HelMod, the solar modulation model of galactic cosmic rays employed within SR-NIEL framework for obtaining ion spectra at Earth or in other Heliospheric Locations

By exploiting experimental results, the combined effort of the physicists involved with the Galprop  model for propagation in galaxy and HelMod for the propagation in heliosphere, the local interstellar spectra (LIS) for Galactic Cosmic Rays species  up to Z=28 (Nickel) were derived. HelMod model allows one to derived the ion modulated spectra from the corresping LIS. These spectra are available and accessible from the current webpage:


- Modulated galactic cosmic rays spectral fluences calculator at 1 AU from HelMod model


HelMod is a 2D Monte Carlo model to simulate the solar modulation of galactic cosmic rays. The model is based on the Parker transport equation which contains diffusion, convection, particle drift and energy loss. Following the evolution of the solar activity in time, we are able to modulate the local interstellar spectra (LIS) of cosmic ray species down to Earth's location inside the heliosphere. The HelMod forecasting of selected cosmic rays species is illustrated in this webpageThe local interstellar spectra (LIS) for Galactic Cosmic Rays species up to Z=28 (Nickel) derived by means of the GalProp-HelMod join effort are available and accessible from here.

The boundary of the heliosphere, called heliopause (HP), is a contact discontinuity separating the solar cavity -- in which the SW plasma is flowing -- from the interstellar space. It also represents the extreme limit beyond which solar modulation does not affect CR flux. Thus, outside HP the truly pristine LIS of GCR spectra could be observed. After being accelerated in the solar corona (Parker, 1958) SW adiabatically expands in radial direction with supersonic speed. In its journey towards the external regions of the heliosphere SW flow changes its supersonic regime, through the formation of a physical boundary called Termination Shock (TS) which, in practice, separates the inner part of the heliosphere (i.e.,  the space region from the Sun up to the TS) from the outer region (i.e., the space region from the TS up to the HP), also known as heliosheath (HS). The actual dimensions of the heliosphere are accounted for by scaling the position of TS by the time dependent values obtained as described in Heliospheric boundaries section. The HS is included as a single additional region on top of the 15 inner regions with its actual size as calculated in Heliospheric boundaries section.

It has to be remarked that HelMod modulated spctra exhibit an overall better agreement with AMS-02 data when compared to the other solar modulation models, commonly employed (e.g., see this webpage).

Furthermore, it is worth to note that - as advertised on the GALPROP website - HelMod website can be used as a service package to seamlessly calculate the effects of the heliospheric modulation for GALPROP output files.


How to use this HelMod Calculator

This tools evaluates the modulated spectrum at Earth orbit for theorical LIS evaluated with GALPROP. The particle transport is described using the Helmod Model. For information about the computation method please refear to Monte Carlo Integration page.

The input parameters and options for the tool are described below. Once the input form has been completed,  "Submit" button will start the calculation and open the "Results" page (allow for pop-up in your browser settings).

Solar Modulation Model

The website is always updated with the latest HelMod version available, as indicated in the output result.

Cosmic Rays Species

The user can select the wished Cosmic Rays Species with atomic number up to Z=28.
HelMod spectra are averaged over a Carrington rotation duration (e.g., 27.2753 days).

Expected Mission Duration/ Past Missions

User can select the cosmic rays species and the time interval for the interested simulation.


The result page contains the figure of modulated spectrum for free space and correspondent tabulated data. The spectral fluence of the selected cosmic rays species can be used as input data file for the SEE Calculator. The lower energy limit of the spectral cosmic rays fluence corresponds to values indicated here.


Galprop-HelMod join effort

Currently published articles regarding local interstellar spectra (LIS):


Relevant Bibliography for Helmod