Diurnal characteristics of transfer functions at pulsation periods

Within a particular induction region the geomagnetic response function possesses a dependence on the wavenumber of the inducing field. To investigate possible relationships between response function and wave­ number, the local time dependence of the magnetic variation fields used to determine the response function can be retained. Such an analysis has been carried out at five UK sites using single-station transfer function analysis in the period range from 2000 to 40 s. To allow a level of significance to be established the local time estimates are compared with the time-averaged determinations. At periods greater than 500 s there is no significant local time variation of the transfer function estimates. At periods less than 500 s, corresponding to mid-latitude pulsation fields, significant local time variations are observed. At four of the five sites studied, the diurnal character in the transfer function estimate consists of a maximum response on the dayside and a corresponding nightside minimum. The behaviour is qualitatively related to a dayside/nightside asymmetry in the source region of the mid­ latitude pulsation field.