Whether the Weather E-Book

• Herausgeber: Books on Demand
• Kategorie: Lebensstil
• Sprache: Englisch

Seitenzahl: 157

Veröffentlichungsjahr: 2017

Beschreibung

"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.

Leseprobe

The Author:

Roger Peter Frey was born in Berne, Switzerland. Some years ago he made his hobby his profession and obtained his paragliding instructor licences for Switzerland (SHV) and later also for Germany (DHV) and Austria (ÖAeC). On the Canary island of La Palma, he developed, together with his business partner Spanish paragliding instructor Javier López Redondo, a “GuideService” for licenced paragliding pilots in their Paragliding School Palmaclub which specializes in further education for pilots. Roger lives and works on La Palma and in Switzerland.

Whether the weather be fine

Or whether the weather be not

Whether the weather be cold

Or whether the weather be hot

We’ll weather the weather

Whatever the weather

Whether we like it or not.

anonymous british poem

Content

Preface

The Atmosphere

2.1 The Layers of the Atmosphere

2.1.1 The Tropopause

2.1.2 The Troposphere

2.1.3 The Planetary Boundary Layer

2.1.4 Peplopause

2.2 Radiation on Earth

2.3 Characteristics of the Air

2.4 Air Pressure and Air Density

2.5 Vertical Decrease of Pressure

2.6 Values of Air Pressure / QNH / QFE / QFF / Standard / QNE

2.6.1 QFE (Query Field Elevation)

2.6.2 QNH (Query Normal Height)

2.6.3 QFF

2.6.4 Standard Pressure

2.6.5 QNE (Query Normal Elevation)

2.7 Anticyclone and Cyclone on Ground

2.7.1 Warm Anticyclone

2.7.2 Cold Cyclone

2.7.3 Warm Cyclone

2.7.4 Cold Anticyclone

2.8 Displacement of a Pressure Area in Altitude

2.9 The International Standard Atmosphere (ISA)

2.10 Changes in the Atmosphere

Wind

3.1 Gradient Force

3.2 Centrifugal Force

3.3 Coriolis Force

3.4 Geostrophic Wind

3.5 Cyclostrophic Wind

3.6 Gradient Wind

3.7 Friction

3.8 Vertical Wind Circulation

3.9 Wind Measurement

3.10 Global Wind Circulation

3.10.1 The Hadley Cells

3.10.2 The Ferrel Cells

3.10.3 The Polar Cells

3.11 Land and Sea Breeze

3.12 Mountain and Valley Breeze

3.13 Lee

3.14 Lee Waves

3.15 Foehn

3.16 Convergence and Divergence

3.17 Turbulence

3.17.1 Wind Shear

3.17.2 Friction Turbulence

3.17.3 Thermal Turbulence

3.17.4 Turbulence at Inversions

3.17.5 Orographic Turbulence

3.18 Downburst

3.19 Kármán Waves

3.20 Jet Stream

3.20.1 Polar-Front Jet Stream

3.20.2 Subtropical Jet Stream

3.20.3 Low Level Jet Stream

3.21 Some Wind Systems

3.21.1 Bise

3.21.2 Bora

3.21.3 Chinook

3.21.4 Etesien

3.21.5 Levante

3.21.6 Mistral

3.21.7 Northe(r)

3.21.8 Nor’easter

3.21.9 Pampero

3.21.10 Poniente

3.21.11 Santa Ana

3.21.12 Scirocco

3.21.13 Tramontana

Thermodynamics

4.1 States of Matter

4.2 Humidity

4.2.1 Maximum Humidity

4.2.2 Relative Humidity

4.2.3 Absolute Humidity

4.2.4 Mixing Ratio

4.2.5 Specific Humidity

4.3 Dew Point (Td)

4.4 Dew Point Spread

4.5 Air Temperature

4.6 The Inversion

4.6.1 Subsidence Inversion

4.6.2 Ground Inversion

4.6.3 Inversion at Friction Layers

4.6.4 Front Inversion

4.7 Seasonal Fluctuation of Air Temperature

4.8 Influence of Continents and Oceans on the Temperature

4.9 Seasons

4.10 Heat Transfer

4.10.1 Conduction

4.10.2 Convection

4.10.3 Advection

4.11 Influence of Clouds on the Temperature

4.12 Dry Adiabat

