Contribution of form drag on pressure ridges to the air stress on Arctic ice

Various methods of measuring air stress on the arctic ice surface are discussed; however, none of them could possibly take into account the form drag due to pressure ridges. An expression is derived for the form drag per unit area in terms of certain key parameters of ridge statistics and a suitable drag coefficient. By using the available field and laboratory measurements of these parameters an estimate is made of the ratio of the form drag to the frictional stress. It depends on the geographical location in the Arctic, the season of the year, and the meteorological conditions in the atmospheric surface layer. It is found, contrary to the common assumption, that the form drag on pressure ridges may be much larger than the frictional stress on the ice surface, especially under stably stratified conditions.