Temporal modulation of the four-peaked longitudinal structure of the equatorial ionosphere by the 2 day planetary wave

Observations of electron densities by the Constellation Observing System for Meteorology, Ionosphere, and Climate in August to October 2008 have shown a prominent four-peaked longitudinal structure in the height of the F-2 layer (h(m)F(2)) in the equatorial ionosphere. The development of this ionospheric structure in daytime is found to be consistent with the forcing by the eastward-propagating nonmigrating diurnal tide with zonal wave number 3 (DE3). It is believed that tidal winds can modify the E region electric fields and subsequently produce variations in the ionosphere through the dynamo effect. This study reveals that the amplitude of the h(m)F(2) four-peaked longitudinal structure is subject to a 2 day periodic modulation on certain intervals in the two-month time period. Simultaneously, wind measurements from the SKiYMET meteor radar at Thumba (8.5 degrees N, 77 degrees E), India indicate corresponding 2 day planetary wave activity in the mesosphere and lower thermosphere (MLT). The 2 day planetary wave has both zonal and meridional wind components, and it is the variability in the zonal component that most closely corresponds to F-2 layer changes. The zonal wind observations by the radar also show that the amplitude of the diurnal tide is modulated by the 2 day wave. This study suggests that the identified 2 day variation of the h(m)F(2) four-peaked longitudinal structure in the equatorial ionosphere is caused by the interaction between the DE3 tide and the 2 day planetary wave.