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Molkov S.,Russian Academy of Sciences | Lutovinov A.,Moscow Institute of Physics and Technology | Falanga M.,International Space Science Institute ISSI | Tsygankov S.,University of Turku | Bozzo E.,University of Geneva
Monthly Notices of the Royal Astronomical Society | Year: 2017

In this paper, we investigated the long-term evolution of the pulse period in the high-mass X-ray binary LMC X-4 by taking advantage of more than 43 yr of measurements in the X-ray domain. Our analysis revealed for the first time that the source is displaying near-periodical variations of its spin period on a time-scale of roughly 6.8 yr, making LMC X-4 one of the known binary systems showing remarkable long-term spin torque reversals. We discuss different scenarios to interpret the origin of these torque reversals. © 2016 The Authors.


Wilkinson D.M.,Liverpool John Moores University | Wilkinson D.M.,Swiss Federal Institute of forest | Wilkinson D.M.,Ecole Polytechnique Federale de Lausanne | Koumoutsaris S.,International Space Science Institute ISSI | And 4 more authors.
Journal of Biogeography | Year: 2012

Aim We investigate the long-standing question of whether the small size of microbes allows most microbial species to colonize all suitable sites around the globe or whether their ranges are limited by opportunities for dispersal. In this study we use a modelling approach to investigate the effect of size on the probability of between-continent dispersal using virtual microorganisms in a global model of the Earth's atmosphere. Location Global. Methods We use a computer model of global atmospheric circulation to investigate the effect of microbe size (effective diameters of 9, 20, 40 and 60μm) on the probability of aerial dispersal. Results We found that for smaller microbes, once airborne, dispersal is remarkably successful over a 1-year period. The most striking results are the extensive within-hemisphere distribution of virtual microbes of 9 and 20μm diameter and the lack of dispersal between the Northern and Southern Hemispheres during the year-long time-scale of our simulations. Main conclusions Above a diameter of 20μm wind dispersal of virtual microbes between continents becomes increasingly unlikely, and it does not occur at all (within our simulated 1-year period) for those of 60μm diameter. Within our simulation, the success of small microbes in long-distance dispersal is due both to their greater abundance and to their longer time in the atmosphere - once airborne - compared with larger microbes. © 2011 Blackwell Publishing Ltd.


Dieng H.B.,CNRS Geophysical Research and Oceanographic Laboratory | Cazenave A.,CNRS Geophysical Research and Oceanographic Laboratory | Cazenave A.,International Space Science Institute ISSI | Von Schuckmann K.,University of Toulon | And 2 more authors.
Ocean Science | Year: 2015

Based on the sea level budget closure approach, this study investigates the residuals between observed global mean sea level (GMSL) and the sum of components (steric sea level and ocean mass) for the period January 2005 to December 2013. The objective is to identify the impact of errors in one or several components of the sea level budget on the residual time series. This is a key issue if we want to constrain missing contributions such as the contribution to sea level rise from the deep ocean (depths not covered by observations). For that purpose, we use several data sets as processed by different groups: six altimetry products for the GMSL, four Argo products plus the ORAS4 ocean reanalysis for the steric sea level and three GRACE-based ocean mass products. We find that over the study time span, the observed differences in trend of the residuals of the sea level budget equation can be as large as ∼ 0.55 mm yr-1 (i.e., ∼ 17 % of the observed GMSL rate of rise). These trend differences essentially result from differences in trends of the GMSL time series. Using the ORAS4 reanalysis (providing complete geographical coverage of the steric sea level component), we also show that lack of Argo data in the Indonesian region leads to an overestimate of the absolute value of the residual trend by about 0.25 mm yr-1. Accounting for this regional contribution leads to closure of the sea level budget, at least for some GMSL products. At short timescales (from sub-seasonal to interannual), residual anomalies are significantly correlated with ocean mass and steric sea level anomalies (depending on the time span), suggesting that the residual anomalies are related to errors in both GRACE-based ocean mass and Argo-based steric data. Efforts are needed to reduce these various sources of errors before using the sea level budget approach to estimate missing contributions such as the deep ocean heat content. © Author(s) 2015. CC Attribution 3.0 License.


