equatorial air

According to some authors, the air of the doldrums or the equatorial trough, to be distinguished somewhat vaguely from the tropical air of the trade-wind zones.
Tropical air "becomes" equatorial air when the former enters the equatorial zone and stagnates. There is no significant distinction between the physical properties of these two types of air in the lower troposphere.
Grimes, A. 1951. Compendium of Meteorology. p. 881.

A type of air mass with characteristics developed over low latitudes.

1. The study of the physics, chemistry, and dynamics of the earth's atmosphere, including the related effects at the air–earth boundary over both land and the oceans. Fundamental topics include the composition, structure, and motion of the atmosphere. The goals ascribed to meteorology are the complete understanding and accurate prediction of atmospheric phenomena.