Near real-time evaluation of the ionisation of the Earth's atmosphere and of the radioactive dosage by cosmic rays based on the real-time database of neutron monitor measurements during short and long time variations of cosmic ray flux near Earth.
Cosmic rays are the primary source of the ionisation in the Earth's atmosphere below ~40 km altitude. Recent progress in the development of computer software makes possible to determine the ionisations of the Earth's atmosphere and radioactive dosage in function of the characteristics of the cosmic ray flux near Earth, the geographic coordinates, and the altitude. If the cosmic ray energy spectrum and the anisotropy of the cosmic ray flux near Earth are known in real-time, the new tools allow the determination of the Earth's ionisation and radioactivity dosage without delay. This is of particular importance during solar energetic particle events. The cosmic ray flux in the relevant energy range can be evaluated by the measurements of the neutron monitor network. The pooling of the neutron monitor measurements into a database in real-time enables to determine the characterstics of the cosmic ray flux near Earth and therefore the computation of the ionisation and of the dosage in the Earth's atmosphere.
The radiation exposure of aircrew and frequent flyers to cosmic rays has became an issue of increasing interest in the last years. At typical commercial aircraft altitudes of 9-12 km, the exposure rate due to galactic cosmic rays is ~5-10 microSv/h depending on altitude, geomagnetic latitude and solar activity. The additional radiation exposure during short time solar cosmic ray ground level enhancements (GLEs) depends aside from altitude and geomagnetic latitude, on the amplitude, the spectrum shape, and the anisotropy of the solar cosmic ray flux, as well as on the direction of the interplanetary magnetic field (IMF) near Earth. Investigations during the gigantic GLE on 20 January 2005 has shown that during giant solar cosmic ray events the effective radiation rate at aircraft altitudes can increase by several orders of magnitudes at high geomagnetic latitudes (up to a factor of 850 during the January 2005 event). The January 2005 event clearly showed that estimations of radiation dose exposures at airplane altitudes must be improved by also considering the anisotropy of the solar cosmic ray flux. From this event we also learned that space weather forecasts must strive for the earliest possible warning of major solar energetic proton (SEP) events because the duration from onset to peak may be extremely short, e.g. 6 minutes for the 20 January 2005 event. The development of a real-time database of neutron monitor measurements is an important step to improve the alert systems to predict the arrival of solar energetic particles near Earth to carry out the necessary precautions in time.
In addition to the advantages of a real-time database the neutron monitor database also facilitates considerably the investigations of long term studies. The ionisation of the Earth's atmosphere has an important impact on the chemistry and physics of the atmosphere. The ionsiation data derived from the neutron monitor measurements can be used e.g. to study a possible impact of the atmospheric ionisation due to galactic cosmic rays on cloud formation during the 11-year activity cycle of the Sun or during short time variations of the cosmic ray flux near Earth as e.g. GLEs or Forbush decreases.
For the determination of the ionisation and radioactive dosage in the Earth's atmosphere the software package PLANETOCOSMICS code based on Geant4 will be used. This computer program developed at the university of Bern computes the transport of cosmic ray particles through the Earth's magnetosphere. In a subsequent step the energy deposited in the atmosphere is evaluated for specific locations and on a global scale.
Last modified: Thu Apr 12 17:37:26 CEST 2007