Local winds

050-02-04Pablo Asensio Martínez2026-04-012 min

Local winds are small-scale air circulations caused by topography or local thermal differences.

Sea and Land Breezes

Caused by differential heating/cooling between land and sea.

Sea and Land Breezes

Sea Breeze

  • When: During the day (especially sunny days).
  • Mechanism: Land heats up faster than the sea $\rightarrow$ Air over land rises (Low Pressure) $\rightarrow$ Cool air from the sea flows towards the land.
  • Direction: From Sea to Land.
  • Intensity: Stronger than the land breeze.

Land Breeze

  • When: During the night.
  • Mechanism: Land cools down faster than the sea $\rightarrow$ High Pressure over land $\rightarrow$ Air flows towards the sea (which is relatively warmer).
  • Direction: From Land to Sea.
  • Intensity: Weaker (~5 kt), as the temperature difference is smaller than during the day.

Slope and Valley Winds

Anabatic and Katabatic Winds

Anabatic Wind

  • When: During the day.
  • Direction: Up the slope.
  • Cause: The sun heats the slope $\rightarrow$ Air in contact warms up and rises.
  • Characteristics: Light wind (~5 kt).

Katabatic Wind

  • When: During the night.
  • Direction: Down the slope.
  • Cause: The slope cools by radiation $\rightarrow$ Air in contact cools, becomes dense, and "falls" towards the valley.
  • Characteristics:
    • Stronger than the anabatic wind (~10 kt or more).
    • Cold air accumulates at the bottom of the valley, favoring the formation of radiation fog or frost.
    • More pronounced with clear skies (greater cooling) and snow-covered slopes.

Venturi Effect in Valleys

When wind is forced through a narrow valley:

  • Speed increases.
  • Pressure decreases (Bernoulli's Principle).
  • Hazard: The altimeter will overread (indicate higher than actual), so the true altitude will be lower.

Low Level Jet Streams

These are fast air currents in the lower atmosphere, typically nocturnal.

  • Formation: Occur just above a nocturnal inversion.
  • Necessary conditions:
    • Clear skies (to allow radiative cooling and form the inversion).
    • Moderate geostrophic wind (if too strong it breaks the inversion, if too weak it doesn't form the jet).
  • Location: Common in great plains (e.g., central USA, southern Germany).
  • Hazard: Can generate significant wind shear near the ground.
Written and reviewed by

Pablo Asensio · 2026-04-01

Aeronautical engineer. Passed the thirteen EASA ATPL(A) theoretical knowledge exams studying from these very notes. Writes and reviews each topic against the Part-FCL Learning Objectives.

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