maximum intensity in winter, the westerlies increase in strength. As the cyclone reaches its weakest intensity in summer, the Westerlies weaken. An example of the impact of the westerlies is when dust plumes, originating in the Gobi desert combine with pollutants and spread large distances downwind, or eastward, into North America. The westerlies can be particularly strong, especially in the Southern Hemisphere, where there is less land in the middle to cause the progression of west to east winds to slow down. In the Southern hemisphere, because of the stormy and cloudy conditions, it is usual to refer to the westerlies as the roaring forties, furious fifties, or shrieking sixties according to the varying degrees of latitude. Impact on ocean currents Due to persistent winds from west to east on the poleward sides of the subtropical ridges located in the Atlantic and Pacific oceans, ocean currents are driven in a similar manner in both hemispheres. The currents in the Northern Hemisphere are weaker than those in the Southern Hemisphere due to the differences in strength between the westerlies of each hemisphere. The process of western intensification causes currents on the western boundary of an ocean basin to be stronger than those on the eastern boundary of an ocean. These western ocean currents transport warm, tropical water polewards toward the polar regions. Ships crossing both oceans have taken advantage of the ocean currents for centuries. The Antarctic Circumpolar Current (ACC), or the West Wind Drift, is an ocean current that flows from west to east around Antarctica. The ACC is the dominant circulation feature of the Southern Ocean and, at approximately 125 Sverdrups, the largest ocean current. In the northern hemisphere, the Gulf Stream, part of the North Atlantic Subtropical Gyre, has led to the development of strong cyclones of all types at the base of the Westerlies, both within the atmosphere and within the ocean. The Kuroshio (Japanese for "Black Tide") is a strong western boundary current in the western north Pacific Ocean, similar to the Gulf Stream, which has also contributed to the depth of ocean storms in that region. Extratropical cyclones An extratropical cyclone is a synoptic scale low-pressure weather system that has neither tropical nor polar characteristics, being connected with fronts and horizontal gradients in temperature and dew point otherwise known as "baroclinic zones". The descriptor "extratropical" refers to the fact that this type of cyclone generally