Experimental evidence of relatioship between possible foreshocks in the surface quasi-static electric fields and in the ionosphere

Simultaneous measurements of Es- and F2-layer parameters and of vertical gradient of electric potential in the surface atmosphere are studied. The data were obtained during the crustal earthquake preparations with М=5.0÷6.2 in the Kamchatka region. We revealed occurrence of anomalously high Es accompanied with increase in frequency parameters of the sporadic layer and F2 regular layer on the days when previously detected possible foreshocks were observed in atmospheric electric fields. Supposed foreshocks in the ionosphere were divided into 2 groups according to the lead time of earthquake - from some hours to 2 weeks. We present empirical dependences that connect the lead time (from the moment of occurrence of a corresponding anomaly in the ionosphere or in the surface atmospheric electric field to the moment of the shock) and epicentral distance to the observation point with the earthquake magnitude. These dependences are different in two groups of supposed foreshocks. However, they are similar inside each group for possible foreshocks derived from measurements of the quasi-static electric field and from changes in ionospheric parameters.