The heliospheric modulation of cosmic ray protons during increased solar activity: effects of the position of the solar wind termination shock and of the heliopause

U W Langner,M S Potgieter

doi:10.5194/angeo-23-1499-2005

U W Langner, M S Potgieter

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https://doi.org/10.5194/angeo-23-1499-2005

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Abstract. The effects on the modulation of cosmic ray protons of different positions for the solar wind termination shock and for the heliopause are illustrated for moderate solar maximum conditions. This is done with a numerical model which includes diffusive termination shock acceleration, a heliosheath and drifts. The modulation is computed for the heliospheric equatorial plane and at 35° heliolatitude and for both magnetic polarity cycles of the Sun. It was found that the differences between the modulation for the two solar polarity cycles are less significant at a heliolatitude of 35° than in the equatorial plane. The modulation for the different heliopause positions are qualitatively similar, although there are clear quantitative differences which should be observable with the two Voyager spacecraft in the outer heliosphere. It is illustrated that the motion of the termination shock from 90 AU to 100 AU, with the heliopause fixed at 120 AU, is not crucially important to global modulation. What is of primary importance is the location of the heliopause. It can also be concluded from the results that significant asymmetric modulation is to be expected between the up-wind and down-wind directions of the heliosphere but this may become measureable only when spacecraft move beyond the termination shock into the heliosheath. Keywords. Interplanetary physics (Cosmic rays; Heliopause and solar wind termination) – Space plasma physics (Transport processes)

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The effects of changing the position of the solar wind termination shock (TS) and the position of the heliopause on the modulation of cosmic ray protons were illustrated for solar minimum conditions by Langner and Potgieter (2005)
The purpose of this work is to extend the work of Langner and Potgieter (2005), and the work done by Ferreira et al (2001) for cosmic ray electrons, in studying the effects on the modulation of cosmic ray protons of varying TS and heliopause positions, in particular during moderate solar maximum conditions, and for the up-wind and down-wind directions with respect to the interstellar wind
The local interstellar spectrum (LIS) is specified at the heliopause, first assumed at rH P =120 AU and with rHP =160 AU

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The effects of changing the position of the solar wind termination shock (TS) and the position of the heliopause on the modulation of cosmic ray protons were illustrated for solar minimum conditions by Langner and Potgieter (2005). It is not expected that the TS position will be more than 90– 100 AU away from the Sun towards the tail of the heliosphere so that the assumption of a spherical TS is still considered quite reasonable. The position of the heliopause, on the other hand, is less certain, probably at least 30–50 AU beyond the TS in the nose direction, but significantly further away in the tail direction. This is because the geometry of the heliosphere should be affected by the relative motion of the heliosphere through the local interstellar medium This is because the geometry of the heliosphere should be affected by the relative motion of the heliosphere through the local interstellar medium (e.g. Scherer and Fahr, 2003; Zank and Muller, 2003)

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