Orographic control of storm zones on Mars

Low-pressure cyclones and their accompanying frontal systems in the middle latitudes of the Earth's troposphere develop, travel eastwards and decay preferentially within latitudinally and longitudinally confined geographical regions known as storm zones' These zones can be readily identified in the circulation statistics of terrestrial weather systems(2). Mars, like the Earth, is a rapidly rotating solid planet and has a seasonally varying shallow atmosphere, large-scale orography, and (in a broadly defined context) continental structures(3). Although there are also important differences between the two planets, travelling weather systems do exist on Mars(3). This raises the question of whether storm zones also occur there, and if so, by what mechanisms. Here we report the results of numerical simulations of global atmospheric circulation patterns on Mars, We find that storm zones can exist during the northern winter, and that continental-scale orography (rather than surface thermal contrasts) is the main factor determining the development of these zones. Storm zones on Mars should play an important role in the martian climate cycle(4,5), by influencing the transport of (for example) heat, momentum, water vapour and atmospheric dust(3,6-8) towards the poles.