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ELECTROMAGNETIC RADIATION AND SEVERE WEATHER

Building An Electrostatic and Magnetic Pulse Monitor

by Richard W. Fergus

Start • Monitoring Parameters • Analysis Procedures • Pattern Observations • Hardware • Monitor Programs • Forecast • Sources

PATTERN OBSERVATIONS

The timing factors have cyclic variations with periods of nearly an hour. Large polarity variations with reference to direction-of-arrival (across a front) have been observed. Reoccurring patterns of the timing factor, polarity, and pulse shape are observed as a function of time. These patterns occur over a wide variation of timespans. The polarity distribution can change slowly throughout the day or rapidly in a few minutes. Generally, the pulse-width distributions are similar to the polarity patterns.

Distance effects (signal strengths and activity rate) are minimized by using graphic plots of distribution factors (e.g., ratios or percentages). Although quantitative data is available, it is seldom used for pattern observation.

The relative timing between events occurring in a short period (less than 1 s) has been studied for several years. This data is generated from the time between successive events that arrive from the same direction.

Each series of three events is used to determine one bit of data. As each event triplet arrives, the time between the first and second is compared to the time between the second and third event. If the time between the first and second is greater than the time between the second and third, one accumulator is advanced. The opposite condition advances a second accumulator.

There is an accumulator pair referenced to each of 120 direction channels. If the relative timing between events were truly random, you would expect the two accumulators to be nearly equal (there is some statistical error). When the timing factor (ratio of the two accumulators) is plotted with respect to time, it does not show a flat line but varies over a wide range.

The timing factor patterns have been compared with severe weather for several years. The earlier timing factor analysis sorted the time-between-events into two categories based on the actual time rather than the current less-than or greater-than comparison. This simpler comparison was incorporated after considering the Chaos Theory, which suggests that one event would influence the next event. The patterns from this comparison are similar to the earlier method of comparison.

The following interpretations are somewhat subjective because the data is from a single monitoring site with limited access to real-time weather information. When two or more weather formations are located in the same general direction or the activity is too distant (greater than 500 mi.), the confidence of the monitored data is reduced. In many cases, some evidence of the expected patterns are present. After many hours of observation, the following conclusions have been assembled.

In the early stages of the severe weather, the timing factor varies over a wide range in a periodic manner. The period of some of these variations can be nearly an hour. Minutes before severe weather (large hail, funnel cloud, tornado, etc.), the variation becomes much smaller. During the severe weather, the large variation returns. The quantity of multiple events also decreases at the time of severe weather.

Numerous severe weather occurrences have been analyzed with respect to the timing data with varying degrees of correlation. The best example is the Lemont, Illinois, tornado of March 27, 1991. In this case, the timing variation decreased about 35 min. before the tornado and remained low until a few minutes before the actual tornado. As you can see in Figure 1, the burst activity increased rapidly and then decreased at the same time that the timing factor variation increased. From the many observations of other severe occurrences, this seems to be a picture-book representation. Other observations generally have one or more of these unique patterns.

Figure 1—This was the range and burst-level variation recorded for the Lemont tornado.

The Lemont tornado came from a rapid buildup. Some severe systems build up rapidly and then maintain a relatively constant activity level for several hours before the severe weather develops. During this constant activity level, the timing factor can vary across a wide range in a periodic manner. It appears that the severe weather will either occur during the rapid buildup or after several hours of relatively constant activity.

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