We examine the influence of temperature fluctuations on the formation of sporadic sodium layers (SSLs) with particular emphasis on AIDA (Arecibo Initiative in the Dynamics of the Atmosphere) results. We present evidence suggesting that sodium abundance is very sensitive to the temperature. A 10 K increase in mesopause temperature may double the sodium concentration. Thus the sodium profile may change significantly if appropriate thermal fluctuations due to tides and/or acoustic-gravity waves (AGWs) occur. Gravity wave theory predicts that the ion convergence node, without other influences, coincides with a temperature maximum for a westward propagating wave. In this case, the ion layer coincides with the temperature maximum which results in a higher sodium concentration at or near the ion layer height. This proposed temperature dependency can, for the tidal wind field, account for the observed correlation between sodium and ion column abundances and is supported by the average O2(0-1) rotational temperature determinations made at Arecibo. Specifically, we propose that the formation of SSLs is due to the temperature fluctuations induced by AGWs, or other wave processes, in conjunction with a background tidal wind system. Additionally, we argue that when an AGW propagates westward, the SSL coincides with an existing tidal ion layer or with a true sporadic-E layer which forms in the net wave field convergence zone. We also note that roughly the same processes may apply to the production of intense sporadic-E layers.
All Science Journal Classification (ASJC) codes
- Environmental Science(all)
- Atmospheric Science
- Earth and Planetary Sciences(all)