Spring 2004 Issue

The Sporadic-E Files

In part one of this series, WB2AMU explains the E-region
reservoir and the transport theory of sporadic-E.

By Ken Neubeck,* WB2AMU

No matter how you look at it, sporadic-E is the major VHF propagation mode for much of the world. However, while it is extremely important for hams on 6 and 2 meters and occasionally on 220 MHz, it is probably the most misunderstood mode and the one about which many myths are circulated.
It is important to first understand that sporadic-E is not a single phenomenon, but rather is a collection of individual phenomena that contribute to the overall complex phenomenon. It thus would be of benefit to list the known facts that have been determined through radio observations, as well as the scientific studies that have taken place over the course of the past decades. The vehicle to cover this topic will be a series of articles in CQ VHF, each of which will discuss a particular aspect of sporadic-E along with the facts that have been determined concerning the specific aspect covered.

The Basic Behavior of Sporadic-E

Before we discuss the transport theory of sporadic-E in this initial article, we will provide a simple overview of the basic behavior of the phenomenon as observed by hams on the VHF bands.

For the temperate zones of the Earth, sporadic-E has two seasons, a major summer season and a minor winter season. They are separated by significant absence of the phenomenon during the spring and fall equinox. For stations in the northern temperate zone, the summer season starts around May 1st and ends more or less around mid-August. During some parts of June and July, sporadic-E may appear as a daily event, usually lasting for several hours. The winter season is less distinct as far as specific start and end dates, but generally it appears on an occasional basis in late October and lasts through mid-January. It is the major propagation mode for 6 meters during these time periods and also sometimes for 2 meters. The mode makes for lots of fun on these VHF bands during the summer months, as has been documented in CQ VHF over the past several years!

Sporadic-E has been of intense interest to the scientific community as well as hams. In 1962 Ernest K. Smith and Matsushita published the book Ionospheric Sporadic-E (Pergamon Press), which was dedicated entirely to the phenomenon. Dr. Smith had previous experience with this phenomenon; his doctoral thesis, published during the late 1950s, was entitled “World Occurrence of Sporadic-E.” Both works remain a valuable starting point for someone first studying the phenomenon. However, it is important to realize that much of the data at that time was collected by ionosondes (or sounding stations) and radio observations, the best that could be accomplished at the time. Since then significant data has been collected through the use of rocket probes sent into the ionosphere, as well as EISCAT radar plots. Figure 1 is an example of an EISCAT plot.
 

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