Aleutian Lightning

Tropical islands often are the locations of lightning storms, but lightning is rarely seen in the Aleutian Islands. Residents of Adak have asked for an explanation of why this is through a teacher who has spent some time there, Virginia Van den Noort.

Lightning is an electrical discharge of the air that can occur only when the atmospheric electric field is strong enough to break down the air. Such strong electric fields develop only when there is considerable vertical mixing of the air.

A condition that leads to thunderstorms and lightning is one where the ground surface is warmer than the air just above it. The ground warms the near-surface air, which then rises causing an overturn of the air mass. Upward-moving air together with downward- falling water droplets are thought to create the high electric fields required for production of lightning.

Such conditions occur over tropical islands and over warm land masses. But in the North Pacific, in the region of the Aleutians, the ground and water surface often is colder than the air above, at least in summer. Consequently the air near the land and sea surface is kept cool. That coolness stabilizes the air rather than causing it to convect vertically.

Thus, the reason why the Aleutians have so little lightning is the same one that creates so much low cloud and fog there--stable moist air in contact with a comparatively cold sea and land surface.