Cosmic-ray atmospheric cutoff energies of polar neutron monitors
|Author:||Poluianov, Stepan1,2; Batalla, Oscar3|
1Sodankylä Geophysical Observatory (Oulu Unit), University of Oulu, 90014 Oulu, Finland
2Space Physics and Astronomy Research Unit, University of Oulu, 90014 Oulu, Finland
3Facultad de Ciencias, UNAM, Av. Universidad 3000, Circuito Exterior S/N, Alcaldía Coyoacán, C.P. 04510 Ciudad Universitaria, CDMX, Mexico
|Online Access:||PDF Full Text (PDF, 2 MB)|
|Persistent link:|| http://urn.fi/urn:nbn:fi-fe2022090757762
|Publish Date:|| 2022-09-08
The atmospheric cutoff, similarly to the geomagnetic cutoff, is the lower energy limit for cosmic ray particles that can reach a given location on the ground and be registered by a detector there, e.g., by a neutron monitor. It is caused by the decreasing intensity of a cosmic-ray cascade in the lower atmosphere. Although the geomagnetic cutoff is higher than atmospheric over the most of the Earth’s surface, the latter is dominant and therefore defines the neutron monitor count rate in the polar regions. The atmospheric cutoff decreases with the altitude, and this provides additional sensitivity of high-altitude polar neutron monitors to low-energy particles, mainly solar energetic protons during the so-called ground-level enhancement events.
In this work, we quantitatively estimated the atmospheric cutoff energies for 21 polar neutron monitor stations in conditions without a significant solar energetic particle event. The cutoff value can be as low as about 300 MeV for protons (VOSTOK and DOMC/DOMB stations), which is notably lower than about 430 MeV at sea level. In addition to that, we estimated the worst case scenario of the strongest-ever observed ground-level enhancement event GLE#05, occurred on the 23rd of February, 1956, and showed that the atmospheric cutoff becomes as low as about 100 MeV. In other words, some neutron monitor stations can register particles with energies of even about 100 MeV during an exceptionally strong solar particle event. It is explained by the highly intensive and soft spectrum of the event in its early delayed phase.
Advances in space research
|Type of Publication:||
A1 Journal article – refereed
|Field of Science:||
115 Astronomy and space science
The work was motivated with discussions in the International Space Science Institute team 441: High EneRgy sOlar partICle events analysis (HEROIC). The authors are thankful to Alexander Mishev and Sergey Koldobskiy for valuable discussions, to Du Toit Strauss and Eugene Maurchev for the atmospheric pressure data of NM stations. Oscar Batalla thanks the research initiation program CNBBBJ-UNAM of the National Autonomous University of Mexico. Stepan Poluianov acknowledges the support from the Academy of Finland (project 321882 ESPERA). The authors are grateful to the neutron monitor database NMDB (https://www.nmdb.eu) founded under the European Union’s FP7 programme (contract No. 213007) for provided data.
|Academy of Finland Grant Number:||
321882 (Academy of Finland Funding decision)
© 2022 COSPAR. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).