Space Weather and its Surprisingly Bizarre Effects on the Earth

Effects of solar flares on human technology
The effects of space weather on the Earth are most famous in the form of aurora, but there are various other ways in which the Earth can be affected too. This Buzzle post explains what space weather is, and the numerous ways in which it affects life on Earth.
Space Weather Could Affect Global Warming
The Sun's 11-year sunspot cycle is said to be linked with the rise and fall of temperatures on the Earth. This hasn't been proven irrefutably, but a significant cooling was observed during periods (before the industrial revolution) of absence of sunspots.
Changes in the space between the Sun and the planets in the solar system are known as space weather. Solar flares, coronal mass ejections, and the consequent geomagnetic storms, are factors of space weather pertinent to its effects on the life on Earth.
Solar flares and coronal mass ejections (CME) are giant, haphazard expulsions of solar mass and energy. These two events are usually related (CME usually follows a solar flare), but have been observed independently. Solar flares release up to 160 billion megatons of TNT-equivalent energy. For a measure of scale, the largest nuclear device ever detonated by mankind - the Tsar Bomba testing - was 57 megatons!
What Is Space Weather?
Solar flares
Solar Flares
Solar flares and CME are connected to the Sun's sunspot cycle as well, with many instances occurring in areas of high intensity, where sunspots were present in large numbers and intensity. The high magnetic forces acting in the supercharged, superheated environment cause solar ejections.
The particles and plasma (a superheated fourth state of matter) released by such solar ejections is collectively called solar wind. It is mainly a stream of electrons and protons, along with other charged particles.
Solar winds put spacecrafts at risk, because spacecrafts lack the protection of the Earth's magnetosphere. The ill-effects on spacecrafts are explained in detail further in this article. Celestial bodies that don't have well-developed magnetospheres, such as Mars and the Moon, are subjected to the full fury of solar winds.
Geomagnetic storm magnetosphere
Depiction of a Geomagnetic Storm (Not to Scale)
Geomagnetic storms are caused when a blast of solar wind encounters the Earth's magnetosphere - an area over which the Earth's magnetic influence is exerted. Incidentally, this clash causes aurora in the polar regions.
The onslaught of the solar radiation causes an increase in the atmosphere's heat and electric activity. This shift away from the normal state of the atmosphere (mainly ionosphere) causes most of the effects of space weather observed on the Earth. Geomagnetic storms also temporarily wipe out the outermost layer of the ionosphere.
How Does All This Affect Us?
Space weather doesn't have much effect on the surface of the Earth. It is our near-complete dependence on electricity and space communication that puts us at risk from solar emissions. Otherwise, space weather, and the resultant radiation, is largely blocked and negated by our astonishingly efficient atmosphere, and rarely reaches the Earth's surface. Its effect is primarily limited to the upper reaches of the Earth's atmosphere, particularly the ionosphere.
Layers of atmosphere
Layers of Our Atmosphere
The ionosphere, which is a region of the atmosphere ionized by ultraviolet radiation from the Sun, contains electrically charged ions (thus the name). Ions are formed when an atom loses or gains an electron, and thus attains a positive or negative charge, respectively. In the case of the ionosphere, the layer of gas is ionized by UV radiation, and 'ion pairs' of positive ions and free electrons are created. Ions are usually extremely reactive and seek out equilibrium by whatever means, but the atmosphere is so thin at this height, that the ion pairs can go for hundreds of miles without encountering each other.

Satellites in geosynchronous orbit and airplanes at high altitudes in polar regions are at risk from radiation, but apart from the benign link between the Sun's 11-year sunspot cycle and the Earth's temperatures, space weather doesn't have much effect on terrestrial weather.

Here's how solar flares, radiation, and geomagnetic storms can affect life on Earth.
Spacecrafts
Overcharging and Discharge
Spacecrafts are at most risk from changes in space weather. Exposure to solar radiation, when it has not been filtered and weakened by the Earth's atmosphere, can cause serious damage. This damage can occur both to the structure and the programming of the spacecraft. Solar radiation can create a high static charge on non-conducting components of spacecrafts. If this charge exceeds a certain limit, it discharges in the form of a large spark, which can damage components.
Misinterpreted Radio Signals
Solar radiation disturbs the ionosphere, which is crucial in transmitting ground-to-air radio signals. These signals are corrupted by passing through a disturbed ionosphere, and can be lost, or worse, can incite an unintended response from the spacecraft's programming system.
Changes in Orbit
Satellites put in place around the Earth constantly lose velocity and lower their orbits due to resistance from the atmosphere's outermost reaches. If this is not counterbalanced, satellites would eventually fall out of orbit. The deceleration is naturally a very slow process, and modern satellites often just fire a small rocket to gain some height and postpone the drop by more than a year. If precise information about the satellite's orbit and the degree to which it is affected by the friction with the atmosphere is not available, the misinformation can destroy satellites by forcing them to drop down to the Earth and burn up during reentry. Geomagnetic storms inject extra energy into the Earth's atmosphere. This makes it warmer, which increases its volume, and brings about a change in the dynamics of the satellite, that would require years to come true naturally. This can cause satellites to burn up or collide with other satellites.
Radiation Exposure
Astronauts in space are at high risk from solar radiation, and can suffer from radiation poisoning. The Van Allen belts of radioactive material - formed by the Earth's magnetosphere holding on to particles in solar wind - are an ever-present threat, but solar radiation can increase the risk by several orders of magnitude!
Terrestrial
Ground-Induced Current
Due to the interlinked nature of magnetism and electricity, geomagnetic storms produce a ground-based electric current. This current can disrupt electric and communication services over a large area. The infamous 1989 blackout in the Hydro-Quebec power network was caused by a geomagnetic storm, which was caused by a CME 4 days before the blackout. Because the Earth is a magnet, the polar regions experience minor conditions like these frequently, accompanied by aurora. Due to our incredible dependence on electricity, a large geomagnetic storm could be catastrophic.
Exposure to Radiation
As mentioned before, the Earth's atmosphere is incredibly good at its job - keeping out harmful solar radiation. However, airplanes flying at high altitudes in polar areas are at risk from severe radiation poisoning. The risk is much lower in lower latitudes and altitudes.
Global Positioning System Distortion
In this case, think of the ionosphere as a pool of water. Like a pencil appearing bent inside the water, GPS signals are bent in a set way by the electrically-active ionosphere. If the water is suddenly replaced by something with a different refractive index, the amount of bend on the pencil would change. GPS signals rely on the ionosphere to 'refract' them in a set way, and a disturbed ionosphere can disturb GPS signals beyond recognition.
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High Frequency Radio Distortion
HF radio (shortwave) uses the ionosphere to bend and reflect the transmission in an analogous way to the formation of a mirage. Radio signals through a disturbed atmosphere can get severely distorted, or even lost.
These are the major effects of space weather on the Earth. As explained, space weather is not dangerous for life on Earth, but causes ill-effects on ground-based communication technology, and puts spacecrafts at serious risk.