Differential Measurement and Model Calculations of Cosmic-Ray Latitudinal Gradient with Respect to the Heliospheric Current Sheet

Simultaneous magnetic field and charged particle measurements from the Voyager spacecraft with heliographic latitude separations of >10° are used to investigate the distribution of ∼1-GeV galactic cosmic ray protons with respect to the heliospheric current sheet in the outer solar system. By comparing the ratio of cosmic ray flux at Voyager 1 to that at Voyager 2 during periods of relatively quiet interplanetary conditions when the spacecraft are either both north or both south of the heliospheric current sheet, we derive an average latitude component of the gradient of the cosmic ray flux on opposite sides of the current sheet under restricted interplanetary conditions of −0.22±0.03%/deg, equivalent to a decrease of ∼1%/AU away from the current sheet at ∼12 AU. Our results for these limited periods are in qualitative agreement with propagation models incorporating particle drifts