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Davos, Switzerland

Haberreiter M.,World Radiation Center | Haberreiter M.,University of Colorado at Boulder
Solar Physics | Year: 2011

We present spectral synthesis calculations of the solar extreme UV (EUV) in spherical symmetry carried out with the 'Solar Modeling in 3D' code. The calculations are based on one-dimensional atmospheric structures that represent a temporal and spatial mean of the chromosphere, transition region, and corona. The synthetic irradiance spectra are compared with the recent calibration spectrum taken with the EUV Variability Experiment during the Whole Heliospheric Interval. The good agreement between the synthetic and observed quiet Sun spectrum shows that the employed atmospheric structures are suitable for irradiance calculations. The validation of the quiet Sun spectrum for the present solar minimum is the first step toward the modeling of the EUV variations. © 2011 Springer Science+Business Media B.V.

Grobner J.,World Radiation Center
Metrologia | Year: 2012

A new reference radiometer for downwelling atmospheric longwave irradiance has been designed and built. The new infrared integrating sphere (IRIS) radiometer is designed to acquire measurements with a time constant of less than 1s. Based on a thorough characterization, the IRIS radiometer is able to measure longwave irradiance with an expanded uncertainty of 1.8Wm -2 and 2.4Wm -2 in the summer and winter seasons, respectively, which is equivalent to a temperature range between +15°C and -15°C for typical conditions at Davos, Switzerland. The long-term stability of the IRIS radiometer was determined over a one year period, yielding a calibration reproducibility in the laboratory of 0.5%. Outdoor measurements with four IRIS radiometers were performed during 13 clear nights in April 2011. The four radiometers measured atmospheric longwave irradiance with differences ranging from -1.1Wm -2 to +0.7Wm -2, which were well within their estimated uncertainties. © 2012 BIPM & IOP Publishing Ltd.

Frohlich C.,World Radiation Center
Contributions of the Astronomical Observatory Skalnate Pleso | Year: 2011

The last solar activity minimum during 2008/09 was unusually long and with extended periods without sunspots. During this period the total solar irradiance (TSI) was much lower than during the previous minima and no solar activity proxies show similarly low values. Proxy models for TSI use a measure for the darkening of sunspots, the so-called photometric sunspot index (PSI) and for the brightening of faculae and network a chromospheric index. Because none of these can explain the low TSI, a further component is needed, which describes the trend between minima due to a still controversially discussed mechanism. A new algorithm for the calculation of PSI is described which uses individual factors for the different observing stations and a better representation of the size-dependent contrast of spots. The proxy model based on the new PSI, the long- and short-term MgII index and a trend based on the minima values of the open field explains almost 85% of the variance of TSI over the last three solar cycles. Moreover, it confirms the factor of ≈ 4 between the observed trend of TSI and those of the chromospheric and other solar activity indices.

Kretzschmar M.,CNRS Physics Laboratory | De Wit T.D.,CNRS Physics Laboratory | Schmutz W.,World Radiation Center | Mekaoui S.,Royal Meteorological Institute of Belgium | And 2 more authors.
Nature Physics | Year: 2010

Flares are powerful bursts of energy released by relatively poorly understood processes that take place in the atmospheres of stars1. However, although solar flares, from our own Sun, are the most energetic events in the solar system, in comparison to the total output of the Sun they are barely noticeable 2,3. Consequently, the total amount of radiant energy they generate is not precisely known, and their potential contribution to variations in the total solar irradiance 4 incident on the Earth has so far been overlooked. In this work, we identify a measurable signal from relatively moderate solar flares in total solar irradiance data. We find that the total energy radiated by flares exceeds by two orders of magnitude the flare energy radiated in the soft-X-ray domain only, indicating a major contribution in the visible domain. These results have implications for our understanding of solar-flare activity and the variability of our star. © 2010 Macmillan Publishers Limited. All rights reserved.

Calisto M.,ETH Zurich | Usoskin I.,University of Oulu | Rozanov E.,ETH Zurich | Rozanov E.,World Radiation Center | Peter T.,ETH Zurich
Atmospheric Chemistry and Physics | Year: 2011

This study investigates the influence of the Galactic Cosmic Rays (GCRs) on the atmospheric composition, temperature and dynamics by means of the 3-D Chemistry Climate Model (CCM) SOCOL v2.0. Ionization rates were parameterized according to CRAC:CRII (Cosmic Ray induced Cascade: Application for Cosmic Ray Induced Ionization), a detailed state-of-the-art model describing the effects of GCRs in the entire altitude range of the CCM from 0-80 km. We find statistically significant effects of GCRs on tropospheric and stratospheric NOx, HOx, ozone, temperature and zonal wind, whereas NOx, HOx and ozone are annually averaged and the temperature and the zonal wind are monthly averaged. In the Southern Hemisphere, the model suggests the GCR-induced NOx increase to exceed 10 % in the tropopause region (peaking with 20 % at the pole), whereas HOx is showing a decrease of about 3 % caused by enhanced conversion into HNO 3. As a consequence, ozone is increasing by up to 3 % in the relatively unpolluted southern troposphere, where its production is sensitive to additional NOx from GCRs. Conversely, in the northern polar lower stratosphere, GCRs are found to decrease O3 by up to 3 %, caused by the additional heterogeneous chlorine activation via ClONO2 + HCl following GCR-induced production of ClONO2. There is an apparent GCR-induced acceleration of the zonal wind of up to 5 m s−1 in the Northern Hemisphere below 40 km in February, and a deceleration at higher altitudes with peak values of 3 m s−1 around 70 km altitude. The model also indentifies GCR-induced changes in the surface air, with warming in the eastern part of Europe and in Russia (up to 2.25 K for March values) and cooling in Siberia and Greenland (by almost 2 K). We show that these surface temperature changes develop even when the GCR-induced ionization is taken into account only above 18 km, suggesting that the stratospherically driven strengthening of the polar night jet extends all the way down to the Earth's surface. © 2011 Author(s).

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