viii
Chapter 15. Adverse Wind15-1
15.1 Introduction15-1
15.2 Crosswind15-1
15.3 Gust15-1
15.4 Tailwind15-2
15.5 Variable Wind/Sudden Wind Shift15-2
15.6 Wind Shear15-2
Chapter 16. Weather, Obstructions to Visibility, Low Ceiling, and Mountain Obscuration16-1
16.1 Weather and Obstructions to Visibility16-1
16.1.1 Fog16-1
16.1.2 Mist16-5
16.1.3 Haze16-5
16.1.4 Smoke16-5
16.1.5 Precipitation16-5
16.1.6 Blowing Snow16-6
16.1.7 Dust Storm16-6
16.1.8 Sandstorm16-6
16.1.9 Volcanic Ash16-7
16.2 Low Ceiling and Mountain Obscuration16-8
16.2.1 Low Ceiling16-8
16.2.2 Mountain Obscuration16-9
Chapter 17. Turbulence17-1
17.1 Introduction17-1
17.2 Causes of Turbulence17-1
17.2.1 Convective Turbulence17-1
17.2.2 Mechanical Turbulence17-3
17.2.3 Wind Shear Turbulence17-5
17.3 Turbulence Factors17-6
Chapter 18. Icing18-1
18.1 Introduction18-1
18.2 Supercooled Water18-1
ix
18.3 Structural Icing18-1
18.3.1 Rime Icing18-1
18.3.2 Clear Icing18-1
18.3.3 Mixed Icing18-2
18.3.4 Icing Factors18-2
18.3.5 Icing in Stratiform Clouds18-4
18.3.6 Icing in Cumuliform Clouds18-4
18.3.7 Icing with Fronts18-4
18.3.8 Icing with Mountains18-5
18.3.9 Icing Hazards18-6
18.4 Engine Icing18-7
18.4.1 Carburetor Icing18-7
18.4.2 High Ice Water Content (HIWC)18-7
Chapter 19. Thunderstorms19-1
19.1 Introduction19-1
19.2 Necessary Ingredients for Thunderstorm Cell Formation19-1
19.3 Thunderstorm Cell Life Cycle19-1
19.4 Thunderstorm Types19-2
19.5 Factors that Influence Thunderstorm Motion19-5
19.6 Hazards19-6
19.6.1 Lightning19-6
19.6.2 Adverse Wind19-6
19.6.3 Downburst19-6
19.6.4 Turbulence19-8
19.6.5 Icing19-8
19.6.6 Hail19-9
19.6.7 Rapid Altimeter Changes19-10
19.6.8 Static Electricity19-10
19.6.9 Tornado19-10
x
Chapter 20. Weather Radar20-1
20.1 Principles of Weather Radar20-1
20.1.1 Antenna20-1
20.1.2 Backscattered Energy20-1
20.1.3 Power Output20-2
20.1.4 Wavelengths20-2
20.1.5 Attenuation20-3
20.1.6 Resolution20-4
20.1.7 Wave Propagation20-7
20.1.8 Intensity of Precipitation20-9
Chapter 21. Tropical Weather21-1
21.1 Circulation21-1
21.1.1 Subtropical High Pressure Belts21-1
21.1.2 Trade Wind Belts21-3
21.1.3 The Intertropical Convergence Zone (ITCZ)21-5
21.1.4 Monsoon21-5
21.2 Transitory Systems21-7
21.2.1 Remnants of Polar Fronts and Shear Lines21-7
21.2.2 Tropical Upper Tropospheric Trough (TUTT)21-8
21.2.3 Tropical Wave21-9
21.2.4 West African Disturbance Line (WADL)21-10
21.2.5 Tropical Cyclones21-11
Chapter 22. Arctic Weather22-1
22.1 Introduction22-1
22.2 Climate, Air Masses, and Fronts22-1
22.2.1 Long Days and Nights22-2
22.2.2 Land and Water22-2
22.2.3 Temperature22-2
22.2.4 Clouds and Precipitation22-2
22.2.5 Wind22-3
22.2.6 Air Masses—Winter22-3
xi
22.2.7 Air Masses—Summer22-3
22.2.8 Fronts22-3
22.3 Arctic Peculiarities22-3
22.3.1 Effects of Temperature Inversion22-3
22.3.2 Light Reflection by Snow-Covered Surfaces22-3
22.3.3 Light from Celestial Bodies22-3
22.4 Weather Hazards22-4
22.4.1 Fog and Ice Fog22-4
22.4.2 Blowing and Drifting Snow22-4
22.4.3 Frost22-4
22.4.4 Whiteout22-4
Chapter 23. Space Weather23-1
23.1 The Sun—Prime Source of Space Weather23-1
23.2 The Sun’s Energy Output and Variability23-1
23.3 Sunspots and the Solar Cycle23-1
23.4 Solar Wind23-1
23.5 Solar Eruptive Activity23-2
23.6 Geospace23-2
23.7 Galactic Cosmic Radiation23-3
23.8 Geomagnetic Storms23-4
23.9 Solar Radiation Storms23-4
23.10 Ionospheric Storms23-5
23.11 Solar Flare Radio Blackouts23-5
23.12 Effects of Space Weather on Aircraft Operations23-6
