Characteristics of Earth-
Source: https://www.nasa.gov/topics/earth/index.html
Earth Our home, is the third planet from the sun. It is the only planet known to have an atmosphere containing free oxygen, oceans of liquid water on its surface, and, of course, life.
Earth is the fifth largest of the planets in the solar system — smaller than the four gas giants, Jupiter, Saturn ,Uranus and Neptune, but larger than the three other rocky planets, Mercury, Mars and Venus.Earth has a diameter of roughly 8,000 miles (13,000 kilometers), and is round because gravity pulls matter into a ball, although it is not perfectly round, instead being more of an "oblate spheroid" whose spin causes it to be squashed at its poles and swollen at the equator.Roughly 71 percent of Earth's surface is covered by water, most of it in the oceans. About a fifth of Earth's atmosphere is made up of oxygen, produced by plants. While scientists have been studying our planet for centuries, much has been learned in recent decades by studying pictures of Earth from space.
Orbital Characteristics:
Source: https://www.google.com.ng/amp/scienceblogs.com/startswithabang/2010/10/07/counterclockwise-but-there-are/amp/
Earth spins on an imaginary line called an axis that runs from the North Pole to the South Pole, while also orbiting the sun. It takes Earth 23.439 hours to complete a rotation on its axis, and roughly 365.26 days to complete an orbit around the sun.Earth's axis of rotation is tilted in relation to the ecliptic plane, an imaginary surface through Earth's orbit around the sun.
This means the northern and southern hemispheres will sometimes point toward or away from the sun depending on the time of year, varying the amount of light they receive and causing the seasons.Earth's orbit is not a perfect circle, but is rather an oval-shaped ellipse, like that of the orbits of all the other planets. Earth is a bit closer to the sun in early January and farther away in July, although this variation has a much smaller effect than the heating and cooling caused by the tilt of Earth's axis. Earth happens to lie within the so-called "Goldilocks zone" around its star, where temperatures are just right to maintain liquid water on its surface.
Composition & structure:
AtmosphereEarth's atmosphere is roughly 78 percent nitrogen, 21 percent oxygen, with trace amounts of water, argon, carbon dioxide and other gases. Nowhere else in the solar system can one find an atmosphere loaded with free oxygen, which ultimately proved vital to one of the other unique features of Earth — us.
Air surrounds Earth and becomes thinner farther from the surface. Roughly 100 miles (160 km) above Earth, the air is so thin that satellites can zip through with little resistance. Still, traces of atmosphere can be found as high as 370 miles (600 km) above the surface.The lowest layer of the atmosphere is known as the troposphere, which is constantly in motion,
causing the weather. Sunlight heats the planet's surface, causing warm air to rise. This air ultimately expands and cools as air pressure decreases, and because this cool air is denser than its surroundings, it then sinks, only to get warmed by the Earth once again.Above the troposphere, some 30 miles (48 km) above the Earth's surface, is the stratosphere. The still air of the stratosphere contains the ozone layer, which was created when ultraviolet light
caused trios of oxygen atoms to bind together into ozone molecules.
Ozone prevents most of the sun's harmful ultraviolet radiation from reaching Earth's surface.Water vapor, carbon dioxide and other gases in the atmosphere trap heat from the sun, warming Earth. Without this so-called "greenhouse effect," Earth would probably be too cold for life to exist, although a runaway greenhouse effect led to the hellish conditions now seen on Venus. Earth-orbiting satellites have shown that the upper atmosphere actually expands during the day and contracts at night due to heating and cooling.
Magnetic field:
Source: http://www.crystalinks.com/earthsmagneticfield.html
Earth's magnetic field is generated by currents flowing in Earth's outer core. The magnetic poles are always on the move, with the magnetic North Pole recently accelerating its northward motion to 24 miles (40 km) annually, likely exiting North America and reaching Siberia in a few decades.Earth's magnetic field is changing in other ways, too — globally, the magnetic field has weakened 10 percent since the 19th century, according to NASA.
