Synoptic Scale Motion The General Circulation

Three regions of the atmosphere are seen to have significant zonal components of flow and thus of advection. The mid-latitude troposphere at the surface tends to exhibit westerly flow (i.e. flow from west to east) on the average. This region contains the familiar high- and low-pressure systems that cause periodicity in mid-latitude weather. Depending on the lifetime of the substances of concern, the motion in these weather systems may be important. 

The tropical regions of the northern hemisphere s troposphere exhibit easterly flow called the trade winds (of course, these also exist in the southern hemisphere). Finally, the jet stream - sometimes described as a river of air - flows with velocities of 25-50 m/s from west to east, often carrying material 

Horizontal motion of the atmosphere, or wind, is a response of the air to the forces that are present. These include the force due to the pressure gradient, the Coriolis force associated with the rotation of the Earth, and frictional forces acting to retard any motion. If the acceleration of the air mass and frictional effects are small, the horizontal velocity is described by the following expression  

---