1.2. Natural Magnetism
Near the Earth's surface, geomagnetic effects are readily detectable with a simple compass. A natural bar magnet, mounted on a pivot, will do. The Earth's magnetic field strength near the surface is half a Gauss ( 50 microTesla), and surface magnetic field lines are pointing towards and entering the Earth's crust near the North geographic pole - the entry point in the crust is currently near 70 - 75° longitude West, and near 79 - 80° latitude North.
Are some animals endowed with a sixth (magnetic) sense ? Migratory sea turtles can detect changes in the Earth's magnetic field strength at different places in their trips, as well as changes in the Earth's magnetic field inclination/direction (Lohmann & Lohmann, 1996). The Earth's magnetic field direction can also be detected or sensed by many types of bees and birds, notably pigeons and garden warblers (Weindler et al. 1996; Gould 1996b), as well as by many types of whales and fish, notably eels, salmons, yellowfin tunas, sea turtles, and trouts (e.g., Gould 1996a; Kirschvink 1997).
The threshold of magnetic intensity variation necessary to induce behavioral responses is around 1000 milliGauss for some birds, honeybees, pigeons, and whales, while it is 500 milliGauss in rainbow trouts (Walker et al. 1997).
In rainbow trouts, a study identified an area in the olfactory nose of the trout where a form of biogenic magnetite could be found, attached to the ramus (ros V) of the trigeminal sensory nerve going to the brain. The apparent proximity of the magnetic sensor and the olfactory reception raises the possibility that olfactory impairment would also produce magnetic impairment, which is the case in homing pigeons (e.g., Walker et al. 1997).
From time to time, energetic jets of particles are emitted by the Sun and are channeled by the Earth's magnetic field toward the two poles of the Earth, where they encounter at high speed the gas particles in the atmosphere. The ensuing collisions energize the local gas particles; these auroral particles then de-excite by emitting flashes of optical light at an altitude of about 100 km. Against solar particles, the Earth's magnetic field acts as a shield protecting Life, and as a channel for space particles. The existence of the Earth's magnetic field is thus revealed when illuminated by the auroral particles in the atmosphere, producing a show often described as 'dancing curtains'. The dancing is due to the intermittent and varied arrivals of different amounts of solar particles at different times and directions.
1.2.3. Space Storms
Figure 1 shows typical transmission lines on Earth, above the ground. Solar magnetic storms can have effects on these above-ground transmission lines, through their magnetic induction. In 1989, the Canadian province of Québec suffered a massive electricity blackout, brought on by a space surge, costing Hydro-Québec $10 M Cdn; the large surge in electrical activity from space had short-circuited these electric transmission lines and the overall system on Earth.
Figure 1. Typical example of electrical transmission lines to transport electricity on Earth. Magnetic fields are shown following the usual right-handed screw system (right thumb towards direction of electric current I). Since the electric currents are mostly alternating, the senses of the assoicated magnetic fields will also reverse with time. The above-ground lines can be seriously affected by the passage of solar magnetic storms speeding away from the Sun and encountering the Earth.
In 1994, Canada's Anik-E1 and Anik-E2 communication satellites were hit by a magnetic blast from the Sun, disrupting Canadian TV operations for days. In January 1997, another solar energy burst permanently disabled the US AT&T satellite, costing nearly $150 millions US (e.g., Curren 1997) - it did this pushing the Earth's magnetosphere boundary much closer to Earth, inside the satellite's orbit around Earth, exposing the satellite to the Sun's blasts (e.g., Kiernan 1997).