Time filter

Source Type

Bengtsson L.,University of Reading | Bengtsson L.,International Space Science Institute
Tellus, Series B: Chemical and Physical Meteorology | Year: 2013

The climate of the Earth, like planetary climates in general, is broadly controlled by solar irradiation, planetary albedo and emissivity as well as its rotation rate and distribution of land (with its orography) and oceans. However, the majority of climate fluctuations that affect mankind are internal modes of the general circulation of the atmosphere and the oceans. Some of these modes, such as El Niño-Southern Oscillation (ENSO), are quasi-regular and have some longer-term predictive skill; others like the Arctic and Antarctic Oscillation are chaotic and generally unpredictable beyond a few weeks. Studies using general circulation models indicate that internal processes dominate the regional climate and that some like ENSO events have even distinct global signatures. This is one of the reasons why it is so difficult toseparate internal climate processes from external ones caused, for example, by changes in greenhouse gases and solar irradiation. However, the accumulation of the warmest seasons during the latest two decades is lending strong support to the forcing of the greenhouse gases. As models are getting more comprehensive, they show a gradually broader range of internal processes including those on longer time scales, challenging the interpretation of the causes of past and present climate events further. © 2013 L. Bengtsson. Source

Von Steiger R.,International Space Science Institute | Von Steiger R.,University of Bern | Zurbuchen T.H.,University of Michigan
Journal of Geophysical Research: Space Physics | Year: 2011

During its nearly 19-year mission, Ulysses pioneered novel measurements of the three-dimensional heliosphere and particularly in situ observations of high-latitude solar wind from polar coronal holes (PCHs). Winds from PCHs exhibit constant elemental abundances to within the limits of the measurements, indicative of the fact that such winds truly provide a ground state of solar wind composition. However, these solar wind streams show long-term variability in the composition of ionic charge states frozen into the low corona. The C and O freeze-in temperatures measured in high-latitude solar wind have decreased ∼10% as compared to the previous solar minimum and are now around 0.87 and 1.01 MK, respectively. The ionization states of Si and Fe also exhibit a substantial cooling with a reduction of 0.4 and 0.5 charge states, respectively. We show that these observations are indicative of an overall decrease of coronal temperature, forming a trend toward cooler PCH temperature persisting for over 14 years. We support these observations with a detailed and comprehensive description of the data analysis processes relevant for Ulysses SWICS and similar instruments. Copyright 2011 by the American Geophysical Union. Source

Koumoutsaris S.,International Space Science Institute | Bey I.,ETH Zurich
Atmospheric Chemistry and Physics | Year: 2012

Quantifying trends in surface ozone concentrations is critical for assessing pollution control strategies. Here we use observations and results from a global chemical transport model to examine the trends (1991-2005) in daily maximum 8-h average concentrations in summertime surface ozone at rural sites in Europe and the United States (US). We find a decrease in observed ozone concentrations at the high end of the probability distribution at many of the sites in both regions. The model attributes these trends to a decrease in local anthropogenic ozone precursors, although simulated decreasing trends are overestimated in comparison with observed ones. The low end of observed distribution show small upward trends over Europe and the western US and downward trends in Eastern US. The model cannot reproduce these observed trends, especially over Europe and the western US. In particular, simulated changes between the low and high end of the distributions in these two regions are not significant. Sensitivity simulations indicate that emissions from far away source regions do not affect significantly summer ozone trends at both ends of the distribution in both Europe and US. Possible reasons for discrepancies between observed and simulated trends are discussed. © 2012 Author(s). CC Attribution 3.0 License. Source

Balogh A.,International Space Science Institute | Balogh A.,Imperial College London
Space Science Reviews | Year: 2010

The nature and diversity of the magnetic properties of the planets have been investigated by a large number of space missions over the past 50 years. It is clear that without the magnetic field measurements that have been carried out in the vicinity of all the planets, the state of their interior and their evolution since their formation would not be understood even though questions remain about how the different planetary dynamos (in six of the eight planets) work. This paper describes the motivation for making magnetic field measurements, the instrumentation that has been used and many of the missions that carried out the pioneering observations. Emphasis is given to the historically important early missions even if the results from these have been in some cases bettered by later missions. © 2010 Springer Science+Business Media B.V. Source

Strub P.,Max Planck Institute for Solar System Research | Kruger H.,Max Planck Institute for Solar System Research | Sterken V.J.,International Space Science Institute | Sterken V.J.,Max Planck Institute for Nuclear Physics
Astrophysical Journal | Year: 2015

The Ulysses spacecraft provided the first opportunity to identify and study interstellar dust (ISD) in situ in the solar system between 1992 and 2007. Here we present the first comprehensive analysis of the ISD component in the entire Ulysses dust data set. We analyzed several parameters of the ISD flow in a time-resolved fashion: flux, flow direction, mass index, and flow width. The general picture is in agreement with a time-dependent focusing/defocusing of the charged dust particles due to long-term variations of the solar magnetic field throughout a solar magnetic cycle of 22 years. In addition, we confirm a shift in dust direction of 50° ± 7° in 2005, along with a steep, size-dependent increase in flux by a factor of 4 within 8 months. To date, this is difficult to interpret and has to be examined in more detail by new dynamical simulations. This work is part of a series of three papers. This paper concentrates on the time-dependent flux and direction of the ISD. In a companion paper we analyze the overall mass distribution of the ISD measured by Ulysses, and a third paper discusses the results of modeling the flow of the ISD as seen by Ulysses. © 2015. The American Astronomical Society. All rights reserved.. Source

Discover hidden collaborations