Table of contents

1. Overview of Magnetocosmics
2. Magnetocosmics in the SPENVIS environment
3. Scenario
   • Calculation of cut-off rigidities
   • Particle trajectory visualisation
   • Magnetic field line visualisation
4. Geometry
5. Magnetic field
6. Results
7. References

Overview of Magnetocosmics

As the computation of cut-off rigidities for many positions can be highly time-consuming and since the CPU time available on SPENVIS for a single user is limited, the calculations are stopped if the program duration time exceeds a limit. This can be often the case for calculations on maps or orbit trajectories. Therefore, users are welcome to utilize SPENVIS to produce and download the macro-file but is recommended that they download the stand-alone version of Magnetocosmics to make a run.

Note that the Magnetocosmics application makes use of the Geant4 toolkit ^[2]. The complete Magnetocosmics user manual is available online as a PDF-document.

Magnetocosmics in the SPENVIS environment

As the model uses a Monte-Carlo simulation-based code, execution times can be very long, certainly for cut-off calculations. The execution is limited to five minutes of CPU-time on the simulation machine. If the Magnetocosmics run exceeds this limit, the simulation will be terminated and intermediate results returned to the user.

Scenario

Calculation of cut-off rigidities

Particle trajectory visualisation

The user can first choose the particle type: Electron Positron Proton Anti Proton Alpha He3 Deuteron Triton Ion If the particle type is Ion, the atomic and the mass number must be entered as well. The default for Ion is a C₁₂ nucleus.

Next, one can specify the type of trajectory i.e. forward or backward trajectory. In the case of 'Single position' the user can define more than one trajectory and assign different energies or rigidities to them. When the 'Orbit' or the 'Grid' option is selected the number of trajectories corresponds to the number of orbital or coordinate grid points. Then, only one energy or rigidity value can be defined and is assumed to be the same for all the trajectories. The energies can be entered in GeV, MeV, or keV; the rigidities in GV, MV, or kV.

The last option is the selection of the colour for particle trajectory visualisation.

Magnetic field line visualisation

Geometry

The position is then defined by specifying the altitude (in km or Earth’s radius, R_E), longitude and latitude (both in degrees) in the chosen coordinate system.

For the calculation of cut-off rigidities and particle trajectory visualisation scenarios ('Single position', 'Orbit' or 'Grid') a user has the additional option for specifying directions.

In the case of cut-off rigidity calculatuions, the user defined directions correspond to the incident directions expressed in terms of the zenith and azimuthal angle. The coordinate system specifying the direction is always assumed to be same as the one specifying the position.

In the case of particle trajectory visualisation the user has three choices for specifying the initial direction, Predefined Pitch angle and gyration phase Zenith and azimuth angle. The predefined directions include the local zenith, the magnetic and geographic north pole axis, the direction of the Sun, the local magnetic east and the local magnetic west. For any of the above predefined direction an appropriate coordinate system is assumed. For the second option is suffice to define the pitch angle and the gyration phase. Finally, for specifying the zenith and azimuthal angle the user has also the possibility to choose a coordinate system: Geographic (GEO) Geomagnetic (MAG) Geocentric Equatorial Inertial (GEI) Geocentric Solar Ecliptic (GSE) Geocentric Solar Magnetospheric (GSM) Solar Magnetic (SM)

Note that the SPENVIS background pages contain a detailed description of all the coordinate systems used in Magnetocosmics.

Magnetic field

• Internal magnetic field:
  • IGRF
  • Tilted centered dipole
  • Tilted excentered dipole
    These three options require the user to specify a reference date for the epoch of the calculation. Note that when the 'Orbit' option is selected, the magnetic field reference date is overwritten by the orbital time. Also, the reference date can be modified by grid time when 'Grid' option is chosen.
    
