Understanding the Stevenson Screen and Weather vs. Climate

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Questions and Answers

What is the primary purpose of placing the Stevenson screen on grass?

To provide a stable foundation

To minimize heat absorption from the ground (correct)

To make it more visible to the public

To prevent moisture from affecting the instruments

Why are the sides of the Stevenson screen slatted?

To allow free movement of air around the instruments (correct)

To enhance the aesthetic appeal of the structure

To provide extra insulation from heat

To prevent rain from entering the screen

At what height is the Stevenson screen placed to avoid ground heat affecting the thermometer?

175 cm

150 cm

100 cm

121 cm (correct)

Which of the following instruments is NOT typically found inside a Stevenson screen?

Anemometer Signup and view all the answers

What is the required distance for wind vanes and anemometers from the nearest obstacle?

Three times the height of the obstacle Signup and view all the answers

What type of thermometer is used inside a Stevenson screen?

Maximum-minimum thermometer (Six's thermometer) Signup and view all the answers

How often are readings taken from the instruments inside the Stevenson screen?

Once a day Signup and view all the answers

What is a critical factor for the placement of the rain gauge?

It must be in an open space at least twice its height from any object Signup and view all the answers

What device measures wind speed?

Anemometer Signup and view all the answers

What is the primary unit of measurement for precipitation?

Millimetres Signup and view all the answers

Which thermometer is used to measure the minimum and maximum temperatures?

Six's thermometer Signup and view all the answers

What is the correct formula to calculate the mean daily temperature?

$\frac{max + min}{2}$ Signup and view all the answers

How is the diurnal temperature range calculated?

Maximum temperature - Minimum temperature Signup and view all the answers

What does a hygrometer measure?

Relative humidity Signup and view all the answers

What happens to the wet bulb temperature of a hygrometer when air is saturated?

It is equal to the dry bulb temperature Signup and view all the answers

For the accurate measurement of wind speed, where should an anemometer be placed?

Far from buildings and trees Signup and view all the answers

What is recorded if a precipitation reading is too small?

Trace Signup and view all the answers

What does a thermograph use to record temperature changes?

An exposed bimetallic strip Signup and view all the answers

What weather is commonly associated with nimbostratus clouds?

Steady rain or drizzle Signup and view all the answers

Which type of clouds typically extends to high levels and is known for dense storm activity?

Cumulonimbus Signup and view all the answers

At what wind speed does a tropical storm become classified as a category 3 storm?

111-129 mph Signup and view all the answers

What is the maximum wind speed for a category 5 tropical storm?

157 mph or higher Signup and view all the answers

What is the typical altitude range for stratocumulus clouds?

0-2 km Signup and view all the answers

Which disaster is NOT typically caused by tropical storms?

Earthquakes Signup and view all the answers

What is the primary purpose of a barometer?

To measure air pressure Signup and view all the answers

What characterizes the center of a hurricane?

Calm area known as the eye Signup and view all the answers

Which type of tropical storm is referred to as a typhoon?

In the South China Sea Signup and view all the answers

Which instrument continuously records atmospheric pressure changes over a week?

Barograph Signup and view all the answers

At what pressure level is the sea level pressure approximately measured?

1.03 kg/cm² Signup and view all the answers

What does the term 'isobar' refer to on a weather map?

Lines connecting areas of equal air pressure Signup and view all the answers

What feature primarily characterizes an aneroid barometer?

It has a corrugated metal chamber Signup and view all the answers

What type of cloud is associated with precipitation?

Cumulonimbus Signup and view all the answers

How is cloud cover quantified?

Using oktas Signup and view all the answers

What distinguishes the Campbell-Stokes sunshine recorder?

It records sunshine duration Signup and view all the answers

What type of clouds typically form at high altitudes, above 6 km?

Cirrus Signup and view all the answers

What happens to the mercury in a mercury barometer when atmospheric pressure increases?

It rises in the tube Signup and view all the answers

What type of clouds are characterized by having a thick, white, or gray appearance and could produce fine weather?

Altostratus Signup and view all the answers

What is the maximum visibility indicated by 8 oktas of cloud cover?

