The Imprint of $Ω$ on the Cosmic Microwave Background

We investigate the dependence of large angular scale cosmic microwave background anisotropies on various initial conditions, including both adiabatic and isocurvature perturbations and the initial power law index $n$, in a variety of low-$\Omega$ cosmological models. Cosmological constant- dominated flat models and inflationary open adiabatic models, with $n_{\rm eff}<1$, and open isocurvature models, with $n_{\rm eff} \simeq 2$, are significantly constrained by the present observations.