97 research outputs found
The CRUTEM4 land-surface air temperature data set:Construction, previous versions and dissemination via Google earth
The CRUTEM4 (Climatic Research Unit Temperature, version 4) land-surface air temperature data set is one of the most widely used records of the climate system. Here we provide an important additional dissemination route for this data set: online access to monthly, seasonal and annual data values and time series graphs via Google Earth. This is achieved via an interface written in Keyhole Markup Language (KML) and also provides access to the underlying weather station data used to construct the CRUTEM4 data set. A mathematical description of the construction of the CRUTEM4 data set (and its predecessor versions) is also provided, together with an archive of some previous versions and a recommendation for identifying the precise version of the data set used in a particular study
Stereo-SCIDAR: optical turbulence profiling with high sensitivity using a modified SCIDAR instrument
The next generation of adaptive optics systems will require tomographic reconstruction techniques to map the optical refractive index fluctuations, generated by the atmospheric turbulence, along the line of sight to the astronomical target. These systems can be enhanced with data from an external atmospheric profiler. This is important for Extremely Large Telescope scale tomography. Here we propose a new instrument which utilizes the generalized Scintillation Detection And Ranging (SCIDAR) technique to allow high sensitivity vertical profiles of the atmospheric optical turbulence and wind velocity profile above astronomical observatories. The new approach, which we refer to as ‘stereo-SCIDAR’, uses a stereoscopic system with the scintillation pattern from each star of a double-star target incident on a separate detector. Separating the pupil images for each star has several advantages including increased magnitude difference tolerance for the target stars; negating the need for re-calibration due to the normalization errors usually associated with SCIDAR; an increase of at least a factor of 2 in the signal-to-noise ratio of the cross-covariance function and hence the profile for equal magnitude target stars and up to a factor of 16 improvement for targets of 3 mag difference and easier real-time reconstruction of the wind-velocity profile. Theoretical response functions are calculated for the instrument, and the performance is investigated using a Monte Carlo simulation. The technique is demonstrated using data recorded at the 2.5-m Nordic Optical Telescope and the 1.0-m Jacobus Kapteyn Telescope, both on La Palma
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How will organic carbon stocks in mineral soils evolve under future climate? Global projections using RothC for a range of climate change scenarios
We use a soil carbon (C) model (RothC), driven by a range of climate models for a range of climate scenarios to examine the impacts of future climate on global soil organic carbon (SOC) stocks. The results suggest an overall global increase in SOC stocks by 2100 under all scenarios, but with a different extent of increase among the climate model and emissions scenarios. The impacts of projected land use changes are also simulated, but have relatively minor impacts at the global scale. Whether soils gain or lose SOC depends upon the balance between C inputs and decomposition. Changes in net primary production (NPP) change C inputs to the soil, whilst decomposition usually increases under warmer temperatures, but can also be slowed by decreased soil moisture. Underlying the global trend of increasing SOC under future climate is a complex pattern of regional SOC change. SOC losses are projected to occur in northern latitudes where higher SOC decomposition rates due to higher temperatures are not balanced by increased NPP, whereas in tropical regions, NPP increases override losses due to higher SOC decomposition. The spatial heterogeneity in the response of SOC to changing climate shows how delicately balanced the competing gain and loss processes are, with subtle changes in temperature, moisture, soil type and land use, interacting to determine whether SOC increases or decreases in the future. Our results suggest that we should stop looking for a single answer regarding whether SOC stocks will increase or decrease under future climate, since there is no single answer. Instead, we should focus on improving our prediction of the factors that determine the size and direction of change, and the land management practices that can be implemented to protect and enhance SOC stocks
Evaluating Process-Based Integrated Assessment Models of Climate Change Mitigation