Bozzo E.,University of Geneva | Pavan L.,University of Geneva | Ferrigno C.,University of Geneva | Falanga M.,International Space Science Institute ISSI | And 4 more authors.
Astronomy and Astrophysics | Year: 2012

We present the results of the XMM-Newton observations of five hard X-ray emitters: IGR J08262-3736, IGR J17354-3255, IGR J16328-4726, SAX J1818.6-1703, and IGR J17348-2045. The first source is a confirmed supergiant high mass X-ray binary, the following two are candidates supergiant fast X-ray transients, SAX J1818.6-1703 is a confirmed supergiant fast X-ray transient and IGR J17348-2045 is one of the still unidentified objects discovered with INTEGRAL. The XMM-Newton observations permitted the first detailed soft X-ray spectral and timing study of IGR J08262-3736 and provided further support in favor of the association of IGR J17354-3255 and IGR J16328-4726 with the supergiant fast X-ray transients. SAX J1818.6-1703 was not detected by XMM-Newton, thus supporting the idea that this source reaches its lowest X-ray luminosity (≈ 10 32 erg s -1) around apastron. For IGR J17348-2045 we identified for the first time the soft X-ray counterpart and proposed the association with a close-by radio object, suggestive of an extragalactic origin. © 2012 ESO.


Calisto M.,International Space Science Institute ISSI | Usoskin I.,University of Oulu | Rozanov E.,Physical Meteorological Observatory | Rozanov E.,ETH Zurich
Environmental Research Letters | Year: 2013

This study investigates the influence of a major solar proton event (SPE) similar to the Carrington event of 1-2 September 1859 by means of the 3D chemistry climate model (CCM) SOCOL v2.0. Ionization rates were parameterized according to CRAC:CRII (Cosmic Ray-induced Atmospheric Cascade: Application for Cosmic Ray Induced Ionization), a detailed state-of-the-art model describing the effects of SPEs in the entire altitude range of the CCM from 0 to 80 km. This is the first study of the atmospheric effect of such an extreme event that considers all the effects of energetic particles, including the variability of galactic cosmic rays, in the entire atmosphere. We assumed two scenarios for the event, namely with a hard (as for the SPE of February 1956) and soft (as for the SPE of August 1972) spectrum of solar particles. We have placed such an event in the year 2020 in order to analyze the impact on a near future atmosphere. We find statistically significant effects on NOx, HO x, ozone, temperature and zonal wind. The results show an increase of NOx of up to 80 ppb in the northern polar region and an increase of up to 70 ppb in the southern polar region. HOx shows an increase of up to 4000%. Due to the NOx and HOx enhancements, ozone reduces by up to 60% in the mesosphere and by up to 20% in the stratosphere for several weeks after the event started. Total ozone shows a decrease of more than 20 DU in the northern hemisphere and up to 20 DU in the southern hemisphere. The model also identifies SPE induced statistically significant changes in the surface air temperature, with warming in the eastern part of Europe and Russia of up to 7 K for January. © 2013 IOP Publishing Ltd.


Calisto M.,International Space Science Institute ISSI | Verronen P.T.,Finnish Meteorological Institute | Rozanov E.,Physical Meteorological Observatory | Rozanov E.,ETH Zurich | Peter T.,ETH Zurich
Atmospheric Chemistry and Physics | Year: 2012

We have modeled the atmospheric impact of a major solar energetic particle event similar in intensity to what is thought of the Carrington Event of 1-2 September 1859. Ionization rates for the August 1972 solar proton event, which had an energy spectrum comparable to the Carrington Event, were scaled up in proportion to the fluence estimated for both events. We have assumed such an event to take place in the year 2020 in order to investigate the impact on the modern, near future atmosphere. Effects on atmospheric chemistry, temperature and dynamics were investigated using the 3-D Chemistry Climate Model SOCOL v2.0. We find significant responses of NOx, HOx, ozone, temperature and zonal wind. Ozone and NOx have in common an unusually strong and long-lived response to this solar proton event. The model suggests a 3-fold increase of NOx generated in the upper stratosphere lasting until the end of November, and an up to 10-fold increase in upper mesospheric HOx. Due to the NOx and HOx enhancements, ozone reduces by up to 60-80% in the mesosphere during the days after the event, and by up to 20-40% in the middle stratosphere lasting for several months after the event. Total ozone is reduced by up to 20 DU in the Northern Hemisphere and up to 10 DU in the Southern Hemisphere. Free tropospheric and surface air temperatures show a significant cooling of more than 3 K and zonal winds change significantly by 3-5 m sĝ̂'1 in the UTLS region. In conclusion, a solar proton event, if it took place in the near future with an intensity similar to that ascribed to of the Carrington Event of 1859, must be expected to have a major impact on atmospheric composition throughout the middle atmosphere, resulting in significant and persistent decrease in total ozone. © 2012 Author(s).


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.


