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Sep 2012
Lesson 4.4
Meteorology
Winds
Reference
From the Ground Up
Chapter 6.4:
Winds
Pages 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 – Meteorology
Humidity, Temperature & Stability
From the Ground Up
Chapter 6.5:
Humidity, Temperature and Stability
Pages 136 - 140