Ulysses COSPIN High Energy Telescope observations of cosmic ray and solar energetic particles intensities since its distant Jupiter flyby in 2004 R.B. McKibben, J.J. Connell, and C. Lopate Space Science Center Institute for the Study of Earth, Oceans and Space University of New Hampshire Durham, NH, USA EGU 2006, Vienna Paper EGU06-A-05301 University of New Hampshire Space Science Center, EOS

Ulysses Trajectory Ulysses is heading towards its 3rd set of polar passes in 2007-2008. As of the end of 2005, the spacecraft was at ~37°south and about 4.5 AU from the Sun. The solar activity level is declining, but very large solar particle events were still observed both at Earth and Ulysses in January and September of 2005. The period since the distant flyby of Jupiter in 2004 offers an excellent chance to look at radial and latitudinal effects of both modulated cosmic ray intensities and large, isolated solar particle events. EGU 2006, Vienna Paper EGU06-A-05301 University of New Hampshire Space Science Center, EOS

Ulysses and the Solar Cycle Sunspot Number are now nearing solar minimum levels The Solar polar magnetic polarities are now clearly reversed, but the fields are weaker than at the last solar minimum The current sheet tilt remains large. By the end of 2005, Ulysses was near the top of the current sheet zone. High energy cosmic ray intensities at Earth and Ulysses remain below the levels reached at the last solar minimum. Intensity profiles of modulated high energy cosmic rays have been very similar at Earth and Ulysses except near the 1995 solar minimum. EGU 2006, Vienna Paper EGU06-A-05301 University of New Hampshire Space Science Center, EOS

Protons < ~35-95 MeV At low energies, modulated cosmic ray spectra should be proportional to T+1, as observed. Differences in cosmic ray fluxes at Earth and Ulysses arise from radial and/or latitudinal gradients. For the new polarity of the solar dipole magnetic field, both observation (Voyager 1986-87) and theory (including drifts) predict that the latitude gradients should be negative, leading to a lower flux at high latitude (Ulysses) than in the ecliptic (IMP-8). In the observations so far, we see no clear evidence for either radial or latitudinal gradients in the proton flux below ~100 MeV. EGU 2006, Vienna Paper EGU06-A-05301 University of New Hampshire Space Science Center, EOS

Helium ~35-95 MeV/n The signature of anomalous helium is a spectral index significantly smaller than +1 (as in 1994-95). The spectrum has flattened slightly since 2004, suggesting some contribution from the anomalous component at Ulysses. As for protons, we see no clear evidence for either radial or latitudinal gradients in the Helium flux below ~100 MeV/n. EGU 2006, Vienna Paper EGU06-A-05301 University of New Hampshire Space Science Center, EOS

A closer look at observations since 2000 There is no clear evidence for significant radial or latitudinal gradients in the fluxes of low energy proton and helium nuclei between Earth and Ulysses at any time since 2000. In the fast latitude scan at the previous solar minimum in 1994-95 there was evidence for suppression of latitude gradients in the region swept by the current sheet. Ulysses is now emerging from the current sheet region, so we may soon see clearer evidence for development of latitude gradients. EGU 2006, Vienna Paper EGU06-A-05301 University of New Hampshire Space Science Center, EOS

Recent Solar Energetic Particle Events The three most significant periods of solar activity since the start of 2003 have been: Oct/Nov 2003 Jan 2005 Sep 2005 The Oct/Nov events have been extensively studied, and the observations are discussed in a special section of J. Geophys. Res. (Vol. 110, A09S19, 2005) The January events had comparatively soft spectra, but high intensities at low energies The September events had hard spectra, and were among the most intense events observed during the Ulysses mission. EGU 2006, Vienna Paper EGU06-A-05301 University of New Hampshire Space Science Center, EOS

January, 2005 Events The January events had a soft spectrum, producing almost no protons with energy >92 MeV. The largest flare, the X7.1 event on Jan. 20, produced the highest intensities observed at both IMP and Ulysses. While it is risky to talk of connection longitudes in a very active period, Ulysses was formally very poorly connected to observe particles from the event while IMP was reasonably well connected. Accordingly, the onset at Ulysses was delayed, no significant anisotropies were observed during onset, and the event was much smaller than at IMP. EGU 2006, Vienna Paper EGU06-A-05301 University of New Hampshire Space Science Center, EOS

September, 2005 Events The September 7 X17.1 event produced particles with a very hard spectrum extending well above 90 MeV. The magnetic connection for Ulysses was slightly better than that for IMP, but poor for both. Ulysses observed strong field-aligned anisotropy in the ~39-95 MeV protons for a period of approximately 25 hours beginning at ~0315 on day 251. The maximum intensities were comparable at IMP and Ulysses, and the longer duration at Ulysses implies a higher fluence at Ulysses. Thus, for radiation hazard, greater distance from the Sun is no guarantee of reduced risk. EGU 2006, Vienna Paper EGU06-A-05301 University of New Hampshire Space Science Center, EOS

Summary • At the end of 2005, modulated cosmic ray intensities were still well below intensities observed at the last solar minimum and the tilt of the current sheet remained high enough that Ulysses continued to encounter the current sheet through 2005, to radius 4.8 AU and latitude 37°S. As of the end of 2005 Ulysses had not yet found clear evidence for radial or latitude gradients in the cosmic ray intensity. For solar energetic particles at energies >30 MeV, the period 2004-2005 was characterized by isolated periods of intense activity, including the periods of extreme activity in January 2005 and September 2005. The largest of the September 2005 series of events (X17.0 on Sept. 7) produced intensities among the highest that have been observed by the Ulysses HET at any radius or latitude in the course of the mission. Significant SEP proton fluxes extended to energies >90 MeV. Strong, persistent anisotropies during the first day of the event indicate direct arrival of particles by streaming along interplanetary field lines. Maximum fluxes at Earth and Ulysses were comparable, but lasted longer at Ulysses. The total fluence was thus larger at Ulysses near 4.8 AU and 30°S than at Earth. Thus, for manned missions, greater distance from the Sun does not necessarily guarantee reduced radiation risk. EGU 2006, Vienna Paper EGU06-A-05301 University of New Hampshire Space Science Center, EOS