---------------------------------------- Type of abstract: Invited Presenter Name: Jeff Thayer Status of first author: non-student ---------------------------------------- Title: Polar Aeronomy: Where the Field Lines End ---------------------------------------- Authors: Jeff Thayer SRI International 333 Ravenswood Avenue, Menlo Park CA 94025 ph: 650-859-3557 fax: 650-322-2318 email: thayer@sri.com ---------------------------------------- Abstract: A transition occurs in the polar regions of 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 polar ionosphere called the E region, extending from 90 to 150 km altitude. In this region 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 aeronomy. The polar E region also represents the final link in a long and complex chain of energy conversion that characterizes space weather. The dramatic conversion of energy that takes place in the polar E region, extracted from the fields and currents provided by the magnetosphere, strongly modifies the E region properties. However, in the process we must consider the ionospheric condition that enables this energy transfer and ask the question: How might the ionospheric condition influence the severity of space weather on the ionosphere? 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 polar aeronomy in the space weather arena. ---------------------------------------- Polar Aeronomy (CEDAR initiative)