Baroclinic instability is recognized to be one of the dominant energetic processes in the large-scale atmospheres of terrestrial planets, such as Earth and Mars, e.g., Pierrehumbert and Swanson, and in the oceans. With the exponential increase in computing power these last decades, direct numerical simulation has become an indispensable tool for investigating the complex spatiotemporal behaviors of baroclinic instability in the laboratory, complementarily with experiments. It is useful to explore the different nonlinear flow regimes in the parameter space in order to accurately delineate a bifurcation diagram. Moreover, direct numerical simulation provides relevant information about the small-scale fluctuations that progressively destroy the regularity of the flow during the transition toward geostrophic turbulence.