WEBVTT NOTE Space Weather and Propagation Prediction 1 00:00:00.000 --> 00:00:16.760 The indices, extended. The General track covered sunspot number, solar flux, and the A and K indices. Extra adds three more, and each answers a question the others cannot. 2 00:00:16.760 --> 00:00:23.800 Question. What does the value of Bz (B sub z) represent? 3 00:00:24.700 --> 00:00:30.466 Answer. North-south strength of the interplanetary magnetic field. 4 00:00:31.066 --> 00:00:44.106 Question. What orientation of Bz (B sub z) increases the likelihood that charged particles from the Sun will cause disturbed conditions? 5 00:00:45.006 --> 00:00:47.312 Answer. Southward. 6 00:00:47.912 --> 00:01:04.264 Bz is the best short-term predictor there is. The Earth's field points north at the equator, so a southward interplanetary field is antiparallel to it, the two reconnect, and solar particles pour in. 7 00:01:04.264 --> 00:01:20.451 A northward Bz deflects them and conditions stay quiet, even during a fast solar wind. A CME can arrive with a northward Bz and do almost nothing, or with a southward Bz and produce a severe storm. 8 00:01:20.451 --> 00:01:23.245 Same particles, opposite outcomes. 9 00:01:23.245 --> 00:01:29.255 Question. What does the 304A solar parameter measure? 10 00:01:30.155 --> 00:01:38.257 Answer. UV emissions at 304 angstroms, correlated to the solar flux index. 11 00:01:38.857 --> 00:01:53.337 An ultraviolet emission line from ionised helium, measured by satellite. It correlates with solar flux and responds faster, so it is a leading indicator of ionisation. 12 00:01:53.337 --> 00:01:59.790 Question. Which of the following indicates the greatest solar flare intensity? 13 00:02:00.690 --> 00:02:03.744 Answer. Class X. 14 00:02:04.344 --> 00:02:24.504 Flares are classed A, B, C, M, X, each a factor of ten stronger than the last. X is the top, and an X-class flare produces the sudden ionospheric disturbance from the General track, eight minutes later, with no warning. 15 00:02:24.504 --> 00:02:32.032 Question. Which of the following is the space-weather term for an extreme geomagnetic storm? 16 00:02:32.932 --> 00:02:35.723 Answer. G5. 17 00:02:36.323 --> 00:03:00.243 NOAA's G-scale runs G1 (minor) to G5 (extreme). There are parallel scales for radio blackouts (R1 to R5) and solar radiation storms (S1 to S5). All three are published and all three matter to HF. Effects. 18 00:03:00.243 --> 00:03:05.386 Question. What is the cause of short-term radio blackouts? 19 00:03:06.286 --> 00:03:09.020 Answer. Solar flares. 20 00:03:09.620 --> 00:03:16.140 Question. What is indicated by a rising A-index or K-index? 21 00:03:17.040 --> 00:03:21.825 Answer. Increasing disturbance of the geomagnetic field. 22 00:03:22.425 --> 00:03:34.425 Question. Which of the following signal paths is most likely to experience high levels of absorption when the A-index or K-index is elevated? 23 00:03:35.325 --> 00:03:39.372 Answer. Through the auroral oval. 24 00:03:39.972 --> 00:03:56.655 The auroral oval is where field lines funnel particles into the atmosphere, so it absorbs first and hardest. Any path crossing high latitudes, most transatlantic and transpolar paths, degrades before anything else does. 25 00:03:56.655 --> 00:04:08.692 The practical response is not to give up but to route around it: a southerly path to the same destination may be entirely usable while the polar path is dead. 26 00:04:08.692 --> 00:04:20.132 Question. Which of the following is indicated by a sudden rise in radio background noise across a large portion of the HF spectrum? 27 00:04:21.032 --> 00:04:27.740 Answer. A coronal mass ejection impact or a solar flare has occurred. 28 00:04:28.340 --> 00:04:35.094 The Sun is a broadband radio source, and a flare makes it a much louder one. 29 00:04:35.094 --> 00:04:51.535 A sudden rise in noise across many bands at once is the Sun, not your station, and it is worth recognising before you go looking for a local noise source. The radio horizon, quantified. 30 00:04:51.535 --> 00:05:01.295 Question. How does the VHF/UHF radio horizon compare to the geographic horizon? 31 00:05:02.195 --> 00:05:07.515 Answer. It is approximately 15 percent farther. 32 00:05:08.115 --> 00:05:21.810 The General track's "the atmosphere refracts radio waves slightly", with the number: about 15% beyond the visual horizon, from the standard atmospheric refraction model. 33 00:05:21.810 --> 00:05:30.075 It is why the "4/3 Earth radius" approximation appears in path calculations. Prediction and reporting. 34 00:05:30.075 --> 00:05:35.930 Question. What does VOACAP software model? 35 00:05:36.830 --> 00:05:39.910 Answer. HF propagation. 36 00:05:40.510 --> 00:05:58.644 The Voice of America Coverage Analysis Program, in the public domain and still the standard. Give it two locations, a date, a time, and a solar flux figure, and it predicts which bands will work and how reliably. 37 00:05:58.644 --> 00:06:05.884 Question. What type of data is reported by amateur radio propagation reporting networks? 38 00:06:06.784 --> 00:06:11.424 Answer. Digital-mode and CW signals. 39 00:06:12.024 --> 00:06:26.272 The Reverse Beacon Network and PSK Reporter listen continuously and log CW and digital signals, because those are machine-decodable, complete with a call sign and a signal report. 40 00:06:26.272 --> 00:06:43.624 Voice is not, which is why these networks carry no SSB data. That is why the General operating lesson recommended a short CW or WSPR transmission to test a path: the network is only listening for signals it can decode. 41 00:06:43.624 --> 00:07:05.407 The dashboard, complete. Parameter, Sunspot number, solar flux, 304A; Good is, high; Timescale, days to years. Parameter, A-index, K-index; Good is, low; Timescale, hours to days. 42 00:07:05.407 --> 00:07:31.814 Parameter, Bz; Good is, northward; Timescale, minutes to hours. Parameter, Flare class (A to X); Good is, low; Timescale, minutes. Parameter, G-scale (G1 to G5); Good is, low; Timescale, hours to days. Check yourself. 43 00:07:31.814 --> 00:07:54.692 A CME is due to arrive in six hours. What single parameter most determines whether it wrecks the bands? Your transatlantic path is dead with K = 6, but a station in Argentina is loud. Why? 44 00:07:54.692 --> 00:08:02.480 Why does the Reverse Beacon Network never report your SSB calls? 45 00:08:08.480 --> 00:08:25.034 Bz. Southward and it reconnects with the Earth's field and lets particles in; northward and the same CME may do very little. The transatlantic path crosses the auroral oval, which absorbs heavily when K is high. 46 00:08:25.034 --> 00:08:38.449 The southerly path avoids it. It listens for machine-decodable signals, CW and digital modes, that carry a call sign it can extract. Voice cannot be decoded automatically.