Geophysical and Astrophysical Fluid Dynamics

Abstract:

We calculate a Lorenz energy budget for the Martian atmosphere from reanalysis derived from Mars Global Surveyor data for Mars years 24-27. We present global, annual mean energy and conversion rates per unit area and per unit mass and compare these to Earth data. The directions of the energy conversion terms for Mars are similar to Earth, with the exception of the barotropic conversion between zonal and eddy kinetic energy reservoirs. Further, seasonal and hemispheric decomposition reveals a strong conversion between zonal energy reservoirs over the year, but these balance each other out in global and annual mean. On separating the diurnal timescale, the contribution to the conversion terms and eddy kinetic energy for diurnal and shorter timescales in many cases (especially during planet-encircling dust storms) exceeds the contribution of longer timescales. This suggests that thermal tides have a significant effect on the generation of eddy kinetic energy. Key Points Comprehensive analysis of global and hemispheric energy exchanges within the Mars atmosphere Thermal tides have a significant impact on eddy energy and conversion terms Most conversion occurs in zonal component but is canceled out in annual and global mean

Abstract:

We investigate the predictability of the thermally driven rotating annulus, a laboratory experiment used to study the dynamics of planetary atmospheres under controlled and reproducible conditions. Our approach is to apply the same principles used to predict the atmosphere in operational weather forecasting. We build a forecasting system for the annulus using the analysis correction method for data assimilation, the breeding method for ensemble generation, and the Met Office/Oxford Rotating Annulus Laboratory Simulation as the forecast model. The system forecasts the annulus in steady (2S), amplitude vacillating (3AV), and structurally vacillating (3SV) flow regimes, verifying the forecasts against laboratory data. The results show that a range of flow regimes from this experiment can be accurately predicted. Forecasts in the steady wave flow regime perform well, and are predictable until the end of the available data. Forecasts in the amplitude and structural vacillation flow regimes lose quality and skill by a combination of wave drift and wavenumber transition. Amplitude vacillation is predictable up to several hundred seconds ahead, and structural vacillation is predictable for a few hundred seconds. The wavenumber transitions are partly explained by hysteresis in the rotating annulus experiment and model.