Data recorded by the Geostationary Operational Environmental Satellites, frequency deviations derived from a CW-HF Doppler sounding system, and geomagnetic field strength variations obtained from ground-based magnetometers were analyzed to study the ionospheric and geomagnetic solar flare effects. A model of flare radiation was constructed from synthetic flux intensities and satellite X ray observations, and corresponding ionospheric frequency deviation and electron density at various altitudes were calculated. The evolution of solar EUV and X ray radiation and associated maximum values responsible for frequency deviation and geomagnetic field strength for various flux intensities of the excess solar radiation were studied in detail. It was found that during a solar flare, not only the magnitude of solar radiation, but also the rate of its change dramatically affects the maximum ionospheric frequency deviation. However, the results confirmed that only the intensity of solar radiation determines the magnitude of geomagnetic field strength. ¿ American Geophysical Union 1996