  • User defined dipole
    This option requires three additional inputs:
    • The strength of the dipole (default 30000 nT)
    • Orientation of the dipole axis (polar and azimuth angle)
    • Position of the dipole with respect to the Earth's centre.
• External magnetic field:
  • None: No parameters are required
  • Tsyganenko 89 C: One additional parameter is required
    • Planetary (K_p) index
  • Tsyganenko 96: Four additional parameters are needed:
    • Disturbance storm time (D_st) index in nT
    • The interplanetary magnetic field Y-component in nT (GSM coordinate system)
    • The interplanetary magnetic field Z-component in nT (GSM coordinate system)
    • Solar wind dynamic pressure in nPa
  • Tsyganenko 2001: Besides the four parameters described for the Tsyganenko 96 model, there are two more parameters G1 and G2. This model is currently disabled on the online SPENVIS system.

Results

The macro file spenvis_mco.g4mac contains the Geant4 Macro file. The log file spenvis_mco.g4log records the output from Magnetocosmics to stdout and stderr. The output file spenvis_mco.txt contains tabulated results according to the selected scenario (cut-off rigidities, particle trajectory or magnetic field line visualisation). The graphics file spenvis_mco.wrl shows the particle trajectories or the magnetic field .

To generate plots, select the plot type(s), options and graphics format when applicable, and click the button. The current page will be updated with the newly generated plot files.

References

1. Cooke, D. J., J. E. Humble, M. A. Shea, D. F. Smart, N. Lund, I. L. Rasmussen, B. Byrnak, P. Goret, and N. Petrou, On cosmic-ray cutoff terminology, Il Nuovo Cimento, 14C, 213-234, 1991.
2. Geant4
3. Hapgood, M. A., Space Physics Coordinate Transformations: a user guide, Planet. Space Sci., 40, No 5, 711-717, 1992.
4. IGRF model of the International Association of Geomagnetism and Aeronomy (IAGA)
5. Langel, R. A., Main field in geomagnetism, Vol I, ed. J. A. Jacobs, Academic Press, London, 249-512, 1987.
6. Miroshnichenko, L., Radiation Hazard in Space, Astrophysics and Space Science Library, Vol 297, Kluwer Academic Publishers, Dordrecht, 2003.
7. Press W. H., S. A. Teukolsky, B. P. Flannery, and W. T. Vetterling, Runge-Kutta method, in 'Numerical Recipes in C++, The art of scientific computing, 2^nd ed., Cambridge University Press, p 715, 2001.
8. Press W. H., S. A. Teukolsky, B. P. Flannery, and W. T. Vetterling, Richardson extrapolation and the Bulirsh-Stoer method, in 'Numerical Recipes in C++, The art of scientific computing, 2^nd ed., Cambridge University Press, p 729, 2001.
9. Russell, C. T., Geophysical Coordinate Transformations, Cosmic Electrodyn., 2, 184, 1971.
10. Tsyganenko, N. A., Global quantitative models of the geomagnetic field in the cislunar magnetosphere for different disturbance levels, Planet. Space Sci., 35, 1347, 1987.
11. Tsyganenko, N. A., A magnetospheric magnetic field model with a warped tail current sheet, Plant. Space Sci., 37, 5, 1989.
12. Tsyganenko, N. A., Modeling the Earth's magnetospheric magnetic field confined within a realistic magnetopause, JGR, 100, 5599, 1995.
13. Tsyganenko, N. A., Effects of the solar wind conditions on the global magnetospheric configuration as deduced from data-based field models, Eur. Sace Agency Spec. Publ., ESA SP-389, 181, 1996.
14. Tsyganenko, N. A., A model of the near magnetosphere with a dawn-dusk asymmetry, 1. Mathematical structure, JGR, 107, No A8, 10.1029/2001JA000219.
15. Tsyganenko, N. A., A model or the near magnetosphere with a dawn-dusk asymmetry, 2. Parameterization and fitting to observations, JGR, 107, N0 A8, 10.1029/2001JA000220.
16. Wolf, R. A., Magnetospheric configuration, in 'Introduction to space physics', ed. M. G. Kivelson and C. T. Russell, Cambridge University Press, 288-329, 1995.