1B.1 Weather Elements Flashcards
Define weather.
The hour to hour, day to day state of the atmosphere. It includes sunshine, precipitation, cloud cover, temperature and wind. Weather is short term and localised in an area.
Define climate.
The average weather conditions for a place taken over a period of time, usually 30 years. It is the expected rather than actual atmospheric conditions and is long term, often applied to large sections of the globe.
Define temperature.
A measure of the amount of heat in the atmosphere around us.
What unit is temperature measured in?
Degrees Celsius
Describe in detail how temperature is measured.
It is measured using a maximum and minimum thermometer. This is filled with mercury and alcohol and contains 2 metal index pins, one on either side.
- The alcohol heats up during the day and expands, which pushes the mercury higher on the maximum side. This pushes a pin up the tube, and the pin stops and stays at the highest point reached.
- At night, the alcohol cools down and contracts, pulling the mercury up the minimum column where it leaves the minimum pin at the minimum temperature.
- We can read off the highest and lowest temperatures during the previous 24 hours by reading the Degrees Celsius scale at the bottom of the metal index. The pins can be reset to the mercury using a magnet once the measurements have been taken or by pressing the reset button.
- The current temperature can be taken at any time by simply recording the scale at the end of the mercury.
Why is it important that temperatures are recorded at the same time every day?
To ensure a fair recording and to have a measurement of the past 24 hours.
Describe the features of a Stevenson Screen, and explain how these make it suitable to store thermometers.
❄️ Its slatted sides mean only the air flowing through the screen is recorded.
❄️ It is painted white to reflect sunlight.
❄️ The thermometers are stored in the shade to ensure that direct sunlight doesn’t give a false reading.
❄️ It is raised 1 metre above ground in order to avoid extremes caused by ground frost, etc.
❄️ It is sited away from buildings or large trees as these may interrupt the air flow, radiate heat or create a shadow effect which may increase or decrease the temperature.
Define precipitation.
The amount of moisture in the atmosphere usually involving water in all of its states: liquid, solid and gas. It includes rain, dew, hail, sleet and snow.
How is precipitation measured?
Using a rain gauge - a copper cylinder sunk into the ground with a funnel on top. The rain in the gauge should be carefully poured into a measuring cylinder and the amount of water can be read off the scale on the side in millilitres.
Why are rain gauges normally made of copper or plastic?
It doesn’t rust.
Why are rain gauges anchored securely?
It doesn’t get knocked over by the wind, animals, etc.
Why should rain gauges be positioned with the top 30cm above ground level?
To prevent rain splash due to saturated ground and high surface runoff.
How is wind speed measured?
Using an anemometer - this can either be hand held or ideally mounted on a roof top or mast 10 metres above ground. It is made up of cups attached to a handle with a scale. The stronger the wind the faster the cups rotate and the higher the reading on the scale.
What unit is wind speed measured in?
Knots or km/h
Why is a roof top the best location for an anemometer?
It avoids shelter and thus false results.
If an anemometer is hand held, why must it be at arm’s length?
It reduces shelter and the effect of your breath.
How is wind direction measured?
Using a wind vane - ideally this should be mounted on a rood top or mast 10 metres above ground. It is made up of an arrow mounted on top of a spindle, allowing the arrow to move with the wind. The arrow always points in the direction from which the wind is blowing. It is measured using the 8 main compass points.
What is air pressure?
The pressure exerted by the weight of the atmosphere on the earth’s surface. Normal pressure is set as 1000 mb. Low pressure is defined as anything below this, and high pressure as anything above.
What is an aneroid barometer and how does it work?
It contains a capsule which is a vacuum. As the pressure rises and falls the capsule contracts and expands and this is indicated by a needle on a dial at the front. The pressure can then be read in millibars.
What is a barograph and how does it work?
It contains a metal vacuum cyclinder which contracts when the pressure increases. This moves a metal arm with a pen that leaves a trace of the pressure on a revolving drum.
What is a cloud?
A visible mass of tiny particles floating in the atmosphere, consisting of ice crystals or water formed from the condensation of water vapour.
Describe stratus clouds.
These appear as light grey clouds that look like a blanket stretching across the sky. They tend to be low in the atmosphere and are composed of fine water droplets, causing some drizzle.
Describe nimbostratus clouds.
Thick layers of rain bearing clouds found low in the atmosphere.
Describe cumulus clouds.
These are often low in the air and look like cotton wool floating in the sky. Clusters of small, white cumulus clouds are usually a sign of good weather. However if they turn grey at the base, they can bring rain.
