A multi-year survey of dynamics near the surface in the northern hemisphere of Mars: Short-period baroclinic waves and dust storms

Baroclinic waves figure prominently in the dynamics of the northern hemisphere of Mars, and extensive observations by the Viking Landers and two atmospheric sounders on Mars Global Surveyor have revealed many of their basic properties. However, previous investigations considered these data sets individually, so that their cumulative value is not fully appreciated. We have re-examined these data to extract new information about the dynamics near the surface at mid-to-high northern latitudes. By applying the same method of spectral analysis to each type of observation, we derive a uniform, multi-year characterization of basic elements of martian weather. This survey documents the time evolution of baroclinic waves among modes with different periods and zonal wave numbers. We devote particular attention to a recurring “wave-3 mode”, which is distinguished by its capacity to initiate regional dust storms in the topographic basins of the northern hemisphere. Our results include a detailed case study that shows how the intermittence of this mode and the strong zonal modulation of its amplitude influence the timing and location of these distinctive “flushing” dust storms. More generally, we find that the properties of the wave-3 mode are largely the same whenever it appears and that its intermittence plays an important role in the annual dust cycle.