We solve a linear numerical model of Alfv¿n waves reflecting from the high-latitude ionosphere, both to better understand the role of the ionosphere in the magnetosphere/ionosphere coupling process and to compare model results with in situ measurements. We use the model to compute the frequency-dependent amplitude and phase relations between the meridional electric and the zonal magnetic fields due to Alfv¿n waves. These relations are compared with measurements taken by an auroral sounding rocket flown in the morningside oval and by the HILAT satellite traversing the oval at local noon. The sounding rocket's trajectory was mostly parallel to the auroral oval, and it measured enhanced fluctuating field energy in regions of electron precipitation. The rocket-measured phase data are in excellent agreement with the Alfv¿n wave model, and the relation between the modeled and the measured amplitudes is fair, leading us to conclude that the rocket-measured fields are dominated by interfering Alfv¿n waves, forming a standing wave pattern. The field amplitudes measured by HILAT are related by the height-integrated Pedersen conductivity &Sgr;p, indicating that the measured field fluctuations were due mainly to structured field-aligned current systems. A reason for the relative lack of Alfv¿n wave energy in the HILAT measurements could be the fact that the satellite traveled mostly prependicular to the oval and thefore quickly traversed narrow regions of electron precipitation and associated wave activity. Alternatively, the lower velocity and eastward flight path of the rocket lead to Doppler-shifted frequencies of L shell aligned current structures which are much smaller than HILAT would measure and which in fact may be below our range of interest (0.1--1 Hz), leading Alfv¿n waves as the dominant source of fluctuaring field energy in the rocket frame of reference. ¿ American Geophysical Union 1992