Electron and proton data from Isis 1 and 2 have been used to examine the change in the latitudinal morphology of auroral particle fluxes as a function of substorm time in the 2100--0300 dipole magnetic local time period. Clear and repeatable systematics in the latitudinal morphology were observed during the various phases of a substorm, allowing one to identify the substorm phase based on particle data alone. Based on this study, a new phenomenological substorm model is presented that relates particle precipitation from various parts of the magnetotail to auroral oval morphology.