As electromagnetic waves, and in this case, radio signals travel, they interact with objects and the media in which they travel. As they do this the radio signals can be reflected, refracted or diffracted. These interactions cause the radio signals to change direction, and to reach areas which would not be possible if the radio signals travelled in a direct line.
The condition of the Sun has a major impact on ionospheric radio propagation. Accordingly it affects a variety of forms of HF radio communications including two way radio communications, maritime mobile radio communications, general mobile radio communications using the HF bands, point to point radio communications, radio broadcasting and amateur radio communications.
As the Sun provides the radiation that governs the state of the ionosphere and hence HF radio propagation, any flares or other disturbances are of great importance. Under some circumstances these can enhance radio communications and the HF radio propagation conditions. Under other circumstances they can disrupt radio communications on the HF bands, while at the same time providing some radio propagation conditions that can be used at VHF by radio amateurs.
there are a number of types of disturbance that are of particular interest for radio communications. Flares are one of the most obvious. However, apart from solar flares there are other disturbances that occur. One is the coronal mass ejection, and there are also coronal holes.
The US power grid is a complex electrical apparatus that has well-known sensitivities to space weather disturbances. Recent changes in its design and utilization have significantly reduced its operating margins to supply us with on-demand electricity. This means there is less flexibility available with which to deal with power shortages and blackouts.
Space weather events can damage equipment over wide geographic regions so that recovery delays become substantially longer and more costly.
The 23rd Cycle - Chapter 4 - Describes in detail the state of the US power grid, and the forces which are driving it to be far more vulnerable to solar storms than at any time in the past.
"As North America has evolved into a unified power-sharing network of regions, each buying and selling a diminishing asset, US domestic power has become more vulnerable to solar storms buffeting the power grid in the more fragile northern-tier states and Canada. So long as one region continues to have a surplus at a time when another region needs a hundred megawatts, power is 'wheeled' through 1000-mile power lines to keep supply and demand balanced across the grid. In 1972, a typical utility might need to conduct only a few of these electromagnetic transactions each week. Now, it is common for thousands to be carried out, often by computer, in much the same way that stocks are traded on Wall Street...
The electrical power grid is composed of many elements, and you can think of it as a set of rivers flowing overhead. Large rivers carry the electricity from distant generation stations (Dams, Hydroelectric Facilities and Nuclear Plants) on supply lines of 138,000 volts or higher. These are carried as three cables (2 'hot' and one defining the 'ground' in a 3-phase system) suspended atop 100-foot tall towers that you will see out in many rural areas. These supply cables terminate at regional substations where the high voltages are converted into lower voltages from 69,000 volts to 13,800 volts. These lines then enter your neighborhoods atop your local telephone poles where a neighborhood transformer steps this voltage down to 220 and supplies a dozen or so individual houses
When space weather disturbances cause 'Geomagnetically Induced Currents' , these GICs can enter a transformer through its Earth ground connection. The added DC current to the transformer causes the relationship between the AC voltage and current to change at the source of the electricity, not just where it is delivered to your electrical appliance. Because of the way that GIC currents affect the transformer, it only takes a hundred amperes of GIC current or less to cause a transformer to overload during one-half of its 60-cycle operation. As the transformer switches 60 times a second between being saturated and unsaturated, the normal hum of a transformer becomes a raucous, crackling whine. Regions of opposed magnetism as big as your fist in the core steel plates crash about and vibrate the 100-ton transformer nearly as big as a house in a process that physicists call magnetostriction.
The impact that magnetostriction has upon specific transformers is that it generates hot spots inside the transformer where temperatures can increase very rapidly to hundreds of degrees in only a few minutes. Temperature spikes like these can persist for the duration of the magnetic storm which, itself, can last for hours at a time. During the March 1989 storm, a transformer at a nuclear plant in New Jersey was damaged beyond repair as its insulation gave way after years of cumulative GIC damage. Allegheny Power happened to be monitoring a transformer that they knew to be flaky. When the next geomagnetic storm hit in 1992. They saw the transformer reply in minutes, and send temperatures in part of its tank to more than 340 F (171 C). Other transformers have spiked fevers as high as 750 F (400 C). Insulation damage is a cumulative process over the course of many GICs, and it is easy to see how cumulative solar storm and geomagnetic effects were overlooked in the past.
Outright transformer failures are much more frequent in geographic regions where GICs are common. The Northeastern US with the highest rate of detected geomagnetic activity led the pack with 60% more failures. Not only that, but the average working lifetimes of transformers is also shorter in regions with greater geomagnetic storm activity. The rise and fall of these transformer failures even follows a solar activity pattern of roughly 11 years.
If your power plant is located over a rock stratum with low resistance, any geomagnetic disturbance will cause a bigger change in the voltages it induces in your local ground, and the bigger this change in ground voltage, the stronger will be the GIC currents that flow into your transformers. Typical daily GICs can run at about 5-10 amperes, but severe geomagnetic storms can cause 100-200 amperes to flow
A conservative estimate of the damage done by GICs to transformers by Minnesota Power and Electric was $100 million during a solar-maximum period. This includes the replacement of damaged transformers, and the impact of shortened operating lifetimes due to GIC activity
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