These changes are mild compared to what Earth's magnetic field has done in the past — sometimes the field completely flips, with the north and the south poles swapping places. When charged particles from the sun get trapped in Earth's magnetic field, they smash into air molecules above the magnetic poles, causing them to glow, a phenomenon known as the aurorae, the northern and southern lights.
Chemical composition:
Oxygen is the most abundant element in rocks in Earth's crust, composing roughly 47 percent of the weight of all rock. The second most abundant element is silicon at 27 percent, followed by aluminum at 8 percent, iron at 5 percent, calcium at 4 percent, and sodium, potassium, and magnesium at about 2 percent each.
Earth core consists mostly of iron and nickel and potentially smaller amounts of lighter
elements such as sulfur and oxygen. The mantle is made of iron and magnesium-rich silicate
rocks. (The combination of silicon and oxygen is known as silica, and minerals that contain silica
are known as silicate minerals.)
Internal structure:
Earth's core is about 4,400 miles (7,100 km) wide, slightly larger than half the Earth's diameter and roughly the size of Mars. The outermost 1,400 miles (2,250 km) of the core are liquid, while the inner core — about four-fifths as big as Earth's moon at some 1,600 miles (2,600 km) in diameter — is solid. Above the core is Earth's mantle, which is about 1,800 miles (2,900 km) thick. The mantle is not completely stiff, but can flow slowly. Earth's crust floats on the mantle much as a wood floats on water, and the slow motion of rock in the mantle shuffles continents around and causes earthquakes, volcanoes, and the formation of mountain ranges.Above the mantle, Earth has two kinds of crust. The dry land of the continents consists mostly of granite and other light silicate minerals, while the ocean floors are made up mostly of a dark, dense volcanic rock called basalt. Continental crust averages some 25 miles (40 km) thick, although it can be thinner or thicker in some areas. Oceanic crust is usually only about 5 miles (8km) thick. Water fills in low areas of the basalt crust to form the world's oceans. Earth has more than enough water to completely fill the ocean basins, and the rest of it spreads onto edges of the
continents, areas known as the continental shelf. Earth gets warmer toward its core. At the bottom of the continental crust, temperatures reach about 1,800 degrees F (1,000 degrees C), increasing about 3 degrees F per mile (1 degree C per kilometer) below the crust.
Geologists think the temperature of Earth's outer core is about 6,700 to 7,800 degrees F (3,700 to 4,300 degrees C), and the inner core may reach 12,600 degrees F (7,000 degrees C), hotter than the surface of the sun. Only the enormous pressures found at the super-hot inner core keep it solid.Recent exoplanet surveys such as NASA’s Kepler mission suggest that Earth-size planets are common throughout the Milky Way galaxy. Nearly a fourth of sun-like stars observed by Kepler have potentially habitable Earth-size planets.( retrieved from http://www.space.com/54-
earth-history-composition-and-atmosphere.html 12th Dec 2016.
The Earth's Ionosphere:
Source: https://www.britannica.com/science/ionosphere-and-magnetosphere
The ionosphere is defined as the layer of the Earth's atmosphere that is ionized by solar and cosmic radiation. It lies 75-1000 km (46-621 miles) above the Earth. (The Earth’s radius is 6370 km, so the thickness of the ionosphere is quite tiny compared with the size of Earth.) Because of the high energy from the Sun and from cosmic rays, the atoms in this area have been stripped of one or more of their electrons, or “ionized,” and are therefore positively charged. The ionized electrons behave as free particles.
