• Ashwini

GS10: How does the solar wind affect the Earth's magnetic field?

Updated: Jun 20

In the last article, we talked about the basics of Earth’s magnetic field. In that, we got the answer to questions- how does the word of Magnet come into existence? What is the reason for the physical origin of the terrestrial magnetism? How is outer core related to terrestrial magnetism? What is happening in the outer core? How is Earth’s rotation affecting its magnetic field? What was the reason for the origin of magnetism in the primitive Earth which was lacked by other neighboring planets?




IF you still do not have the ANSWER to these questions, you can check the link here. Basics of Earth's Magnetic field.


What's the first thing encountered when you reach the Earth from the space?

Considering you have crossed the Earth's Moon, the Earth's magnetic field is the first thing to be encountered as we approach the Earth from outer space. A magnetic field is a region surrounding the magnet, which is also emanated from it. This magnetic field tends to exert a magnetic force that grows progressively stronger as one approaches the magnet, can attract or repel another magnet, or can cause charged particles to move. Do you know- why Aurora Borealis is observed near the poles?


What is the difference between the geographic poles and geomagnetic poles?

Due to the thermal convection currents that are established in the liquid outer core, resembling the self-exciting dynamo, Earth's magnetic field behaves analogously to a bar magnet which is kept at the center of the Earth. Like a simple bar magnet, it too has two poles (dipoles)- a north pole and south pole. If we represent the Earth's magnetic field as emanating from an imaginary bar magnet in the planet's interior, the north pole of this bar magnet lies near the south geographic pole of the Earth, whereas the south pole of the bar lies near the north geographic pole.


Therefore, the magnetic field lines which depict the magnetic field of the bar magnet seem to eject from the geographic south pole and curve through the space around the magnet and close in the geographic north pole. And this is a reason why the compass' magnetic needle points towards the geographic north pole. Check the diagram below.


Geographic poles are the places on the Earth's surface where Earth's rotation axis intersects the planet's surface.

Arrow head towards the north pole of the assumed magnetic bar at the center of the Earth.

What does a solar wind comprise of?

Our Sun from time to time ejects a stream of charged particles from the upper atmosphere of the Sun, called the Corona, which is known as the solar wind. It consists of gas of ions and free electrons, which is described by the fourth fundamental state i.e. the plasma. This plasma mostly contains electrons, protons, alpha particles, and a mixture of materials such as trace amounts of heavy ions and atomic nuclei C, N, O, Ne, Mg, Si, S, and Fe. The solar wind varies in density, temperature, and speed with time and distance from the source i.e. the Sun.


The temperature of the Sun's corona is more than a million degrees (2,300,000 Kelvin), astonishingly much hotter than the temperature at the Sun's surface which is around 5,500-6000 degrees C. Reason for this is still in discussion. Normally we cannot see the corona because of the extreme brightness of the Sun. However, during the total solar eclipse, when the moon blocks out the Sun, we observe a fainter region around the eclipsed region, which is nothing but the Corona.


Why is the Sun’s upper atmosphere-Corona so hot?

When you go to a camp it is a tradition, few people believe so, to enjoy a campfire if you are spending a night in the camp. Well, the rest of them enjoy sleeping in a calm and poised night away from the city noise. As you stand near the fire you feel the warmth but as soon as you move a distance farther, the chilling night takes on you. However, this is not a case when you, if you, go near the Sun. As soon as you move away, if you can, from the Sun’s surface you will face much higher temperatures than what was on the surface which is in the order of millions. A temperature of 200-500 times than the furnace operating on the surface.


This is one of the many vexing problems in the field of Astrophysics. Solar physicist Bart De Pontieu of the Lockheed Martin Solar & Astrophysics Laboratory says, “there are so many physical processes working together that it is near to impossible to directly measure or hypothesize a physical model working there”. There could be many ways by which the corona is heated so high. One such way is the release of plasma waves from the surface of the Sun or you can say from the operating furnace. These waves rise into the corona and crash or blast releasing their energy which is distributed throughout the upper atmosphere. I guess it is to nice hear more about this from the specialist. Check the link.


More on The Mystery of Corona heat from Science@NASA




How does the solar wind affect the Earth's magnetic field?

As soon as the two interact, distortion of the magnetic field occurs into a huge teardrop pointing away from the Sun. The dangerous, high velocity charged particles, mostly, are deflected by the magnetic field so that they do not reach the Earth's surface. Therefore, in this way the magnetic field becomes a shield against the solar wind; the region inside the shield is called the magnetosphere. Those charged particles which were fast enough to penetrate the outer, weaker portion of the magnetic field are trapped by the Van Allen radiation belts, named for the physicist who first recognized them in 1959 at a distance of about 3000 km and 10,500 km from the Earth.


Approx. 42-43% of Solar Energy is present in the visible region (400-700 nm), 52-55% in the infrared region (>700 nm), and only 2-3% in the UV region (<400 nm).


These belts, yes there are two at the mentioned distances, trap solar wind as well as cosmic rays (nuclei of atoms emitted from the supernova explosion from nearby). Some charged particles may also move past these belts and are channeled along magnetic field lines to the polar regions of Earth. When these particles interact with gaseous atoms in the upper atmosphere, they cause the gases to glow, like the gases in neon signs, creating spectacular aurorae. These spectacular and colossal views can be observed in both the hemispheres, for the northern hemispheres they are known as the Aurora Borealis, and for the southern hemisphere it is known as the Aurora Australis.


Answers to more questions in the coming articles.



References:

  1. Stephen Marshak- Essentials of Geology

  2. Principle of Physical Geology- Arthur Holmes

  3. NASA- The Sun's Corona

  4. Temperature of the Solar corona

  5. Science@NASA


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FactoSphere

  • Earth orbits around the Sun in 365.25 days. 0.25 days add to form 1 day after 4 years resulting in the leap year.

  • Earth completes its rotation about its axis in 23.9 days, defining days and nights.

  • Earth's axis of rotation is 23.5 degrees inclined from the normal to the elliptical equatorial plane of planets, giving rise to the seasons on the planet.

  • On two days of the year- Equinoxes, both the hemisphere is equally illuminated by the Sun.

  • Whichever hemisphere is close to the Sun experiences summer, while the one away from the Sun experiences winter.

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