Whether the Weather

Aviation Meteorology from A to Z

Roger P. Frey

• Publisher: Books on Demand
• Year: 2017
• Print ISBN:
  9783738615746
• Edition: 3
• eBook ISBN:
  9783739277424
• Topic: Biological Sciences
• Subtopic: Science General
• Index: Biological Sciences

"Whether the Weather" is not only for air sports enthusiasts such as paragliding, hang-gliding and ultralight pilots; it is also an invaluable meteorological guide for anyone interested in weather conditions.The most important safety element is making correct decisions before take-off, because misjudging the weather situation is a common cause of accidents. The correct decision is even more important than flying skills and requires a fundamental understanding of meteorology. Many pilots recognise this and want to learn more about meteorology, without going to a scientific level. "Whether the Weather" fills this gap from A to Z. On 180 pages with innumerable graphics, it explains with outstanding clarity from the most basic to the most complex processes in aviation meteorology.

1Preface

Paragliding and hang-gliding have evolved over the last 25 years to become safe and popular sports. Today material and education have reached a high level.

The most important safety element is the right decision before starting, because misjudgement of the weather situation is a common cause of accidents; and correct decision-making is based on a good meteorological education.

Many pilots have realized the importance of this and therefore want to learn more about meteorology without going to an academic level. The book “Whether the Weather” aims to close this gap.

The world is full of local weather phenomena and it is impossible to describe them all in a book. This is why I focused in the examples on the northern hemisphere and the regions with the highest number of para- and hang-gliding pilots: Europe and particularly the Alps. I do not consider this a limiting factor because the base of all weather development is physics. If you understand it, you can easily adapt the knowledge gained to your region, whether it be Africa, the Americas, Asia, Australasia or Europe.

Enjoy gaining new knowledge and always:

safe flying and happy landings!

Roger P. Frey

Susan Overton

2The Atmosphere

2.1The Layers of the Atmosphere

The earth is surrounded by the atmosphere, which consists of different gases, mainly Nitrogen (N₂) and Oxygen (O₂) which constitute 78% and 21% respectively. There are also traces of rare gases such as Argon, Neon, Helium, Krypton and Xenon. From a meteorological point of view, the most important part is the water content, which varies between 0% and 4%.

Fig. 2.1: The Atmosphere

In addition, there are traces of carbon dioxide(CO₂), carbon monoxide (CO), sulphur dioxide (SO₂), methane (CH₄) and ozone (O₃) amongst others.

The atmosphere is divided into different layers: the weather pattern and civil aviation take place in the troposphere up to 15km altitude. From ground level up to the tropopause the temperature decreases to about -55 ºC. As a result of the absorption of UV-radiation in the ozone layer, the temperature increases in the stratosphere. At an altitude of about 50 km, the temperature is roughly the same as on the ground.

The layer of the atmosphere reaches a height of about 640km (400 miles), but the proportion of the different gases is only constant up to 100km (60 miles) (Homosphere). According to NASA’s definition space begins at a height of 80 km; according to FAI it begins at 100 km.

2.1.1The Tropopause

In between the troposphere and the stratosphere is a separate layer named the tropopause.¹ This layer, which represents the most important barrier in the atmosphere, is formed by a clear change in temperature. The tropopause is a thin but steady inversion around the globe.

The tropopause is very important for earth since it acts as a barrier to keep water vapour and therefore rain from escaping. Without this protective layer, the earth would very quickly lose its water.

2.1.2The Troposphere

The troposphere is the layer from ground level up to the tropopause. At the poles it is only approximately 8km (26,000 ft) thick, but at the equator reaches a height of about 16 km. In addition, its thickness varies seasonally: in Europe it fluctuates from 10km up to 12 km. About 90% of the planet’s air mass, as well as almost all the water vapour is found in the troposphere. Most of the weather pattern that concerns us takes place in the troposphere, also known as the weather or advection layer.

Absorption of the sun’s radiation by water vapour and dust only accounts for a small part of the heat in the troposphere: most radiation is absorbed by the ground, which in turn heats the surrounding air.

The air temperature decreases in the troposphere at an average of about 0.65 °C each 100m (3.6 °F each 1,000 ft).

2.1.3The Planetary Boundary Layer

The planetary boundary layer (PBL) also named peplosphere or convective boundary layer (CBL), forms the lower part of the atmosphere and the most important living space for humans. In this layer, the sun’s radiation has its most important effect: a thermal exchange of air, which generates usable upwinds. Not only does the terrain release heat into the air, it also has a major influence on local wind development. This wind is slowed by friction and blows closer to the ground in the same direction as the lower atmospheric pressure, not parallel to the isobars.

The planetary boundary layer is the weather layer in which paragliders and hang-gliders mainly fly. This layer often forms a hazy tier as a result of the accumulation of aerosols. The height of this layer depends on the terrain, being higher for example in the Alps than in the lowlands. In Fig. 2.2 the ceiling is shown at 1,500m (5,000 ft). At this boundary, there is an inversion 50% of the time, the so-called peplopause (Chap. 2.1.4), formed when an air mass sinks slowly (subsidence) from high altitudes. During this subsidence the air gets warmer at the dry adiabatic lapse rate and therefore increases its temperature by 1 °C every 100m (330 ft). The accumulated heat then forms this inversion. It is a stabilizing layer and is a barrier for most vertical air exchange. Below the inversion, there is an active exchange of air mass. Due to this mixing process, the temperature gradient can rise to the dry adiabatic rate of 1 °C per 100m (5.5 °F / 1,000 ft), which favours good thermal development. In addition, the humidity is also well mixed and the gradient of the dew point up to the peplopause is therefore around 0.2 °C / 100 m.

Fig. 2.2: Ground Layer of the Tropopause

2.1.4Peplopause

A peplopause is a boundary formed by subsiding air from high altitudes. Normally this subsidence does not continue down to the surface but stops around 1,000m to 2,000m above the ground, forming the inversion. A peplopause forms a ba...

Table of contents

• About the Author
• Table of Contents
• 1 Preface
• 2 The Atmosphere
• 3 Wind
• 4 Thermodynamics
• 5 Clouds and Precipitation
• 6 Thunderstorms
• 7 Weather Fronts
• 8 Climatology
• 9 Weather Maps
• 10 Weather Forecasts
• 11 Hazards
• 12 Air Weather Service
• 13 Internet Meteo
• 14 Abbreviations
• 15 Glossary
• 16 Units / Conversions
• 17 Prefixes in the Metric System
• 18 Formulae
• 19 Bibliography
• 20 Index
• 20 Acknowledgement
• Copyright