The Sun's upper atmosphere, the corona, is very hot and produces a constant stream of plasma and UV and X-rays that flow out from the Sun and affect, or ionize, the Earth's ionosphere. Only half the Earth’s ionosphere is being ionized by the Sun at any time. During the night, without interference from the Sun, cosmic rays ionize the ionosphere,though not nearly as strongly as the Sun. These high energy rays originate from sources throughout our own galaxy and the universe -- rotating neutron stars, supernovae, radio galaxies, quasars and black holes. Thus the ionosphere is much less charged at nighttime, which is why a lot of ionospheric effects are easier to spot at night – it takes a smaller change to notice them. The ionosphere has major importance to us because, among other functions, it influences radio propagation to distant places on the Earth, and between satellites and Earth. For the very low frequency (VLF) waves that the space weather monitors track, the ionosphere and the ground produce a “waveguide” through which radio signals can bounce and make their way around the curved Earth.
The Ionospheric layers:
At night the F layer is the only layer of significant ionization present, while the ionization in the
E and D layers is extremely low. During the day, the D and E layers become much more heavily
ionized, as does the F layer, which develops an additional, weaker region of ionisation known as the F1 layer. The F2 layer persists by day and night and is the region mainly responsible for the refraction of radio waves.
D layer:
Source: http://solarviews.com/eng/earthint.htm
The D layer is the innermost layer, 60 km (37 mi) to 90 km (56 mi) above the surface of the
Earth. Ionization here is due to Lyman series-alpha hydrogen radiation at a wavelength of
121.5 nanometre (nm) ionizing nitric oxide (NO). In addition, high solar activity can generate
hard X-rays (wavelength < 1 nm) that ionize N2 and O2. Recombination rates are high in the D
layer, so there are many more neutral air molecules than ions. Medium frequency (MF) and lower high frequency (HF) radio waves are significantly reduced in strength within the D layer, as the passing radio waves cause electrons to move, which then collide with the neutral molecules, giving up their energy. The lower frequencies move the electrons farther, with a greater chance of collisions.
This is the main reason for absorption of HF radio waves, particularly at 10 MHz and below, with progressively less absorption at higher frequencies. This effect peaks around noon and is reduced at night due to a decrease in the D layer's thickness; only a small part remains due to cosmic rays. A common example of the D layer in action is the disappearance of distant AM broadcast band stations in the daytime. During solar proton events, ionization can reach unusually high levels in the D-region over high and polar latitudes. Such very rare events are known as Polar Cap Absorption (or PCA) events, because the increased ionization significantly enhances the absorption of radio signals passing through the region. In fact, absorption levels can increase by many tens of dB during intense events, which is enough to absorb most (if not all) transpolar HF radio signal transmissions. Such events typically last less than 24 to 48 hours.
E layer:
The E layer is the middle layer, 90 km (56 mi) to 150 km (93 mi) above the surface of the Earth.
Ionization is due to soft X-ray (1–10 nm) and far ultraviolet (UV) solar radiation ionization of
molecular oxygen (O₂). Normally, at oblique incidence, this layer can only reflect radio waves having frequencies lower than about 10 MHz and may contribute a bit to absorption on
frequencies above.
However, during intense Sporadic E events, the Es layer can reflect frequencies up to 50 MHz and higher. The vertical structure of the E layer is primarily determined by the competing effects of ionization and recombination. At night the E layer weakens because the primary source of ionization is no longer present. After sunset an increase in the height of the E layer maximum increases the range to which radio waves can travel by reflection from the layer.
This region is also known as the Kennelly–Heaviside layer or simply the Heaviside layer. Its
existence was predicted in 1902 independently and almost simultaneously by the American
electrical engineer Arthur Edwin Kennelly (1861–1939) and the British physicist Oliver
Heaviside (1850–1925). However, it was not until 1924 that its existence was detected
by Edward V. Appleton and Miles Barnett.
OBSERVATIONS OF THE EARTH’S MAGNETIC FIELD:
Representation of the field:-
Electric and magnetic fields are produced by a fundamental property of matter, electric charge. Electric fields are created by charges at rest relative to an observer, whereas magnetic fields are produced by moving charges. The two fields are different aspects of the electromagnetic field, which is the force that causes electric charges to interact. The electric field, E, at any point around a distribution of charge is defined as the force per unit charge when a positive test charge is placed at that point. For point charges the electric field points radially away from a positive charge and toward a negative charge.A magnetic field is generated by moving charges—i.e., an electric current. The
magnetic induction, B, can be defined in a manner similar to E as proportional to the force per unit pole strength when a test magnetic pole is brought close to a source of magnetization. It is more common, however, to define it by the Lorentz-force equation.
