Measurements of cosmic-ray low-energy antiproton and proton spectra in a transient period of solar field reversal.

The energy spectra of cosmic-ray low-energy antiprotons (p's) and protons (p's) have been measured by BESS in 1999 and 2000, during a period covering reversal at the solar magnetic field. Based on these measurements, a sudden increase of the p/p flux ratio following the solar magnetic field reversal was observed, and it generally agrees with a drift model of the solar modulation.