High-pressure area Hadley cells help form the subtropical ridge, steer tropical waves and tropical cyclones across the ocean and is strongest during the summer. The subtropical ridge also helps form most of the world's deserts. On English-language weather maps, high-pressure centers are identified by the letter H. Weather maps in other languages may use different letters or symbols. The direction of wind flow around an atmospheric high-pressure area and a low-pressure area, as seen from above, depends on the hemisphere. High-pressure systems rotate clockwise in the northern Hemisphere; low-pressure systems rotate clockwise in the southern hemisphere. The scientific terms in English used
High-pressure steam locomotive High-pressure steam locomotive A high-pressure steam locomotive is a steam locomotive with a boiler that operates at pressures well above what would be considered normal. In the later years of steam, boiler pressures were typically . High-pressure locomotives can be considered to start at , when special construction techniques become necessary, but some had boilers that operated at over . Maximising the efficiency of a heat engine depends fundamentally upon getting the temperature at which heat is accepted (i.e. raising steam in the boiler) as far as possible from the temperature at which it is rejected (i.e. the steam when