23.12.1 Communications23-6
23.12.2 Navigation and Global Positioning System (GPS)23-6
23.12.3 Radiation Exposure to Flight Crews and Passengers23-6
23.12.4 Radiation Effects on Avionics23-6
xii List of Figures
Figure 1-1. Vertical Structure of the Atmosphere1-4
Figure 1-2. U.S. Standard Atmosphere within the Troposphere1-6
Figure 2-1. Comparison of Kelvin, Celsius, and Fahrenheit Temperature Scales2-3
Figure 2-2. Radiation Example2-4
Figure 2-3. Temperature’s Effect on Radiation Wavelength2-5
Figure 2-4. Solar Zenith Angle2-6
Figure 2-5. Heat Transfer Examples2-8
Figure 2-6. Specific Heat Capacity: Water Versus Sand2-10
Figure 2-7. Variation of Mean Daily Temperatures for San Francisco (Maritime)
and Kansas City (Continental)2-11
Figure 2-8. Sounding with an Isothermal Layer2-12
Figure 2-9. Sounding with a Temperature Inversion2-13
Figure 3-1. The Hydrologic Cycle3-1
Figure 3-2. Temperature Effects on Relative Humidity3-4
Figure 3-3. Temperature-Dewpoint Spread Effect on Relative Humidity3-5
Figure 3-4. Latent Heat Transactions when Water Undergoes Phase Transition3-6
Figure 4-1. Earth-Atmosphere Energy Balance4-1
Figure 4-2. Greenhouse Effect on Nighttime Radiational Cooling4-2
Figure 4-3. Development of a Thermal4-3
Figure 4-4. Example of Convection in the Atmosphere4-4
Figure 4-5. Solar Zenith Angle Variations with Latitude4-5
Figure 4-6. Solar Zenith Angle Variations with Northern Hemisphere Seasons4-6
Figure 4-7. Average Seasonal Temperature Variation in the Northern Hemisphere4-6
Figure 4-8. Clear Sky Diurnal Temperature and Radiation Variations Over Land4-7
Figure 5-1. Air Has Weight5-1
Figure 5-2. Aneroid Barometer5-2
Figure 5-3. Station Pressure5-3
Figure 5-4. Air Pressure in the Standard Atmosphere5-4
Figure 5-5. Temperature Effect on Pressure5-5
Figure 5-6. Reduction of Station Pressure to Sea Level5-5
Figure 5-7. Surface Chart Pressure Patterns5-7
Figure 5-8. Weather Balloon and Radiosonde5-8
xiii
Figure 5-9. 500 Millibar Constant Pressure Chart5-9
Figure 5-10. Density is Mass (Weight) per Volume5-10
Figure 5-11. Volume Effects on Density5-10
Figure 5-12. Pressure Effects on Density in the Atmosphere5-11
Figure 5-13. Temperature Effects on Density5-12
Figure 5-14. Water Vapor Effects on Density5-12
Figure 5-15. True Versus Indicated Altitude5-13
Figure 5-16. Pressure Change Effects on Altimeter Readings5-14
Figure 5-17. Temperature Change Effects on Altimeter Readings5-15
Figure 5-18. High Density Altitude Effects on Flight5-17
Figure 6-1. Weather Observation Sources6-1
Figure 6-2. Analysis Procedure Step 1: Determine the Optimal Contour Interval
and Values to be Analyzed6-3
Figure 6-3. Analysis Procedure Step 2: Draw the Isopleths and Extrema6-4
Figure 6-4. Analysis Procedure Step 3: Interpret Significant Weather Features6-6
Figure 6-5. Example of a Surface Chart6-7
Figure 6-6. Example of a 500 Millibar Constant Pressure Chart6-8
Figure 7-1. Direction of Pressure Gradient Force7-1
Figure 7-2. Magnitude of Pressure Gradient Force7-2
Figure 7-3. Illustration of Coriolis Force7-2
Figure 7-4. Coriolis Force Variations Across the Earth7-3
Figure 7-5. Coriolis Force Magnitude Variations with Wind Speed7-4
Figure 7-6. Friction Force Magnitude Variations with Terrain Roughness7-4
Figure 7-7. Friction Force Magnitude Variations with Wind Speed7-4
Figure 7-8. Geostrophic Wind7-5
Figure 7-9. Upper Air Wind Flow7-5
Figure 7-10. Surface Wind Forces7-6
Figure 7-11. Surface Wind Flow7-6
