Cosmic ray and solar energetic particle flux in paleomagnetospheres

Abstract

The geomagnetic field is part of the shield prohibiting energetic particles of solar and cosmic origin directly hitting the Earth surface. During geomagnetic polarity transitions the geomagnetic field strength significantly decreases with energetic particles having a much better access to the atmosphere and surface. To study in more detail the flux of energetic particles into the paleomagnetosphere we use a potential field approach to model the paleomagnetosphere which generalizes the parametric model of Voigt (1981) by taking into account a non-zero quadrupole moment of the core field. We study in particular the quadrupolar situation as a geomagnetic polarity transition is also characterized by a significant increase of non-dipolar contributions. Our model is used as a tool for tracing particle trajectories in such paleomagnetospheres and to assess variations of high-energy particle fluxes into the atmosphere. As a first application of the particle tracing scheme we determine cutoff latitudes and impact areas for different paleomagnetospheric configurations. For configurations with equivalent magnetic field strength or magnetic energy the impact area is very similar.

GEOMAGIA50.v3: 2. A new paleomagnetic database for lake and marine sediments

“…Furthermore, additional excursion-like behavior has been noted at distinctly different times, e.g., the Hilina Pali/Tianchi excursion (Coe et al 1978;Singer 2014;Singer et al 2014;Teanby et al 2002), occurring at approximately 17 ka . A better documentation of excursions is integral to a fuller understanding of geodynamo processes (Amit et al 2010;Olson et al 2011;Wicht 2005); the interaction between the geomagnetic field, the paleomagnetosphere, and space climate during times of extreme geomagnetic change (Constable and Korte 2006;Stadelmann et al 2010;Vogt et al 2007; and the dramatic modulation of cosmogenic isotopes such as 10 Be and 14 C, with associated implications for dating (e.g., Muscheler et al 2014). However, the physical origin of excursions is unclear, with multiple mechanisms proposed (see Amit et al 2010).…”

Magnetic Polarity Transitions and Biospheric Effects

“…This does not imply, however, that the absolute fluxes into such weak field surface areas are larger than today. The scaling relations presented by Stadelmann (2004) and Stadelmann et al (2010) for the sizes of magnetospheres generated by higher-order multipoles show that quadrupolar magnetospheres are significantly smaller than their dipolar counterparts even for identical surface field strengths. Hence both their trapping capacity and their means to energize particles during substorms are expected to be limited.…”

“…Stadelmann (2004), Vogt et al (2007), and Stadelmann et al (2010) introduced and used the concept of an impact area to describe the influence of energetic particles on the atmosphere. The impact area is defined as the surface area reached by particles of a given energy normalized to the total surface area of Earth.…”

“…This can be an empirically determined model such as described by Tsyganenko and Sitnov (2007) or a potential field model as used by Stadelmann et al (2010). As the exact topology of the paleofield is not known it is advisable to use a reduced field model to understand essential features of particle access to the atmosphere.…”

Estimating a planetary magnetic field with time-dependent global MHD simulations using an adjoint approach

“…Thereby, the tensor structure of the Cartesian representation becomes more complex for higher orders. For example, the quadrupole can be expressed by a symmetric, traceless matrix Q, which is defined by (e.g., Vogt and Glassmeier, 2000;Stadelmann et al, 2010) …”