This equation states that the force felt by a charge q, moving with velocity v, is given by F = q(vxB).In this equation bold characters indicate vectors (quantities that have both magnitude and direction) and nonbold characters denote scalar quantities such as B, the length of the vector B.
The x indicates a cross product (i.e., a vector at right angles to both v and B, with length vBsin
θ). Theta is the angle between the vectors v and B. (B is usually called the magnetic field in spite
of the fact that this name is reserved for the quantity H, which is also used in studies of magnetic fields.) For a simple line current the field is cylindrical around the current. The sense of the field depends on the direction of the current, which is defined as the direction of motion of positive charges. The right-hand rule defines the direction of B by stating that it points in the direction of the fingers of the right hand when the thumb points in the direction of the current.In the International System of Units (SI) the electric field is measured in terms of the rate of change of potential, volts per metre (V/m). Magnetic fields are measured in units of tesla (T).
The tesla is a large unit for geophysical observations, and a smaller unit, the nanotesla (nT; one nanotesla equals 10−9tesla), is normally used. A nanotesla is equivalent to one gamma, a unit originally defined as 10−5 gauss, which is the unit of magnetic field in the centimetre-gram-second system. Both the gauss and the gamma are still frequently used in the literature on geomagnetism even though they are no longer standard units.
Magnetic field lines associated with the earth
CHARACTERISTICS OF THE EARTH’S MAGNETIC FIELD:
To a first approximation the magnetic field observed at the surface of the Earth is like that of a magnet aligned with the planet’s rotation axis. The figure shows such a field for a bar magnet located at the centre of a sphere. If the sphere is taken to be the Earth with the north geographic pole at the top, the magnet must be oriented with its north magnetic pole downward toward the south geographic pole. Then, magnetic field lines leave the north pole of the magnet and curve around until they cross the Earth’s Equator pointing geographically northward. They
curve still more reentering the Earth in northern latitudes, finally returning to the south pole of
the magnet. At the present time, the north geographic pole corresponds to the south pole of the equivalent bar magnet. This has not always been the case. Many times in the history of the Earth the direction of the equivalent magnet has pointed in the opposite direction (see below Reversals of the main field).
Dipolar field:
Source:https://www.wolfram.com/mathematica/new-in-9/built-in-symbolic-tensors/electric-potential-and-field-of-a-dipole.html
The magnetic field lines are not real entities, although they are frequently treated as such. A magnetic field is a continuous function that exists at every point in space. A field line is simply a means for visualizing the direction of this field. It is defined as a curve in three dimensions that is everywhere tangential to the local magnetic field. The pattern of field lines created by a bar magnet is called a dipolar field because it has the same shape as the electric field produced by two (di-) slightly separated charges (poles) of opposite sign. The dipole field of the Earth is, of course, not produced by a bar magnet at its centre. As will be discussed later, it is instead produced by electric currents within the Earth’s liquid core. To produce the present field, the equivalent current must be a westward equatorial loop, as shown in the bar-magnet figure.
The magnetic field of a dipole is vertical along the polar axis and horizontal along the equator.
These properties lead to definitions of equator and pole in the Earth’s more complex field. Thus, the geomagnetic equator is defined as the line around the Earth’s surface where the actual field is horizontal. Similarly, the magnetic dip poles are the two points at which the field is vertical. If observations are extended above or below the surface, the location of the equator is a surface (planar for a dipole) and the poles lie along curves. (culled from
https://www.britannica.com/science/geomagnetic-field 12th Dec 2016 1:58pm).
