What is the corona effect in electrical system

Explain the corona effect in an electrical system

The phenomena of CORONA EFFECT occurs on high voltage transmission lines.Off course produce due to ionisation around the conductor caused by electrical discharge.In this effect a blue light and a hissing audible Sound is produce not VIBRATION.One can easily be observe Corona Effect on transmission line by their eyes and can listen the hissing sound the effect is more when weather has more moisture contents in air