Ion velocity and temperature measurements at Arecibo for two winter days were analyzed to determine the large-scale dynamical structure of the E region. Southward neutral winds were derived directly from the ion velocity, while the southward electric field was obtained with a reasonable extrapolation of the measured ion-neutral collision frequency. Eastward winds were estimated after assuming a model eastward electric field taken from previous F region measurements at Arecibo. The main results are as follows: (1) Large oscillations in the ion drifts, neutral winds, and temperatures were present on the days of observation. The oscillations possessed a characteristic downward phase progression and dominant periods that were near semidiurnal. (2) Wind and temperature amplitudes were 40--100 m/s and 30¿-60¿K, respectively. Vertical wavelengths for a semidiurnal period were about 50 km. The calculated southward electric fields are typical of daytime F region values at Arecibo, -1 to -2 mV/m. (3) The observed semidiurnal amplitudes, phases, and vertical wavelengths of the wind and temperature oscillations do not closely match the predictions of classical tidal theory or the theory of Lindzen and Hong which includes dissipation and background winds.