University of Oulu

Larsen, N., Mishev, A., & Usoskin, I. (2023). A new open-source geomagnetosphere propagation tool (OTSO) and its applications. Journal of Geophysical Research: Space Physics, 128, e2022JA031061.

A new open-source geomagnetosphere propagation tool (OTSO) and its applications

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Author: Larsen, Nicholas1,2; Mishev, Alexander1,2; Usoskin, Ilya1,2
Organizations: 1Sodankylä Geophysical Observatory, University of Oulu, Oulu, Finland
2Space Physics and Astronomy Research Unit, University of Oulu, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 2 MB)
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Language: English
Published: American Geophysical Union, 2023
Publish Date: 2023-08-16


We present a new open-source tool for magnetospheric computations, that is modeling of cosmic ray (CR) propagation in the geomagnetosphere, named “Oulu—Open-source geomagneToSphere prOpagation tool” (OTSO), available on GitHub ( and Zenodo ( A tool of this nature is required in order to interpret experiments and study phenomena within the CR research field. Within this work, OTSO is applied to the investigation of several ground-level enhancement events. Here, we demonstrated several applications of OTSO, namely the computation of asymptotic directions of selected CR stations, effective rigidity cut-off across the globe at various conditions within the design, and general properties, including the magnetospheric models employed. Comparison and validation of OTSO with older widely used tools such as MAGNETOCOSMICS was performed, and good agreement was achieved. An application of OTSO for providing the necessary background for the analysis of two notable ground-level enhancements is demonstrated and their spectral and angular characteristics are presented.

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Series: Journal of geophysical research. Space physics
ISSN: 2169-9380
ISSN-E: 2169-9402
ISSN-L: 2169-9380
Volume: 128
Issue: 3
DOI: 10.1029/2022ja031061
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: This work was supported by the Academy of Finland (project 330064 QUASARE and 321882 ESPERA) and the University of Oulu Grant SARPEDON. The Finnish Academy of Science and Letters provided additional funding for this work via the Vilho, Yrjö and Kalle Väisälä grant.
Academy of Finland Grant Number: 330064
Detailed Information: 330064 (Academy of Finland Funding decision)
321882 (Academy of Finland Funding decision)
Dataset Reference: OTSO is available from GitHub ( and Zenodo ( (Larsen, 2022). The fortran source of Tsyganenko models are freely available at The NM count rate increase during GLE # 66 and GLE # 71 are available on-line at International GLE database Kp index values are provided by Space Weather Prediction Center of The National Aeronautics and Space Administration (NASA) The ACE satellite data are retrieved from Data provided for the COR comparison in the appendix was obtained via the COR website We provide as electronic supplement the computed with OTSO asymptotic directions used for the analysis of GLE # 66, GLE # 70, and GLE # 71 for the purposes of peer review, this data is publicly available from a Zenodo repository ( (Larsen et al., 2022). The unfolding of the NM data is performed using Levenberg-Marquardt algorithm employed in the frame of MINPACK freely available at
Copyright information: © 2023. American Geophysical Union. All Rights Reserved.