In the long era of sporadic E layer (Es) ionosonde research, the ordinary wave critical frequency foEs is used as a measure of Es layer occurrence and intensity. This practice, however, undermines that sporadic E layers are in fact metal ion layers, whereas foEs relates inherently to the sum of both the layer metal and the regular E region plasma densities. This means that foEs acts as an overestimate of Es intensity, a fact that somehow has been overlooked and escaped attention. To deal with this deficiency, an algorithm is introduced which combines the ionosonde-measured foEs and virtual height h'Es parameters with International Reference Ionosphere model predictions of E region electron densities, to arrive at a new critical frequency which depends on sporadic E metal plasma density only; therefore, it represents an unbiased estimate of Es layer intensity. The extensive use of foEs in numerous sporadic E studies must have introduced errors in various results in relation with the Es variability in the time, frequency, and space domains. It is therefore important that this new parameter, notated as foμEs, is now adopted and used instead of foEs in the evaluation of sporadic E. The same methodology applies also for the sporadic E blanketing critical frequency fbEs, which at times is taken as an alternative estimate of Es intensity; similarly, a new parameter, notated as fbμEs, should be used instead of fbEs.
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