Trans-Continental opening on the 40 MHz band in the USA - 14th Apr 2022

On the 14th of April 2022, there was an interesting Transcontinental opening on the 40 MHz band in the USA.

There are currently seven US radio amateurs using experimental callsigns and licenses for the 40 MHz band. Three of these... WM2XCC in California, WM2XCW in Washington State and WM2XAN in Michigan are using the WSPR digital mode and their signals were heard by W4WLO in Alabama and N2OTO in Florida.

The WSPR reports for each of the three stations are shown below...

 Local   (y-m-d) TX txGrid RX rxGrid MHz W SNR drift km
2022-04-14 21:52 WM2XAN EN74oh WLO/O5 EM50vo 40.6636 100 -26 -4 1553

2022-04-14 22:14 WM2XCC DM13ji N2OTO EL96wi 40.663493 2 -9 0 3640
2022-04-14 22:02 WM2XCC DM13ji N2OTO EL96wi 40.663492 2 -14 0 3640
2022-04-14 21:52 WM2XCC DM13ji N2OTO EL96wi 40.663493 2 -20 0 3640
2022-04-14 21:44 WM2XCC DM13ji N2OTO EL96wi 40.663493 2 -16 1 3640
2022-04-14 21:34 WM2XCC DM13ji N2OTO EL96wi 40.663493 2 -24 0 3640

2022-04-14 21:34 WM2XCC DM13ji W4WLO/S32 EM50vo 40.663489 2 -11 0 2743
2022-04-14 21:24 WM2XCC DM13ji N2OTO EL96wi 40.663495 2 -24 0 3640
2022-04-14 21:24 WM2XCC DM13ji W4WLO/S11 EM50vo 40.663449 2 -8 0 2743
2022-04-14 21:16 WM2XCC DM13ji N2OTO EL96wi 40.663493 2 -23 1 3640
2022-04-14 21:16 WM2XCC DM13ji W4WLO/S11 EM50vo 40.663449 2 -3 0 2743
2022-04-14 21:08 WM2XCC DM13ji N2OTO EL96wi 40.663493 2 -11 0 3640
2022-04-14 20:58 WM2XCC DM13ji N2OTO EL96wi 40.663492 2 -8 0 3640
2022-04-14 20:48 WM2XCC DM13ji N2OTO EL96wi 40.663492 2 -9 0 3640
2022-04-14 20:38 WM2XCC DM13ji N2OTO EL96wi 40.663491 2 -9 0 3640
2022-04-14 20:28 WM2XCC DM13ji N2OTO EL96wi 40.663492 2 -12 0 3640
2022-04-14 20:20 WM2XCC DM13ji N2OTO EL96wi 40.663493 2 -7 0 3640
2022-04-14 20:12 WM2XCC DM13ji N2OTO EL96wi 40.663494 2 -1 0 3640

2022-04-14 21:16 WM2XCW CN88lx WLO/O5 EM50vo 40.663601 10 -20 0 3561
2022-04-14 21:16 WM2XCW CN88lx W4WLO/S32 EM50vo 40.663538 10 -27 0 3561
2022-04-14 21:06 WM2XCW CN88lx W4WLO/S32 EM50vo 40.66354 10 -17 0 3561

Some observations...

1) WM2XAN to WLO/05 (W4WLO) at 1553kms is normal enough. Some weak Sporadic-E could account for this reception report.

2) WM2XCC in California to W4WLO in Alabama and N2OTO in Florida is 2743kms and 3640kms respectively. These were the most numerous reports and are well beyond the normal 2300km limit or so for single hop Sporadic-E. In that respect, it's a very unusual opening.

3) WM2XCC in Washington state to W4LO in Alabama is 3561kms and is again an unusually long distance path.

Analysis... What caused the opening and what was the propagation mode? 

First of all, let's look at the times. The opening was at roughly 21:00 UTC which was roughly 3pm local time in the centre of the United States.

Theory 1: Double hop / Chordal hop Sporadic-E - It's possible that Sporadic-E with more than 1 hop was involved which extended the range beyond the normal 2300kms or so. Even though the Summer Sporadic-E season has started, it's still only the 14th of April. It's possible it was double hop but I think it's unlikely.

Theory 2: F2 layer propagation - The solar flux on the day was at 103 but note how the opening happened just before a major aurora.

It is often observed that there is an improvement in the upper HF bands like 28 MHz as an aurora is commencing or about to start.

At the moment, East-West paths across the USA have a maximum usable frequency (MUF) in the low VHF spectrum just above 30 MHz. I suspect the onset of the aurora caused to MUF to jump upwards and propagation via the F2 layer at 40 MHz was possible.

While we can never be 100% certain what the reason was, I think the fact the 40 MHz opening happened at the start of an aurora is significant.

In conclusion... Over the next few weeks, the Sporadic-E season will really begin to get going and I suspect there will be plenty of double hop Sp-E openings in May and June.

As the sunspot numbers improve, F2 layer openings like this will be become a lot more common and I think 40 MHz WSPR reports will be of particular value to those operating on the 50 MHz band waiting for an trans-continental opening in the United States.