Universal Time Control of the Polar Ionosphere

Abstract

SEVERAL authors have demonstrated that, at very high latitudes, the critical frequency and height of the ionospheric F2 layer are strongly dependent on Universal Time. For example, Duncan1 has shown that, in winter, a maximum occurs in the F2 layer critical frequency (f0F2) near 0600 UT for Antarctic stations close to the magnetic pole. Piggott and Shapley2 have confirmed this and demonstrated a similar behaviour in the height of maximum electron density (hmF2). Duncan has suggested that the daily transport of the eccentric geomagnetic field through the interplanetary plasma could cause a tide in the geomagnetic field, which in turn would cause dumping of charged particles into the polar ionosphere. Hill3 has proposed that the phenomenon, being sporadic, is caused by electromagnetic drifts associated with polar-cap events. In contrast, Wilkes4 has pointed out that a global standing wave could explain the observed UT control of the polar tropospheric pressure; such an oscillation could also affect the atmosphere at ionospheric heights. Recently, King et al.5 have suggested that the phenomenon could be explained by vertical drifts in ionization, caused by atmospheric winds in the F layer.