The study of the tropical atmosphere. The dividing lines, in each hemisphere, between the tropical easterlies and the midlatitude westerlies in the middle troposphere roughly define the poleward boundaries of this region. Whereas many circulation systems in middle and high latitudes are nearly adiabatic and quasigeostrophic, tropical systems are often strongly influenced by cumulus convection and surface heating, and can be less often dealt with using quasigeostrophic techniques. Many tropical circulations are driven or strongly influenced by coupling with the ocean. Examples of important tropical systems include the Hadley and Walker circulations, monsoons, tropical cyclones, the Madden–Julian oscillation, easterly waves, and El Niño–Southern Oscillation. The stratospheric circulation is dominated by the quasi-biennial oscillation and also contains the ascent branch of the Dobson circulation. Although tropical meteorology may be said to be a distinct endeavor, there are strong interactions between tropical and extratropical circulation systems.