Comparison of atmospheric inoziation models

Comparison of atmospheric inoziation models

Models: basic information Responsible person: Dr. Laurent Desorgher Physikalisches Institut, University of Bern, Sidlerstrasse 5, CH-312 Bern, Switzerland Also: Prof. Erwin Flückiger Dr. Fan Lei, QinetiQ, ESA/ESTEC Program basis: GEANT 4 application Physics behind: Monte-Carlo, all included (cascade + thin target) Particles: protons (factor 1.31 to account for α-particles). Energy range: max. energy (currently 1 GeV/nucleon, potentially higher) Claimed validity: the whole range Responsible person: Dr. Ilya Usoskin Sodankylä Geophysical Observatory (Oulu unit), P.O.Box 3, FIN-914 University of Oulu, Finland Also: Dr. Gennady Kovaltsov Ioffe Phys-Tech. Institute, St. Petersburg, Russia Program basis: CORSIKA package Physics behind: Monte- Carlo, the program starts only in the first interaction. Particles: protons and α- particles explicitly Energy range: from 1 MeV - 5 GeV/nucleon Claimed validity: 3-133 g/cm 2 (-1 km) Responsible person: Dr. Lachezar Mateev, Marussia Bucharova Space Res. Institute, Bulgarian Academy of Sciences, Sofia, Bulgaria Also: Prof. Peter Velinov Program basis: Theoretical model, spherical atmosphere Physics behind: Direct ionization (Thin target), no cascade Particles: protons, α, L, M, H, VH Energy range: 1 MeV 1 GeV Claimed validity: > 16 km (<1 g/cm 2 ) - minimum > 12 km (<18 g/cm 2 ) - maximum

Comparison: Polar regions (Pc<1.5 GV) 35 Solar maximum 6 Solar minimum 3 5 Ion. rate (cm 3 sec) -1 25 2 15 1 Oulu, 1 MV Bern, 1 MV Sofia (max) Ermakov,97 Yu, 22 Neher, 1971 Rosen,85 Ion. rate (cm 3 sec) -1 4 3 2 Bern, 3 MV Oulu, 3 MV Sofia (min) Rosen, 1985 Neher, 1971 5 1 2 4 6 8 1 h (g/cm2) 2 4 6 8 1 h (g/cm2) Comparison of Bern, Oulu and Sofia models with observations (fragmentary, short balloon flights). Similar for low atmosphere (h>5 g/cm 2 ); Oulu model seems to underestimate ionization, while Bern model seems to overestimate; Sofia model is consistent with observations above 1 g/cm 2

Comparison: Equatorial regions (Pc=14-15 GV) Ion. rate (cm 3 sec) -1 18 16 14 12 1 8 6 4 2 Bern, 3 MV Oulu, 3 MV Sofia (min) Neher, 1967 Neher, 1971 2 4 6 8 1 h (g/cm2) Comparison of Bern, Oulu and Sofia models with balloon-borne observations. Oulu model seems to overestimate with respect to the Bern model; Sofia model underestimates the ionization;

Comparison: Ionization at 3 g/cm 2 4 Ionization at 3 g/cm 2 (cm 3 sec) -1 35 3 25 2 15 1 5 1 MV 3 MV Neher, 1971 Bern oulu Measur. Neher (1971) Bern model Oulu model max 22.3 24.5 21.4 min 29 35.5 25.8 ratio 1.3 1.45 1.2 1955 1957 1959 1961 1963 1965 1967 1969 Measurements were done in Thule (polar region) Oulu model systematically underestimate the ionization and the cycle variation; Bern model seems to overestimate the cycle variation;

Comparison: Q-vs-Φ (Pc=7 GV) 25 2 Bern Oulu Ion. rate (cm 3 sec) -1 15 1 5 2 4 6 8 1 12 14 (MV) The models agree for 7 g/cm 2, more or less agree for 5 g/cm 2, and disagree for 3 g/cm 2

Atmospheric profile 25 2 h (km) 15 1 5 1 2 3 4 5 6 7 8 9 1 h (g/cm 2 )

Summary Polar Equator Solar max. Bern (whole range) Oulu (>3 g/cm2) Bern (whole range, but > 3 g/cm2) Oulu (>3 g/cm2) Solar min Bern (>5 g/cm2) Oulu (>3 g/cm2) Sofia (< 5 g/cm2) Sofia underestimate Conservative validity range (models agree with each other and with observations): > 5 g/cm 2 (< 7 km) Acceptable validity range : Bern model: the whole range (some questions for polar regions around solar minima) Oulu model: > 3 g/cm 2 (< 1 km) for all conditions Sofia model: < 1 g/cm 2 (> 16 km) (questions for equatorial regions) < 15 g/cm 2 (>12 km) for solar maximum

Questions and solutions Questions Oulu model: The program starts only after the first interaction neglect direct ionization (thin target) This leads to underestimate ionization at high altitude (< 3 g/cm 2 ) and underestimate of the Φ-dependence; Bern model: Does the model account for CR (>1 GeV)? can be essential contribution; Indirect account for α-particles (by a constant factor of 1.31) This may lead to overestimate of the Φ-dependence and underestimate of the flux at the equator. Sofia model: Contribution of CR (>1 GeV); heavier species. Recommendations: Oulu: ionization during the first nuclear path length; Bern: Direct account for α-paticles and increase the max energy. Sofia: Increase the energy range and account for heavier species

α-particles Flux (GeV/nucleon m 2 sr s) -1 1 1 AMS, June 1998 1 1 1.1.1.1 1 1 1 E (Gev/nucleon).2.15 AMS, June, 1998 1 1 1 1 1.1.2.15 CAPRICE, August 1994.1 1 1 1 E (Gev/nucleon) CAPRICE, August 1994 He/p Ratio.1.1.5.5.1 1 1 1 E (GeV/nucleon).1 1 1 1 E (GeV/nucleon)