Summer Revision 2025 Part2 Flashcards
(14 cards)
What is atmospheric pressure and how is it measured?
• Atmospheric pressure is the weight of the atmosphere pushing down on the Earth.
• It is measured in millibars (mb) using an instrument called a barometer.
How does a barometer measure atmospheric pressure?
• A vacuum chamber inside the barometer is sensitive to atmospheric pressure.
• As pressure changes, the main needle moves:
•. Clockwise as pressure increases.
• Anticlockwise as pressure decreases.
• The second needle is a marker that can be moved by rotating the stud in the center of the barometer.
•By aligning the marker with the main needle, you can ‘mark’ the existing pressure for later observation of pressure changes.
How is precipitation measured and how does the equipment work?
Precipitation is measured with a rain gauge in millimetres, mainly rainfall.
The equipment consists of an outer cylinder with a funnel that directs water into a measuring cylinder.
It is partially buried in the ground in an open space, away from buildings or trees, to avoid interference.
What are climate graphs and what do they show?
Climate graphs are used to illustrate the average temperature and average precipitation of an area over the twelve months of the year.
What are the different types of clouds and their characteristics?
Cirrus clouds form above 8000 m. They are thin and wispy, made of tiny ice crystals instead of water droplets.
Cumulus clouds form below 5000 m. Their base is flat, and their top is rounded (like a cauliflower). White cumulus are ‘fair weather’ clouds, while dark cumulus can bring heavy rain showers.
Stratus clouds form below 2000 m. They are large, thick, grey clouds that fill the sky and can bring long periods of precipitation.
How is wind direction and speed measured?
Wind direction is indicated using a wind vane, which shows the direction of the moving air in the atmosphere.
Wind speed or strength is measured with an anemometer in units of kilometres per hour (km/h).
How is wind speed measured with an anemometer?
An anemometer has three cups that rotate when the wind blows.
The stronger the wind, the faster the cups move.
The number of times the cups rotate is used to calculate the wind speed, and the result is recorded and displayed on the meter.
How is humidity measured?
Humidity is the amount of water vapour in the air.
A hygrometer is used to measure relative humidity, which is expressed as a percentage
How does a Wet and Dry Bulb Hygrometer work?
One thermometer measures the air temperature with a dry bulb.
The other thermometer has a bulb kept wet by a cloth cover that dips into a container of water.
The difference in temperature between the two thermometers indicates relative humidity, which is calculated using a special set of tables
How are certain weather instruments stored and why?
Some instruments, like the barograph, maximum and minimum thermometer, and hygrometer, are stored in a wooden box called a Stevenson screen.
The Stevenson screen is painted white to reflect the sun, ensuring that the instruments are not affected by direct sunlight.
It allows for more accurate measurements by letting air flow through but preventing direct sunlight from entering the box.
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What are tropical storms and how are they named in different regions?
Tropical storms are huge storms that develop in the Tropics, a region north and south of the Equator.
In the USA and the Caribbean, they are called hurricanes.
In Australia and Southeast Asia, they are known as cyclones.
In Japan, they are called typhoons.
How do hurricanes form?
When wind speed reaches 120 km per hour, the storm is officially labelled a tropical storm.
The storm develops an ‘eye’ in its middle, which is an area of calm weather.
Several thunderstorms join together to form the storm.
The storm is carried across the ocean by winds, getting stronger as it moves.
More water is drawn upwards from the ocean, fueling the storm.
When it reaches land, friction with the land’s surface can weaken the storm.
How are hurricanes measured and what scale is used?
Hurricanes are measured using the Saffir-Simpson scale, a 1-5 rating based on the hurricane’s sustained wind speed.
The scale estimates the potential damage the hurricane could cause.
