<P> In addition to standard troughs, some may be described further with a qualifying term indicating a specific or a set of characteristics . </P> <P> An inverted trough is an atmospheric trough which is oriented opposite to most troughs of the mid-latitudes . Most (but not all) inverted troughs are tropical waves (also commonly called easterly waves). </P> <P> Most troughs of low pressure in the mid-latitudes of the Northern Hemisphere are characterized by decreasing atmospheric pressure from south to north while inverted troughs are characterized by decreasing pressure from north to south . The situation is opposite in the Southern Hemisphere . Inverted troughs in both hemispheres move to the west from the east, while mid-latitude troughs generally move with the westerlies toward the east . </P> <P> A lee trough, also known as a dynamic trough, is "A pressure trough formed on the lee side of a mountain range in situations where the wind is blowing with a substantial component across the mountain ridge; often seen on United States weather maps east of the Rocky Mountains, and sometimes east of the Appalachians, where it is less pronounced ." It can be formed either as a result of the adiabatic compression of sinking air on the lee side of a mountain range, or through cyclogenesis resulting from "the horizontal convergence associated with vertical stretching of air columns passing over the ridge and descending the lee slope ." </P>

Winds within the base of a trough tend to be