| 1. |
- Aad, G., et al.
(author)
-
Readiness of the ATLAS Tile Calorimeter for LHC collisions
- 2010
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 70:4, s. 1193-1236
-
Journal article (peer-reviewed)abstract
- The Tile hadronic calorimeter of the ATLAS detector has undergone extensive testing in the experimental hall since its installation in late 2005. The readout, control and calibration systems have been fully operational since 2007 and the detector has successfully collected data from the LHC single beams in 2008 and first collisions in 2009. This paper gives an overview of the Tile Calorimeter performance as measured using random triggers, calibration data, data from cosmic ray muons and single beam data. The detector operation status, noise characteristics and performance of the calibration systems are presented, as well as the validation of the timing and energy calibration carried out with minimum ionising cosmic ray muons data. The calibration systems' precision is well below the design value of 1%. The determination of the global energy scale was performed with an uncertainty of 4%.
|
|
| 2. |
- Aad, G., et al.
(author)
-
Studies of the performance of the ATLAS detector using cosmic-ray muons
- 2011
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 71:3
-
Journal article (peer-reviewed)abstract
- Muons from cosmic-ray interactions in the atmosphere provide a high-statistics source of particles that can be used to study the performance and calibration of the ATLAS detector. Cosmic-ray muons can penetrate to the cavern and deposit energy in all detector subsystems. Such events have played an important role in the commissioning of the detector since the start of the installation phase in 2005 and were particularly important for understanding the detector performance in the time prior to the arrival of the first LHC beams. Global cosmic-ray runs were undertaken in both 2008 and 2009 and these data have been used through to the early phases of collision data-taking as a tool for calibration, alignment and detector monitoring. These large datasets have also been used for detector performance studies, including investigations that rely on the combined performance of different subsystems. This paper presents the results of performance studies related to combined tracking, lepton identification and the reconstruction of jets and missing transverse energy. Results are compared to expectations based on a cosmic-ray event generator and a full simulation of the detector response.
|
|
| 3. |
- Aad, G., et al.
(author)
-
The ATLAS Inner Detector commissioning and calibration
- 2010
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 70:3, s. 787-821
-
Journal article (peer-reviewed)abstract
- The ATLAS Inner Detector is a composite tracking system consisting of silicon pixels, silicon strips and straw tubes in a 2 T magnetic field. Its installation was completed in August 2008 and the detector took part in data-taking with single LHC beams and cosmic rays. The initial detector operation, hardware commissioning and in-situ calibrations are described. Tracking performance has been measured with 7.6 million cosmic-ray events, collected using a tracking trigger and reconstructed with modular pattern-recognition and fitting software. The intrinsic hit efficiency and tracking trigger efficiencies are close to 100%. Lorentz angle measurements for both electrons and holes, specific energy-loss calibration and transition radiation turn-on measurements have been performed. Different alignment techniques have been used to reconstruct the detector geometry. After the initial alignment, a transverse impact parameter resolution of 22.1 +/- 0.9 mu m and a relative momentum resolution sigma (p) /p=(4.83 +/- 0.16)x10(-4) GeV(-1)xp (T) have been measured for high momentum tracks.
|
|
| 4. |
- Divine, D. V., et al.
(author)
-
Modelling the regional climate and isotopic composition of Svalbard precipitation using REMOiso : a comparison with available GNIP and ice core data
- 2011
-
In: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 25:24, s. 3748-3759
-
Journal article (peer-reviewed)abstract
- Simulations of a regional (approx. 50 km resolution) circulation model REMOiso with embedded stable water isotope module covering the period 1958-2001 are compared with the two instrumental climate and four isotope series (d18O) from western Svalbard. We examine the data from ice cores drilled on Svalbard ice caps in 1997 (Lomonosovfonna, 1250 m asl) and 2005 (Holtedahlfonna, 1150 m asl) and the GNIP series from Ny-angstrom lesund and Isfjord Radio. The surface air temperature (SAT) and precipitation data from Longyearbyen and Ny-angstrom lesund are used to assess the skill of the model in reproducing the local climate. The model successfully captures the climate variations on the daily to multidecadal times scales although it tends to systematically underestimate the winter SAT. Analysis suggests that REMOiso performs better at simulating isotope compositions of precipitation in the winter than summer. The simulated and measured Holtedahlfonna d18O series agree reasonably well, whereas no significant correlation has been observed between the modelled and measured Lomonosovfonna ice core isotopic series. It is shown that sporadic nature as well as variability in the amount inherent in precipitation process potentially limits the accuracy of the past SAT reconstruction from the ice core data. This effect in the study area is, however, diminished by the role of other factors controlling d18O in precipitation, most likely sea ice extent, which is directly related with the SAT anomalies.
|
|
| 5. |
- Edwards, Thomas W. D., et al.
