We have undertaken an extensive program to investigate atmospheric shock dynamics in Mira variables through monitoring the MgII emission strengths versus phase. Theoretical calculations of Bowen (1987), which represent the structural variations in the extended atmosphere of a pulsating Mira, are presented in addition to the MgII observations. The model calculations generate density, temperature and velocity structures as determined by stellar parameters and by interactions of the driving amplitude, dust opacity and thermal relaxation processes. The main diagnostic provided by the models is the total emitted shock luminosity versus phase, which can be compared to the observed MgII emission. Models and observations are presented for three Miras: S Car, R Car and T Cep.