Solar-cycle dependence of the radial gradient of cosmic-ray intensity. Progress report for period ending 1988

Technical Report · Thu Dec 01 04:00:00 EST 1988

OSTI ID:6200602

Van Allen, J A

Observation of the interplanetary intensity of cosmic rays (E/sub p/ > 80 MeV) by Pioneers 10 and 11 now spans a sixteen-year time period 1972-1988 and heliocentric radial distances, r10 and r11, out to 43.7 AU for Pioneer 10 and 25.8 AU for Pioneer 11. Solar modulation continues to be present at the current distances of both spacecraft. The radial gradient of intensity is measured continuously over the slowly varying, outward moving radial segment Delta = r10 - r11. The 50-day mean values of the gradient G vary systematically and cyclically in phase with solar activity as measured by sunspot number, with a maximum value of about 2.1 percent/(AU) at sunspot maximum and a minimum value of about 1.2 percent/(AU) at sunspot minimum. Thus, the apparent scale size of the heliospheric modulation region as measured by 1/G is about 48 AU at solar max and about 83 AU at solar min-a result that is the inverse of the conjectural inference of using most of the same body of data but a different analytical point of view. There is persuasive evidence that G is independent of radial distance over the range 2.5 to 34 AU in the mid-point of the segment Delta r. No dependence of G on heliographic latitude is evident, but this result does not lend itself to a quantitative statement.

• Research Organization: Iowa Univ., Iowa City (USA). Dept. of Physics and Astronomy
• OSTI ID: 6200602
• Report Number(s): AD-A-204377/6/XAB
• Country of Publication: United States
• Language: English

Related Subjects

640101* -- Astrophysics & Cosmology-- Cosmic Radiation
640104 -- Astrophysics & Cosmology-- Solar Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COSMIC RADIATION
DOCUMENT TYPES
INTERPLANETARY SPACE
IONIZING RADIATIONS
MODULATION
PIONEER SPACE PROBES
PROGRESS REPORT
RADIATIONS
SOLAR ACTIVITY
SOLAR CYCLE
SPACE
SPACE VEHICLES
STARSPOTS
STELLAR ACTIVITY
SUNSPOTS
VARIATIONS
VEHICLES