4.13 Moist Adiabat

4.14 Thermal Lift

4.15 Radio Sounding

4.16 Thermodynamic Diagram

4.17 Thermodynamic Foehn Model

Clouds and Precipitation

5.1 Cirrus

5.2 Alto-Clouds

5.3 Stratus

5.4 Cumulus

5.5 Altocumulus Lenticularis

5.6 Cloud Cover

5.7 Fog, Mist and Haze

5.7.1 Advection Fog

5.7.2 Radiation Fog

5.7.3 Up-Slope Fog

5.7.4 Precipitation Fog

5.8 Precipitation

5.8.1 Bergeron-Findeisen Process

5.8.2 Langmuir Process

5.8.3 Rain Records

Thunderstorms

6.1 Classification of Thunderstorms

6.1.1 Front Thunderstorm

6.1.2 Heat Thunderstorm

6.1.3 Orographic Thunderstorm

6.2 Life Cycle of a Thunderstorm

6.2.1 Growth Stage

6.2.2 Maturation Stage

6.2.3 Dissipation Stage

6.3 Single-Cell Thunderstorm

6.4 Multicellular Thunderstorm

6.5 Supercell Thunderstorm

6.6 Electrical Appearances

6.6.1 Lightning

6.6.2 Ball Lightning

6.6.3 Spherics

6.7 Thunderstorm Indices

6.7.1 Total-Totals-Index

6.7.2 CAPE

6.7.3 DCAPE (Downdraft Convective Available Potential Energy)

6.7.4 K-Index (George Index)

6.7.5 KO-Index

6.7.6 LI-Index

6.7.7 Soaring Index

Weather Fronts

7.1 Genesis of Cyclones

7.2 Warm Front

7.3 Cold Front

7.4 Occluded Front

Climatology

8.1 General Meteorological Conditions

8.1.1 High Pressure Conditions

8.1.2 Flat Pressure Conditions

8.1.3 West Wind Conditions

8.1.4 Bise Conditions

8.1.5 Cyclone Conditions

8.1.6 Foehn Conditions

8.1.7 Congested Conditions (North Foehn)

8.2 Cold Core Low

8.3 Tropical Cyclones

Weather Maps

9.1 Ground Maps

9.2 Altitude Maps

9.2.1 500 hPa Altitude Map

9.2.2 700 hPa Altitude Map

9.2.3 850 hPa Altitude Map

9.3 Cloud Map with relative topography (ReTop)

9.4 Ensemble Maps

9.5 Forecast Chart

9.6 Equivalent Potential Temperature (Theta-E)

9.7 Thickness

Weather Forecasts

10.1 Reliability

10.2 Cross-Country Flying Weather

10.3 soarWRF, soarGFS

Hazards

11.1 Cold Front

11.2 Cold Occlusion

11.3 Thunderstorms

11.4 Increase of Wind Strength

11.5 Flying in Rain

11.6 Lee

11.7 Cloud Flying

11.8 Altitude Sickness

Air Weather Service

12.1 METAR and TAF

12.2 Volmet Transmitter

12.3 WX AWOS

12.4 WX ASOS

12.5 GAFOR

Internet Meteo

Abbreviations

Glossary

Units / Conversions

16.1 Altitude

16.2 Distance

16.3 Temperature

16.4 Pressure

16.5 Velocity

Prefixes in the Metric System

Formulae

18.1 Potential Temperature

18.2 Equivalent Temperature (Te)

18.3 Equivalent Potential Temperature (Theta-E)

18.4 Air Density

18.5 Hennig Formula

Bibliography

Index

Acknowledgement

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 barrier between the planetary boundary layer and the free atmosphere. Peplopauses are frequent occurrences: in winter they form on about 55% of the days, in summer on about 35% of the days. Below the peplopause independent weather often develops, mainly because there is no exchange of air with the higher layers: the inversion slows down or stops thermals; if the inversion continues sinking, the wind accelerates.

2.2Radiation on Earth

Thirty percent of short-wave solar radiation is reflected by the atmosphere and the ground, the remaining 70% is absorbed: 20% by the atmosphere and 50% by the ground. This energy is then released to the atmosphere in the form of heat, and is eventually responsible for weather development. Fig. 2.3 is not to scale, but illustrates the process of radiation.

