Although there is a rich literature on modelling the effects of broad spectrum gravity waves (GW) in General circulation Models (GCM), the effect of a coupled interactive broad spectrum and monochromatic GW has not been studied in detail. Such a study is of paramount importance as it could conclusively demonstrate that the coupled interactive broad spectrum and monochromatic GW can be parameterized in a GCM and its effects on atmospheric circulations can be studied. The main objective of this thesis is to investigate how the climate simulated by the Unified Model (UM), a state-of-the-art GCM, responds to more physically realistic gravity wave parameterizations, beginning with the addition of a spectral gravity wave scheme, and then progressing to a scheme which couples both orographic and spectral gravity waves. Behaviour of the schemes are analyzed using a set of four idealized experiments in a single column test-bed based on the architecture of the UM. Results from these experiments are discussed before implementing the schemes in the UM. These findings provide the necessary backdrop around which more complex interactions modelled by the UM are discussed. The UM is run for six years with the two GW schemes. Monthly means of a range of diagnostic fields results are compared qualitatively with the U.K. Met. Office global assimilated data. Both schemes simulate the overall structure of the atmospheric circulation. The simulations based on the two GW schemes are also compared against each other to observe any potential effect on the climatology of the UM due to their different underlying assumptions. The results show sensitivity of the model in the dynamics of middle atmosphere. Some degree of variability is also exhibited in tropospheric circulation. A major conclusion that emerges from the extension of the spectral gravity wave scheme to the coupled interactive scheme is that the latter is equivalent to a change in the global mean gravity wave strength.