A Study of Whistling Atmospherics. IV. Comparison of Observations at Widely Spaced Stations

Whistlers observed at stations separated from one another by up to 3000 km are examined statistically and by comparing simultaneous whistlers. It is shown that whistlers are not commonly observed further than 1000 km away from their "ionospheric source", i.e. the limited region through which they emerge from the ionosphere, and that a lightning stroke may produce whistlers with different dispersions at stations with a separation of this order of magnitude. Ionospheric sources are most common around (geomagnetic) latitude 44-46 in winter and around latitude 50-52 in summer (southern hemisphere). It is suggested that this change is related to changes in the electron density of the ionosphere.