The inversion of temperature lapse rate with height over a major zone of the trade-wind belt, which is very significant in tropical meteorology. Moist tropical air, extending up to 2–3 km above the surface, is ‘boxed in’ or ‘trapped’ by dry, clear, warmer air above, resulting from subsidence in subtropical anticyclones. The inversion forms where the subsiding air meets a surface flow of cooler maritime air. The top of a cloud layer marks the base of the inversion.