Time-dependent transport of energetic particles in the atmosphere, magnetosphere and heliosphere, reconstruction of the long-term flux heliospheric environment, atmospheric ionisation, production of neutrons and cosmogenic isotopes

• Applicants: Privatdozent Dr. Horst Fichtner; Professor Dr. Bernd Heber
• Subject Area: Atmospheric Science
• Term: from 2005 to 2013
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5453810

• Final Report Year: 2013

Final Report Abstract

While the solar-terrestrial relationship has been established to be important for our modern society, that relies on sensitive electronic devices, the importance of the interstellar terrestrial relationship for the Earth environment is discussed seriously only since the 1990's. While most studies are based on correlations with proxies of the Earth climate, the goal of our project was to estimate and even quantify the variation of energetic particle intensities in the Earth's atmosphere caused by Galactic Cosmic Rays. These particles interact with the Earth's atmosphere and produce cosmogenic isotopes and ionise the atmosphere. We focused on the understanding of the long-term variation of the Be10 production rate as the last link in a long chain of processes ranging from galactic to terrestrial scales. This rate is determined by the physics of energetic particles in the atmosphere. We found that only due to the uncertainty of the different cross-sections the resulting uncertainty of the production rate is in the order of 25 percent. The radiation (energetic particle) field in the atmosphere consisting mainly of secondaries has been determined using a Monte-Carlo Simulation. A comparison with measurements results in a similar uncertainty for the flux of secondary particles. The magnetosphere acts as a magnetic filter, which means that the lowest energy for a 'primary' cosmic ray hitting the Earth's atmosphere depends on the geomagnetic position. As a consequence we have shown that a detailed knowledge of the Earth magnetic field is essential to understand the variation of ground based measurements. The intensity of cosmic rays outside of the Earth magnetosphere depends on the local interstellar spectrum and its modulation in the heliosphere, respectively. These topics are tied close together and cannot be discussed separately, since the local interstellar spectra had not been measured in-situ. Using the force-field solution we could demonstrate that all proposed models are able to reproduce observations close to Earth with different modulation parameters. These parameters, however, depend on numerous physical processes and boundary conditions. One of them is the dynamical heliosphere. In contrast to last millennium propagation models, hybrid models (combining plasma and propagation models) reveal the importance of the outer heliosphere beyond the termination shock for the local interstellar spectrum and long-term modulation. In addition, using the full description of the particle transport in the heliosphere, we proposed a criterion to distinguish between cosmic ray and photon induced variations of parameters describing the Earth's climate: determining the importance of the Hale cycle (22 years, cosmic rays) relative to the Schwabe cycle (11 years, photons) in such parameters. From our research project the following conclusion can be given: in order to model the variation of the cosmic ray intensities as imprinted in terrestrial archives it is mandatory to achieve a detailed knowledge of (i) item the local interstellar spectra of all elements of interest, (ii) the galactic cosmic ray modulation volume and the modulation processes in the different regions of the heliosphere, (iii) the Earth's magnetic field and its variation over the last million years in structure as well as magnitude, (iv) the secondary particle energy spectra and their modelling in the Earth atmosphere, and (v) the cross-sections for the production of cosmogenic isotopes. Although already a major step forward has been achieved in our understanding the radiation field causing the different cosmic ray archives, further investigations are needed, namely of the atmospheric transport of these tracers and its ability of reflecting the global or local radiation environment.

Publications

• A criterion to discriminate between solar and cosmic ray forcing of the terrestrial climate. Atmos. Chem. Phys. Discuss., 61:10811–10836, 2006
  H. Fichtner, K. Scherer, and B. Heber
  
• Energetic particles in the atmosphere: A monte-carlo simulation. Adv. Space Res., 37:1597–1601, 2006
  J. Schröter, B. Heber, F. Steinhilber, and M. B. Kallenrode
  
• Interstellar-terrestrial relations: Variable cosmic environments, the dynamic heliosphere, and their imprints on terrestrial archives and climate. Space Sci. Rev., 127:327–465, 2006
  K. Scherer, H. Fichtner, T. Borrmann, J. Beer, L. Desorgher, E. Flükiger, H.-J. Fahr, S. E. S. Ferreira, U. W. Langner, M. S. Potgieter, B. Heber, J. Masarik, N. Shaviv, and J. Veizer
  
