A comprehensive study of lightning-associated amplitude and phase perturbations on multiple VLF/LF signals (Trimpi events) observed at Stanford, California and at Palmer Station, Antarctica, has revealed a number of new properties that appear to be characteristic of the particular signal paths. (1) Signal amplitude changes are on the whole evenly distributed between enhancement and attenuation, but some individual signal paths have strong preferences for one or the other. (2) Phase changes on almost all paths show a strong preference for advancement, with phase retardation occurring rarely. (3) The range in size of amplitude and phase changes appears to be relatively constant for a given path, but it is found to vary between different paths. None of the existing models of the Trimpi effect are found to explain all of the observed new features. Instead, the new experimental findings provide an empirical framework to guide the evaluation of more sophisticated models. Analysis also indicates that the magnitudes of simultaneous amplitude and phase changes are only weakly correlated and that the recovery signatures of amplitude and phase events can be substantially different, with the signal amplitude generally recovering faster. This apparent independence of amplitude and phase perturbations is interpreted to result from the altitude distributed nature of the ionospheric disturbances. ¿American Geophysical Union 1990