Maximum sustained wind 50% of the geostrophic wind speed aloft; while over open water or ice, the reduction is between 10% and 30%. In most basins, maximum sustained winds are used to define their category. In the Atlantic and northeast Pacific oceans, the Saffir–Simpson scale is used. This scale can be used to determine possible storm surge and damage impact on land. In most basins, the category of the tropical cyclone (for example, tropical depression, tropical storm, hurricane/typhoon, super typhoon, depression, deep depression, intense tropical cyclone) is determined from the cyclone's maximum sustained wind. Only in Australia is this quantity not used to
RRS Discovery over the Christmas period the ship was blocked in by pack ice. A Norwegian whaler was met on December 29, which gifted the "Discovery" a further 50 tons of coal. On December 31 the ship was struck by a violent storm with winds of up to 70 mph (Force 11 on the Beaufort Scale). The ship was driven against the ice, while larger bergs were blown onto the ship by the wind. For eight hours the "Discovery" was repeatedly slammed into and onto thick ice and battered by bergs but MacKenzie was able to slowly work the ship offshore by