Abstract
Life on Earth is protected from the inhospitable nature of space by two fundamental shields. One is our intrinsic magnetosphere protecting us from the continuous onslaught of energetic particles from the sun. The other is the gaseous neutral atmosphere that prevents harmful radiation from reaching the Earth's surface. These two regions interact by coupling processes that occur along common geomagnetic field lines. A transition occurs in the Earth's upper atmosphere where the magnetic field lines end their reign over plasma behavior and the neutral atmosphere begins to impose its influence. This collisionless to collision-dominated transition occurs primarily over a relatively thin shell of the ionosphere called the E region, extending from 90 to 180 km altitude. At polar latitudes the Earth's E-region is particularly dynamic. In this region strong currents flow perpendicular to the field line, precipitating plasma particles are halted, neutral molecules and atoms are ionized, conductivities peak, heating of plasma and neutral gas intensifies, a wide range of chemical processes evolve that produce the aurora, and the neutral gas is accelerated. Unraveling the physics and chemistry of this complex interplay between charged and neutral gases is central to polar ionosphere-thermosphere studies. The polar E region also represents the final link in a long and complex chain of energy conversion from a variety of distant energy sources. This energy may be transported by waves from the lower atmosphere, by solar radiation, by accelerated electrons and protons from the magnetosphere, or by the electromagnetic energy flux produced from magnetosphere-solar wind interactions. These different energy fluxes converge within the IT system and, as such, deposit their energy in the medium, but each in their own way. The state of the IT system and its response to these sources of energy can alter how and where future energy deposition occurs. In some cases, the IT system response can actually modify the energy source. In this talk, the basic ionospheric state and the processes of energy conversion in the polar E region will be presented, leading to a discussion regarding the role of the polar ionosphere in coupling with the magnetosphere.