Help: Galactic cosmic ray particle models

Table of Contents	ECSS	Model Page
Background Information	Radiation sources and effects
	Galactic Cosmic Ray (GCR) particle models

SPENVIS can run GCR particle models to predict fluxes. The models yield fluxes outside the magnetosphere, which are then corrected for magnetic shielding.

In order to run these models, a spacecraft trajectory is needed. If no trajectory has been generated yet, the orbit generator should be run first.

The input parameters and options for the GCR particle flux models are described below. When the input form has been completed, pressing the button will start the calculation and bring up the "Results" page.

The button calls up the model selection page for consecutive runs of multiple models. This feature is available for advanced users only.

Warning: using these buttons deletes all existing output from the GCR particle flux models and from any model that uses this output, in order to ensure consistency in the outputs.

Input parameters

Model selection

The following models for GCR particle fluxes are available in SPENVIS:

the ISO 15390 model;
This is the International Standard for estimating the radiation impact of galactic cosmic rays on hardware and on biological and other objects when in space. (ref.: Galactic Cosmic Ray model, International Standard ISO Draft 15390). The model accounts for the variations of GCR particle fluxes due to variations in solar activity and in the large scale heliospheric magnetic field (the sun's polar magnetic field) throughout 22-year cycles. The solar activity is characterized by 12-month averages of Wolf numbers.
the CREME96 (Sol. Minimum) model [Tylka et al., 1997];
The CREME96 GCR model is based on the GCR model by Nymmik et al. (1992). The version implemented in SPENVIS corresponds with the cosmic ray maximum, last observed in 1986-1987, during solar minimum. We remark that the model also contains anomalous cosmic rays and a low-energy component (see Tylka et al. (1996) for a detailed description of the model).

the CREME86 models [Adams, 1986];

These implemented models are part of the original CREME86 software package:

**CREME86 models for GCR particle fluxes.**
Index M	Description
1	galactic cosmic rays only
2	galactic cosmic rays + fully-ionized anomalous component
3	90% worst case cosmic ray level
4	galactic cosmic rays + singly-ionized anomalous component

the Nymmik et al. (1996) model;
The model by Nymmik et al. (1996) is similar to the ISO model except for energies below 10 MeV/nucleon where the model estimates an increase instead of a decrease of the ion flux.

For all the models the fluxes are calculated for energies from 1 MeV/nucleon up to 20 GeV/nucleon.

Solar activity data

For the models ISO and Nymmik et al. (1996) the user can set the epoch or enter his own solar cylce data i.e.

solar minimum (May 1996), corresponding to the epoch of solar minimum conditions
mission epoch, corresponding to the epoch for which the orbit is generated
user defined (only for the advanced user!)

By default tabulated solar cycle data are used. For future epochs the solar cycle is propagated by substracting 22*n years from the epoch. As an advanced user you can enter the solar cycle data. In this case one of the required user inputs is the sunspot number at (epoch - lag) where the lag is the delay time of the cosmic ray particle flux variations relative to the solar activity variations. We remark that as user input the the lag time is considered as a constant, while it varies with the particle rigidity.

Ion range

The composition of the galactic cosmic ray environment is specified by means of a lower and upper limit for the elements to be considered in the calculation. The upper limit should be greater than or equal to the lower limit.

Magnetic shielding

GCR particles are shielded by the planet's magnetic field if present. This shielding effect can be turned off to simulate the environment outside the magnetosphere.

The magnetic shielding of cosmic ray particles is lower during stormy conditions than for a quiet magnetosphere. A selection between these conditions is available only for Earth.

Interplanetary missions

Currently in SPENVIS, for interplanetary missions the user has two options for propagating the GCR particle flux:

the conservative approximation
The GCR flux is taken uniform throughout the heliosphere which is a reasonable engineering approximation for current missions.
the force field approximation
The modulation of the GCR differential spectrum is described by a single parameter Φ called the modulation potential which varies with the heliocentric distance (Gleeson and Axford, 1968). The required input parameters are the averaged radial solar wind velocity and the radial diffusion coefficient (constant or power law).

Results

The GCR particle flux models produce the files listed in the table below. A description of the file formats can be brought up by clicking on their description in the table.

The report file spenvis_gcr.html contains the input parameters and summary tables. The spectrum file spenvis_gcf.txt contains the flux spectrum.

**Output files generated by the short-term solar particle flux models**
File name	Description
`spenvis_gcr.html`	Report file
`spenvis_gcf.txt`	Flux spectra for NEWUPSETO, MULASSIS

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

The button calls up the output page for consecutive runs of multiple models. This button only appears when the short-term solar particle flux models have been included in the combined model run selection. This feature is available for advanced users only.

References

Adams, J. H., Cosmic Ray Effects on Microelectronics, Part IV, NRL Memorandum Report 5901, Washington, D.C., 1986.

Gleeson, L. J., and W. I. Axford, Solar modulation of galactic cosmic rays, Astrophys. J., 154, 1011, 1968.

Nymmik, R.A., Panasyuk, M.I., Pervaja, T. I. and Suslov, A.A., A Model of Galactic Cosmic Ray Fluxes, Nucl. Tracks & Radiat. Meas, 20, 427-429 (1992).

Nymmik, R.A., Panasyuk, M.I. and Suslov, A.A., Galactic cosmic ray flux simulation and prediction: Adv. Space Res., Vol. 17, No. 2, 1996.

Tylka, A.J., Dietrich, W.F. and Boberg, P.R., Probability Distributions of High-Energy Solar-Heavy-Ion Fluxes from IMP-8: 1973-1996, IEEE Trans. on Nucl. Sci., 44, 2140-2149 (1997)

Last update: Wed, 25 Apr 2018