What process leads to the concentric layering observed in hailstones?

The concentric layering observed in hailstones is a result of the process by which the hailstones move up and down within cumulonimbus clouds. As hailstones are propelled by powerful updrafts, they encounter supercooled water droplets in the cloud. When these droplets come into contact with the hailstone, they freeze almost instantly, adding a new layer of ice to the surface of the hailstone. This continuous cycle of rising and falling in the cloud allows for multiple layers to be formed, leading to the characteristic structure of hailstones.

The other options do not accurately describe the formation of hailstones. Temperature variations alone do not create layers, as they would not account for the movement and repeated accumulation of ice layers. The notion that hailstones are formed from frozen raindrops is misleading; they are actually formed from layered ice growth rather than simply accumulating on the surface. Lastly, ocean currents do not impact the structure or formation of hailstones, which occur within the localized environment of thunderstorms, not influenced by larger oceanic systems.