Interplanetary Causes of Middle Latitude Ionospheric Disturbances

The solar and interplanetary causes of major middle latitude ionospheric disturbances are reviewed. Solar flare photons can cause abrupt (within ~5 min), 30% increases in ionospheric total electron content, a feature that can last for tens of minutes to hours, depending on the altitude of concern. Fast interplanetary coronal mass ejection sheath fields and magnetic clouds can cause intense magnetic storms if the field in either region is intensely southward for several hours or more. If the field conditions in both regions are southward, "double storms" will occur. Multiple interplanetary fast forward shocks "pump up" the sheath magnetic field, leading to conditions that can lead to superstorms. Magnetic storm auroral precipitation and Joule heating cause pressure waves that propagate from subauroral latitudes to middle and equatorial latitudes. Shocks can create middle latitude dayside auroras as well as trigger nightside subauroral supersubstorms. Solar wind ram pressure increases after fast shocks can lead to the formation of new radiation belts under proper conditions. Prompt penetration electric fields can cause a dayside ionospheric superfountain, leading to plasma transport from the equatorial region to middle latitudes. The large amplitude Alfven waves present in solar wind highspeed streams cause sporadic magnetic reconnection, plasma injections, and electromagnetic chorus wave generation. Energetic electrons interacting with chorus (and PC5) waves are accelerated to hundreds of keV up to MeV energies.