Total coverage Signup and view all the answers

What process leads to the formation of clouds?

Rising, cooling, and condensing air Signup and view all the answers

The feature used to determine sunshine duration in a Campbell-Stokes recorder is primarily:

Glass sphere focusing sunlight Signup and view all the answers

Study Notes

Stevenson Screen

Constructed of wood, painted white to reflect sunlight
Four legs, 121 cm high, to avoid ground heat
Sides are louvred (slatted) to allow air circulation.
Double-layered wood with airspace for insulation to prevent heat transfer.
Located on grass to minimize ground heat absorption.
Instruments within the screen are placed to protect from direct sunlight and heat from the ground.
Readings taken at the same time daily.
Modern stations use digital recording equipment connected to the Met Office computers.

Weather vs. Climate

Weather: Daily variations of rain, sun, snow, etc., measured over days.
Climate: Long-term average conditions (e.g., warm summers, cold winters) measured over 30 years.

Ideal Stevenson Screen Location

Open area: Avoid heat from buildings.
Clear of trees: Prevent shade and undisturbed airflow.
Grass: Reduces heat absorption from ground.
Away from public: Minimizes tampering.

Wind Vane

Measures wind direction.
Unit of measurement: compass points (north, south, etc.)
The broad end catches the wind, indicating the wind's origin.
Positioned away from buildings and trees to avoid blocked airflow that affects reading accuracy.

Anemometer

Measures wind speed.
Units of measurement: m/s or km/hr.
Consists of 3 or 4 cups on metal arms that rotate freely, speed recorded using calibrated dials and mechanisms.
Positioned away from buildings and trees to avoid blockages.

Precipitation

Any form of water falling to Earth (rain, snow, hail, sleet).
Unit of measurement: millimetres (mm).
Measured using a rain gauge.
Water collected is poured into a graduated cylinder to measure the level.

Temperature

Measured using a thermometer or thermograph to determine the daily minimum, maximum, and average temperatures.
Measurements are in °C or °F.
Shade temperature is recorded to exclude direct sunlight.
Six's thermometer measures both maximum and minimum temperatures
Thermographs measure and record temperature continuously.
Diurnal temperature range is the difference between the maximum and minimum temperatures in a 24-hour period.

Humidity

Hygrometer measures relative humidity.
Relative humidity is the amount of water vapor in the air compared to the maximum it can hold at a given temperature.
Warm air holds more water vapor than cold air.
Wet bulb thermometer measures the effect of evaporation on air temperature.
Water vapor evaporation from the wet bulb muslin causes cooling and lowering of the reading.

Air Pressure

Air exerts pressure on Earth's surface.
Unit of measurement: millibars (mb).
Barometer measures atmospheric pressure; there are:
- Mercury barometer
- Aneroid barometer
- Barograph
Mercury barometer measures pressure by the height of the mercury column.
Aneroid barometer uses a partially vacuumed metal chamber to measure pressure changes.
Barograph records atmospheric pressure continuously over time on a chart.

Sunshine Recorder (Campbell-Stokes)

Measures sunshine hours.
Consists of a glass sphere that focuses sunlight onto a recording card below it.
Positioned in an open space, facing south in northern hemisphere, north in southern hemisphere.
The burn length on the card represents the hours of sunshine.

Clouds

Cloud cover is measured in oktas (1/8ths of the sky).
Different cloud types have different descriptions, heights and shapes.
Cloud formation relies on rising, cooling, and condensation of air.
Cloud type dictates likelihood of precipitation.
Cumulonimbus and nimbostratus are the primary precipitation clouds.

Tropical Storms

Collective name for low-pressure systems (typhoons, hurricanes, cyclones).
Rated on the Saffir-Simpson scale based on wind speed categories.
Category 3 and above are considered major.
Formation occurs over warm tropical ocean waters.
Wind speed categorized to assess hurricane risk.

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Description

This quiz explores the construction and significance of the Stevenson Screen in weather measurement, as well as the difference between weather and climate. Discover how proper placement of the screen impacts data collection and why long-term climate assessment is crucial. Test your knowledge on these fundamental meteorological concepts.