The virtual height of the E layer, h'E

Like the predicted values of foE, ADEP sets a default value of 90km for any ionogram with no h'E. This results in the misleadingly high values of 'Chilton only' data in the graph of h'E occurrence. For the common data, the scatter of points is so large that for most months there appears to be no obvious correlation between the two instruments and indeed the data set as a whole (49%). This could be due to the fact that the E-layer critical frequency is around the minimum frequency response of the ionosondes. If this were the case, the part of the E-trace measured would be changing rapidly with virtual height, and a 'true' value of h'E would be hard to measure. To test this hypothesis, a subset of the data, whose foEs values were within 2 Mhz of fmin, were studied to see if their values of h'E were anomalous. Only six points fell into this category and the results of this test were inconclusive.

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15/05/97 Chris Davis