Solar proton event of April 16, 1970. 3. Evolution of pitch angle distribution as < or approx. =1-MeV protons propagate into the high-latitude magnetotail

Journal Article · Mon Jan 01 04:00:00 EST 1979 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JA084iA01p00109· OSTI ID:6468986

Palmer, I D; Jackson, J C; Hones, Jr, E W

The solar proton event of April 16, 1970 was monitored by Vela satellites, of orbit r=18 R/sub E/, in the solar wind and high-latitude magnetotail (lobe). Intensity structure at < or approx. =1 MeV indicates a delay of 85--102 min in access of protons to near the center of the north lobe, corresponding to entry points at 340--370 R/sub E/ from the earth. In three sequential periods, of 16, 181, and 124 min duration, the average intensity in the north lobe was lower, higher, and lower, respectively, than that in interplanetary space, by factors which varied from 2 to 5. These reversals were a consequence of reversals in field-aligned anisotropy in interplanetary space, the interplanetary magnetic field remaining southward. Pitch angle distributions were measured in three dimensions in interplanetary space and in the north lobe. In the lobe the distributions were essentially isotropic at r=18 R/sub E/. Comparison is made with theoretical propagation of solar particles along field lines in an open tail model, under the following conditions along a trajectory: (1) adiabatic motion all the way (Liouville theorem) : the 'adiabatic access model' (2) isotropization at the magnetopause followed by adiabatic motion: the 'nonadiabatic access model'. Neither mode of access explains the observations adequately. A hybrid mode is proposed, in which a minimal amount of scattering occurs as particles enter the tail, followed by amplification (attenuation) of intensity as the pitch distribution is transformed to near 18 R/sub E/ in the favored (unfavored) lobe. In this mode a large part of the isotropization at Vela orbit is accomplished by the Liouville transformation, since particles entering the tail beyond approx. =100 R/sub E/ will see an increase in magnetic field by a factor of 3 as they propagate along the tail. The amount of scatter at the magnetopause is estimated to be ..delta mu.. (rms) =0.3, where ..mu.. is cosine of pitch angle.

• Research Organization: Oral Roberts University, Tulsa, Oklahoma 74171
• OSTI ID: 6468986
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 84:A1; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

640203* -- Atmospheric Physics-- Magnetospheric Phenomena-- (-1987)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ADIABATIC PROCESSES
ANGULAR DISTRIBUTION
BARYONS
DISTRIBUTION
ELEMENTARY PARTICLES
ENERGY RANGE
FERMIONS
HADRONS
INCLINATION
INTERPLANETARY MAGNETIC FIELDS
INTERPLANETARY SPACE
MAGNETIC FIELDS
MAGNETOTAIL
MEV RANGE
MEV RANGE 01-10
NUCLEONS
PROTONS
RADIATIONS
SOLAR ACTIVITY
SOLAR PARTICLES
SOLAR PROTONS
SOLAR RADIATION
SOLAR WIND
SPACE
STELLAR RADIATION