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Carlund T.,Physikalisch Meteorologisches Observatorium Davos World Radiation Center | Carlund T.,Swedish Meteorological and Hydrological Institute | Kouremeti N.,Physikalisch Meteorologisches Observatorium Davos World Radiation Center | Kazadzis S.,Physikalisch Meteorologisches Observatorium Davos World Radiation Center | And 2 more authors.
Atmospheric Measurement Techniques | Year: 2017

The determination of aerosol properties, especially the aerosol optical depth (AOD) in the ultraviolet (UV) wavelength region, is of great importance for understanding the climatological variability of UV radiation. However, operational retrievals of AOD at the biologically most harmful wavelengths in the UVB are currently only made at very few places. This paper reports on the UVPFR (UV precision filter radiometer) sunphotometer, a stable and robust instrument that can be used for AOD retrievals at four UV wavelengths. Instrument characteristics and results of Langley calibrations at a high-altitude site were presented. It was shown that due to the relatively wide spectral response functions of the UVPFR, the calibration constants (V0) derived from Langley plot calibrations underestimate the true extraterrestrial signals. Accordingly, correction factors were introduced. In addition, the instrument's spectral response functions also result in an apparent air-mass-dependent decrease in ozone optical depth used in the AOD determinations. An adjusted formula for the calculation of AOD, with a correction term dependent on total column ozone amount and ozone air mass, was therefore introduced. Langley calibrations performed 13-14 months apart resulted in sensitivity changes of ≤ĝ€1.1ĝ€%, indicating good instrument stability. Comparison with a high-accuracy standard precision filter radiometer, measuring AOD at 368-862ĝ€nm wavelengths, showed consistent results. Also, very good agreement was achieved by comparing the UVPFR with AOD at UVB wavelengths derived with a Brewer spectrophotometer, which was calibrated against the UVPFR at an earlier date. Mainly due to non-instrumental uncertainties connected with ozone optical depth, the total uncertainty of AOD in the UVB is higher than that reported from AOD instruments measuring in UVA and visible ranges. However, the precision can be high among instruments using harmonized algorithms for ozone and Rayleigh optical depth as well as for air mass terms. For 4 months of comparison measurements with the UVPFR and a Brewer, the root mean squared AOD differences were found <ĝ€0.01 at all the 306-320ĝ€nm Brewer wavelengths. © Author(s) 2017. CC Attribution 3.0 License.


Gray L.J.,National Center for Atmospheric Science | Gray L.J.,University of Oxford | Ball W.,ETH Zurich | Ball W.,Physikalisch Meteorologisches Observatorium Davos World Radiation Center | Misios S.,University of Oxford
AIP Conference Proceedings | Year: 2017

There is growing evidence that variability associated with the 11-year solar cycle has an impact at the Earth's surface and influences its weather and climate. Although the direct response to the Sun's variability is extremely small, a number of different mechanisms have been suggested that could amplify the signal, resulting in regional signals that are much larger than expected. In this paper the observed solar cycle signal at the Earth's surface is described, together with proposed mechanisms that involve modulation via the total incoming solar irradiance and via modulation of the ultra-violet part of the solar spectrum that influences ozone production in the stratosphere. © 2017 Author(s).


Broomhall A.-M.,University of Birmingham | Chaplin W.J.,University of Birmingham | Elsworth Y.,University of Birmingham | Simoniello R.,Physikalisch Meteorologisches Observatorium Davos World Radiation Center
Monthly Notices of the Royal Astronomical Society | Year: 2012

We investigate the spherical harmonic degree (l) dependence of the 'seismic' quasi-biennial oscillation (QBO) observed in low-degree solar p-mode frequencies, using Sun-as-a-star Birmingham Solar Oscillations Network data. The amplitude of the seismic QBO is modulated by the 11-yr solar cycle, with the amplitude of the signal being largest at solar maximum. The amplitude of the signal is noticeably larger for the l= 2 and 3 modes than for the l= 0 and 1 modes. The seismic QBO shows some frequency dependence but this dependence is not as strong as observed in the 11-yr solar cycle. These results are consistent with the seismic QBO having its origins in shallow layers of the interior (one possibility being the bottom of the shear layer extending 5per cent below the solar surface). Under this scenario the magnetic flux responsible for the seismic QBO is brought to the surface (where its influence on the p modes is stronger) by buoyant flux from the 11-yr cycle, the strong component of which is observed at predominantly low latitudes. As the l= 2 and 3 modes are much more sensitive to equatorial latitudes than the l= 0 and 1 modes the influence of the 11-yr cycle on the seismic QBO is more visible in l= 2 and 3 mode frequencies. Our results imply that close to solar maximum the main influence of the seismic QBO occurs at low latitudes (<45°), which is where the strong component of the 11-yr solar cycle resides. To isolate the latitudinal dependence of the seismic QBO from the 11-yr solar cycle we must consider epochs when the 11-yr solar cycle is weak. However, away from solar maximum, the amplitude of the seismic QBO is weak making the latitudinal dependence hard to constrain. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