Figure 8-1. Non-Rotating, Non-Tilted, Waterless, Earth Circulation System8-1
Figure 8-2. Earth Circulation System8-2
Figure 8-3. Speed Relative to the Earth’s Axis Versus Latitude8-3
Figure 8-4. Three Cell Circulations and Jet Stream Location8-4
Figure 8-5. Polar and Subtropical Jet Streams8-4
xiv
Figure 8-6. Jet Stream Wind Speeds8-5
Figure 9-1. Local Wind Circulation9-1
Figure 9-2. Sea Breeze9-2
Figure 9-3. Sea Breeze Front9-3
Figure 9-4. Effects of Coastline Shape on a Sea Breeze9-4
Figure 9-5. Land Breeze9-5
Figure 9-6. Lake Breeze9-6
Figure 9-7. Sea Breeze/Lake Breeze Example9-7
Figure 9-8. Valley Breeze9-7
Figure 9-9. Mountain-Plains Wind System9-8
Figure 9-10. Mountain Breeze9-9
Figure 10-1. Air Mass Classification10-2
Figure 10-2. Air Mass Modification—Warm, Moist Air Mass Moving Over
a Cold Surface10-2
Figure 10-3. Lake Effect10-3
Figure 10-4. Fronts10-4
Figure 10-5. Cold Front10-5
Figure 10-6. Warm Front10-5
Figure 10-7. Stationary Front10-6
Figure 10-8. Occluded Front10-6
Figure 10-9. Wave Cyclone Model—Stage 110-7
Figure 10-10. Wave Cyclone Model—Stage 210-7
Figure 10-11. Wave Cyclone Model—Stage 310-8
Figure 10-12. Wave Cyclone Model—Stage 410-8
Figure 10-13. Wave Cyclone Model—Stage 510-8
Figure 10-14. Dryline Example10-9
Figure 11-1. Unsaturated Ascending/Descending Air Parcel Example11-2
Figure 11-2. Ascending Air Parcel that Becomes Saturated Example11-3
Figure 11-3. Descending Air Parcel Example11-4
Figure 11-4. Orographic Effects Example11-5
Figure 11-5. Frictional Effects11-6
Figure 11-6. Frontal Lift11-7
Figure 12-1. Absolute Stability Example12-2
xv
Figure 12-2. Neutral Stability Example12-3
Figure 12-3. Absolute Instability Example12-4
Figure 12-4. Conditional Instability Example12-5
Figure 12-5. Stability Types12-6
Figure 12-6. Temperature Lapse Rate Effects on Stability12-7
Figure 12-7. Vertical Motion Effects on Stability12-8
Figure 12-8. Diurnal Temperature Variation Effects on Stability12-9
Figure 12-9. Lifted Index Example12-10
Figure 13-1. Cirrus (Ci)13-3
Figure 13-2. Cirrocumulus (Cc)13-4
Figure 13-3. Cirrostratus (Cs)13-5
Figure 13-4. Altocumulus (Ac)13-6
Figure 13-5. Altocumulus Standing Lenticular (ACSL)13-7
Figure 13-6. Thin Altostratus (As)13-8
Figure 13-7. Thick Altostratus (As) or Nimbostratus (Ns)13-9
Figure 13-8. Cumulus (Cu) with Little Vertical Development13-10
Figure 13-9. Towering Cumulus (TCu)13-11
Figure 13-10. Stratocumulus (Sc)13-12
Figure 13-11. Stratus (St)13-13
Figure 13-12. Stratus Fractus (StFra) and/or Cumulus Fractus (CuFra) of Bad Weather13-14
Figure 13-13. Cumulonimbus (Cb) without Anvil13-15
Figure 13-14. Cumulonimbus (Cb) with Anvil13-16
Figure 14-1. The Collision-Coalescence or Warm Rain Process14-2
Figure 14-2. Snow Temperature Environment14-3
Figure 14-3. Ice Pellets Temperature Environment14-3
Figure 14-4. Freezing Rain Temperature Environment14-4
Figure 14-5. Rain Temperature Environment14-4
Figure 15-1. Crosswind15-1
Figure 16-1. Radiation Fog16-1
Figure 16-2. Advection Fog16-2
Figure 16-3. Advection Fog Formation16-3
Figure 16-4. Frontal Fog Formation16-4
Figure 16-5. Haboob16-7
xvi
Figure 16-6. Layer Aloft Ceiling Versus Indefinite Ceiling16-9
Figure 17-1. Convective Turbulence17-2
Figure 17-2. Thermals17-2
Figure 17-3. Mechanical Turbulence17-3
Figure 17-4. Mountain Waves17-4
Figure 17-5. Mountain Wave Clouds17-5
Figure 17-6. Wind Shear Turbulence17-5
Figure 17-7. Wind Shear Turbulence Associated with a Temperature Inversion17-6
