Field dependent cosmic ray streaming at high rigidities

Abstract

Data from underground µ meson telescopes at depths of 25, 40, and 80 mwe covering the period 1965–1973 have been analyzed as a function of interplanetary magnetic field direction. Cosmic ray streaming both in and perpendicular to the ecliptic plane, with directions dependent on the sense of the interplanetary magnetic field, is observed throughout the period at all depths. The field dependent streaming in the ecliptic plane exhibits some variability in amplitude and phase but contains a component in the direction perpendicular to the interplanetary magnetic field direction which is consistent with B × ▽N streaming due to a perpendicular cosmic ray density gradient pointing southward (higher density below the ecliptic plane than above it). In the case of the field dependent streaming perpendicular to the ecliptic plane the direction of the streaming has remained remarkably consistent over the 9‐year period. One possible source of this streaming is B × ▽N streaming due to a radial heliocentric cosmic ray density gradient; this possibility is discussed along with other possible sources. There does not appear to be an obvious variation in the amplitude of the field dependent streaming either in or perpendicular to the ecliptic plane with increasing rigidity; both effects are still apparent at rigidities well above the 52‐GV threshold rigidity of the Socorro 80‐mwe telescope. The amplitudes of both anisotropies appear larger at solar maximum than at solar minimum.

Modulation of high‐energy cosmic rays in the heliosphere

“…The gradient was shown to have a dependence on rigidity of P -0.6 . Swinson (1976) extended his analysis to encompass the period 1965-73 (which includes the solar polarity reversal during 1969-71). The results indicated that a south pointing (unidirectional) gradient existed across the ecliptic plane for the entire period.…”

IMF Sector Structure and Cosmic Ray Intensity Variation

“…• The north-south anisotropy which is -distinguishable by the difference between opposite polarity is not so clearly recognized by the nucleonic intensity (Kudo and •Wada, 1977) as by the higher rigidity observation (Swinson, 1976). Plausible causes of such unclearness are contaminations by a polarity dependent effect but symmetric about the boundary, and by the boundary type Forbush decreases mentioned above.…”

The existence of cosmic ray sidereal anisotropies of galactic and solar origins with energies lower than 104 GeV and their modulation caused by the presumed behavior pattern of the heliomagnetosphere and of its neighboring gaseous matter in interstellar magnetic field

“…Especially, the solar activity minimum period in the P-state seems to be a special epoch for the appearance, or the phase change, of the sidereal anisotropy, which occurs every 22 years. The occurrences of the event have been successively observed in 1954 (Conforto and Simpson, 1957), in 1975(Swinson, 1976Nagashima et al, 2010) and in 1996 (Nagashima et al, 2010).…”

“…(Nagashima and Mori, 1976). Solid circle: Morning side (0-12 hr); Open circle: Evening side (12-24 hr); NAG, ITA, MIS and TAK (Ichinose and Murakami, 1976); EMB, SOC and BOL (Swinson, 1976); HOB (Humble and Fenton, 1975;Fenton and Fenton, 1976); CHE, HUA and CHR Forbush, 1948, 1957;Beach and Forbush, 1961 Nagashima and Mori (1976) as being due to some north-south asymmetric sidereal vectors being superposed on a common sidereal vector, in spite of the earlier find- (Nagashima et al, 1983a Fig. 6).…”