Entity

Time filter

Source Type

Coronado, CA, United States

Kopp G.,University of Colorado at Boulder | Fehlmann A.,Physikalisch Meteorologisches Observatorium Davos World Radiation Center | Finsterle W.,Physikalisch Meteorologisches Observatorium Davos World Radiation Center | Harber D.,University of Colorado at Boulder | And 2 more authors.
Metrologia | Year: 2012

Continuity of the 33-year long total solar irradiance record has been facilitated by corrections for offsets due to calibration differences between instruments, providing a solar data record with precision approaching that needed for Earth climate studies. Recent laboratory tests have (1) improved measurement absolute accuracy to mitigate potential future data gaps, (2) helped explain the causes of instrument offsets and (3) improved consistency between the international references upon which various instrument calibrations are based. © 2012 BIPM & IOP Publishing Ltd. Source


Willson R.C.,ACRIM
Astrophysics and Space Science | Year: 2014

The effects of scattering and diffraction on the observations of the ACRIMSAT/ACRIM3 satellite TSI monitoring mission have been characterized by the preflight calibration approach for satellite total solar irradiance (TSI) sensors implemented at the LASP/TRF (Laboratory for Atmospheric and Space Physics/Total Solar Irradiance Radiometer Facility). The TRF also calibrates the SI (International System of units) traceability to the NIST (National Institute of Standards and Technology) cryo-radiometric scale. ACRIM3's self-calibration agrees with NIST to within the uncertainty of the test procedure (~500 ppm). A correction of ~5000 ppm was found for scattering and diffraction that has significantly reduced the scale difference between the results of the ACRIMSAT/ACRIM3 and SORCE/TIM satellite experiments. Algorithm updates reflecting more than 10 years of mission experience have been made that further improve the ACRIM3 results by eliminating some thermally driven signal and increasing the signal to noise ratio. The result of these changes is a more precise and detailed picture of TSI variability. Comparison of the results from the ACRIM3, SORCE/TIM and SOHO/VIRGO satellite experiments demonstrate the near identical detection of TSI variability on all sub-annual temporal and amplitude scales during the TIM mission. The largest occurs at the rotational period of the primary solar activity longitudes. On the decadal timescale, while ACRIM3 and VIRGO results exhibit close agreement throughout, TIM exhibits a consistent 500 ppm upward trend relative to ACRIM3 and VIRGO. A solar magnetic activity area proxy for TSI has been used to demonstrate that the ACRIM TSI composite and its +0.037 %/decade TSI trend during solar cycles 21-23 is the most likely correct representation of the extant satellite TSI database. The occurrence of this trend during the last decades of the 20th century supports a more robust contribution of TSI variation to detected global temperature increase during this period than predicted by current climate models. © 2014 The Author(s). Source


Debernard L.,Compiegne University of Technology | Robert L.,ACRIM | Charleux F.,ACRIM | Bensamoun S.F.,Compiegne University of Technology
Clinical Biomechanics | Year: 2011

Background: Magnetic resonance elastography has been performed in healthy and pathological muscles in order to provide clinicians with quantitative muscle stiffness data. However, there is a lack of data on pediatric muscle. Therefore, the present work studies age-related changes of the mechanical properties. Methods: 26 healthy subjects composed of 7 children (8-12 years), 9 young adults (24-29 years) and 10 middle-aged adults (53-58 years) underwent a magnetic resonance elastography test. Shear modulus (μ) and its spatial distribution, as well as the attenuation coefficient (α) were measured on the vastus medialis muscle at rest and at contracted conditions (10% and 20% of the maximum voluntary contraction) for each group. Findings: The shear modulus linearly increases with the degree of contraction for young adults while it is maximum at 10% of the maximum voluntary contraction for children (μ- children-10% = 14.9 kPa (SD 2.18)) and middle-aged adults (μ- middle-aged-10% = 10.42 kPa (SD 1.38)). Mapping of shear modulus revealed a diffuse distribution of colors reflecting differences in muscle physiological activity as a function of age. The attenuation coefficient showed a similar behavior for all groups, i.e. a decrease from the relaxed to the contracted states. Interpretation: This study demonstrates that the magnetic resonance elastography technique is sensitive enough to detect changes in muscle mechanical properties for children, middle-aged and young adults and could provide clinicians with a muscle reference data base as a function of age, improving the diagnosis of muscular dystrophy. © 2011 Elsevier Ltd. All rights reserved. Source


Scafetta N.,ACRIM | Scafetta N.,Duke University | Willson R.C.,ACRIM
Planetary and Space Science | Year: 2013

The historical Hungarian auroral record extends from 1523 to 1960 and is longer than the sunspot record. Harmonic analysis reveals four major multidecadal secular cycles forming an approximate harmonic set at periods of 42.85, 57.13, 85.7 and 171.4 years. These four frequencies are very close to the four major heliospheric oscillations relative to the center of mass of the solar system caused by Jupiter, Saturn, Uranus and Neptune. Similar frequencies are found in solar radiation models based on long cosmogenic isotope records (Steinhilber et al.; 2012) and in long records of naked-eye sunspot observations (Vaquero et al.; 2002). Harmonic regression models are used to reconstruct and forecast aurora and solar activity for the period 1956-2050. The model predicts: (1) the multidecadal solar minimum in the 1970s that is also observed in the sunspot record; (2) a solar maximum in 2000-2002 that is observed in the ACRIM total solar irradiance satellite composite; (3) a prolonged solar minimum centered in the 2030s. These findings support a hypothesis that the Sun, the heliosphere and the terrestrial magnetosphere are partially modulated by planetary gravitational and magnetic forces synchronized to planetary oscillations, as also found in other recent publications (Scafetta, 2010, 2012a, 2012c, 2012d; Abreu et al.; 2012; Tan and Cheng, 2012). © 2013 Elsevier Ltd. Source

Discover hidden collaborations