500 – 690km to 10,000km

Outer space above this level.

Thermopshere

80km to 600km

Temperature increases with height (individual atoms) but still cold to touch (satellites live here).

Mesopause

Upper boundary of mesosphere.

M

Mesosphere

50km to 80km

Air pressure & density continues to decrease. No weather. Temperature decreases with height.

S

Stratosphere

6-20km to 50km

Temp rises to -15^oC at the top due to Ozone layer absorbing heat.

Tp

Tropopause

Around -51^oC.

T

Troposphere

0km to 6-20km

Up to 20,000ft - 65,000ft (thicker at equator)
75% of earth's atmosphere (weight) in this layer

Lapse rate above 11 km (36,000 ft) = 0°C per 1,000 ft (constant) up to 20 km

DALR

Dry adiabatic lapse rate

3^oC per 1,000ft

SALR

Saturated adiabatic lapse rate

1.5^oC per 1,000ft

ELR

Environmental lapse rate

Decrease in temp as altitude increases

Low Pressure - Rising air which cools - water vapour condenses to form clouds and precipitation. Weather is often cloudy, wet and windy (anticlockwise).

A trough is an elongated area of low pressure extending from the centre of the low-pressure region resulting in low cloud, rain and windy conditions.

In the northern hemisphere, if someone stands with their back to the wind, pressure is lower on the left-hand side of that person.

A cold front moves at 40-50 mph, warm front which moves at 20-30 mph.

As the cold front catches the warm front, the warmer air is forced up, away from the surface.

Speed differential is caused by the relative steepness of the fronts.

A cold front is steeper (less contact with the surface).

Generally, in stable air, gradient of mountain forces air upwards, cools, sinks other side. If air is stable, it tries to return to original level and oscillation is established (rotors)

Fohn winds

Winds flowing over a mountain lead to cold, wet weather on one side of the mountain and warmer, drier conditions on the other. It is caused by the consequence of humid/unstable air hitting the side of the

mountain.

Slope winds

Anabatic wind - Sun warms mountains, air rises, cool air of valley drawn to replace lost rising air (valley wind).

Katabatic wind - Process reversed, slopes cool more quickly, dense air descends into valley (mountain wind).

Sea/land breeze

Land & sea warmed at different rates. Land warmed by afternoon, warm air rises (convection), cooler air over sea blows in to replace lost air (sea breeze). Opposite happens at night as land cools quicker (land breeze).

Squall lines

Elongated line of severe thunderstorms, wind & rain (can be over 60 miles in width)

Warm air sits beneath cold air – the cold air sinks and warm air rises.

Moisture

Allows for precipitation and clouds.

Lift

Air mass rises due to:

• Warm air naturally rises

• Two fronts meet and force the air up

• Air forced up by terrain

A single-cell thunderstorm may extend as wide as 10-20 miles and as high as 70,000 ft.

Short burst of high-speed wind.

Squall

Winds that last approximately 1 minute.

Veering

Clockwise movement

Backing

Anti-clockwise movement

Thermal Wind

A thermal wind is caused by the meeting of two air masses of differing temperatures. Coriolis effect deflects winds to the right in N. Hemisphere.

Jet Streams

Narrow, rapidly moving parcel of air, just below the tropopause and can reach speeds of 200 mph. Jet streams can occur in both the northern, and southern hemisphere.

Turbulence

Turbulence exists when wind flow is disturbed for any reason such as:

- Convective clouds (cumulus, cumulonimbus)

- Geographical features (mountains)

- Temperature inversions

This disturbance causes random and often rapid fluctuations in speed and direction over a short distance.

Surface Wind

The wind velocity (speed and direction) indicated by instruments situated close to the runway in use.

Upper Wind

Predicted wind velocity at various altitudes, useful to identify headwinds or tailwinds, especially N. Atlantic.

Ground is heated by the sun, leading to low pressure air which rises creating pressure gradients.

Pressure Gradient Force (PGF)

Strength determined by pressure difference & distance. The larger the pressure difference and closer the areas, the stronger the PGF.

Wind Direction and the Coriolis Effect

Winds deflected 90° with force proportional to the speed of movement. In northern hemisphere, winds are deflected to the right.

Geostrophic Wind

Winds travelling from high-pressure to low-pressure are turned 90°, flowing parallel to isobars. Close isobars indicate strong wind. Accuracy affected by:

- Minimal surface friction from terrain

- Pressure remaining consistent

- Straight & parallel isobars increase likelihood of geostrophic wind representing actual wind

Surface Wind

Friction with Earth’s surface can affect the direction and speed of winds.

Air warmed at surface rises through atmosphere (earth is the heat source)

Orographic lift

Cooling when already fairly saturated

Frontal ascent (warm)

Warm air (shallow leading edge) meets cold air, rises gently above, creating stratus like clouds (cirrus, cirrostratus, alto stratus, nimbostratus)

Frontal ascent (cold)

Cold air (steep leading edge) meets warm air. Warm air forced up quickly and cools rapidly = cumulonimbus clouds (maybe thunderstorm activity)

Turbulent mixing

Air already saturated, then only requires a small bit of mixing (keeps going up & down) blowing over rough terrain causes eddying of air (Not a lot of uplift required)