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