Amplitude evolution and rigidity dependence of the 26-day recurrent cosmic ray decreases - COSPIN/KET results

• Published in: Journal of Geophysical Research 1999-12, Vol.104 (A12), p.28
• Main Authors: Paizis, C, Heber, B, Ferrando, P, Raviart, A, Falconi, B, Marzolla, S, Potgieter, M S, Bothmer, V, Kunow, H, Mueller-Mellin, R
• Format: Article
• Language: English
• ISSN: 0148-0227

In the time interval extending from July 1992 to July 1994, Ulysses climbed from 10 deg S heliographic latitude up to over 70S. During this time lapse, solar minimum conditions were gradually approached, which, in turn, led to stable and long-lasting corotating interaction regions (CIRs). The corotating particle events observed during this period, associated with about 30 registered CIRs, offer a unique opportunity to probe the 3D structures of the heliosphere. In this work we use data from the Cosmic Ray and Solar Particle Investigation Kiel Electron Telescope (COSPIN/KET) instrument on board Ulysses to study the amplitude evolution of the 26-day recurrent cosmic ray decreases, generated by these CIRs, at different energies and derive its rigidity dependence. We find that the amplitude has a maximum around 25-30 deg heliolatitude. We also find that the rigidity dependence of both the latitudinal gradient as well as the 26-day variation amplitude show a remarkable similarity. We discuss these observations within the framework of our current understanding of heliospheric phenomena. (Author)