The solar proton event of July 13, 1982, produced considerable ionization in the polar cap mesosphere. Energetic solar proton fluxes were measured by the NOAA-6 satellite. The Dynamics Explorer 2 satellite measured the low-energy electrons, the ion drift velocity, and other atmospheric and ionospheric properties during the event. The measured solar proton flux is used in a proton degradation code to calculate the ionization rates below 100 km and the electron and ion number densities are calculated using an ionospheric D region code with the neutral atmosphere specified by a chemical/dynamic model of the middle atmosphere. Electron and ion densities above 100 km are calculated using a satellite track ionospheric code developed for the Dynamics Explorer satellite project. Electric fields at ionospheric heights map efficiently downward into the mesosphere where the Pedersen conductivity is enhanced. In the region of the measured maximum electric field (189 mV m-1 at 2215 UT near 60¿N), a Joule heating rate of 1¿--3¿K/day is calculated betwen 70 and 80 km, exceeding the heating due to ozone absorption at noon in the summer hemisphere in that altitude range. The Joule heating rate above 90 km greatly exceeded 20¿K/day. The calculated height integrated Joule heating rate above 100 km in the same region exceeded 400 ergs cm-2 s-1 and DE-2 near 350 km measured neutral winds of nearly 1000 ms-1 and neutral gas temperatures of over 2000¿K. The overall ionospheric structure calculated below the DE-2 satellite is described. ¿American Geophysical Union 1987