while the initial peak around midday can be understood in the contest of vertical drift velocity during dytime which is upward and has a broad peak around 11.00 LT. What mechanisms then leads to the post noon peak like the one shown in this figure for adis station

Double peak in daytime foF2, NmF2 or TEC over the equator is a phenomenon known for many years. It is related to the ExB drift velocity causing the Appleton anomaly at low latitudes. The plasma is lifted during the daytime to higher latitudes over the equator by the electrodynamic drift which diffuses down to higher altitudes under the action of gravity and ambipolar diffusion. AS a result, the ionization over the equator is depleted during the peak daytime hours.

You can refer to Sharma et al. (2012) for better understanding.