Weather Flashcards
Climate
The weather conditions prevailing in an area in general or over a long period
Weather
The state of the atmosphere at a particular place and time as regards heat, cloudiness, dryness, sunshine, wind, rain etc.
Measuring the weather - Devices
Rain gauge - Precipitation
Maximum/ Minimum thermometer - Temperature
Sunshine recorder - Sunshine
Wind vane - Wind direction
Barometer - Air pressure
Anemometer - Wind speed
Hygrometer - Humidity
How to measure cloud cover
Hold a card with 8 equal squares up to the sky + count the amount of sqaures filled.
1 square = 1 okta
More oktas = more cloud coverage
Cirrus - Characteristics
- Found at high altitudes
- Wispy, with a silky sheen (tufts of hair)
- White, but can take on colours of sunset / sunrise.
- Made up of ice crystals
Cumulus - Characteristics
- Detached, individual, cauliflower-shaped clouds.
- Usually spotted in fair weather conditions.
- Tops of these clouds = mostly brilliant white tufts when lit by the Sun
- Base is usually relatively dark.
Stratus - Characteristics
- Low-level layers
- Fairly uniform grey or white colour.
- Often overcast days
- Can persist for long periods of time.
- Sometimes appear at surface of fog/mist
Cumulonimbus - Characteristics
- Menacing looking
- Extend high into the sky in towers or plumes.
- Thunderclouds.
- Can produce hail, thunder and lightning.
- Base of the cloud is often flat, + dark wall-like feature hanging underneath,
- May only lie a few hundred feet above the Earth’s surface.
What type of weather do cirrus clouds bring?
- Often form in advance of a warm front.
- Often indicate a change in weather.
What type of weather do cumulus clouds bring?
- Cumulus indicates fair weather, often popping up on bright sunny days.
- Can however, grow into cumulonimbus
What type of weather do stratus clouds bring?
- Little to no rainfall but if it is thick enough, it can produce light drizzle.
- This drizzle can also fall in the form of light snow if cold enough
What type of weather do cumulonimbus clouds bring?
- Extreme weather (Heavy torrential downpours, hail storms, lightning and even tornadoes)
- Usually dissipate within an hour once showers start falling (Short-lived, heavy rainfall)
Hygrometer - How it works
- Two thermometers (wet and dry thermometer)
- Dry thermometer measures current temperature
- Wet thermometer covered with a muslin cloth submerged in water.
- If air is extremely saturated (no water will evaporate from cloth bc air can’t hold more humidity)
- If air isn’t humid, water evaporates from cloth
- Evaporation = endothermic –> therefore temperature of wet thermometer decreases
- Use of relative humidity chart to find percentage in relative humidty using differences in humidity.
Anemometer - How it works
- Measures wind speed (km/h)
- 3 or 4 metal cups that can rotate on a vertical shaft.
- When there is wind, the cups rotate
Faster wind = Faster rotation
- Number of rotations recorded on a meter = speed in km/h
Where should an anemometer be placed?
- Placed far away from trees/ buildings.
- Can slow down winds / buildings can channel air through narrow passages between two buildings.
- Placed high up
- (avoids interference by animals)
Wind vane - How it works
- Measures wind direction
- Wind vane (points of the compass fixed + points in NESW directions)
- Above compass an arrow lies that can be moved by very light winds
- Winds blows it moves the arrow so it points to the direction the wind is coming (bc wind pushes on larger metal feather part on the arrow)
How is wind speed shown on weather diagrams?
- Winds shown by arrows on weather maps
- Shaft of arrow = wind direction
- Feathers on arrow = wind speed (more feathers = faster wind)
Aneroid barometer - How it works
- Measures air pressure in millibars (mb)
- Above 1013 mb is said to be high pressure and below this is low pressure.
- Has a sealed box that can change shape
- As air pushes down on box, it changes shape + moves needle on the dial —> produces a reading on a calibrated scale.
- Readings from an aneroid barometer = shown on a barograph.
(Barometers = often stored inside stevenson screen)
Low air pressure (weather conditions)
- Unsettled conditions –> bc warm air can easily rise of the surface of the earth which leads to condensation + clouds + maybe rain.
High air pressure (weather conditions)
- Settled / clear conditions bc cool air is descending + warming up (no clouds formed from rising air)
Maximum / Minimum thermometer - How it works
- U-shaped tube filled with alcohol + mercury
- Right side of tube shows maximum temp, left side shows minimum temperature
- Temperature increases –> alcohol in left tube expands –> Mercury moves toward right tube –> metal index in right tube also shifts –> Gives maximum temp for the day.
- Temp decreases –> alcohol contracts in left tube –> mercury moves into the left tube –> metal index in left tube shifts –> gies minimum temp
Instrument reset using a magnet
Daily temperature range = difference beteween maximum and minimum temperature
Usually stored inside stevenson screen so temp can be recorded in shade
Rain gauge - How it works
- Precipitation measured in rain gauge
- Collected in a cylinder with a mm scale on the side
- Placed in open space so only raindrops enter funnel + ehld above ground to stop water splashing up from teh ground
- Emptied every 24 hours usually.
Sunshine recorder - How it works
- Glass sphere partially surrounded by metal frame.
- Strip of special card (divided into hours + mintues = placed below sphere)
- When sun shines –> sphere focuses suns rays on card
- As sun moves –> rays burn trace on the card
Card replaced each day
- Length of trace = amount of sunshine the area recieved.
What is a Stevenson Screen?
Shelter used to house metrological instruments.
Protects them from precipitation, sunshine, strong winds + ground heat. (Allows accurate readings to be taken)
Characteristics of a stevenson screen
- Stored away from artificial sources of heat (eg. central heating systems)
- Sited on flat land
- Painted white to reflect sunlight
- Slats allow air to circulate freely
- Kept in fenced off area to avoid damage from people/ animals
- Made from wood bc bad conductor of heat
- Door of screen faces away from sun to prevent sunshine through slats.
- Kept 1.25 meteres above ground to stop ground heat from reflecting upwards.
- Placed on vegetation bc rocks/ concrete absorb heat, making area warmer.
What weather measuring equipment is placed in a stevenson screen?
- Maximum-minimum thermometer
- Barometer
- Hygrometer
How is cloud cover shown on weather station models?
Circle partially filled in.
% of circle filled in = amount of cloud coverage.
Why rain falls….
Water condenses as it rises + forms clouds…
- Sometimes water droplets combine o orm larger drops / crystals.
If they become too large + heavy –> they fall from sky as precipitation.
Relief rainfall
- Relief rainfall occurs when air has been blown over the sea and is then forced up over an area of high land.
- This causes the air to cool and the moisture in the air condenses and rain falls.
Frontal rainfall
- Frontal rainfall occurs when warm air is forced to rise over cold air.
- The moisture in the warm air condenses as it cools which causes clouds and rain.
Convectional rainfall
- Occurs mostly in tropics where it is hot.
- When air is hot is rises and cools and condenses forming rain.
- If the air is hot enough, it rises very quickly and can cause thunderstorms.
