&售 Hadley Cell-Theory: Asymmetry about the equator* Review Lindzen-Hou (1988) Tropopause Angular momentum conserving flow Still make the assumptions: Large zonal flow aloft the circulation is steady or quasi-steady Warm Cool ascent descent (the flow adjusts to a steady circulation on a timescale faster than that on which the solar radiation varies), the upper branch conserves angular Frictional return flow momentum;surface zonal winds are 《 weak; Ground Weak zonal flow at surface summer equator winter the circulation is in thermal wind hemisphere hemisphere balance; the only difference:the heating is centered off the equator. 授课教师：张洋 A授课教师：张洋 4 Hadley Cell - Theory: Asymmetry about the equator* ! Lindzen-Hou (1988) Still make the assumptions: ! the circulation is steady or quasi-steady (the flow adjusts to a steady circulation on a timescale faster than that on which the solar radiation varies); ! the upper branch conserves angular momentum; surface zonal winds are weak; ! the circulation is in thermal wind balance; i i i i i i i i Angular momentum conserving flow Equator Subtropics Latitude Warm ascent Cool descent Tropopause Frictional return flow Weak zonal flow at surface Ground Large zonal flow aloft Fig. 11.4 A simple model of the Hadley Cell. Rising air near the equator moves polewards near the tropopause, descending in the subtropics and returning near the surface. The polewards moving air conserves its axial angular momentum, leading to a zonal flow that increases away from the equator. By the thermal wind relation the temperature of the air falls as it moves poleward, and to satisfy the thermodynamic budget it sinks in the subtropics. The return flow at the surface is frictionally retarded and small. From Vallis (2006) From Vallis (2006) summer equator hemisphere winter hemisphere ! the only difference: the heating is centered off the equator. Review