Horizontal structures in sporadic sodium layers at 23°S

During 1979 and 1980 the INPE lidar located at São José dos Campos, Brazil was operated in a steerable mode, measuring the sodium profiles sequentially at three points in the sky. Twelve sporadic sodium layer events (SSLs) which occurred in this period are studied in the present work. The evolution of the sporadic peaks at the three positions shows short time structures generally separated by consistent time lags in almost all events. On some occasions, the time evolution at one position is very different than at the other two. These data indicate that short duration SSLs have cloud‐like structures which are advected over the measuring station by the horizontal winds, and the long duration layers show a patchy and wave‐like structure. In no case did we observe rapid growth in the sodium density to occur simultaneously at all 3 measuring points. On this basis we believe that there is no evidence for fast production of sodium, and consequently that there is no need for theories for the formation of SSLs to be consistent with such fast production.