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Second orbit of Ulysses

Ulysses Solar Minimum and Maximum Fast Latitude Scan in >2 GEV/n Protons and Alpha-particles: Ulysses COSPIN/KET and Neutron Monitor Network Observations.

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Second orbit of Ulysses

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  1. Ulysses Solar Minimum and Maximum Fast Latitude Scan in >2 GEV/n Protons and Alpha-particles: Ulysses COSPIN/KET and Neutron Monitor Network Observations A. Belov1, E. Eroshenko1, B. Heber2, P. Ferrando3, A. Raviart3,R. Mueller-Mellin4, H. Kunow4, K. Roehrs4, G. Wibberenz4, C. Paizis5, V. Yanke1 (1) IZMIRAN, 142190, Troitsk, Moscow region, Russia(2) Fachbereich Physik, Universitat Osnabruck, Germany,(3) DAPNIA/Service d'Astrophysique, France,(4) IEAP, University of Kiel, Germany,(5) Universita di Milano, Italy Nice 2002

  2. Second orbit of Ulysses Oct. 6, 1990 LaunchFeb. 8, 1992 Encounter with Jupiter, 5.4 auSep. 13, 1994 1st South Polar Pass, S80.2Mar. 5, 1995 Equator Pass (~Perihellion, 1.34 au)Sep.1994-Aug.1995 1st Fast Latitude ScanJul. 31, 1995 1st North Polar Pass, N80.2Dec. 13, 1997 Equator PassMarch-May 1998 Aphelion, 5.41 auNov. 24, 2000 2nd South Polar Pass, S80.2May 16, 2001 Equator Pass (~Perihellion, 1.34 au)Nov.2000-Oct.2001 2nd Fast Latitude ScanOct. 12, 2001 2nd North Polar Pass, N80.2 . Nice 2002

  3. Variations of heliospheric latitude and distance from the Sun along Ulysses orbit in 1994-2001 (upper panel); Daily mean variations of the proton flux and 26-day running average helium flux of >2GeV/n energy measured by KET onboard Ulysses (middle panel); Variation of 10 GV CR, inferred from the ground level neutron monitor network, and, the same variations shifted to the Ulysses location and 26-day running averaged (lower panel). Nice 2002

  4. The model While the spatial variation dominates the temporal variation during Ulysses first orbit from 1994 to fall of 1997, the observed count rate variation from 1998 to 2001 is determined by the changing temporal modulation conditions in the inner heliosphere. Under such conditions Ulysses measurements alone are not sufficient to infer a concept about the CR space distribution and its time variations. However, it is possible to compare the observations with theoretical distributions and check for it consistency. In our model we assume that temporal, radial and latitudinal dependencies of the CR intensities are separable: where I0 is a flux of particles at a moment t0 in the point distanced from the Sun at ro on the latitude o;  is the flux variation during the time (t-to), index i shows a kind of particles (p for protons and h for He). Unfortunately, there are no identical baseline instruments for KET CR measurements available. Therefore the time variation Io(t0, r0, 0) has to be estimated from the observations of high energy particles by the neutron monitors on the Earth. From these data a rigidity spectrum of the CR density variations for every day was derived. An estimation of the temporal variation of >2 GeV/n particles relies on the determination of the temporal variation at higher rigidities (typically 10 to 20 GV) from NM network data and its extrapolation to lower rigidities (~6 GV). While such an approach is useful during solar minimum it is not reliable around solar maximum because of the large uncertainties due to the extrapolation. In order to determine the temporal modulation for >2 GeV/n particles we assume that the variation is proportional to variation 10at 10 GV. The latter can be determined from ground level observations with high accuracy. Taking into account all the assumptions listed above we obtain Nice 2002

  5. r Heliolatitudinal distribution in 1994-1995of >2GeV/n KET protons and helium Glat (proton) =0.190.01 %/° Glat (helium) =0.140.02 %/° The first fast Ulysses scan – minimum solar activity Nice 2002

  6. Spatial distribution in 1994-1996(near minimum of solar activity)of >2GeV/n KET protons and helium Relatively big latitudinal gradient Practically zero radial gradient Nice 2002

  7. Behavior of the radial gradient for >2 GeV protons in 1997,derived from Ulysses data On the beginning of 1997 radial gradient was very low (although it was probable lower during two preceded years). Then, in several months gradient had an increase of 0.5-0.6%/au. These changes may be considered as a beginning of the new solar cycle in CR gradient behavior. Nice 2002

  8. Spatial CR distribution during solar maximum1998-2001 The data are in a good accordance with the simple model: the radial and latitudinal gradients are constants. Within the period 1998.01.15 – 2001.11.03we obtained the following optimal parameters The temporal variations for >2GeV/n protons exceeded 10 GV particle variations by a factor 1.3 Nice 2002

  9. Daily averaged variationof >2 GeV Ulysses proton flux (dots) and its simulation Nice 2002

  10. Daily fluxes of >2 GeV/n Ulysses alpha-particles (dots) and its simulation Nice 2002

  11. 1994-1996 1998-2001 Meridional cut of the >2 GeV/n protons spatial distribution in a sphere of 5 AUaround the Sun during solar minimum and solar maximum.Dark and light regions correspond to low and high intensities, respectively. Nice 2002

  12. Corona in the solar minimun Corona in the solar maximun Nice 2002

  13. Corona in the solar minimum Corona in the solar maximum Nice 2002

  14. Conclusions • We determined the high energy cosmic ray radial and latitudinal gradient for solar minimum and solar maximum by using Ulysses KET and neutron monitor network. • Our analysis indicates a spherical symmetric distribution of CR around solar maximum. The intensities in the inner heliosphere are depending on the radial distance from the sun only, while in 1994 to 1996 (solar minimum) the latitude dependence outside of the streamer belt (~15) dominates the observations. • Spatial distribution of the CR was completely transformed in going from low to high solar activity. A central symmetry replaced the axial symmetry. The main part of these drastic changes occurred very quickly, in the second half of 1997 and in the beginning of 1998. Simultaneously tilt angles of the heliospheric current sheet increased from <15in 1997 to above 50 in the beginning of 1998. Both the modulation depth and shape of the CR space distribution in the inner heliosphere are related to the HCS configuration changing. • Since latitudinal gradient was positive at solar minimum in the last cycle and vanished to zero in maximum, the total 11-year modulation is essentially bigger at polar regions than close to the heliospheric equator, in particular near Earth.  • Since the tilt angle is now decreasing again towards the solar minimum our concept of a close correlation of the CR spatial distribution with the HMF configuration can be tested in the near future. Nice 2002

  15. The End Nice 2002

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