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This article is generally accurate in my estimation, except for the assertion that sporadic-E propagation is "relatively rare". In fact, notwithstanding its fairly predictable seasonality (in the northern hemisphere, mid-May through mid-August and, to a significantly lesser extent, mid-November through mid-February), sporadic-E radio propagation is quite common. (It is relatively rare during other periods of the year). During June and July, sporadic-E propagation occurs somewhere in the northern temperate latitudes on nearly a daily basis. Sporadic-E openings on the 6-meter (50 MHz) amateur radio band during late spring and early summer often last for many hours, occasionally well into the wee hours of the night. Numerous amateur radio websites track and report sporadic-E propagation openings in real time throughout the year.
While it is true that the exact process that creates sporadic-E clouds is not well understood, it should be pointed out that the solar phenomena largely responsible for high-frequency (3-30 MHz) ionospheric radio propagation — i.e., ionization of the F-layer by solar activity proportionate to the presence of sunspots over an 11-year cycle — is not implicated in sporadic-E ionization, which occurs just as frequently and with the same basic characteristics during any part of the 11-year solar activity cycle.
Billvanalstyne 23:51, 3 February 2007 (UTC)Bill VanAlstyne, W5WVO
