Observation of correlated ULF fluctuations in the geomagnetic field and in the phase path of ionospheric HF soundings

Geomagnetic ssc and si events and pi2 pulsations recorded between October 1978 and June 1979 at a midlatitude station (inclination 67) were investigated. About 50% of the ssc/si but only 30% of the pi2 are correlated with radio frequency shifts. A significant annual variation showing frequent occurrence of correlated events at equinoxes and rare occurrence at solstices is found. In most cases of correlation, the associated frequency shift can be interpreted by a vertical motion of the ionospheric F-layer. Bivariate regression analysis (time domain analysis) of single events shows the regression coefficients between Delta f and a combination of Delta H and Delta D to be of the order of the expected absolute values. In accordance with theoretical considerations, day time values are smaller due to a pronounced E-layer ionization.