(author)
-
Seasonal variability in Northern Hemisphere atmospheric circulation during the Medieval Climate Anomaly and the Little Ice Age
- 2017
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 165, s. 102-110
-
Journal article (peer-reviewed)abstract
- Here we report new reconstructions of winter temperature and summer moisture during the past millennium in southeastern Sweden, based on stable-isotope data from a composite tree-ring sequence, that further enhances our knowledge and understanding of seasonal climate variability in the Northern Hemisphere over the past millennium. Key features of these new climate proxy records include evidence for distinctive fluctuations in winter temperature in SE Sweden, superimposed upon the general pattern of cooling between the so-called Medieval Climate Anomaly (MCA) of the early millennium and the Little Ice Age (LIA) of the late millennium, as well as evidence for sustained summer wetness during the MCA, followed by drier and less variable conditions during the LIA. We also explore these new records within a circumpolar spatial context by employing self-organizing map analysis of meteorological reanalysis data to identify potential modern analogues of mid-tropospheric synoptic circulation types in the Northern Hemisphere extratropics that can reconcile varying seasonal climate states during the MCA and LIA in SE Sweden with less variable conditions in southwestern Canada, as portrayed by paleoclimate records developed in the same manner in an earlier study.
|
|
| 6. |
- Insel, Nadja, et al.
(author)
-
Climate controls on Andean precipitation delta O-18 interannual variability
- 2013
-
In: Journal of Geophysical Research: Atmospheres. - : American Geophysical Union (AGU). - 2169-897X. ; 118:17, s. 9721-9742
-
Journal article (peer-reviewed)abstract
- The stable oxygen isotopic composition of precipitation (O-18(p)) is used as a proxy for modern and past atmospheric, biologic, and surface processes. Although the physical processes that fractionate O-18 in vapor are known, regional controls of O-18(p) are not well understood. Here we present results from a limited-domain general circulation model (REMOiso) to quantify regional controls on modern (1976-1999) interannual and spatial variations of O-18(p) across four Andean domains spanning 50 degrees latitude. Results are compared to observed O-18(p) from meteorological stations. Simulated annual amount-weighted mean O-18(p) ranges between -4 and -7 (0-5 degrees S), -8 and -20 (14 degrees S-26 degrees S), -4 and -8.5 (30 degrees S-35 degrees S), and -7 to -10 (45 degrees S-50 degrees S). Relationships between climate and O-18(p) on interannual timescale vary along the Andes and are tied to changes in precipitation and large-scale dynamics. In the northern Andes, interannual variations in O-18(p) are mainly associated with precipitation amounts driven by low-latitude sea surface temperature and Amazon Basin conditions. In the north central Andes, O-18(p) correlates with precipitation amount and wind trajectory, which is related to the position of the Bolivian High. In the south central Andes, O-18(p) variability is mainly influenced by precipitation amounts that are controlled by the position and strength of the westerlies. In the southern Andes, interannual O-18(p) variability is linked to the intensification and weakening of the South Pacific High. The regional climate-O-18(p) relationships are discussed in the context of pre-Quaternary sedimentary O-18 proxy records.
|
|
| 7. |
- Insel, Nadja, et al.
(author)
-
Response of meteoric delta O-18 to surface uplift - Implications for Cenozoic Andean Plateau growth
- 2012
-
In: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X .- 1385-013X. ; 317, s. 262-272
-
Journal article (peer-reviewed)abstract
- The timing and magnitude of surface uplift provide important constraints on geodynamic models of orogen formation. Oxygen isotope (delta O-18) and mass-47 isotopolog (Delta(47)) compositions from terrestrial carbonate sediments have been used with modern isotope and temperature lapse rates to infer past surface elevations of the Andes. However, these paleoaltimeny interpretations are contentious because variations in the oxygen isotope composition in meteoric water (delta O-18(p)) are caused by changes in elevation (orographic) and regional climate. Here, we use a limited-domain isotope-tracking general circulation model to simulate changes in delta O-18(p) and isotopic lapse rates in response to Andean surface uplift, and to re-evaluate delta O-18 and Delta(47) changes in late Miocene carbonates previously associated with rapid Andean growth. Results indicate that Andean surface uplift leads to changes in low-level atmospheric circulation and an increase in precipitation along the eastem Andean flank which influences isotopic source and amount effects. Simulated changes in Andean delta O-18(p) are not systematic with an increase in surface elevation, but are instead a function of orographic thresholds that abruptly change regional climate. A delta O-18(p) decrease of >5%. over the central Andes and an increase in isotopic lapse rates (up to 0.8%. km(-1)) coincide with Andean surface uplift from 75 to 100% of modem elevation. These changes in the isotopic signature could account for the entire 3-4%. delta O-18 depletion in late Miocene carbonate nodules, and suggest an Andean paleoelevation of similar to 3000 m (75% of modem elevations) before 10 Ma.
|
|
| 8. |
- Muschitiello, Francesco, et al.
