The Open Global Glacier Model (OGGM) v1.1 Maussion, Fabien; Butenko, Anton; Champollion, Nicolas ...
Geoscientific Model Development,
03/2019, Letnik:
12, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Despite their importance for sea-level rise, seasonal water availability, and
as a source of geohazards, mountain glaciers are one of the few remaining
subsystems of the global climate system for ...which no globally applicable,
open source, community-driven model exists. Here we present the Open Global
Glacier Model (OGGM), developed to provide a modular and open-source
numerical model framework for simulating past and future change of any
glacier in the world. The modeling chain comprises data downloading tools
(glacier outlines, topography, climate, validation data), a preprocessing
module, a mass-balance model, a distributed ice thickness estimation model,
and an ice-flow model. The monthly mass balance is obtained from gridded
climate data and a temperature index melt model. To our knowledge, OGGM is
the first global model to explicitly simulate glacier dynamics: the model
relies on the shallow-ice approximation to compute the depth-integrated flux
of ice along multiple connected flow lines. In this paper, we describe and
illustrate each processing step by applying the model to a selection of
glaciers before running global simulations under idealized climate forcings.
Even without an in-depth calibration, the model shows very realistic
behavior. We are able to reproduce earlier estimates of global glacier volume
by varying the ice dynamical parameters within a range of plausible values.
At the same time, the increased complexity of OGGM compared to other
prevalent global glacier models comes at a reasonable computational cost:
several dozen glaciers can be simulated on a personal computer, whereas
global simulations realized in a supercomputing environment take up to a few
hours per century. Thanks to the modular framework, modules of various
complexity can be added to the code base, which allows for new kinds of model
intercomparison studies in a controlled environment. Future developments will
add new physical processes to the model as well as automated calibration
tools. Extensions or alternative parameterizations can be easily added by the
community thanks to comprehensive documentation. OGGM spans a wide range of
applications, from ice–climate interaction studies at millennial timescales
to estimates of the contribution of glaciers to past and future sea-level
change. It has the potential to become a self-sustained community-driven
model for global and regional glacier evolution.
The retention and release of liquid water in glacierized basins was modelled with a conceptual, semi-distributed model of the water and ice balance designed for long-term averages with monthly ...resolution for 100 m elevation bands. Here we present the components of the liquid water balance of 86 mostly glacierized basins on either side of the main Alpine divide between 10 and 13°E in the period 1998–2006 and compare them with the records of 30 basins monitored from 1970 to 1997. Basin average of liquid water retention has maxima in excess of 100 mm per month in May, often followed by maximum release when the retaining snow matrix melts. Glacier storage peaks in August partly due to ice melt and the ensuing filling of the englacial reservoirs and partly on account of a precipitation maximum. These two components combined to a common maximum of storage in summer in the first period 1970–97 and developed two distinct maxima in the warmer period 1998–2006. A further maximum of liquid water storage that was often found in October is most likely due to a peak in precipitation in the southern part of the study region.
The Hexacyanodiborane(6) Dianion [B2(CN)6]2 Landmann, Johannes; Sprenger, Jan A. P.; Hailmann, Michael ...
Angewandte Chemie (International ed.),
September 14, 2015, Letnik:
54, Številka:
38
Journal Article
Recenzirano
Diborane(6) dianions with substituents that are bonded to boron via carbon are very reactive and therefore only a few examples are known. Diborane(6) derivatives are the simplest catenated boron ...compounds with an electron‐precise B–B σ‐bond that are of fundamental interest and of relevance for material applications. The homoleptic hexacyanodiborane(6) dianion B2(CN)62− that is chemically very robust is reported. The dianion is air‐stable and resistant against boiling water and anhydrous hydrogen fluoride. Its salts are thermally highly stable, for example, decomposition of (H3O)2B2(CN)6 starts at 200 °C. The B2(CN)62− dianion is readily accessible starting from 1) B(CN)32− and an oxidant, 2) BF(CN)3− and a reductant, or 3) by the reaction of B(CN)32− with BHal(CN)3− (Hal=F, Br). The latter reaction was found to proceed via a triply negatively charged transition state according to an SN2 mechanism.
Highly stable BB σ‐bond: The homoleptic hexacyanodiborane(6) dianion B2(CN)62− (see picture) is chemically very robust and its salts are thermally highly stable. Salts of the diborane(6) dianion are readily accessible in high yields from salts of the anions B(CN)32− and BHal(CN)3− (Hal=F, Br). Mechanistic studies show that the B2(CN)62− dianion is formed by an unprecedented SN2‐type reaction.
Accelerating glacier melt rates were observed during the last decades. Substantial ice loss occurs particularly during heat waves that are expected to intensify in the future. Because measuring and ...modelling glacier mass balance on a daily scale remains challenging, short-term mass balance variations, including extreme melt events, are poorly captured. Here, we present a novel approach based on computer-vision techniques for automatically determining daily mass balance variations at the local scale. The approach is based on the automated recognition of colour-taped ablation stakes from camera images and is tested and validated at six stations installed on three Alpine glaciers during the summers of 2019–2022. Our approach produces daily mass balance with an uncertainty of ±0.81 cm w.e. d−1, which is about half of the accuracy obtained from visual readouts. The automatically retrieved daily mass balances at the six sites were compared to average daily mass balances over the last decade derived from seasonal in situ observations to detect and assess extreme melt events. This allows analysing the impact that the summer heat waves which occurred in 2022 had on glacier melt. Our results indicate 23 d with extreme melt, showing a strong correspondence between the heat wave periods and extreme melt events. The combination of below-average winter snowfall and a suite of summer heat waves led to unprecedented glacier mass loss. The Switzerland-wide glacier storage change during the 25 d of heat waves in 2022 is estimated as 1.27 ± 0.10 km3 of water, corresponding to 35 % of the overall glacier mass loss during that summer. The same 25 d of heat waves caused a glacier mass loss that corresponds to 56 % of the average mass loss experienced over the entire melt season during the summers 2010–2020, demonstrating the relevance of heat waves for seasonal melt.