Figure 18-1. Icing with Fronts18-5
Figure 18-2. Icing with Mountains18-6
Figure 19-1. Necessary Ingredients for Thunderstorm Cell Formation19-1
Figure 19-2. Thunderstorm Cell Life Cycle19-2
Figure 19-3. Multicell Cluster Thunderstorm19-3
Figure 19-4. Multicell Line Thunderstorm19-4
Figure 19-5. Supercell Thunderstorm19-5
Figure 19-6. Factors that Influence Thunderstorm Motion19-5
Figure 19-7. Downburst Life Cycle19-7
Figure 19-8. Landing in a Microburst19-7
Figure 19-9. Thunderstorm with Shelf Cloud19-8
Figure 19-10. Vivian, South Dakota Record Hailstone19-9
Figure 20-1. Radar Antenna20-1
Figure 20-2. Backscattered Energy20-2
Figure 20-3. Wavelengths20-3
Figure 20-4. Precipitation Attenuation20-3
Figure 20-5. Precipitation Attenuation Versus Wavelength20-4
Figure 20-6. Beam Resolution20-5
Figure 20-7. Beam Resolution Comparison Between WSR-88D and
Aircraft Weather Radar20-6
Figure 20-8. Normal Refraction20-7
Figure 20-9. Subrefraction20-8
Figure 20-10. Superrefraction20-8
Figure 20-11. Ducting20-9
Figure 20-12. Reflectivity Associated with Liquid Targets20-10
xvii Figure 21-1. Mean Worldwide Surface Pressure Distribution and Prevailing Winds
Throughout the World in July21-2
Figure 21-2. Mean Worldwide Surface Pressure Distribution and Prevailing Winds
Throughout the World in January21-2
Figure 21-3. A Shear Line and an Induced Trough Caused by a Polar High
Pushing into the Subtropics21-8
Figure 21-4. A TUTT Moves Eastward Across the Hawaiian Islands. Extensive
Cloudiness Develops East of the Trough21-9
Figure 21-5. A Northern Hemisphere Easterly Wave Progressing from A–B21-10
Figure 21-6. Vertical Cross Section along Line A–B in Figure 21-521-10
Figure 21-7. The Tracks of Nearly 150 Years of Tropical Cyclones and their
Strength Weave Across the Globe21-12
Figure 21-8. Radar Image of Hurricane Katrina Observed at New Orleans, Louisiana,
on August 29, 200521-14
Figure 21-9. Hurricane Andrew Observed by Satellite in 199221-14
Figure 22-1. The Arctic Circle22-1
List of Tables
Table 1-1. Composition of a Dry Earth’s Atmosphere1-1
Table 1-2. Selected Properties of the Standard Atmosphere1-6
Table 2-1. Celsius Temperature Conversion Formulae2-2
Table 2-2. Fahrenheit Temperature Conversion Formulae2-2
Table 2-3. Heat (Thermal) Conductivity of Various Substances2-7
Table 2-4. Specific Heat Capacity of Various Substances2-9
Table 3-1. Latent Heat of Water at 0 °C3-7
Table 5-1. Units of Pressure5-3
Table 5-2. Pressure System Symbols5-6
Table 5-3. Common Constant Pressure Charts5-9
Table 6-1. Common Isopleths6-2
Table 6-2. Common Weather Chart Symbols6-5
Table 11-1. Air Parcel Vertical Motion Characteristics11-4
Table 13-1. Cloud Forms13-1
Table 13-2. Approximate Height of Cloud Bases above the Surface13-2
Table 19-1. Enhanced Fujita Scale (Enhanced F Scale) for Tornado Damage19-11
Table 21-1. Wind Speed and Characteristic House Damage for the
Saffir-Simpson Hurricane Wind Scale21-15
1-1 CHAPTER 1. THE EARTH’S ATMOSPHERE
1.1 Introduction. The Earth’s atmosphere is a cloud of gas and suspended solids extending from the surface out many thousands of miles, becoming increasingly thinner with distance, but always held by the Earth’s gravitational pull. The atmosphere is made up of layers surrounding the Earth that holds the air we breathe, protects us from outer space, and holds moisture (e.g., vapor, clouds, and precipitation), gases, and tiny particles. In short, the atmosphere is the protective bubble we live in.
