Returning from the Americas: The Westerlies That Brought Ships Home

European square-riggers exploited a global wind conveyor: trade winds westward, westerlies eastward.

Outbound: Trade Winds (Northeast Trades)

30°N to equator. Steady easterlies (Force 3-5). Columbus's route: Canaries → Caribbean. Reliable November-April. Ships sailed "south 'til the butter melts, then west."

Return: The Westerlies (Mid-Latitude & Polar)

Mid-latitude Westerlies (30°-60°N): Prevailing SW winds. Ferrel cell dynamics. Stronger in winter (temp gradient). "Roaring Forties" (40°-50°S) even stronger—used by clipper ships Cape Horn route.
Polar Easterlies (60°-90°): Weak, cold, variable. Not primary return route.

The Gulf Stream Assist

North Atlantic gyre: Trade winds → Caribbean → Gulf Stream (Florida Current) → Northeast along US/Canada coast → North Atlantic Drift → Europe. Ships rode this 3-4 knot conveyor home.

Volta do Mar (Turn of the Sea)

Portuguese term for the navigational loop: sail west in trades, north to catch westerlies, east to Europe. Mastered 15th century. Enabled reliable round-trip Atlantic commerce.

Modern Context

Great circle routes now optimize for jet streams (air) or great circle + currents (sea). But the planetary wind engine remains: Hadley cell (trades), Ferrel cell (westerlies), Polar cell (easterlies).