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Ulysses COSPIN/KET - Neutron Monitor Network cooperation and Cosmic Ray Distribution in the inner Heliosphere. A. Belov, E. Eroshenko, V. Yanke IZMIRAN, 142190, Troitsk, Moscow region, Russia. Path of Ulysses. The red and green histograms show the evolution of the maximum

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A. Belov, E. Eroshenko, V. Yanke IZMIRAN, 142190, Troitsk, Moscow region, Russia

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A belov e eroshenko v yanke izmiran 142190 troitsk moscow region russia

Ulysses COSPIN/KET - Neutron Monitor Network cooperation and Cosmic Ray Distribution in the inner Heliosphere.

A. Belov, E. Eroshenko, V. Yanke

IZMIRAN, 142190, Troitsk, Moscow region, Russia

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A belov e eroshenko v yanke izmiran 142190 troitsk moscow region russia

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A belov e eroshenko v yanke izmiran 142190 troitsk moscow region russia

Path of Ulysses

.

The red and green histograms show the evolution of the maximum

latitudinal extent of the heliospheric current sheet during the first,

solar minimum and second, solar maximum orbit.

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A belov e eroshenko v yanke izmiran 142190 troitsk moscow region russia

During Ulysses mission the temporal and spatial variations

in the CR were dominated one by one, or presented simultaneously

due to the Ulysses trajectory. Under such conditions the Ulysses

measurements alone are not sufficient to infer a concept about

the CR space distribution.

To separate different type variation the base observations of the

CR variations have to be used. And, it was found, that…

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ULYSSRES-NMN: Friendship FOREVER

There is no more friendly detector for Ulysses in the space than NM

network. Long term CR variation from NMN follow just after KET high

energy channel. Short time variations on NMN are between p>2GeV

and helium >2GeV/n from the COSPIN/KET.

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Neutron Monitor Network-NMN

(about 40 constantly operating stations)

Effective energy 5-30GeV

Accuracy ~0.05%/h

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A belov e eroshenko v yanke izmiran 142190 troitsk moscow region russia

  • Heber, B., Belov, A. V., Raviart, A., Paizis, C., Eroshenko, E. A., Yanke, V., Doege, W.,

  • Green, G., and Roehrs, K. Latitudinal and radial variation of > 2 GeV/n protons derived

  • by Ulysses-COSPIN/KET and neutron monitor network observations. Proc. 25th Int. Cosmic

  • Ray Conf., 1997, Durban. V. 2, P. 85–88.

  • Belov, A. V., Eroshenko, E. A., Heber, B., Yanke, V. G., Ferrando, P., Raviart, A.,

  • Bothmer, V., Droege, W., Kunow, H., Mueller-Mellin, R., Roehrs, K., Wibberenz, W., and

  • Paizis, C., Latitudinal and radial variations of > 2 GeV/n protons and a -particles in the

  • northern heliosphere: Ulysses and neutron monitor network observations.

  • Adv. Space Res. 1999. V. 23. P. 443–447.

  • 3. Belov, A. V., Eroshenko, E., Heber, B., Yanke, V., Raviart, A., Roehrs, K., Mueller-

  • Mellin, R., Kunow, H., Wibberenz, G., and Paizis, C., Latitudinal and radial variation

  • of > 2 GeV/n protons and alpha-particles in the southern heliosphere at solar maximum:

  • ULYSSES COSPIN/KET and neutron monitor network observations. EGS Symposium,

  • Nice, April 2002.

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  • Evolution of the maximum latitudinal extent of the heliospheric current sheet.

  • Solar polar magnetic field strength for the southern (black) and northern hemisphere (red). The smoothed curves display the 20nHz low pass filtered above.(C) Daily averaged count rate of 100-125 MeV (0.3 GV) and (D) 26-day “quiet time” count rates of >2 GeV protons and >2 GeV/n alpha-particles.

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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).

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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 of 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

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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

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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

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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.

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Spatial CR distribution during solar maximum

The data are in a good accordance with the simple model: the radial and latitudinal gradients are the constants.

Within the period 1998.01.15 – 2001.06.03we obtained the following optimal parameters

The temporal variations for >2GeV/n protons exceeded 10 GV particle variations by a factor 1.3

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Daily averaged variationof >2 GeV Ulysses proton flux (dots) and its simulation

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

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Solar activity minimum

Solar activity maximum

Meridional cut of the >2 GeV/n protons spatial distribution in the sphere of 5 AUaround the Sun during solar minimum and solar maximum.Dark and light regions correspond to low and high CR intensity, respectively.

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Corona in the solar minimun

Corona in the solar maximun

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Averaged fluxes of protons (>2 GeV) and helium (>2 GeV/n)

in depend on heliolatitude for the period including the second

fast latitudinal scan.

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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.

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A belov e eroshenko v yanke izmiran 142190 troitsk moscow region russia

What are we going to do?

As it was shown, the latitudinal gradient is much smaller in the SA

maximum than in the minimum. It doesn’t mean that it disappears at all.

This gradient seems to be revealed in the separate periods within some

latitudinal intervals. Our aim is to understand how and why this occurs?

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We have to study:

  • A dynamic of the CR heliolatitudinal dependence in the inner heliosphere during the solar activity maximum. A dynamic and spatial dependence of the CR modulation around the SA Maximum (1997-2003)

  • Variations of the CR spatial distribution within the solar magnetic cycle. We do hope very much here on the Ulysses THIRD fast latitudinal scan.

  • Several smaller problem where the joint use of the Ulysses and NMN observations is necessary:

  • Spatial distribution and dynamic of the 27-day variations;

  • Spatial distribution and essential features of the Forbush effects.

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A belov e eroshenko v yanke izmiran 142190 troitsk moscow region russia

ULYSSRES-NMN: Friendship FOREVER

This relation was predetermined from heaven

There is no more friendly detector for Ulysses in the space than NM

network. Long term CR variation from NMN follow just after KET high

energy channel. Short time variations on NMN are between p>2GeV

and helium >2GeV/n from the COSPIN/KET.

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A belov e eroshenko v yanke izmiran 142190 troitsk moscow region russia

The End

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