OROGRAPHIC CONTROL OF STORM ZONES ON MARS

Low-pressure cyclones and their accompanying frontal systems in the mi ddle latitudes of the Earth's troposphere develop, travel eastwards an d decay preferentially within latitudinally and longitudinally confine d geographical regions known as storm zones' These zones can be readil y identified in the circulation statistics of terrestrial weather syst ems(2). Mars, like the Earth, is a rapidly rotating solid planet and h as a seasonally varying shallow atmosphere, large-scale orography, and (in a broadly defined context) continental structures(3). Although th ere are also important differences between the two planets, travelling weather systems do exist on Mars(3). This raises the question of whet her storm zones also occur there, and if so, by what mechanisms. Here we report the results of numerical simulations of global atmospheric c irculation patterns on Mars, We find that storm zones can exist during the northern winter, and that continental-scale orography (rather tha n surface thermal contrasts) is the main factor determining the develo pment of these zones. Storm zones on Mars should play an important rol e 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.