Since Cassini arrived at the ringed planet, one thing the probe has kept a beady eye on are vast thunder storms within the dense atmosphere. Lightning storms at Saturn are more powerful and longer lived than anything Earth has to offer. They are generated at a location 35 degrees South of the equator (though it is thought this changes with the seasons) and are believed to be due to massive upward convection of water from further within the atmosphere. The storms are often visible even to Earth based amateur observers with appropriate equipment. The diameters of the storms range up to 3,000 km. This storm has been going for eight months, half a month longer than the previous record storm, seen raging in 2007.
As on Earth, the huge discharges of charged particles in lightning create radio waves (this allows lightning radio monitoring stations like this one). However, the radio wave signals are 10,000 times stronger than terrestrial storms. This natural occurrence of radio waves allows Cassini’s Radio and Plasma Wave Science experiment to take measurements relating to the ionosphere of the ringed planet. The atmospheres of the planets are bombarded with charged particles (cosmic rays and aurorae) and high energy UV and X-ray solar radiation, leading to increasing levels of ionisation at higher altitudes. The layers of ions thus created by the balances of physical and chemical processes are together called the ionosphere.
Ions and electrons scatter radio waves through Thompson (Compton) scattering, so by having a radio wave source below the ionosphere, Cassini can investigate the populations of ions and electrons within the ionosphere.