1. The quasi-continuous belt of low pressure lying between the subtropical high pressure belts of the Northern and Southern Hemispheres. This entire region is one of very homogeneous air, probably the most ideally barotropic region of the atmosphere. Yet humidity is so high that slight variations in stability cause major variations in weather. The position of the equatorial trough is fairly constant in the eastern portions of the Atlantic and Pacific, but it varies greatly with season in the western portions of those oceans and in southern Asia and the Indian Ocean. It moves into or toward the summer hemisphere. It has been suggested that this name be adopted as the one general term for this region of the atmosphere. Thus, the equatorial trough would be said to contain regions of doldrums; portions of it could be described as intertropical convergence zones; and within it there might be detected intertropical fronts. However, one weakness of this nomenclature is that it alludes specifically and only to the existence of a trough of low pressure. Perhaps an even more general term might be preferable, for example, atmospheric equator. 2. Same as meteorological equator.