Source induced vertical components in geomagnetic pulsation signals

We show how large vertical components may be induced in geomagnetic pulsation signals because of the localised nature of the source. The effect is greatest when the signal varies on a horizontal scale length which is shorter than the skin depth of the signal in the Earth. However, the horizontal scale length is also constrained to be equal or larger than the height of the ionospheric E-region (～ 120 km) as signals varying on a shorter scale are severely attenuated. Such conditions are best met by high latitude pulsations and some recent high latitude observations are explained by our results. We find that the vertical component is best correlated with the horizontal component in the direction in which the signal varies most rapidly.