Geomagnetic Storm:
Source:https://www.google.com.ng/amp/s/www.pinterest.co.uk/amp/pin/411868328403525414/
A geomagnetic storm is defined[6] by changes in the Dst (disturbance– storm time) index. The
Dst index estimates the globally averaged/change of the horizontal component of the Earth’s magnetic field at the magnetic equator based on measurements from a few magnetometer stations. Dst is computed once per hour and reported in near-realtime.
The geomagnetic storm is a temporary disturbance of the Earth's magnetosphere caused by a solar wind shock wave and/or cloud of magnetic field that interacts with the Earth's magnetic field.
The increase in the solar wind pressure initially compresses the magnetosphere. The solar wind's magnetic field interacts with the Earth’s magnetic field and transfers an increased energy into the magnetosphere. Both interactions cause an increase in plasma movement through the magnetosphere (driven by increased electric fields inside the magnetosphere) and an increase in electric current in the magnetosphere and ionosphere.
During the main phase of a geomagnetic storm, electric current in the magnetosphere creates a magnetic force that pushes out the boundary between the magnetosphere and the solar wind. The disturbance in the interplanetary medium that drives the storm may be due to a solar coronal mass ejection (CME) or a high speed stream (co-rotating interaction region or CIR) of the solar wind originating from a region of weak magnetic field on the Sun’s surface. The frequency of geomagnetic storms increases and decreases with the sunspot cycle. CME driven storms are more common during the maximum of the solar cycle, while CIR driven storms are more common during the minimum of the solar cycle. Several space weather phenomena tend to be associated with or are caused by a geomagnetic storm. These include: solar energetic Particle (SEP) events, geomagnetically induced currents (GIC), ionospheric disturbances that cause radio and radar scintillation, disruption of navigation by magnetic compass and auroral displays at much lower latitudes than normal.( Campbell,
Wallace H. (2003). Introduction to geomagnetic fields).
Some Effects of Geomagnetic storm:
Disruption of electrical:-
Systems It has been suggested that a geomagnetic storm on the scale of the solar storm of 1859 today would cause billions of dollars of damage to satellites, power grids and radio communications, and could cause electrical blackouts on a massive scale that might not be repaired for weeks.
Communications:
High frequency (3–30 MHz) communication systems use the ionosphere to reflect radio signals over long distances. Ionospheric storms can affect radio communication at all latitudes. Some frequencies are absorbed and others are reflected, leading to rapidly fluctuating signals and unexpected propagation paths. TV and commercial radio stations are little affected by solar activity, but ground-to-air, ship-to-shore, shortwave broadcast and amateur radio (mostly the bands below 30 MHz) are frequently disrupted. Radio operators using HF bands rely upon solar and geomagnetic alerts to keep their communication circuits up and running
Navigation systems Systems such as GPS, LORAN and the now-defunct OMEGA are adversely affected when solar activity disrupts their signal propagation. The OMEGA system consisted of eight transmitters located throughout the world. Airplanes and ships used the very low frequency signals from these transmitters to determine their positions. During solar events and geomagnetic storms, the system gave navigators information that was inaccurate by as much as several miles. If navigators had been alerted that a proton event or geomagnetic storm was in progress, they could have switched to a backup system. GPS signals are affected when solar activity causes sudden variations in the density of the ionosphere, causing the GPS signals to scintillate (like a twinkling star).
Radiation hazards to humans:
Intense solar flares release very-high-energy particles that can cause radiation poisoning to humans (and mammals in general) similar to low-energy radiation from nuclear blasts. Earth's atmosphere and magnetosphere allow adequate protection at ground level,
but astronauts are subject to potentially lethal doses of radiation. The penetration of high-energy particles into living cells can cause chromosome damage, cancer and other health problems.
Large doses can be immediately fatal. Solar protons with energies greater than 30 MeV are particularly hazardous.
REFERENCES:
Campbell, Wallace H. (2003). Introduction to geomagnetic fields (2nd ed.). New York: Cambridge University Press. ISBN 978-0-521-52953
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