| dc.description.abstract | Introduction
This project concerns about the Sudden Ionospheric Disturbances caused by the solar flare. Solar flare is defined as a violent explosion from the sun’s atmosphere which releases a vast amount of energy. This takes place in the solar corona and chromosphere heating up plasma up to millions of kelvins and accelerating protons, electrons and heavier ions. A space weather monitoring system measures the effects on Earth Solar flares by tracking changes in very low frequency (VLF, 3-30KHz) transmission as they bounces off Earth’s ionosphere. The earths ionosphere ranges from 100km to 300km and this is comprised of different regions called D, E and F layers. Solar activity like solar flares, sunspot, corona mass ejections, solar wind affect the earths ionosphere. They affect the VLF transmission. The Sudden Ionospheric Disturbances (SID) monitor developed by the Stanford University Solar Centre detects propagation of VLF waves changes as the Sun affects Earth’s ionosphere, adds ionization, and thus alters where the waves bounce. The monitor tracks these changes in signal strength. For this project we are going to determine the disturbances in the D region of the ionosphere. The D region is the inner most layer 48 km to 90km above the surface of the earth. Medium frequency (MF) and lower high frequency (HF) radio waves are
significantly attenuated within the D layer, as the passing radio waves cause electrons to move, which then collide with the neutral molecules, giving up their energy. Lower frequencies experience greater absorption because they move the electrons farther, leading to 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. | en_US |
