Sep 2012

Lesson 4.4

Meteorology

Winds

Reference

From the Ground UpChapter 6.4:WindsPages 130 - 136

Introduction• Wind is the horizontal movement of air in

different areas and altitudes.

• It is important that pilots know where winds are, how strong and from what direction they flow, and how they change.

Outline• Wind Types• Wind Speed and Direction• Wind Effects

Winds• Wind is horizontal movement of air

• Heating of Earth creates pressure differences, air flows from high to low, therefore wind

• Upper Level Winds flow parallel to isobars and from high to low pressure areas

• Surface Winds are below 3000 ft, and are slowed by surface friction

Land & Sea Breezes• Sea Breeze

– Land heats faster than water during day (lower pressure)– Wind blows from water towards land

Land & Sea Breezes• Land Breeze

– Land cools faster than water at night (higher pressure)– Wind blows from land towards water

Mountain Winds• Katabatic Wind (AKA Mountain Breeze)

– At night, slope cools, air becomes denser, wind flows down from mountain

Mountain Winds• Anabatic Wind (AKA Valley Breeze)

– During day, slope heats, air becomes less dense, flows up from valley

Mountain Winds• Mountain Wave

– Air deflected after flowing over mountain oscillates (or bounces) up and down violently in a wave pattern.

Gusts and Squalls• Gust

– Sudden and brief increase in wind speed and direction (several seconds)

– Usually caused by mechanical turbulence

• Squall– Sudden increase in wind speed and direction, but

last longer then a gust (several minutes)– Usually caused by fast moving cold front or

thunderstorm

Wind Speed & Direction• Veering is increase in wind direction

• Backing is decrease in wind direction

• Wind veers and increases with altitude (due to lack of surface friction)

• Diurnal Variation– Wind backs and decreases at night– Wind veers and increases during day (more ground heating)

Wind Effects• Eddies

– Swirling air or vortices– Produced by friction between moving air and ground

Wind Effects• Dust Devils

– Super-heated concentrated lows on hot, clear, stable, days– Made visible by dust or sand

Wind Effects• Tornadoes

– Very concentrated, violent lows formed in unstable weather

Wind Effects• Jet Stream

– Narrow bands of high-altitude and high-speed winds– Normally 2 or 3 over North America

Next Lesson

4.5 – MeteorologyHumidity, Temperature & Stability

From the Ground UpChapter 6.5:Humidity, Temperature and StabilityPages 136 - 140