Ionospheric amplitude and phase scintillation data have been analysed to estimate the 'information dimension' associated with the attractor of the system. For weak scintillations, both amplitude and phase data yield identical results which demonstrate that spatial fluctuations of electron density in the ionosphere may be characterized by a few degrees of freedom. Stronger scintillations are attributed to steepened density irregularities which cause 'focusing' of the incident radio wave. This results in the amplitude scintillations exhibiting higher dimensional chaos but spatial fluctuations in ionospheric density still involve low dimensional chaos. ¿ American Geophysical Union 1990