On Tuesday February 3, 2009, rather remarkable propagation events were observed here in Melbourne, between 0130 and 0230, and 0330 and 0400.
This is during local mid-summer noon and early afternoon periods.
This was represented by extremely strong all-daylight-path signals from Asia, on frequencies as low as 5925, extending up to 10 MHz.
Of particular note were the unprecedented appearances of signals from stations in Laos (6130), Myanmar (7185), India (7125, 7290), Vietnam (5925, 6020), China (6115, 6185, 7170), and Malaysia (Sarawak)(6050).
Some of these signals have never been noted precviously during this time period in Melbourne!
These specialized propagation modes makes their appearances during the Australian summer, with signals appearing and vanishing almost randomly - some are present for a minute or so, others for periods up to an hour or more.
This propagation mode is not confined to Melbourne, and was also observed in central NSW, by my colleague Craig Seager in Bathurst, on Sunday February 1 in the same time period.
There is a reference to the Mode in the Australian Government's Department of Space Services Training Handbook (Ionospheric Prediction Service), as a "Specialized Complex Mode".
The actual propagation mechanism is not clearly understood, and is believed to be supported by reflection off the top layers of Sporadic E clouds, with no intermediate ground reflection, for part of the transmission path. This results in minimal absorption, generating very strong signals, often with no fading, and overriding locally generated power-line interference and noise.
Path lengths are enormous, of over 10,000 km, all-daylight!
The signal patterns resemble those of long-haul VHF reception, mobile telephone reception, or digital broadcasting.
Here is a summary of the events as noted on February 3 - there were two separate events, 0130 to 0230 and 0330 to 0400 - further research continues!
EVENT 1 - window 0130-0230
5925 VIETNAM VOV regional
5975 VIETNAM VOV regional
6020 VIETNAM VOV regional
6050 MALAYSIA RTM Sibu regional
6115 CHINA V. of Strait
6130 LAOS Vientienne, national network
6185 CHINA Chengdu regional network
7125 INDIA Delhi, Sindhi
7170 CHINA Lhasa, Mandarin
7185 MYANMAR Yangon, national network
7197 *CHINA PBS Xinjiang, Urumqui, Uighur (*Note: frequency is actually on
7197, not nominal 7195!)
7210 VIETNAM VOV national network
7225 CHINA PBS Xinjiang, Urumqi, Uighur, parallel 7197, new channel
7230 CHINA CNR1
7250 CHINA CNR8 Urumqi
7270 MALAYSIA RTM regional
7280 CHINA V. of Strait
7285 SRI LANKA DW-Trincomalee German
7295 MALAYSIA RTM Kajang English relaying FM domestic service
EVENT 2 - window 0330-0400:
7160 INDIA Chennai regional
7275 CHINA PBS Xinjiang, Urumqi, Uighur
7290 INDIA regional, huge signal!
9440 THAILAND BBC Nakon, Bengali
9450 CHINA CRI Kashi Mandarin
9570 CHINA CNR1
9630 CHINA CNR1