3.41 Sspd_chapter 1_appendices_space weather research  (Page 23/3)

SUN-SOLAR ACTIVITY&COMMUNICATION

Between the ground and interplanetary space:

1. The troposphere- human population is limited to this level and uses only the first 6 km of atmosphere, a thin layer that has to be reserved.
2. The stratosphere-(between 15km to 45km) very dry, it is characterized chiefly by ozone layer which is an effective barrier to ultra violet light from sun.
3. The mesosphere-(between 45km to 80 km) An icy layer(-90 degree centigrade at the top of this layer)
4. The Thermosphere-(between 80km to 480km).very hot layer(from 850 to 2300 degree centigrade depending on solar activity). This contains a layer of plasma called ionosphere. Ionosphere acts as an effective mirror for Radio Waves-Short Wave i.e. 1MHZ to 30 Mhz.

The Earth behaves like a huge bar magnet with the magnet almost but not exactly aligned along the spin axis. This bar magnet creates a Magnetic Field terminating at the north pole and originating at the South Pole. From a height of 1000km an immense magnetic field surrounds the Earth as shown in the Figure below. This 3-d magnetic field which under normal condition would have a cylindrical symmetry but in presence of solar wind it is flattened on the windward side and elongated on the leeward side as shown. This is called MAGNETOSPHERE. Earth is continuously bombarded by fierce solar Wind and Cosmic rays. This magnetosphere repels the stars high-energy radiation.

Figure(1)The Gaint Magnetic Field of Earth Bar Magnet –Magnetosphere.

SUN-A gigantic Nuclear Fusion Reactor .

Our Sun is a humble star in the Milky Way Galaxy of stars. it was born about 4.56 Billion years ago and it will continue to react for another 5 billion years. That is its total life span is 10 billion years.

Once its nuclear fuel runs out, it will expand to Red Giant and then collapse into White Dwarf. The solar System will be wiped out.

SUN- Its Present Scenario.

The fusion reaction between hydrogen and helium is the primary source of energy. Sun is a main sequence star where a balance is maintained between the gravitational inward collapse and outward expansion due to radiation pressure of the thermonuclear energy released due to Hydrogen atoms fusion. This state of equilibrium has been maintained since the beginning and it will be maintained for the whole life span of 10 billion years.

THE BURNING CORE

At the core of the sun, temperature is 15 million degree Celsius and a pressure equivalent to 160 times the atmospheric pressure.

In the heart of the Sun , 500 million tones of hydrogen fuses into helium Gas . This fusion reaction leads to Mass defect of 4 million tones which by E=mc ² relationship is converted into energy. This released energy radiates to the adjoining zone. From there through convective current of gases it travels to the surface of the sun.

SOLAR PHOTOSPHERE

Beyond the convective layer is solar photosphere. This layer is 200 km thick on an average. Here the matter is cool enough to turn from plasma state to neutral state. Therefore radiation decouples from matter and freely travels out.