A 7-Year 10-Meter Es Propagation Study Using PropNET - Part 3 of 5

Distance Analysis:

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) local hours. Throughout the 7 years that data was collected, most of the longer distant captures would occur 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 whose signal was captured many times during twilight hours.  The peak distance increased the last few years of the study.

  

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 7 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. I also believe that if some solar activity was to influence propagation, it would more than likely be at this distance.

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 during an intense Es opening. 

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 7-Year Study, solar flux was never 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 2009 and 2010 there were more numerous captures from Hawaii. In 2011, Puerto Rican captures again dominated.  During the final 2 years after the change in frequency, a few European non-PropNET captures occurred during the afternoon hours.

Specific Directional Groups:

After five years of this study, there existed sufficient information to display the specific peaks of activity towards 45-degree directional segments.  Although it made statistical sense, it tended to cloud up the trends it was indicating.

The actual number of captures by 45-degree segments was as follows:

Direction	Captures
North	2776
Northeast	28836
East	41415
Southeast	2096
South & S. West	154
West	8440
Northwest	3988

As indicated, the numbers strongly point to an Easterly influence due to the number of participants over the years.  To best display similarities and contrasts, comparing directional groupings seemed to be a better approach to show trends.

Es Directional Characteristics:

One of the characteristics of Es to observe was to compare PropNET captures between different directional groups.  Due to the varying volumes from each directional group, the following capture data is displayed as an “hourly percentage of the total day” for each group, and not the actual volumes.  This allows us to compare groups to each other on an equal scale despite differences in capture volume (population based).  Each hour charted was also based on a 3-Hour average method. For the most part, each directional group displayed similar trends.  Peaks and valleys were usually no more than two hours off between directional groups.  Only the Southern/Southeastern group is different and peaked during the opposite group’s lulls. Reminder, the charts reflect 45 degree segments.

Comparing Data into Directional Halves:

After reviewing each directional group, distinctive patterns were apparent between them. Each group is separated into the following halves:

1. North and South
2. East and West
3. Northwest and Southeast
4. Northeast and Southwest. 
   
   

Comparing North to South:

The following charts shows that as the sun rises, the opportunity to work stations towards the North (270° - 89°) is greater than Southerly (90° - 269°) ones.  Both directional groups show the steadily improvement after sunrise.   Both groups peak the hour prior to noon.  Northerly opportunities decline after noon at a pace much greater than Southerly ones during this time. 

A second peak of activity begins for both groups during the local 5 PM (17:00-17:59) hour. This helps confirms a dual-peaked diurnal pattern for both opposite directional groups. Once the sun sets, opportunities decline more rapidly for the Southerly group.  The sun is located north of west at and after sunset from my QTH.

Therefore, Northern paths are best as the sun rises and as it sets. Southerly propagation is strongest during the afternoon hours when the sun is at a high elevation.  The sun’s influence is quite notable.

Comparing East to West:

Separating the total data into these directional groups (East and West) show one obvious trend, follow the sun. Eastern capture opportunities are better than the Western ones after sunrise and peak during the local 10 AM hour.  Activity declines steadily and peaks again during the 5 PM hour (the dual-peaked diurnal). Western capture opportunities improve at a slower rate after sunrise and peaked at the 1 PM hour (3 hours later).  The Western activity decline after sunset is less than the Eastern counterpart, but opportunities after midnight become best to the east.

Comparing Northwest to Southeast:

Separating activity into Northwest and Southeast halves show that the sun’s location determines the best paths by time of day somewhat equally. Both show the dual peak diurnal.  Of all the directional half groups, these two directions tend to stay closer in the hourly trends. The hours from sunrise to mid-afternoon show the only differences.

Comparing Northeast to Southwest:

Finally, the “follow the sun” scenario is more apparent for Northeast and Southwest divisions.  Peaks in activity are clearly two hours different. Northeast occurs at 10 AM and Southwest at the Noon hour.  For both directions, the late afternoon peaks are almost equal with a slight favoring towards the Southwest.

Next: Probabilities of Es Propagation