A QSOs VE3/ZL in 40M – A Greyline Path?

Lately, VA3PCJ/VE3DTI/CX7RT has not been too active in HF… However, he has been present in the bands several time this year: in addition to several SKCC WES he has been heard in the ARRL DX, the K1USN SST, the CQMM, the OQP and the FQP, which, together added over one hundred QSOs to his logs. Not bad for someone that had not operated the bands since last October… But the big surprise was in the morning of April 18 in the CQMM. While scanning the 40M band, at 07:45 EDT (11:45z) a strong signal was detected at 7.012 MHz. At the time VE3DTI’s rig was the ICOM 706MKIIG, pushing abt. 50W into an EndFed 84-foot wire winding up and down a maple tree.

The station calling CQ in the CQMM was ZM1A, a station near Auckland, New Zealand, operated by Jacky Calvo ZL3CW. The exchange was quickly completed and ZM1A has since confirmed in LoTW. Of course, there are infinite straight routes around the globe for connecting Ottawa to Auckland, but the most direct and within the shortest distance would have been be westward from Ottawa, across the night and the Pacific: 14,500 Km (The next shortest, going East from Ottawa, across the Atlantic, Africa and the Indian Ocean, would have been in the order of 25,000 Km.).  

This was the second time that VA3PCJ/VE3DTI was able to log a station from ZL: the previous Ottawa-Auckland QSO had been with ZM90DX (also confirmed in LoTW) on February 16, 2014 at 18:33z, (13:33 EDT & 06:33 NZST) at the peak of the solar cycle and in the 10M band. At that moment the Sun was South and West of Ottawa, over the Pacific, likely favouring skips along the shortest distance between the two stations.

However, at 11:45z on April 18 2021, the Sun would have been along the longest route somewhere above Africa (see attached figure), which, if the same QSO had been logged in any of the higher bands, would have been, then, the most likely route followed by the waves. The 40M band, on the other hand, is known to depend on the Sun only for short daylight skips of around 500 Km, becoming available for intercontinental DX during the night, particularly “between late afternoon and a few hours after sunrise [when] the band is most useful for inter-continental communication for one or two hours before sunset, during the night and for one or two hours after sunrise.” (https://en.wikipedia.org/wiki/40-meter_band). And these were the approximate conditions on April 18 2021: Sunrise in Ottawa was at 06:21 EDT, hence the contact (07:45 EDT) occurred 1 hr and 24 mins after sunrise. In Auckland, that same day, sunset was at 17:51 NZST (05:51z), and since the QSO was at 23:45 NZST (11:45z), it occurred there 5 hr and 54 mins after sunset, with the Sun almost exactly opposite to the midpoint along the shortest path, somewhere over Africa.

40m can start to open to DX in the afternoon in late autumn and remain open to DX for a period after the sun has risen. In fact, the first 60 minutes after sunrise in the winter on 40m is not called the ‘Golden Hour’ for nothing” says Steve G0KYA (talking about England) in http://www.infotechcomms.co.uk/Understanding_LF_and_HF_propagation.pdf. The path of this QSO could have been a late “greyline path”, which, as Steve goes on to say, happen “where one station is experiencing sunrise while the other has sunset”. And if not “greyline”, at least in this QSO the 40M wave seems to have followed a path that close to its midpoint it would have crossed the projection to the other side of the Earth of the position of the Sun’s Zenith: