Assimilative Canadian High Arctic Ionospheric Model (A-CHAIM)

The Assimilative Canadian High Arctic Ionospheric Model (A-CHAIM) is a near-real-time high latitude ionospheric electron density assimilation system.


The A-CHAIM system, run at UNB every hour, generates output files of assimilated ionospheric states for the previous three hours. These output files can be found here:
A-CHAIM Output Files

Each file corresponds to a 15 minute assimilation time interval. Output files are provided for the three hours prior to the assimilation run time. Note that assimilation reliability will decrease as the output file time approaches the time when the assimilation was run due to ingested data latency. Old time steps are re-run as new data becomes available in later assimilation runs.


To interpret A-CHAIM output files, standalone software in Matlab and C are provided in the link below. These tools interpret A-CHAIM output files to provide electron density and ionospheric parameters at user-defined locations. The standalone software is available at no cost, but you need to register in order to download it and we ask all users to please state the version of the model in any publication or scientific use of A-CHAIM. Once you have registered, you can download the software at the following link:
A-CHAIM Standalone Software


We also provide users with a web application, which is publicly available here:
A-CHAIM Web Application



Assimilation at high latitudes suffers from the classical problem of sparse data availability, a problem made worse in near-real-time. To mitigate this issue, we use E-CHAIM as a background model (being the best-performing empirical model available for high latitudes) and implement a highly nonlinear assimilation scheme. In lieu of a traditional grid, the system uses E-CHAIM’s vertical ionospheric parameterization and spherical cap harmonics as its basis set. Due to the highly nonlinear nature of the chosen basis set, an advanced Sequential Maximum Likelihood assimilation scheme is implemented using particle methods.

Contributing Datasets:

Figure 1 . Map of available near-real-time ground-based GNSS data. Stations incorporated in A-CHAIM are plotted in red while blue stations are found below the A-CHAIM lower assimilation boundary.

Rules of the Road

When using the Empirical-Canadian High Arctic Ionospheric Model (E-CHAIM) for scientific purposes, we ask users to adhere to the following guidelines:

  • List the version number for the version of the E-CHAIM code you are using (ex: v1.4.0).
  • While we do not ask to be included as co-authors to your publications using the model, we do ask that you let us know after you have published a paper that uses the model. This goes a long way to helping us justify further funding support to keep the model available and free.
  • Please include the following acknowledgement in publications using the model: “E-CHAIM is supported under Defence Research and Development Canada contract number W7714‐186507/001/SS and is maintained by the Canadian High Arctic Ionospheric Network (CHAIN) with operations support from the Canadian Space Agency.”

A-CHAIM Project Lead:

David Themens - This email address is being protected from spambots. You need JavaScript enabled to view it.