The effect of a dynamic inner heliosheath thickness on cosmic-ray modulation

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Date
2015Author
Manuel, R.
Ferreira, S.E.S.
Potgieter, M.S.
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The time-dependent modulation of galactic cosmic rays in the heliosphere is studied over different polarity cycles by
computing 2.5 GV proton intensities using a two-dimensional, time-dependent modulationmodel. By incorporating
recent theoretical advances in the relevant transport parameters in the model, we showed in previous work that this
approach gave realistic computed intensities over a solar cycle. New in this work is that a time dependence of the
solar wind termination shock (TS) position is implemented in our model to study the effect of a dynamic inner
heliosheath thickness (the region between the TS and heliopause) on the solar modulation of galactic cosmic rays.
The study reveals that changes in the inner heliosheath thickness, arising from a time-dependent shock position,
does affect cosmic-ray intensities everywhere in the heliosphere over a solar cycle, with the smallest effect in the
innermost heliosphere. A time-dependent TS position causes a phase difference between the solar activity periods
and the corresponding intensity periods. The maximum intensities in response to a solarminimum activity period are
found to be dependent on the time-dependent TS profile. It is found that changing the width of the inner heliosheath
with time over a solar cycle can shift the time of when the maximum or minimum cosmic-ray intensities occur at
various distances throughout the heliosphere, but more significantly in the outer heliosphere. The time-dependent
extent of the inner heliosheath, as affected by solar activity conditions, is thus an additional time-dependent factor
to be considered in the long-term modulation of cosmic rays
URI
http://hdl.handle.net/10394/18439https://doi.org/10.1088/0004-637X/799/2/223
http://iopscience.iop.org/article/10.1088/0004-637X/799/2/223