Abstract:
Mars and Titan have strikingly different atmospheres. Mars's atmosphere is thin and dry with a regular dust storm cycle and global dust events; Titan’s atmosphere is thick with a methane hydrologic cycle and storms that can cover a large fraction of the surface. Yet, in comparing these defining features to Earth, weather systems on each world share many characteristics in structure, size, and frequency. However, because Mars and Titan are smaller than Earth, atmospheric waves reach planetary-scale sizes. The storm/planet size ratio enables particularly strong individual waves to have global impacts. Despite this, the climatological, extratropical storm track on all three worlds remains fairly similar. The shared characteristics emerge because the triggering mechanisms and instabilities driving individual storms are similar. Methane storms on Titan and dust storms on Mars initiate when either or both of the baroclinic and barotropic annular modes enter a favorable part of their oscillation, similar to how Earth's annular modes exert enormous influences on weekly and seasonal variability. The ubiquity of annular modes across planets arises because of their relation to baroclinic instabilities across all three bodies. I will compare our best observations, models, and reanalysis of Mars's and Titan's weather to Earth's to demonstrate how studying the climates of other planets helps solve the mystery of why the baroclinic and barotropic annular modes appear uncorrelated on Earth but are correlated on Mars. This explanation of how the baroclinic wave lifecycle evolves through the annular modes points to better metrics for quantification of the strength of Earth's annular modes.