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Astron. Astrophys. 316, 519-527 (1996)

Ulysses COSPIN/LET: latitudinal gradients of anomalous cosmic ray O, N and Ne

K.J. Trattner1,*, R.G. Marsden1, V. Bothmer1, T.R. Sanderson1, K.-P. Wenzel1, B. Klecker2, and D. Hovestadt2

1 Space Science Department of ESA, Postbus 299, 2200 AG Noordwijk, The Netherlands (trattner@estsck.estec.esa.nl)
2 Max-Planck-Institut für extraterrestrische Physik, Postfach 1603, D-85740 Garching, Germany

Received 23 February 1996 / Accepted 20 May 1996

Abstract. A key goal of the Ulysses mission is the measurement of the latitudinal gradient of the Anomalous Cosmic Ray (ACR) component. Earlier studies using data from the COSPIN/LET experiment on board Ulysses together with in-ecliptic data from the HILT instrument on SAMPEX have shown a small ( img1.gif 2% per degree) positive latitudinal gradient for anomalous oxygen in the energy range 8 to 16 MeV/n. This result is consistent with the effects of curvature and gradient drifts in the heliospheric magnetic field for the current polarity configuration: positively charged particles are expected to flow down to the heliographic equator from the polar regions.

In this paper we extend our previous work and include two additional ACR species, nitrogen (4 to 20 MeV/n) and neon (4 to 30 MeV/n). We also present our latest results on the ACR oxygen latitudinal gradient over an extended energy range (4 to 20 MeV/n). The period covered for all three species include the Ulysses south polar pass, the rapid transit from the south pole to the ecliptic and a significant portion of the climb to high northern latitudes. For all species and energy ranges the latitudinal gradients are between 1% and 2%, consistent with earlier studies, and show a slight tendency to larger gradients for higher magnetic rigidity.

Key words: interstellar medium: general - cosmic rays - interplanetary medium

* Present address: Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK

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