Short-term Variations in the Galactic Environment of the Sun
  The galactic environment of the Sun varies over short timescales as the Sun and interstellar clouds travel through space. Small variations in the dynamics, ionization, density, and magnetic field strength of the interstellar medium (ISM) surrounding the Sun yield pronounced changes in the heliosphere. We discuss essential information required to understand short-term variations in the galactic environment of the Sun, including the distribution and radiative transfer properties of nearby ISM, and variations in the boundary conditions of the heliosphere as the Sun traverses clouds. The most predictable transitions are when the Sun emerged from the Local Bubble interior and entered the cluster of local interstellar clouds flowing past the Sun, within the past 140,000 years, and again when the Sun entered the local interstellar cloud now surrounding and inside of the solar system, sometime during the past 44,000 years. 
Priscilla C. Frisch and Jonathan D. Slavin