Variability of the equatorial ionosphere induced by nonlinear interaction between an ultrafast Kelvin wave and the diurnal tide

The wave forcing from below allows the neutral atmosphere to drive short-term variability in the ionosphere. Recent modeling studies have shown that secondary waves originated from the nonlinear interaction of the atmospheric tides with planetary scale waves can contribute significantly to day-to-day variability of the ionosphere. In this study we used MLT neutral wind measured at Sao Joao do Cariri (7.4 degrees S, 36.5 degrees W) and ionospheric soundings performed by a digisonde installed at Fortaleza (3.9 degrees S, 38.4 degrees W) to investigate the presence and the induced variability by a secondary wave in the mesosphere-ionosphere system over the Brazilian equatorial region. We found evidences of the nonlinear interaction between a 3.5-day ultrafast Kelvin wave and the diurnal tide. The interaction produced a 1.3-day secondary wave that was found to propagate upward with maximum amplitude of 15 m/s and relatively long vertical wavelength (similar to 44 km) in the MLT, which may allow it to penetrate into the ionosphere. In the ionosphere, we observed a common 1.3-day periodic variation in the virtual height (h'F) and critical frequency (f(o)F(2)), which may be connected to the secondary wave observed in the MLT via modulation of the wind system in the E region dynamo. These findings suggest that secondary waves may impose additional variability to ionosphere.