Calisto M.,International Space Science Institute ISSI | Folini D.,ETH Zurich | Wild M.,ETH Zurich | Bengtsson L.,International Space Science Institute ISSI
Annales Geophysicae | Year: 2014

In this paper, radiative fluxes for 10 years from 11 models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) and from CERES satellite observations have been analyzed and compared. Under present-day conditions, the majority of the investigated CMIP5 models show a tendency towards a too-negative global mean net cloud radiative forcing (NetCRF) as compared to CERES. A separate inspection of the long-wave and shortwave contribution (LWCRF and SWCRF) as well as cloud cover points to different shortcomings in different models. Models with a similar NetCRF still differ in their SWCRF and LWCRF and/or cloud cover. Zonal means mostly show excessive SWCRF (too much cooling) in the tropics between 20° S and 20° N and in the midlatitudes between 40 to 60° S. Most of the models show a too-small/too-weak LWCRF (too little warming) in the subtropics (20 to 40° S and N). Difference maps between CERES and the models identify the tropical Pacific Ocean as an area of major discrepancies in both SWCRF and LWCRF. The summer hemisphere is found to pose a bigger challenge for the SWCRF than the winter hemisphere. The results suggest error compensation to occur between LWCRF and SWCRF, but also when taking zonal and/or annual means. Uncertainties in the cloud radiative forcing are thus still present in current models used in CMIP5. © 2014 Author(s) CC Attribution 3.0 License.


Bengtsson L.,University of Reading | Hodges K.I.,University of Reading | Koumoutsaris S.,International Space Science Institute ISSI | Zahn M.,University of Reading | Keenlyside N.,Leibniz Institute of Marine Science
Tellus, Series A: Dynamic Meteorology and Oceanography | Year: 2011

We have examined the atmospheric water cycle of both Polar Regions, polewards of 60°N and 60°S, using the ERA-Interim reanalysis and high-resolution simulations with the ECHAM5 model for both the present and future climate based on the IPCC, A1B scenario. The annual precipitation in ERA-Interim amounts to ~17000 km 3 and is more or less the same in the Arctic and the Antarctic, but it is composed differently. In the Arctic the annual evaporation is ~8000 km 3 but ~3000 km 3 less in the Antarctica where the net horizontal transport is correspondingly larger. The net water transport of the model is more intense than in ERA-Interim, in the Arctic the difference is 2.5% and in the Antarctic it is 6.2%. Precipitation and net horizontal transport in the Arctic has a maximum in August and September. Evaporation peaks in June and July. The seasonal cycle is similar in Antarctica with the highest precipitation in the austral autumn. The largest net transport occurs at the end of the major extra-tropical storm tracks in the Northern Hemisphere such as the eastern Pacific and eastern north Atlantic. The variability of the model is virtually identical to that of the re-analysis and there are no changes in variability between the present climate and the climate at the end of the 21st century when normalized with the higher level of moisture. The changes from year to year are substantial with the 20- and 30-year records being generally too short to identify robust trends in the hydrological cycle. In the A1B climate scenario the strength of the water cycle increases by some 25% in the Arctic and by 19% in the Antarctica, as measured by annual precipitation. The increase in the net horizontal transport is 29% and 22%, respectively, and the increase in evaporation correspondingly less. The net transport follows closely the Clausius-Clapeyron relation. There is a minor change in the annual cycle of the Arctic atmospheric water cycle with the maximum transport and precipitation occurring later in the year. There is a small imbalance of some 4-6% between the net transport and precipitation minus evaporation. We suggest that this is mainly due to the fact that the transport is calculated from instantaneous six hourly data while precipitation and evaporation is accumulated over a 6-h period. The residual difference is proportionally similar for all experiments and hardly varies from year to year. © 2011 The Authors Tellus A © 2011 John Wiley & Sons A/S.


Bini D.,CNR Institute of Neuroscience | Bini D.,University of Rome La Sapienza | Falanga M.,International Space Science Institute ISSI | Geralico A.,University of Rome La Sapienza | Stella L.,National institute for astrophysics
Classical and Quantum Gravity | Year: 2012

The motion of matter immersed in a radiation field is affected by a radiation drag, as a result of scattering or absorption and re-emission. The resulting friction-like drag, also known as the Poynting-Robertson effect, has been recently studied in the general relativistic background of the Schwarzschild and Kerr metric, under the assumption that all photons in the radiation field possess the same angular momentum. We calculate here the signal produced by an emitting point-like specific source moving in a Schwarzschild spacetime under the influence of such a radiation field. We derive the flux, redshift factor and solid angle of the hot spot as a function of (coordinate) time, as well as the time-integrated image of the hot spot as seen by an observer at infinity. The results are then compared with those for a spot moving on a circular geodesic in a Schwarzschild metric. © 2012 IOP Publishing Ltd.

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