Maintenance of zonal wind variability associated with the annular mode on Mars

Results from a Mars general circulation model (MGCM) were used to investigate the maintenance of the annular mode in the Martian atmosphere. Analysis of the Martian northern winter, as represented by the MGCM revealed a prominent transient wave with zonal wave number 1 that had a baroclinic instability structure. An empirical orthogonal function (EOF) decomposition showed that the first two modes of the EOF contained features of the transient wave with wave number 1. The third EOF mode had an annular structure about the Martian North Pole and an equivalent barotropic structure in the vertical. Each term in the transformed Eulerian mean equation was estimated from the MGCM output to investigate the maintenance of the annular mode. Wave forcing (Eliassen-Palm flux divergence) played an important role in maintaining the mode. In the wave forcing term, contributions from transient baroclinic waves with wave numbers 1 and 2 were important.