If one of these flares is pointed towards Earth, a tongue of intense… — Page 56, Lesson 61

I want to walk you through what happens when a solar flare is pointed toward Earth. If one of these flares is directed our way, a tongue of intense ionisation curls around the upper atmosphere. That tongue of ionisation causes several effects, and the most notable one is the Aurora Borealis — you'll know that as the Northern Lights. There's a similar effect around the South Magnetic Pole, called the Aurora Australis. These events are known as magnetic storms, and their effects can be very intense. The excerpt tells us that during the most recent of these 11-year cycles, variation changes of up to 7 degrees were observed. That's a significant shift. Now, sunspot activity and solar flares also occur at other times, not just during the peak of the 11-year cycle, so minor magnetic storms can happen outside that peak period as well. Let's move on to local anomalies. Local magnetic anomalies are caused by magnetic deposits or rock formations that make the magnetic field different within a particular area. So if you're flying over a region with certain mineral deposits, the local magnetic field can be distorted. In addition, scientific surveys have shown that variation can change slightly with altitude. However, the excerpt notes that few aircraft systems would be sensitive enough for this altitude-related effect to be noticed. Now, here's a practical takeaway for you as a pilot. Because of all these factors — magnetic storms, local anomalies, and even altitude effects — it is very difficult to know the precise instantaneous value of variation affecting an aircraft to better than about 2 degrees. And even if great care is taken over finding and correcting for variation, you can only get it to better than about half a degree over a period of time. This is why the emergence of systems based on highly accurate gyros, particularly Inertial Navigation Systems — INS — in the 1960s and 70s was such a major advance in navigation technology. It wasn't just that these systems calculated present position, important though that was. It was because, for the first time, there was a source of accurate, reliable heading that didn't depend on the variable and hard-to-pin-down magnetic field. Now, let's talk about updating isogonals. As a pilot, you should always fly with the most up-to-date chart for flight safety reasons. Aeronautical information is constantly changing: airways are re-aligned, the positions and frequencies of VORs and DMEs are changed, and danger areas alter shape or are moved as civil and defence requirements change within a country. If the chart is republished at frequent intervals, the isogonals — those lines of equal magnetic variation — should be comparatively recent as well. For most radio navigation charts, it is not normally necessary to update the isogonals. However, the interval between reissues of topographical maps may be considerably longer — perhaps every 5 or 10 years. In that case, if the variation has changed significantly, it may be necessary for you, the pilot, to bring the isogonals up to date during the flight planning process. On most maps and charts, the year of origin is shown, and some indication of the annual change — due to the movement of the magnetic poles — is given. This may be done by a small arrow showing the direction and distance of the annual change of the position of the isogonal, as shown in Figure 3.7. Alternatively, it may be done by a statement giving the annual change in the variation quoted on the isogonal, as shown in Figure 3.8.