To better qualify these observed trends throughout the Spring/Summer Es season, I charted probabilities into three hour increments. I first charted probabilities in 1-hour segments and found the information to be overwhelming. This approach shows the seasonal changes in Es opportunities best.
Arranging the probabilities in this pattern will show that the peak of the season is only clearly evident in late evening, twilight and daybreak hours. It is quite difficult to see a seasonal peak during daylight hours.
A reminder… The 9th Week is the Summer Solstice.
6 AM – 9 AM Local Time:
The sun rises at this QTH during this measured period. Although the right-skewed trend was evident in the earliest hour during this period, overall opportunities consistently rose until the Summer Solstice. During this weekly period one can expect an almost 50% chance of an Es opening. Between the 5th and 14th weeks (5/23-8/01) there is at least a one-in-three chance of an opportunity.
9 AM – 12 Noon Local Time:
This segment is the best time to work Es, and is best to call it “primetime”. By the 3rd Week of the season (5/09) the probabilities are greater than 50% for the entire season. During the 6th Week (5/30-6/05) the probability is almost 90%. During the four years of the study, specifics days and hours within this period had a capture occur each year of the 5 year study. The obvious trend shown is that once the Es season begins in earnest, it will not end until the end of August. The 16th week of the season is just as active as the 5th. Any decline in probability as the season progresses is hardly negligible until Week 17.
12 Noon – 3PM Local Time:
The probabilities during this segment clearly indicate and confirm that Es propagation is a daytime (diurnal) phenomenon. The probability of working 10-Meter Es is only slightly lower than the previous 3-hour period. The pattern continues until the Sun approaches due south, the Solar Noon (1:15PM). The 6th Week again is clearly the best and we also begin to notice a slight mid-season lull. The probabilities of a 10-Meter capture are at their best at the noon hour. During this time segment a slow a steady decline appears after the 11th week of the season.
3 – 6 PM Local Time:
The sun is now located further west during this period. The right-skewed and right-tailed progression of the season shows up in this segment. The 6th week of the season was the best until 2009 and had me believing that Es activity was peaking at a period other than the summer solstice. The 11th week displays a very strong rebound in opportunities. The 11th week of the season (Independence Day 7/4) it is well known by many Es enthusiasts as an extremely active week. Much of the rise could be due to an increase in the population of participants during the holiday, although many PropNET participants vacationed.
6 – 9 PM Local Time:
During the latter time in this segment the Sun sets. The right skewed and right tailed probability trend is quite evident in this chart. Seasonal trends are clearer with only the 11th Week showing a sudden surge in probability. This time period best displays the rise and fall of the Es season. By the 3rd week, probability of an Es QSO is above 50% during the time segment and remains at least that high until the 16th week of the season.
9 PM - Midnight Local Time:
For each hour after sunset, overall probabilities continue to decline. Other than the 11th week surge, the decline is quite pronounced beginning the 8th week. The best weeks again are the 6th, through the 8th. As in the daytime segments, by the 5th week probabilities are greater than 50% and remain so until the 12th. A slight increase the 14th week becomes apparent and prevalent into the next 3-hour segment.
Midnight – 6:00AM Local Time:
Probabilities of an Es QSO become much less into the twilight hours. The trends displayed are consistent; probability peaks near the Summer Solstice. Generally when opportunities occur at these hours, Es have been very intense. Some of the best daily openings with numerous high MUF QSOs have occurred when good conditions exist at these hours.
Also, notice that the 14th week peak in probability has now shifted to the 15th week. It brings up some interesting questions to why weekly peaks occur at these early morning hours.
Next: Hour to Hour Probabilities by Week
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