Coordinated measurements of <i>F</i> region dynamics related to the thermospheric midnight temperature maximum

Abstract

As part of the NSF/CEDAR program (Coupling Energetics and Dynamics of Atmospheric Regions) in Multi‐Instrumented Studies of Equatorial Thermospheric Aeronomy (MISETA), an all‐sky CCD airglow imaging system has been in operation in Arequipa, Peru, since October 1993. Here we report on the first such use of a wide‐field imager to document the optical signature and variability of a brightness feature associated with the so‐called midnight temperature maximum (MTM). While theo observational driver of this study is a “brightness wave” (BW) seen in 6300 Å and 5577 Å airglow images, detailed case studies are conducted during two campaign periods when Fabry‐Perot interferometer (FPI) and digital ionosonde data were also available. During the passage of a BW, the FPI observed enhancements in thermospheric temperatures, reversals (from equatorward to poleward) of the meridional neutral winds, and local minima in the zonal neutral winds. The ionosonde recorded decreases in the height of the F‐layer during BW events. This lends support to the concept that the poleward winds generated by the MTM pressure bulge cause the lowering of the F‐layer to regions of enhanced loss (h &lt; 300 km) and corresponding airglow production. The two‐dimensional field‐of‐view of the imager allows identification of the geographical orientation of the BW pattern. We use the orientation angle of the BW as an indicator of the geographical orientation of the MTM. Significant day‐to‐day variability in these patterns suggests a complex mix of tidal mode interactions that lead to the overall MTM phenomena.