Abstract This paper is concerned with the results of an investigation into some observations of the Es-layer with a group delay (Esr) in the main ionospheric trough (MIT) based on data from a high-latitude meridional chain of ionosondes (L = 90°E, Φ = 62–74°N). Esrlayers are broken down according to their association with magnetic activity and extent in time and space. The dependence of Esr-layer occurrence on the value of Kp-index and AE-index is investigated. Possible mechanisms for their formation are discussed. It is concluded that short-lived Esr-layers observed at separate stations in the dayside sector in the presence of low magnetic activity can be identified with isolated patches and arcs as detected in the main ionospheric troughs region from satellites.