Winds: Global, Local and Upper-Air
Global circulation
Unequal heating drives the Hadley, Ferrel and Polar cells. The Coriolis force deflects winds (right in the Northern Hemisphere). Trade winds (NE in NH), westerlies, and polar easterlies result. The jet stream is a fast upper-level westerly near the tropopause, associated with strong temperature gradients and clear-air turbulence.
Local winds
- Sea breeze: daytime, blows from sea to land (land heats faster).
- Land breeze: night, land to sea.
- Anabatic/katabatic: upslope/downslope; katabatic flows at night can cause low-level wind shear.
- Föhn/chinook: warm dry downslope wind.
Upper-air winds
Wind veers (turns clockwise) with height in the NH when warm advection occurs and backs with cold advection. The thermal wind relationship links vertical shear to horizontal temperature gradient.
Worked example
At a coastal airport, a strong sea breeze develops by mid-afternoon; expect a wind shift from offshore to onshore, cooler temperature, and higher humidity. On approach, anticipate wind shear at low level as the sea-breeze front passes.
Traps
Sea breeze is daytime (sea to land) - students flip it. Coriolis deflects to the right in NH. Veering = clockwise; backing = counter-clockwise.