Forced release of sodium from upper atmospheric dust particles

The almost explosive growth of narrow sodium layers at altitudes near 95 km was observed by ground‐based LIDAR located at 69°N, 16°E. Starting from typical conditions at these altitudes (sodium density approximately 1 to 2× 10³ cm−3) the density is observed to increase by large factors within a few minutes in a narrow layer, the half height of which is typically 1 km only. One of the more spectacular cases involved an increase by a factor 25 within 5 min and a layer width of 0.8 km (full width at half maximum). We propose that the sodium forming these sudden layers is released from upper atmospheric dust by energetic auroral particles. Prior to the auroral bombardment the dust particles were concentrated into a narrow layer by appropriate meteorological processes. Our observations thus imply that considerable amounts of sodium are stored on the surface of upper atmospheric dust.