Energetic Particle Influences on the Ozonosphere mediated by the Geomagnetic Field

Transcription

1 Energetic Particle Influences on the Ozonosphere mediated by the Geomagnetic Field M.-B. Kallenrode University of Osnabrück, Germany Joachim Vogt, Bertalan Zieger, Int. University Bremen Anja Stadelmann, TU Braunschweig Miriam Sinnhuber, U Bremen

2 Basic Idea geomagnetic field reversals often appear to be associated with extinction of plant species possible explanations: increased radiation damage (reduced screening of galactic cosmic rays) certain species of the microfauna are sensitive to the geomagnetic field catastrophe theory: external reason for both, field reversal and species extinction field reversals also can be associated with climate change we explore the scenario: reduced geomagnetic field increase in precipitating particles ozone depletion climate change? SPP Kolloquium

3 Scienctific Objective influence of solar energetic particles on atmospheric chemistry (ozone) long-term variations: solar activity geomagnetic field reversals consequences for the climate and the biosphere SPP Kolloquium

4 Is it Worth Studying this Effect? Contra: energy densities by 6 orders of magnitude lower than that of the electromagnetic radiation Pro: observable effects in large solar energetic particle events (SEPs) Quack, 2001 Jackman et al., 2001 SPP Kolloquium

5 Short or Long-Term Influence? 70 N 70 N 70 N Example at N75: top: HOx production, middle: NOx production, bottom: Ozone depletion. Resulting Time Scales: influences short (days) at high altitudes, duration increases with decreasing altitude, NOx is transported downwards, ozone depletion moves downwards. Questions: cumulative effects? particles precipitate everywhere? SPP Kolloquium

6 Ingredients: a particle source: the Sun (flares), space (galactic cosmic rays), the magnetosphere (magnetospheric particles). a magnetosphere: the planetary magnetic field, the ambient solar wind. both combined: particle transport through the magnetosphere. an atmosphere: the primary interaction: ionization, the secondary interaction: chemical processes. SPP Kolloquium

7 Particle Populations Different sources imply: different composition and spectrum, different temporal variations, different signal-to-noise ratios, different modifications by the geomagnetic field Particle sources: Solar Energetic Particles (SEPs): large amplitude, δ-like signal, more frequent at times of solar maximum, precipitate over the polar caps down to altitudes of about 15 km Galactic Cosmic Rays (GCRs): continuous background, slow variation by some 20% during the solar cycle, reach the ground almost everywhere Magnetospheric Particles (MPs): radiation belt particles released during geomagnetic storms SPP Kolloquium

8 The Active Sun solar activity: sunspots flares coronal mass ejections (CMEs) time scales: solar rotation 11-year solar cycle ~80-year Gleissberg cycle variability? SPP Kolloquium

9 Ionization During the Solar Cycle SPP Kolloquium

10 Atmospheric Consequences 70 N 70 N a few large events stick out during each solar cycle consequences of individual events can last a year or longer ozone depletion also is observed at lower latitudes transport solar cycle variation at about 50 N similar to the natural variation Sinnhuber 2002, priv. comm. SPP Kolloquium

11 The Present Day Sun is unusually Quiet Even During Solar Maximum Space age 1989 McCracken et al., 2000 SPP Kolloquium

12 The Magnetosphere Ermakov et al., 1997 solar wind and solar energetic particles precipitate over the polar caps. magnetospheric particles precipitate inside a ring around the polar cap. galactic cosmic rays precipitate globally but with reduced intensities at low latitudes. SPP Kolloquium

13 Particles in the Active Magnetosphere with increasing geomagnetic acivity particles of fixed energy precipitate at lower latitudes magnetospheric particles precipitate in the auroral oval (which moves south) Leske et al., 1999 SPP Kolloquium

14 The Changing Magnetosphere Two scenarios: rotation of dipole axis reduced dipole moment, multipoles taking over SPP Kolloquium

15 Magnetospheric Configuration and Particle Precipitation present day magnetosphere: red: solar energetic particles blue: magnetospheric particles SPP Kolloquium

16 Magnetospheric Configuration and Particle Precipitation strongly reduced dipole: SEP precipitation extends to lower latitudes no magnetospheric particles left multipole: more complex patterns SPP Kolloquium

17 Worst Case Scenario: Vanishing Field particles precipitate everywhere: no change over the poles particles at low latitudes stronger decrease at high latitudes equatorial variations almost unchanged Questions: why? (its counterintuitive) Ozone has radiative properties consequences for atmospheric circulation and climate? SPP Kolloquium

18 Magnetospheric Configuration and Particle Precipitation rotating dipole with dipole axis in equatorial plane: SEP precipitation rotates in an equatorial belt highly dynamic magnetosphere magnetospheric particles? SPP Kolloquium

19 Rotating Dipole Ozone loss [%] present day field rotated dipole SPP Kolloquium

20 Summary with decreasing dipole moment of the geomagnetic field the area of SEP precipitation increases the importance of magnetospheric particles decreases a shift of SEP precipitation patterns from high to low latitudes leads to reduced particle-related ozone depletion global precipitation leads to strong polar ozone depletion but only rather weak equatorial depletion SPP Kolloquium

21 Consequences for Biosphere and Climate increased UV radiation at the ground limited to high latitudes although bio-productivity in the polar oceans is high, the effect of increased UV probably is low (absorption in water) almost no higher organisms on land no direct radiation damage, although possibly increased rate of mutations strong polar ozone depletion might affect atmospheric circulation and climate more accurate models required, for instance HAMMONIA consequences for biosphere difficult to asses SPP Kolloquium