We describe two sporadic Na (Nas) layer events observed on September 26 and October 6, 1993 by the Na Wind/Temperature (W/T) lidar above Haleakala, Maui (20.8N, 156.2W) during ALOHA-93. Both events occurred between 90 and 95 km altitude and appeared to be associated with large amplitude gravity waves. Both were accompanied by temperature enhancements of more than 40 K. The temperature and Na density variations at the peak of the Nas, as well as the vertical motions of the Nas layers and regions of elevated temperature were highly correlated. The vertical wind structure exhibited no unusual characteristics in the vicinities of the Nas. The zonal wind profile for the 6 October event exhibited a very strong vertical shear approximately 1 km below the Nas layer that approached the dynamic instability limit of 42 m/s/km. However the polarity of the shear was opposite that predicted by the classical wind shear theory of sporadic E layers (Es ) formation.
Reference: Chester S. Gardner, Xin Tao, and George C. Papen, Observations of strong wind shears and temperature enhancements during several sporadic Na layer evens above Haleakala, Geophysical Research Letter, 22, 2809-2812, 1995.
