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Electric vertical and horizontal NS and EW components of natural ELF electromagnetic noises were observed through a year from February, 1967, to January, 1968, Mean diurnal variations of the Schumann resonance power were obtained for the first three modes from noise spectra. The variations show completely different patterns for each component, and change considerably month by month. The diurnal amplitude also varies by 1 to 7 db from the mean daily values. The results are compared with the diurnal variations derived from the simple theory considering worldwide thunderstorm activity as noise sources. There are fairly good agreements between the experimental and theoretical results, especially for EW component. For vertical and NS components thunderstorm effect from Africa seems relatively smaller then expected. The time of this effect is in local night. This shows that local night conditions of the lower ionosphere as the upper boundary of the earth-ionosphere cavity, make the received intensity of vertical and NS components decrease.

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