ed him to planetologists (actually to all scientists) It is unfortunate that his brilliance and courage were not recognized until recently MAGNETIC FIELD Arrakis has its own magnetic field (see ARRAKIS-GEOLOGY for details) However, Canopus emits an abnor mally high flux of charged particles with imbedded magnetic field segments This severely contracts the planet s own magnetic field and allows particles to impinge directly on atmospheric molecules No known effect on Arrakis weather has been proven to be a result of this interaction However magnetic disturbances make the main field unreliable for navigation Alternative means for direc tion finding, such as the paracompass were developed to overcome this problem Today our techniques far exceed these rudimentary nagivational efforts WEATHER PREDICTION Modem techniques make weather prediction by the Arrabans (about 5000 years ago) seem extremely primitive However their method was well suited to the conditions on Arrakis Indeed, the predictions were remarkably accurate and thus merit note Who would believe that emplacement of poles without sophisticated monitonng equipment could predict weather9 But it did work on Airdkib because all weath er phenomena m inhabited regions were associated with dust storms This simplified the problem over that on other planets A line of poles (or double line) was placed on the lower slopes of garres and ridges Each line ran along the direction of the slope Siting was particularly important The slope had to face a large open area as well as the direction from which storm winds blew had to be devoid of large boulders which could produce eddies required a slope angle of 15 5 degrees and had to be backed by a steep walled topographic feature rising at least 500 meters atx^e the surroundings When these specific conditions were satisfied the upslope winds impacting the topographic feature were not only deflected upward sud ARRAKIS, ATMOSPHERE 27 ARRAKIS ECOLOGY denly but also crested a wind shadow zone on the upwind side of the obstacle This is not meant to imply that a calm prevailed within the shadow zone Rather, with the specific geometry chosen, die winds are slightly less with the degree of difference increasing as wind speed increased Poles within the shadow zone were thus slightly less exposed to wind action than those down the slope Hie prevailing winds always earned dust The Franco chose the most easily abradable material they could find (known today as ambonte) to coat die poles This coating would be slowly worn away by even die lightest of winds Measurement of the mass loss each day in itself gave the integrated product of wind speed and dust content to an accuracy somewhat greater than could be determined with instruments in existence at the time By taking the ratio of this product for the down-slope poles to the shadow zone poles, one obtains a wind-speed ratio The accuracy of this determination far exceeded capabilities of other instruments, and even today is better than some of our present instruments (manufacturer claims not withstanding) One can calculate wind speed from the wind-speed ratio and knowledge of the surface geometry, but mere is no record that the Fremen dtd so or had the mathematical knowledge to do so However, there was no need to make this calculation since the speed ratio was all that was needed for weather prediction on Arrakis It is well established that Arrakian storms were preceded by an extremely small decrease in integrated wind speed (also die speed ratio, which in that case was directly proportional to wind speed) On most other habitable planets this decrease is large, readily noticeable, and is commonly called "the calm before the storm " On Arrakis, the decrease occurred one day before a minor storm, increasing to two days for a major storm, and five days for the greatest Conolis storms The size of the storm to be expected was proportional to the squareof the magnitude of the decrease It is still a source of wonder to many scientists how the Fremen were able to discern these relationships J R NOTES 'Pardot Kynes Atmosphere of Arrakis ' Bulletin of Planetology NS 127 135 55 ^arta Ptahtercicah Water Vapor in the Life Cycles of Organisms Imperial Biology Papers Ser 5, 15 106 68 *L L Nefad, Rotation and Conohs ' Bull Planet OS 784 86 117 4Joon F Hohshas Internaction of Temperature Rotation, and Radiation m Conohs, Bull Planet NS 1301 48 68 5Dont Pachtra Storm Effects on Arrakis Bull Planet OS 1630 230 "R V Aster3k Macro Effects in Charged Dust Particles, Soil Science (Caladan) 27 422 99 7Dont Pachtra Transmission of Sound in Sand Under Conditions Unique to Arrakis Bull Planet NS 5 80-108 Further reference Th Zed Ghralic Arrakian Climato logical Studies from Atreidean Times to the Present M rological Forum whole issue 59 ARRAKIS, Ecological Transformation of.