Fig. 2.3:Radiation on Earth

2.3Characteristics of the Air

As already pointed out, air is a mixture of gases. Air is compressible and is able to absorb water, depending on its pressure and temperature. On average this is only 0.4 %, but this apparently tiny amount is essential for weather development. The molecular mass of water2 is only 62.5% of the weight of air, thus surprisingly the more water air contains the lighter it is. In addition, air also contains small particles of dust which play an important role in the condensation of water vapour. The total mass of the atmosphere on the planet is 5.148 x 1015 tons, or 5.148 peta tons.3

2.4Air Pressure and Air Density

Due to gravity, air exerts pressure on the surface of the earth. We can imagine this as a column of air, in which the weight of the gas molecules adds up. The resulting pressure depends on the height of the column of air, as well as on its temperature and density. Contrary to water, air is compressible, which is why air density is highest at ground level. Conversely, its density decreases in an nonlinear way as height increases. Torricelli4 was the first to describe this: he put one end of a tube filled with mercury (Hg) (and sealed at the other end) into a mercury-filled sump. The air pressure was such that the column of mercury was kept at a height of 760mm. This is where the old unit Torr comes from. One Torr is therefore the pressure which corresponds to a column of 1mm mercury.

Air pressure should not be confused with air density: air density designates the weight of air in relation to its volume. The following values are valid for standard atmosphere in totally dry air (zero water vapour):

Fig. 2.4:Air Pressure

Air Pressure: 1,013.25 hPa

Air Density: 1.225 kg/m3 at 15 °C (59 °F)

Because water vapour has a lower density than air, the density of humid air is lower than that of dry air.

2.5Vertical Decrease of Pressure

Air pressure halves every 5,500m (18,000 ft); thus air pressure, which is approx. 1,000 hPa at sea level is 500 hPa at 5,500m AMSL.5 This is a reduction of 16m (52.5 ft) per hPa at 5,000m (16,000 ft) and 32m (105 ft) per hPa at 10,000m (33,000 ft) AMSL.

As a rule of thumb in aviation, a mean decrease of 1hPa each 30 ft is used for rough calculations. If pressure and temperature are known, it should be possible to calculate air density using the following formula:

2.6Values of Air Pressure / QNH / QFE / QFF / Standard / QNE

One of the most important parameters in aviation is the cruise altitude. Where altitude in aviation can have different meanings, it is qualified by adding a modifier (e.g. “indicated altitude”). Weather stations deliver this information at different altitudes. The correct pressure therefore needs to be calculated with a standard height.

Fig. 2.5:Air Pressure Values

The basis for these calculations is mean sea level (MSL), but air pressure also depends on temperature; with increased temperature, air molecules move faster and therefore need more space. As a result, the pressure of an air column on the ground decreases with increased temperature. This is why there is also a standard temperature needed. This is defined as 15 °C (59°F). To compare different air pressure values, they are therefore recalculated in a uniform height. For observation stations below 700m AMSL (2,300 ft), values are reduced to MSL. This process is therefore also named Air Pressure Reduction. If the observation station is situated higher than 700m AMSL, the next standard pressure level is used (p. 124). If the air pressure difference is used in the Alps for foehn prediction (North-South), only stations below 700m AMSL might be used to compare. If you compare two stations at similar heights, the error is minimal.

2.6.1QFE (Query Field Elevation)

The QFE is the measured pressure at the respective station. If you set the QFE on your altimeter, you will get the height above the airfield; on the airfield therefore the altimeter shows 0m. The QFE is used sometimes by acrobatics pilots in order to get exact altitude above the airfield.

2.6.2QNH (Query Normal Height)

The QNH is the pressure reduced to mean sea level while the standard atmosphere applies. The air column below the station is added as standard atmosphere. In many countries, QNH is used as a reference below 5,000 ft AMSL or 2,000 ft GND. QNH is therefore used for take-off and landing, to get a relatively accurate height above ground. The QNH is reported by all airports in their meteorological aerodrome reports (METAR) followed the code Q.

2.6.3QFF

The QFF is the reduced air pressure calculated with the actual temperature rather than a standard value. The QFF is used to paint the lines of equal barometric pressure in the ground weather charts (Chap. 9.1).

2.6.4Standard Pressure

Standard pressure (also named pressure altitude) is 1,013.25hPa at sea level. Flight Levels (FL) always refer to 1,013.25 hPa and are reported in hecto feet. Thus FL 100 is 10,000 ft above standard pressure. Above a defined transition altitude, in US 18,000 ft, all pilots set their altimeters from QNH to 1,013.25 hPa. By doing so, aeroplanes fly at a pressure level rather than at an absolute height. This does not ensure the right height above the ground, but more importantly, correct security distances from one plane to another.

2.6.5QNE (Query Normal Elevation)

QNE reports the elevation of an air field above standard pressure on 1,013.25 hPa. The unit of scale is mostly feet. One foot equals 30.48 cm, 1,000 ft therefore 305 m.

2.7Anticyclone and Cyclone on Ground