| Nighttime observations of the atmospheric potassium and iron layers were performed using lidar, between September 2001 and December 2005, to determine the frequency and characteristics of potassium (Ks) and iron (Fes) sporadic metal layers over the Arecibo Observatory. Ks and Fes were observed to occur once every six hours of measurements, lasting about 90 minutes. Occurrence probability, peak height and full width half maxima (FWHM), strength factor and duration were determined from 1312 and 299 hours of observations for potassium and iron, respectively.;Ab initio and density functional calculations were carried out to calculate the geometry and vibrational frequencies of the neutral and ionic form of KN2 and KCO2 to study the binding energy, the adiabatic ionization energy (AIE), and the vertical ionization energy (VIE). KCO 2+ and KN2+ have a significant role in Ks, acting as sinks and reservoirs in the ligand-switching recombination reactions used to describe the mesospheric potassium ion-chemistry.;Finally, we present an analysis of two separate and distinct sporadic layer events in the mesosphere and lower thermosphere region above the Arecibo Observatory. One sporadic event was a high altitude layer, in which both atomic and ion sporadic layers were positioned above 100 km altitude. This represents a rather typical sporadic layer visible in both ions and neutrals at Arecibo. The other observation was less typical, with a lower altitude and more diffuse sporadic E layer, extending from below 90 km to above 95 km, which dissipated coincident with growth of a sporadic neutral K layer. We analyze these separate events using a temperature-dependent chemical model. First, we find that the high altitude layer of 12–13 June 2002 has a distinct and important temperature dependence, and that the neutral layer would not have formed had the temperature profile matched the MSIS-90 model. Second, the temperature dependent chemistry model reproduced K+ in close agreement with electron densities on 14–15 June 2002, but the neutrals do not agree well with model above 90 km and it likely requires inclusion of dynamical forcing and advection. The model, using commonly accepted chemical processes, successfully reproduces results on 12–13 June 2002. We speculate that the deficiency of the model is primarily due to the lack of realistic gravity wave parameterization. |
