Have you realized that, on some days in the night sky near the poles, it looks like shining or even mixed brighten lights? Yes! Those bright lights are called Aurora. They are due to interaction of external magnetic fields with very fast and energetic radiation from the sun. This gives us an idea that there are some magnetic fields far out there around Earth that cause all these to happen! Here down I have tried to explain in brief to you about these external magnetic fields, Just keep reading.
Magnetic field of External origin is strongly affected by solar wind. Solar wind is a stream of electrically charged particles (consisting mainly of e-, P & He) that is constantly emitted by the sun.
Solar wind is a plasma considered as conducting fluid.
Plasma: Is a physical term for ionized gas of low particle density with equal +ve and -ve charges.
Interaction of charged particles can be expressed from
F = BeV
where F - Lorentz force
Also
Fc = mv2/r
Then,
mv2/r = BeV
Then, r = mV/Be
Hence, W = V/r = Be/m
On approaching the geomagnetic field two things may happen to the solar wind.
a/ The wind may be deflected so as to travel around the field.
b/ Magnetic field may be pushed out of the way by the travelling conducting fluid.
It depends on the pressure of the magnetic field and solar wind.
I: If the pressure of the solar wind is greater than the magnetic field it will push it out of the way.
II: If the pressure of the magnetic field is greater it will force the conducting fluid to avoid the region containing the field.
N.B : Above situations do happen depending on the distance from the Earth.
- At distant (far) places from the Earth's field is weak and therefore is compressed by the solar wind.
- At near (closer) to the Earth the pressure of the field is sufficient to force the solar wind to flow around it.
MAGNETOSPHERE: Is the region where solar wind interacts with the field of the Earth.
The region field of the Earth is confined and hence solar can not penetrate. Hence it plays an important role in preventing harmful radiation from the sun from reaching the Earth's surface. This can be described as a Shielding function
Outer boundary of the magnetosphere is marked by the shock front-like wave pattern called BOW - SHOCK REGION.
At the bow - shock region the solar wind is slowed down and heated up.
Two (2) factors determine the structure and behavior of the magnetosphere
i/ Internal field of the Earth
It is generated in the core by a dynamo process associated with the circulation of liquid metal in the core driven by internal heat sources resembling a dipole field.
ii/ The solar wind.
MAGNETOSHEATH: Is a region of turbulent motion at which solar wind diverted after passing through the shock front. It is separated from magnetopause by the bow - Shock region.
Since solar wind are electric current like produces an Interplanetary magnetic field, which reinforces and compresses the geomagnetic field on the day side and weakens and stretches it out on the night side of the Earth. This results Geomagnetic Tail / magnetotail which extends to great distances from the downwind from the Earth.
MAGNETOPAUSE: Is the transition between the deformed magnetic field and the magnetosheath.
Concepts on VAN - ALLEN RADIATION BELT.
It occurs when charged particles that penetrate magnetopause are trapped by the geomagnetic field.
It comprises of two (2) region
i/ Inner belt: This consists of protons
ii/ Outer belt: This consists of energetic electrons moving in helical fashion.
Inner belt start 1000 Km above the Earth to 3000 Km.
Figure: Van Allen radiation belt. (Credit: NASA)
DIURNAL VARIATION AND MAGNETIC STORMS
Diurnal Variation: Diurnal means day
It is the fluctuation of geomagnetic field intensity with time a day.
Magnitude of diurnal variations depends on the latitude at which it is observed.
Intensity of the diurnal variation depends on the degree of ionization of the ionosphere and therefore determined by the state of solar activity.
Hence, Diurnal variation is due to Solar activity. The solar activity induces currents in the Ionosphere that causes the variation in the magnetic field.
It is mainly caused by changes in strength and direction of the Ionospheric currents.
Characteristics of Diurnal Variations.
1: The variation varies with local time; its amplitude is maximum during noon and minimum during midnight.
2: Amplitude variations are high during the summer and low in winter.
3: The amplitude varies with latitude, the diurnal variations are high towards the equator and low towards the poles.
Magnetic Storms
Is the disturbance in the geomagnetic field caused by coronal mass ejections or solar flares from the sun. They last for about 24hrs to 48hrs.
Causes
Enhanced emission of solar radiation which increases the ionospheric currents.
- They are highly in the horizontal components, due to increase of velocity or density of solar wind, particles pushing the magnetic field closer to the Earth and thus changing the position of the magnetopause.
Common features of magnetic Storms
1: Storm sudden commencement: Means storms start with a sudden increase in H - which is followed by a decrease within 2 - 3 minutes.
2: Initial phase: Within an hour or less H - increases and remains 30 - 50 nT, higher than its prestorm value for a period of one to two hours. Many do not have this stage.
3: The main phase: Starts at a time varying between 2 to 10 hrs, characterized by a steady decrease in H with amplitude of 100 to 200 nT lasting for several hours.
4: Amplitude of the decrease H is a maximum, near equator & decrease towards the poles.
EFFECTS
- Disruption of communications and navigation system
- Intense Auroras
- Damage to satellite
- Corrosion and power Outages such as induced currents in power lines and pipelines.
How to Measure
- By measuring magnetic field on the Earth's surface, sum of all these fields such as main field, remnant field, induced field, diurnal variations, storms.
Equatorial Anomaly: Deviation of magnetic equator by +/- 20 degree where magnetic field lines are horizontal.
N.B: Micropulsations, have amplitudes of less than 10 nT and periods of a few seconds to 300s
- They are very common and occur randomly.
- Amplitude varies across survey areas.
IONOSPHERE: It is an Ionized region of the atmosphere between 50 - 1500 Km. It is ionized because very short wavelength radiations of solar radiations such as U.V rays, X - rays, gamma rays, penetrate the atmosphere and cause ionization of air molecules (N2 and O2) in the upper atmosphere.
It is divided into five (5) layers labelled the D, E, F1, F2 and G layers, from base to the top.
D - layer 50 - 90 Km: It reflects long wavelength radio waves.
E - layer 90 - 120 Km: It is used by shortwave amateur radio enthusiasts.
F - layer 120 - 1500 Km: Most intensely ionized.
Electron density increases from D region to the F region, where it will typically reach 105 - 1063 Cm3 at mid - day.
Particles at ionosphere affected by
- Rotation of the Earth.
- Tidal forces from Moon and Sun
PLASMASPHERE: Upward extension of the Ionosphere. During the day there are multiple reflections between ground and Ionosphere hence best in radio communication.
On the day it thickens while at night it disappears.
Although I like to keep telling you about these fields, the time is not friendly, to continue with this discussion, here I have described their scientific contribution. Thanks for your time.
Scientific Contribution of the Magnetic Fields.
- The study of remnant magnetization, reveals the history of the Earth.
- Analysis of daily variations of magnetic fields has suggested that the upper atmosphere is a conductor.
- Concept of sea - floor spreading based on linear oceanic magnetic anomalies and strengthened by paleomagnetic data from variaties continents.
- Interaction between the Earth and particle radiations from the sun revealed by magnetic storms.
- Evidence of motion in the liquid core suggested by the presence of the field and long term variations
Thank you for having interest in this blog!
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