This project will investigate natural irregularities in the earth’s ionosphere, the layer of the upper atmosphere that contains charged constituents, at altitudes of about 100 km, near the edge of space. The irregularities affect radio wave propagation and constitute a form of space weather that affects several ground- and space-based operational systems such as radar, global navigation systems, and satellite imagery, especially during summer evenings when irregularities occur most often. The irregularities occur in so-called “sporadic E” layers that are among the first phenomena that were detected in space about 100 years ago. The specific causes of the irregularities remain unknown, however. This project seeks to find and understand causes rooted in the lower and middle atmosphere associated with regular weather phenomena. It also seeks to understand if space-weather phenomena higher in the ionosphere are causally related to the irregularities that exist near 100 km altitude. The study will use radars located at Cornell and Clemson University along with other regional radars, GNSS receivers, and other instruments. Observations will be interpreted using a combination of theory and computer modeling and simulation. The experimental and computational tools to be developed for this problem will be incisive and groundbreaking. The proposal will address the influence of two-way atmosphere-ionosphere coupling on mesosphere/lower thermosphere neutral dynamics, plasma processes