(author)
-
New evidence of Holocene atmospheric circulation dynamics based on lake sediments from southern Sweden : a link to the Siberian High
- 2013
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 77, s. 113-124
-
Journal article (peer-reviewed)abstract
- Oxygen (delta O-18) and carbon (delta C-13) isotope records of calcitic carbonate components (Chara sp. algal encrustations and Bithynia tentaculata gastropod opercula) from a lake-sediment succession on the Baltic Sea island of Gotland, south-eastern Sweden, have been obtained to investigate regional climate dynamics during the Holocene. The hydrological sensitivity of the small lake, particularly in terms of spring snowmelt contribution to the local water budget, provides a means of tracing past changes in the influence of snow-bearing easterly winds across the Baltic Sea Proper, which signifies the wintertime strength of the Siberian High. Repeated episodic depletions in O-18 at the centennial scale correlate with events of increased potassium concentration in the GISP2 ice-core record from Greenland, which indicates a coupling to large-scale fluctuations in atmospheric circulation patterns. A corresponding correlation with simultaneous depletions in C-13 suggests repeated responses of the local lake hydrology to snow-rich winters through decreasing water residence time, perhaps augmented by methanogenesis due to prolonged ice-cover seasons under the influence of an expanding Siberian High. Frequency analysis of the isotopic records reveals well-defined fluctuations at quasi-500-520-, 670-, 830- and 1430-yr periodicities, and a gradually stronger impact of Polar air outbreaks across the southern Baltic Sea region with time after ca 6000 cal. BP.
|
|
| 9. |
- Risi, Camille, et al.
(author)
-
Process-evaluation of tropospheric humidity simulated by general circulation models using water vapor isotopic observations : 2. Using isotopic diagnostics to understand the mid and upper tropospheric moist bias in the tropics and subtropics
- 2012
-
In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 117, s. D05304-
-
Journal article (peer-reviewed)abstract
- Evaluating the representation of processes controlling tropical and subtropical tropospheric relative humidity (RH) in atmospheric general circulation models (GCMs) is crucial to assess the credibility of predicted climate changes. GCMs have long exhibited a moist bias in the tropical and subtropical mid and upper troposphere, which could be due to the mis-representation of cloud processes or of the large-scale circulation, or to excessive diffusion during water vapor transport. The goal of this study is to use observations of the water vapor isotopic ratio to understand the cause of this bias. We compare the three-dimensional distribution of the water vapor isotopic ratio measured from space and ground to that simulated by several versions of the isotopic GCM LMDZ. We show that the combined evaluation of RH and of the water vapor isotopic composition makes it possible to discriminate the most likely cause of RH biases. Models characterized either by an excessive vertical diffusion, an excessive convective detrainment or an underestimated in situ cloud condensation will all produce a moist bias in the free troposphere. However, only an excessive vertical diffusion can lead to a reversed seasonality of the free tropospheric isotopic composition in the subtropics compared to observations. Comparing seven isotopic GCMs suggests that the moist bias found in many GCMs in the mid and upper troposphere most frequently results from an excessive diffusion during vertical water vapor transport. This study demonstrates the added value of water vapor isotopic measurements for interpreting shortcomings in the simulation of RH by climate models.
|
|
| 10. |
- Risi, Camille, et al.
(author)
-
Process-evaluation of tropospheric humidity simulated by general circulation models using water vapor isotopologues : 1. Comparison between models and observations
- 2012
-
In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 117, s. D05303-
-
Journal article (peer-reviewed)abstract
- The goal of this study is to determine how H2O and HDO measurements in water vapor can be used to detect and diagnose biases in the representation of processes controlling tropospheric humidity in atmospheric general circulation models (GCMs). We analyze a large number of isotopic data sets (four satellite, sixteen ground-based remote-sensing, five surface in situ and three aircraft data sets) that are sensitive to different altitudes throughout the free troposphere. Despite significant differences between data sets, we identify some observed HDO/H2O characteristics that are robust across data sets and that can be used to evaluate models. We evaluate the isotopic GCM LMDZ, accounting for the effects of spatiotemporal sampling and instrument sensitivity. We find that LMDZ reproduces the spatial patterns in the lower and mid troposphere remarkably well. However, it underestimates the amplitude of seasonal variations in isotopic composition at all levels in the subtropics and in midlatitudes, and this bias is consistent across all data sets. LMDZ also underestimates the observed meridional isotopic gradient and the contrast between dry and convective tropical regions compared to satellite data sets. Comparison with six other isotope-enabled GCMs from the SWING2 project shows that biases exhibited by LMDZ are common to all models. The SWING2 GCMs show a very large spread in isotopic behavior that is not obviously related to that of humidity, suggesting water vapor isotopic measurements could be used to expose model shortcomings. In a companion paper, the isotopic differences between models are interpreted in terms of biases in the representation of processes controlling humidity.
|
|
