Diurnal variations in characteristics of sporadic layer Eₛ over Irkutsk

We have studied the morphological features of semidiurnal variations in the occurrence of the sporadic Es layer (PEs) and height of the layer (hEs), using data from the Irkutsk DPS-4 ionosonde (52.3° N, 104.3° E) for 2003–2021. By averaging over all the years, we calculate diurnal variations in PEs and hEs for each month. It is observed that the maximum of occurrence PEs is achieved when the height hEs decreases; and there is an asymmetry in the maximum of occurrence PEs: morning maxima are larger than evening ones. These features are interpreted based on the concept of the optimal height for Es formation and the role of photoionization in forming the sporadic layer.