Process-based integrated assessment models (IAMs) analyse transformation pathways to mitigate climate change. Confidence in models is established by testing their structural assumptions and comparing their behaviour against observations as well as other models. Climate model evaluation is concerted, and prominently reported in a dedicated chapter in the IPCC WG1 assessments. By comparison, evaluation of process-based IAMs tends to be less visible and more dispersed among modelling teams, with the exception of model inter-comparison projects. We contribute the first comprehensive analysis of process-based IAM evaluation, drawing on a wide range of examples across eight different evaluation methods testing both structural and behavioural validity. For each evaluation method, we compare its application to process-based IAMs with its application to climate models, noting similarities and differences, and seeking useful insights for strengthening the evaluation of process-based IAMs. We find that each evaluation method has distinctive strengths and limitations, as well as constraints on their application. We develop a systematic evaluation framework combining multiple methods that should be embedded within the development and use of process-based IAMs
Daytime site characterisation of La Palma, and its relation to night-time conditions
This paper presents preliminary daytime profiles taken using a Wide-Field Shack-Hartmann Sensor at the Swedish Solar Telescope (SST), La Palma. These are contrasted against Stereo-SCIDAR data from corresponding nights to assess the validity of the assumptions currently used for simulating the performances of possible Multi-Conjugate Adaptive Optics (MCAO) systems for future solar telescopes, especially the assumption that the structure of the high altitude turbulence is mostly similar between the day and the night. We find that for our data both the altitude and the strength of the turbulence differ between the day and the night, although more data is required to draw any conclusions about typical behaviour and conditions
Zero Modes and the Atiyah-Singer Index in Noncommutative Instantons
We study the bosonic and fermionic zero modes in noncommutative instanton
backgrounds based on the ADHM construction. In k instanton background in U(N)
gauge theory, we show how to explicitly construct 4Nk (2Nk) bosonic (fermionic)
zero modes in the adjoint representation and 2k (k) bosonic (fermionic) zero
modes in the fundamental representation from the ADHM construction. The number
of fermionic zero modes is also shown to be exactly equal to the Atiyah-Singer
index of the Dirac operator in the noncommutative instanton background. We
point out that (super)conformal zero modes in non-BPS instantons are affected
by the noncommutativity. The role of Lorentz symmetry breaking by the
noncommutativity is also briefly discussed to figure out the structure of U(1)
instantons.Comment: v3: 24 pages, Latex, corrected typos, references added, to appear in
Phys. Rev.
Propagators in Noncommutative Instantons
We explicitly construct Green functions for a field in an arbitrary
representation of gauge group propagating in noncommutative instanton
backgrounds based on the ADHM construction. The propagators for spinor and
vector fields can be constructed in terms of those for the scalar field in
noncommutative instanton background. We show that the propagators in the
adjoint representation are deformed by noncommutativity while those in the
fundamental representation have exactly the same form as the commutative case.Comment: 28 pages, Latex, v2: A few typos correcte
Decoherence and CPT Violation in a Stringy Model of Space-Time Foam
I discuss a model inspired from the string/brane framework, in which our
Universe is represented as a three brane, propagating in a bulk space time
punctured by D0-brane (D-particle) defects. As the D3-brane world moves in the
bulk, the D-particles cross it, and from an effective observer on D3 the
situation looks like a ``space-time foam'' with the defects ``flashing'' on and
off (``D-particle foam''). The open strings, with their ends attached on the
brane, which represent matter in this scenario, can interact with the
D-particles on the D3-brane universe in a topologically non-trivial manner,
involving splitting and capture of the strings by the D0-brane defects. Such
processes are described by logarithmic conformal field theories on the
world-sheet. Physically, they result in effective decoherence of the string
matter on the D3 brane, and as a result, of CPT Violation, but of a type that
implies an ill-defined nature of the effective CPT operator. Due to electric
charge conservation, only electrically neutral (string) matter can exhibit such
interactions with the D-particle foam. This may have unique, experimentally
detectable, consequences for electrically-neutral entangled quantum matter
states on the brane world, in particular the modification of the pertinent EPR
Correlation of neutral mesons in a meson factory.Comment: 41 pages Latex, five eps figures incorporated. Uses special macro
The Importance of Context in Managerial Work: The Case of Senior Hotel Managers in Greece
Qualitative research on the interplay between context and hospitality managerial work has not been previously addressed in the literature. Based on the works of Johns (2006) and Dierdorff et al. (2009), this research suggests that luxury senior hotel managers (GMs and department managers) are to a certain degree recipients of contextual/cultural influences, depending on the ownership status of the hotel. It is also argued that managerial work is shaped and exercised by a set of moderating factors, which are unique for each individual. Overall, the aim of this research is to increase the level of awareness and trigger further research in this topic area. © 2014 Copyright © Taylor & Francis Group, LLC
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