We report the observation of a small, yet remarkably stable, metal-free hexacyanodiborate dianion B2(CN)62– in the gas phase. Negative ion photoelectron spectroscopy (NIPES) was employed to measure ...its spectra at multiple laser wavelengths, yielding a 1.9 eV electron binding energy (EBE) a remarkably high value of electronic stability and a ∼2.60 eV repulsive Coulomb barrier (RCB) for electron detachment. This rationalizes the observation of this dianion, although homolytic charge-separation dissociation into two B(CN)3•– is energetically favorable. Quantum chemical calculations demonstrate a D 3d staggered conformation for both the dianion and radical monoanion, and the calculated EBE and RCB match the experimental values well. The simulated density of states spectrum reproduces all measured electronic transitions, while the simulated vibrational progressions for the ground state transition cover a much narrower EBE range compared to the experimental band, indicating appreciable auto-photodetachment via electronically excited dianion resonances.
Here, we report the observation of a small, yet remarkably stable, metal-free hexacyanodiborate dianion B2(CN)62– in the gas phase. Negative ion photoelectron spectroscopy (NIPES) was employed to ...measure its spectra at multiple laser wavelengths, yielding a 1.9 eV electron binding energy (EBE) —a remarkably high value of electronic stability and a ~2.60 eV repulsive Coulomb barrier (RCB) for electron detachment. This rationalizes the observation of this dianion, although homolytic charge-separation dissociation into two B(CN)3•– is energetically favorable. Quantum chemical calculations demonstrate a $D_{3d}$ staggered conformation for both the dianion and radical monoanion, and the calculated EBE and RCB match the experimental values well. The simulated density of states spectrum reproduces all measured electronic transitions, while the simulated vibrational progressions for the ground state transition cover a much narrower EBE range compared to the experimental band, indicating appreciable auto-photodetachment via electronically excited dianion resonances
A set of mixed-substituted potassium alkylcyano- and alkylcyanofluoroborates has been synthesized using easily accessible starting compounds and characterized by elemental analysis, NMR and ...vibrational spectroscopy, and mass spectrometry. In addition, single-crystal structures of salts of the cyanoborate anions have been derived from X-ray diffraction experiments. The 1-ethyl-3-methylimidazolium room temperature ionic liquids (EMIm+-RTILs) with the new borate anions have been synthesized and their physicochemical properties, i.e. high thermal and electrochemical stability, low viscosity, and high conductivity, have been compared to the properties of related EMIm+-RTILs. The influence of the different alkyl substituents at boron has been assessed. The exemplary study on the properties with the EMIm+-ILs with the mixed water stable alkylcyanoborate anions points towards the potential of these fluorine-free borate anions, in general.
Deboronation of closo-1,7-C
B
H
and 1-R
-closo-1,2-C
B
H
(R
= Me, Ph) with anhydrous Me
NF yields Me
NBHF
that is the first structurally characterized anion of the series BH
F
(x = 1-3). ...Deboronation of 9,12-R
-closo-1,7-C
B
H
(R
= H, I) gives a mixture of Me
NBHF
and Me
N1-HF
B-9,12-R
-closo-1,2-C
B
H
.
The hexacyanodiborane(6) dianion [B2(CN)6](2-) Landmann, Johannes; Sprenger, Jan A P; Hailmann, Michael ...
Angewandte Chemie International Edition,
2015-Sep-14, 20150914, Letnik:
54, Številka:
38
Journal Article
Recenzirano
Diborane(6) dianions with substituents that are bonded to boron via carbon are very reactive and therefore only a few examples are known. Diborane(6) derivatives are the simplest catenated boron ...compounds with an electron-precise B-B σ-bond that are of fundamental interest and of relevance for material applications. The homoleptic hexacyanodiborane(6) dianion B2 (CN)6 (2-) that is chemically very robust is reported. The dianion is air-stable and resistant against boiling water and anhydrous hydrogen fluoride. Its salts are thermally highly stable, for example, decomposition of (H3 O)2 B2 (CN)6 starts at 200 °C. The B2 (CN)6 (2-) dianion is readily accessible starting from 1) B(CN)3 (2-) and an oxidant, 2) BF(CN)3 (-) and a reductant, or 3) by the reaction of B(CN)3 (2-) with BHal(CN)3 (-) (Hal=F, Br). The latter reaction was found to proceed via a triply negatively charged transition state according to an SN 2 mechanism.
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![Isolated [B2(CN)6]2–: Small...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1948-7185/small "Isolated [B2(CN)6]2–: Small Yet Exceptionally Stable Nonmetal Dianion")