Rozanov E.,Physikalisch Meteorologisches Observatorium Davos World Radiation Center | Rozanov E.,ETH Zurich | Calisto M.,International Space Science Institute ISSI | Egorova T.,Physikalisch Meteorologisches Observatorium Davos World Radiation Center | And 2 more authors.
Surveys in Geophysics | Year: 2012

We evaluate the influence of the galactic cosmic rays (GCR), solar proton events (SPE), and energetic electron precipitation (EEP) on chemical composition of the atmosphere, dynamics, and climate using the chemistry-climate model SOCOL. We have carried out two 46-year long runs. The reference run is driven by a widely employed forcing set and, for the experiment run, we have included additional sources of NO x and HO x caused by all considered energetic particles. The results show that the effects of the GCR, SPE, and EEP fluxes on the chemical composition are most pronounced in the polar mesosphere and upper stratosphere; however, they are also detectable and statistically significant in the lower atmosphere consisting of an ozone increase up to 3 % in the troposphere and ozone depletion up to 8 % in the middle stratosphere. The thermal effect of the ozone depletion in the stratosphere propagates down, leading to a warming by up to 1 K averaged over 46 years over Europe during the winter season. Our results suggest that the energetic particles are able to affect atmospheric chemical composition, dynamics, and climate. © 2012 Springer Science+Business Media B.V.


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.


Simoniello R.,University Paris Diderot | Jain K.,U.S. National Solar Observatory | Tripathy S.C.,U.S. National Solar Observatory | Turck-Chieze S.,University Paris Diderot | And 2 more authors.
Astronomische Nachrichten | Year: 2012

The solar magnetic activity consists of two periodic components: the main cycle with a period of 11 yr and a shorter cycle with a period of ≈2 yr. The origin of this second periodicity is still not well understood. We use almost 15 years of long high-quality resolved data provided by the Global Oscillation Network Group (GONG) to investigate the solar cycle changes in p-mode oscillations with spherical degree Ł = 0-120 and in the range of 1600 μHz ≤ ν ≤ 3500 μHz. For both periodic components of solar magnetic activity our findings locate the origin of the frequency shift in the subsurface layers with a sudden enhancement in the amplitude of the shift in the last few hundred kilometers. We also show that the size of the shift increases towards equatorial latitudes and from minimum to maximum of solar activity. On the other hand, the signatures of the 2-yr cycle differ from the one of the 11-yr cycle in the magnitude of the shift, as the 2-yr cycle causes a weaker shift in mode frequencies and a slower enhancement in the last few hundred kilometers. Based on these findings we speculate that a possible physical mechanism behind the quasi biennial periodicity (QBP) could be the beating between different dynamo modes (dipole and quadrupole mode). © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Simoniello R.,University Paris Diderot | Simoniello R.,Physikalisch Meteorologisches Observatorium Davos World Radiation Center | Jain K.,U.S. National Solar Observatory | Tripathy S.C.,U.S. National Solar Observatory | And 5 more authors.
Astrophysical Journal | Year: 2013

Manifestations of the solar magnetic activity through periodicities of about 11 and 2 years are now clearly seen in all solar activity indices. In this paper, we add information about the mechanism driving the 2-year period by studying the time and latitudinal properties of acoustic modes that are sensitive probes of the subsurface layers. We use almost 17 years of high-quality resolved data provided by the Global Oscillation Network Group to investigate the solar cycle changes in p-mode frequencies for spherical degrees ℓ from 0 to 120 and 1600 μHz ≤ν ≤ 3500 μHz. For both periodic components of solar activity, we locate the origin of the frequency shift in the subsurface layers and find evidence that a sudden enhancement in amplitude occurs in just the last few hundred kilometers. We also show that, in both cases, the size of the shift increases toward equatorial latitudes and from minimum to maximum solar activity, but, in agreement with previous findings, the quasi-biennial periodicity (QBP) causes a weaker shift in mode frequencies and a slower enhancement than that caused by the 11-year cycle. We compare our observational findings with the features predicted by different models, that try to explain the origin of this QBP and conclude that the observed properties could result from the beating between a dipole and quadrupole magnetic configuration of the dynamo. © 2013. The American Astronomical Society. All rights reserved.


