&会 Hadley Cell Theories Held-Hou model (1980) Make assumptions: (Vallis,2006) Z=H Tropopause Angular momentum conserving flow the circulation is steady; Large zonal flow aloft the upper branch conserves Mass flux V angular momentum;surface zonal Warm Cool winds are weak; ascent descent the circulation is in thermal wind balance. Mass flux -V Frictional return flow Z=0,Ground Weak zonal flow at surface Equator Latitude Subtropics 授课教师：张洋 4授课教师：张洋 4 Hadley Cell - Theories 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) (Vallis, 2006) n Held-Hou model (1980) Make assumptions: n the circulation is steady; n the upper branch conserves angular momentum; surface zonal winds are weak; n the circulation is in thermal wind balance. Review Mass flux V Mass flux -V Z = 0, Z = H