This chapter covers our atmosphere’s composition, vertical structure and the standard atmosphere.
1.2 Composition. The Earth’s atmosphere consists of numerous gases (see Table 1-1) with the top four making up 99.998 percent of all gases. Nitrogen, by far the most common, dilutes oxygen and prevents rapid burning at the Earth’s surface. Living things need it to make proteins. Oxygen is used by all living things and is essential for respiration.
Plants use carbon dioxide to make oxygen. Carbon dioxide also acts as a blanket and prevents the escape of heat to outer space.
Table 1-1. Composition of a Dry Earth’s Atmosphere Gas Symbol Content (by Volume) Nitrogen N2 78.084% Oxygen O2 20.947% Argon Ar 0.934% Carbon Dioxide CO2 0.033% Neon Ne 18.20 parts per million Helium He 5.20 parts per million Methane CH4 1.75 parts per million Krypton Kr 1.10 parts per million Sulfur dioxide SO2 1.00 parts per million Hydrogen H2 0.50 parts per million Nitrous Oxide N2O 0.50 parts per million Xenon Xe 0.09 parts per million
1-2 Gas Symbol Content (by Volume) Ozone O3 0.07 parts per million Nitrogen dioxide NO2 0.02 parts per million Iodine I2 0.01 parts per million Carbon monoxide CO trace Ammonia NH3 trace Note: The atmosphere always contains some water vapor in amounts varying from trace to about four percent by volume. As water vapor content increases, the other gases decrease proportionately.
Weather, the state of the atmosphere at any given time and place, strongly influences our daily routine as well as our general life patterns. Virtually all of our activities are affected by weather, but, of all our endeavors, perhaps none more so than aviation.
1.2.1 Air Parcel. An air parcel is an imaginary volume of air to which any or all of the basic properties of atmospheric air may be assigned. A parcel is large enough to contain a very large number of molecules, but small enough so that the properties assigned to it are approximately uniform. It is not given precise numerical definition, but a cubic centimeter of air might fit well into most contexts where air parcels are discussed.
In meteorology, an air parcel is used as a tool to describe certain atmospheric processes, and we will refer to air parcels throughout this document.
1.3 Vertical Structure. The Earth’s atmosphere is subdivided into five concentric layers (see Figure 1-1) based on the vertical profile of average air temperature changes, chemical composition, movement, and density. Each of the five layers is topped by a pause, where the maximum changes in thermal characteristics, chemical composition, movement, and density occur.
1.3.1 Troposphere. The troposphere begins at the Earth’s surface and extends up to about 11 kilometers (36,000 feet) high. This is where we live. As the gases in this layer decrease with height, the air becomes thinner. Therefore, the temperature in the troposphere also decreases with height. As you climb higher, the temperature drops from about 15 °C (59 °F) to -56.5 °C (-70 °F). Almost all weather occurs in this region.
The vertical depth of the troposphere varies due to temperature variations which are closely associated with latitude and season. It decreases from the Equator to the poles, and is higher during summer than in winter. At the Equator, it is around 18-20 kilometers (11-12 miles) high, at 50° N and 50° S latitude, 9 kilometers (5.6 miles), and at the poles, 6 kilometers (3.7 miles) high. The transition boundary between the troposphere and the