The Neupert Effect and the Chromospheric Evaporation Model for Solar Flares

The Neupert effect is the name given to the apparent causal relationship between hard and soft X-ray emissions observed in many solar flares. It is shown that the observed distributions of flare hard X-ray fluence and soft X-ray flux are incompatible with the simple statement of the Neupert effect commonly found in the literature. The more fundamental energy relationship predicted by the chromospheric evaporation model may also be incompatible with the observations unless a well-defined temperature-density scaling exists. Without such a scaling, additional heating by an agent other than accelerated electrons (e.g., turbulence) is necessary to explain the observations.