Two-day oscillation of electron concentration in the lower ionosphere

A strong two-day modulation in electron concentration was observed by the A recibo incoherent scatter radar during January 21-28, 1993, in the altitude range between 85-94 km. The modulation of the electron density and the alt itude variation of the lower edge of the electron density enhancement were associated with a quasi two-day planetary wave observed in the winds. On th e days when the Lorentz force associated with the two-day wave pointed down ward, the ions were observed to penetrate to lower altitudes. At 90 km, the difference in electron concentration between consecutive days was about 40 00/cm(3). Our analysis suggests that molecular ion transport can only accou nt for less than 300/cm(3) enhancement for typical mesopause conditions. Th e large enhancement in electron concentration is likely due to transport of metallic ions from higher altitudes. (C) 1999 Elsevier Science Ltd. All ri ghts reserved.