PPL Meteorology
Col area
A neutral area of pressure between two areas of high pressure and two areas of low pressure. Causes light variable winds and generally good weather
Orographic lift
Air rising as a result of blowing against a mountain or other raised surface
Naming protocol for wind
Always named after where it comes from
Humidity
Amount of water vapour in the air - 2types: absolute (total amount) and relative (% of total air can hold)
Saturation depends on:
Amount of water vapour in the air, and the temperature of the air
Water Vapour
An invisible gas made of water
High Pressure system
Anticlockwise circulation of air, descending, and diverging (moving away from the centre). Indicates light winds, good weather, but poor visibility
Adiabatic Cooling
As air rises it expands and cools
Land breeze
Blows from the land to the sea, happens at night, and caused by land cooling down after sunset
Sea breeze
Blows from the sea to the land during the day. Results from sun heating up the land, which draws in moist cooler air from the sea
Katabatic winds
Caused by cold air descending down the shady side of mountains. Can be powerful and require caution
Anabatic winds
Caused by mountain side being heated by the sun
Condensation
Changing water vapour into a liquid
Synoptic chart
Chart showing all air pressures over an area joined by isobars
Low pressure system
Clockwise circulation of rising air, converging (air moving towards centre). Indicates strong winds, poor weather with good visibility
Trough of low pressure
Clockwise movement of air around the low
Polar continental air mass
Cold, dry, coming from the land
Polar maritime air mass
Cold, moist, coming across from the sea
Warm front clouds
High cirrus, cirrostratus, and cirrocumulus
Cirrus family clouds
High clouds - above 20 000feet
Cirrostratus clouds
High layered clouds
Cirrocumulus clouds
High puffy clouds
Aneroid Barometer
Household method for measuring air pressure
Squalls
Increases in wind speed of longer duration than a gust. Associated with cold fronts and thunderstorms
What causes cooling of the air, and clouds to form?
Lack of heating, mixing with cold air, contact with cool surfaces, and rising and cooling of air
Nimbostratus
Layered rain bearing clouds
Lenticular clouds
Lens shaped with strong winds and severe turbulence
Isobars
Lines on a synoptic chart of equal air pressure
Stratus clouds
Low clouds - below 8000 ft
Mammatus clouds
Mammary shaped - severe turbulence
Altimeter
Measures atmospheric pressure
Anemometer
Measures surface winds at 33feet or 10metres above the ground
Alto clouds
Medium clouds - 8000 - 20 000 feet
Altostratus clouds
Medium height layered clouds
Altocumulus
Medium height puffy clouds
Ridge of high pressure system
Moves anticlockwise around the high
International Standard Atmosphere ISA
Pressure 1013.2Hpa Temperature 15*C Temperature decreases x 1.98*C every 1000ft
Cumulonimbus
Puffy black storm clouds
Cumulus clouds
Puffy, cotton wool clouds - sometimes produce showers
Environmental Lapse Rate (ELR)
Rate at which temperature decreases with height. High ELR indicates unstable conditions and vice versa
Dry Adiabatic Lapse Rate (DALR)
Rate at which temperature of dry air decreases as it rises. Fixed = 3 degrees C per 1000feet
ELR less than 3degrees Celsius
Results in stability
ELR greater than 3degrees Celsius
Results in unstable conditions
Gusts
Short sudden increases in wind speed
Saturation
State where the air cannot hold any more water vapour
Gales
Surface winds that are greater than 34knots, or gusts greater than 43knots
Dewpoint
Temperature when a sample of air becomes saturated and condensation begins
Cumulonimbus Charlie Bravo clouds
Thunderstorm activity with anvil shaped clouds - keep away
Absolute Humidity
Total amount of water in the air
Mercury barometer
Used by the Met Office to measure atmospheric pressure
Tropical continental air mass
Warm, dry, coming from tropical land
Tropical maritime air mass
Warm, moist, coming from the tropics
Atmospheric pressure
Weight of air above us
Nimbus
Wet, black, grey cloud
Cold front
When a cold air mass moves in and wedges under a stationery warm air mass
Warm front
When a warm air mass hits a stationary cold air mass
Frontal lift
When a warmer air mass rides up and over a cooler air mass
Convergent lift
When air moves into an area of low pressure from all sides and is forced up as it has nowhere else to go
Convection lift
When hotter ground causes the air above it to heat and rise
Evaporation
When liquid water turns into water vapour
Occlusion
Where a warm and cold front join together
Backing wind
Wind changing in an anticlockwise direction
Veering wind
Wind which is changing clockwise
Local winds
Winds not part of the general weather pattern
Valley winds
Winds that hit a range of mountains at near right angles and rushes down the valley instead of going over the top
Rime Ice
Frosty granular stuff like sugar
Unstable air
Gives bumpy flying conditions. Associated with cumulus clouds
Stable air
Gives nice smooth flying conditions. Associated with stratus cloud
Glaze or clear ice
Glassy looking sheet of ice - very hard to see
Relative Humidity
% of the total amount of water the air can hold
Cold front clouds
Cumulus or cumulonimbus clouds
Stratus clouds
Flat sheet or layered cloud that produce more continuous rain