Junk J.,Center De Recherche Public Gabriel Lippmann | Feister U.,Meteorological Observatory Lindenberg Richard Amann Observatory | Helbig A.,University of Trier | Gorgen K.,Center De Recherche Public Gabriel Lippmann | And 4 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2012

Solar erythemal UV radiation (UVER) is highly relevant for numerous biological processes that affect plants, animals, and human health. Nevertheless, long-term UVER records are scarce. As significant declines in the column ozone concentration were observed in the past and a recovery of the stratospheric ozone layer is anticipated by the middle of the 21st century, there is a strong interest in the temporal variation of UV ER time series. Therefore, we combined ground-based measurements of different meteorological variables with modeled ozone data sets to reconstruct time series of daily totals of UVER at the Meteorological Observatory, Potsdam, Germany. Artificial neural networks were trained with measured UVER, sunshine duration, the day of year, measured and modeled total column ozone, as well as the minimum solar zenith angle. This allows for the reconstruction of daily totals of UVER for the period from 1901 to 1999. Additionally, analyses of the long-term variations from 1901 until 1999 of the reconstructed, new UVER data set are presented. The time series of monthly and annual totals of UVER provide a long-term meteorological basis for epidemiological investigations in human health and occupational medicine for the region of Potsdam and Berlin. A strong benefit of our ANN-approach is the fact that it can be easily adapted to different geographical locations, as successfully tested in the framework of the COSTAction 726. © 2012. American Geophysical Union. All Rights Reserved.


Fox N.,National Physical Laboratory United Kingdom | Kaiser-Weiss A.,University of Reading | Schmutz W.,Physikalisch Meteorologisches Observatorium Davos World Radiation Center | Thome K.,NASA | And 4 more authors.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2011

The Earth's climate is undoubtedly changing; however, the time scale, consequences and causal attribution remain the subject of significant debate and uncertainty. Detection of subtle indicators from a background of natural variability requires measurements over a time base of decades. This places severe demands on the instrumentation used, requiring measurements of sufficient accuracy and sensitivity that can allow reliable judgements to be made decades apart. The International System of Units (SI) and the network of National Metrology Institutes were developed to address such requirements. However, ensuring and maintaining SI traceability of sufficient accuracy in instruments orbiting the Earth presents a significant new challenge to the metrology community. This paper highlights some key measurands and applications driving the uncertainty demand of the climate community in the solar reflective domain, e.g. solar irradiances and reflectances/radiances of the Earth. It discusses how meeting these uncertainties facilitate significant improvement in the forecasting abilities of climate models. After discussing the current state of the art, it describes a new satellite mission, called TRUTHS, which enables, for the first time, high-accuracy SI traceability to be established in orbit. The direct use of a 'primary standard' and replication of the terrestrial traceability chain extends the SI into space, in effect realizing a 'metrology laboratory in space'. © 2011 The Royal Society.


Wacker S.,Physikalisch Meteorologisches Observatorium Davos World Radiation Center | Grobner J.,Physikalisch Meteorologisches Observatorium Davos World Radiation Center | Vuilleumier L.,Meteo Swiss
AIP Conference Proceedings | Year: 2013

We analyzed 15 years (1996-2010) of high quality observations of surface down-welling short-wave and longwave radiation from four Swiss sites. Down-welling short-wave radiation at Locarno-Monti has significantly increased by 9 Wm-2 in the 1996-2010 period, whereas no significant trends at the 95% confidence level are observed at the other three stations. In addition, long-wave radiation has not significantly changed in the corresponding period. The cloud radiative effect was determined using radiative transfer calculations for the cloud-free short-wave radiation and an empirical scheme for the cloud-free long-wave radiation. Results indicate that the net cloud radiative effect has decreased by up to 7.5 Wm-2 which implies a reduction in fractional cloud cover over the four Swiss sites. © 2013 AIP Publishing LLC.

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