Sporadic sodium layers and the average vertical distribution of atmospheric sodium

We have used atmospheric sodium profiles obtained at São José dos Campos over the period 1993–2004 to study the influence of sporadic layers on the average sodium distribution. All the profiles for the time period 19–22 h local standard time were individually classified as either normal or sporadic. Profiles were considered sporadic if they contained sharp increases above the background profile by more than a factor of 2, occurring on the topside of the layer, with a width of less than 5 km. For each night’s data, the averages of the normal and sporadic profiles were stored separately. A comparison between the long-term means of these two average profiles, for those days on which both normal and sporadic profiles were observed, showed no significant difference between them. This indicates that, on average, there is no additional sodium in the sporadic profiles. This analysis suggests that at least part of the topside of the normal sodium layer originates in a source that also gives rise to sporadic layers, which would occur when the source itself becomes layered. The most likely source is sodium-containing ions, which would be layered by the tide and/or gravity wave driven wind-shear mechanism generally accepted as being responsible for some types of ionospheric sporadic-E.