Wind: Global, Local and Upper-Level Circulation
Global circulation
Heating differences drive the general circulation. Trade winds blow from the subtropical highs toward the equatorial trough, deflected by the Coriolis force (right in the Northern Hemisphere). The westerlies lie in mid-latitudes, and the polar easterlies near the poles. The jet stream - a band of strong upper winds - follows the polar front and steers depressions. Upper winds are geostrophic: balance between pressure gradient and Coriolis, parallel to isobars, faster where isobars are close.
Local winds
Sea and land breezes result from differential heating: a sea breeze blows onshore by day, a land breeze offshore at night. Valley winds flow upslope by day (anabatic) and downslope at night (katabatic). Mountain waves and Föhn winds occur downwind of ridges. Surface friction causes wind to cross isobars toward low pressure at roughly 30–45° over land, less over sea; wind veers with height in the Northern Hemisphere (Ekman spiral).
Traps
Questions confuse sea and land breezes, or forget that friction causes inflow toward the low. Others mix geostrophic (straight isobars) with gradient wind (curved isobars).
Worked example
Surface wind 060°/15 kt over land. At 2000 ft, expect the wind to veer (become more easterly/southerly) and increase, perhaps 090°/25 kt, because friction decreases with height and the geostrophic balance strengthens.
Rule of thumb
Surface wind ≈ two-thirds of the 2000 ft wind speed, backed 30–45° from the upper wind over land.