• Solar and heliospheric modulation of galactic cosmic rays. Space Sci. Rev., 125:81–93, 2006
  B. Heber, H. Fichtner, and K. Scherer
  
• Are anomalous cosmic rays the main contribution to the low-energy galactic cosmic ray spectrum? Astrophys. J., 680:L105–L108, 2008
  K. Scherer, H. Fichtner, S. E. S. Ferreira, I. Büsching, and M. S. Potgieter
  
• Cosmic ray flux at the earth in a variable heliosphere. Adv. Space Res., 41:1171–1176, 2008
  K. Scherer, H. Fichtner, B. Heber, S. E. S. Ferreira, and M. S. Potgieter.
  
• Latitudinal gradients of galactic cosmic rays during the 2007 solar minimum. Astrophys. J., 689:1443–1447, 2008
  B. Heber, J. Gieseler, P. Dunzlaff, R. Gómez-Herrero, A. Klassen, R. Müller-Mellin, R. A. Mewaldt, M. S. Potgieter, and S. E. S. Ferreira
  
• Observations of recurrent cosmic ray decreases during solar cycles 22 and 23. Annales Geophysicae, 26:3127–3138, 2008
  P. Dunzlaff, B. Heber, A. Kopp, O. Rother, R. Müller-Mellin, A. Klassen, R. Gómez-Herrero, and R. Wimmer-Schweingruber
  
• A new trend in forecasting solar radiation hazards. Space Weather, 70:5001, 2009
  A. Posner, S. Guetersloh, B. Heber, and O. Rother
  
• Modulation of galactic cosmic ray protons and electrons during an unusual solar minimum. Astrophys. J., 699:1956–1963, 2009
  B. Heber, A. Kopp, J. Gieseler, R. Müller-Mellin, H. Fichtner, K. Scherer, M. S. Potgieter, and S. E. S. Ferreira
  
• Temporal and spatial evolution of the solar energetic particle event on 20 january 2005 and resulting radiation doses in aviation. J. Geophys. Res., 114(A13):8104, 2009
  D. Matthiä, B. Heber, G. Reitz, M. Meier, L. Sihver, T. Berger, and K. Herbst
  
• Comparison of different analytic heliospheric magnetic field configurations and their significance for the particle injection at the termination shock. Astron. Astrophys., 521:A1, 2010
  K. Scherer, H. Fichtner, F. Effenberger, R. A. Burger, and T. Wiengarten
  
• On the definition and calculation of a generalised mcilwain parameter. Astrophysics and Space Sciences Transactions, 6:9–17, 2010
  J. Pilchowski, A. Kopp, K. Herbst, and B. Heber
  
• On the importance of the local interstellar spectrum for the solar modulation parameter. J. Geophys. Res., 115(A14), 2010
  K. Herbst, A. Kopp, B. Heber, F. Steinhilber, H. Fichtner, K. Scherer, and D. Matthiä
  
• 10be production in the atmosphere by galactic cosmic rays. Space Sci. Rev., page 290, 2011
  D. Matthiä, K. Herbst, B. Heber, T. Berger, and G. Reitz
  
• Cosmic rays through the solar hale cycle. Space Sci. Rev., page 137, 2011
  B. Heber
  
• On cosmic ray modulation beyond the heliopause: Where is the modulation boundary? Astrophys. J., 735:128, 2011
  K. Scherer, H. Fichtner, R. D. Strauss, S. E. S. Ferreira, M. S. Potgieter, and H.-J. Fahr
  
• Solar activity, the heliosphere, cosmic rays and their impact on the earth’s atmosphere. In F.-J. Lübken, editor, Climate And Weather of the Sun-Earth System (CAWSES): Highlights from a priority program, pages 383–408. Springer, Springer, Dordrecht, The Netherlands, 2013
  H. Fichtner, B. Heber, K. Herbst, A. Kopp, and K. Scherer