced
at their lateral and ocean surface boundaries by (usually coarser) global
atmospheric datasets, However, RCMs fail to capture the two-way coupling
between the regional domain and the global climate system. Conversely,
running high-spatial-resolution models globally is computationally
expensive and can produce vast amounts of data.
Alternatively, variable-resolution grids can retain the benefits of high
resolution over a specified domain without the computational costs of
running at a high resolution globally. Here we evaluate a historical
simulation of the Community Earth System Model version 2 (CESM2)
implementing the spectral element (SE) numerical dynamical core (VR-CESM2)
with an enhanced-horizontal-resolution (0.25∘) grid over the
Antarctic Ice Sheet and the surrounding Southern Ocean; the rest of the
global domain is on the standard 1∘ grid. We compare it to
1∘ model runs of CESM2 using both the SE dynamical core and the
standard finite-volume (FV) dynamical core, both with identical physics and
forcing, including prescribed sea surface temperatures (SSTs) and sea ice concentrations from
observations. Our evaluation reveals both improvements and degradations in
VR-CESM2 performance relative to the 1∘ CESM2. Surface mass
balance estimates are slightly higher but within 1Â standard deviation of
the ensemble mean, except for over the Antarctic Peninsula, which is
impacted by better-resolved surface topography. Temperature and wind
estimates are improved over both the near surface and aloft, although the
overall correction of a cold bias (within the 1∘ CESM2 runs) has
resulted in temperatures which are too high over the interior of the ice
sheet. The major degradations include the enhancement of surface melt as
well as excessive cloud liquid water over the ocean, with resultant impacts
on the surface radiation budget. Despite these changes, VR-CESM2 is a
valuable tool for the analysis of precipitation and surface mass balance
and thus constraining estimates of sea level rise associated with the
Antarctic Ice Sheet.</p
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