One of the characteristics of Es that might be unknown is how propagation of the E layer changes during the course of a day. I noticed into the second year of the study that many of the longer distance captures were occurring late into the afternoon. Using the distance calculation and data provided from the PropNetPSK software for each station captured, I was able to determine the average distance of the captures (in kilometers) for each hour of the day.
As I suspected, the longest distant PropNET captures do occur late in the afternoon during the 5 and 6 PM (17-18 on chart) local hours. Throughout the 5 years that data was collected, most of the longer distant captures would occur during this period and raise the average capture distance. This was contrary to the higher number of captures that occur in the morning. The long distance captures to Hawaii, Puerto Rico, and the northeast and northwest corners of the United States would occur late in the afternoon. In the morning daytime hours as 10-Meters becomes active, average distance declines as activity increases followed by a steady increase throughout the afternoon. As sunset is approached, distance declines steadily until 10 PM. The late evening and early morning peaks were influenced by the appearance of NH7O in Hawaii.
Using the 3-hour averaging method produces very similar results as well. The longest distances for 10-Meter captures peak at 7 AM, 5 & 6 PM, 11PM and 2 AM local time (Central Daylight).
There is not much difference in the MUF of E clouds at the charted distances (SE Prop). At 1330 kilometers, the MUF of the Es cloud is 32.1 MHz. At 1390 kilometers, the MUF is 31.5 MHz. At 1430 kilometers, the MUF is 31.1 MHz. The questions that are raised:
1. Is a lowering or rising E-Cloud MUF resulting in longer distance captures, or are there more aligned Es clouds with adequate MUF’s that are creating multi-hop opportunities?
2. Are the reflective characteristics of Es in the morning hours different from those experienced in the afternoon?
Es Distance Statistics:
To make better judgments on how Es occur by distance, all 5 years of captures were separated into 500 kilometer segments beginning at the 750 kilometer mark. Clearly, the vast majority of Es captures at this location occurred from stations within in “1250-1750” kilometer range (775-1090 miles). The next largest segment was “750-1250” kilometers (470-775 miles), which totaled less than half of the largest group.
Including the closest range (0-750 kilometers), a morning active dual-peaked diurnal is quite clear for distances to 1750 kilometers. As the distance extends beyond 1750 kilometers the dual-peaked diurnal exists, but becomes afternoon active.
1250 – 1750 Kilometers (775 – 1090 miles):
The vast majority of Es propagation occurs at the 1250-1750 kilometer level. Whenever Es first develop on 10-Meters, signals generally appeared within these distances first. Again, the best time for propagation is clearly during the morning hours after sunrise occurs. At the normal height for an E cloud (105 km) and at this range midpoint, the MUF for the cloud is approximately 30.4 MHz (SE-Prop). The range closely resembles the overall captured trend experienced.
750 – 1250 Kilometers (465 - 775 miles):
The next most active distance is was at the “750-1250” kilometer range. These distances tend to occur as overall Es intensity increases. It also is a way to determine that MUF has increased and help forewarn of further opportunities on 6 and 2 Meters. Similar to the previous distance segment, it favors the morning hours after sunrise. This range clearly displays the dual-diurnal pattern. At the midpoint of this range, the MUF is approximately 38 MHz (SE-Prop).
1750 - 2250 Kilometers (1090 – 1400 miles):
Within the “1750-2250” kilometer range (1090-1400 mile), the majority of these captures are more than likely double reflections (hops) of signals at the Es layer. At 2000 kilometers, the MUF of a normal Es cloud is at 28.3 MHz (SE-Prop) and minimal for Es propagation. The first indication of an afternoon active diurnal occurs at these distances and influences the average distance increase.
0 – 750 Kilometers (0 - 465 miles):
For this segment (0-750 kilometers), Es are extremely intense. Reflections of 10-Meter signals are probably at lower levels in the E-layer. At 750 km, the MUF of a normal Es cloud is approximately 46 MHz. Some of these paths experienced equated to a MUF greater than 90 MHz (SE-Prop). I have witnessed the beginning of several 2-Meter Es openings when these 10-Meter paths were extremely short. Also worth noting, although these short paths favor morning hours, the “absolute” shortest paths in this study generally occurred in the late afternoon hours. Past experiences working VHF Es indicated that these captures (< 300 km) were actually Es backscatter. It was not uncommon to see this phenomenon on 6 Meters as well.
2250+ Kilometers (1400+ miles):
These final distance segments noted (greater than 2250 kilometers or 1400+ miles), represent multi-reflections of 10-Meter signals within the E-layer. Approximately 2300 kilometers is the farthest distance for single Es on 10-Meters (SE-Prop). Two aligned clouds that have an MUF of 33-34 MHz would support it. It does not represent F2 propagation because during the 5-year study, solar flux was not a high enough to create the required F2 MUF (near 18 MHz from Digisonde readings and propagation prediction programs such as, W6ELProp). 10-Meter Es propagation at these distances clearly does occur in the late afternoon hours and were fairly rare in occurrence until 2009. For the first 4 years, the furthest distances experienced in the study and charted below were between my QTH and Puerto Rico. In the final year were more numerous captures from Hawaii.
Next: Directional Analysis
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