Chapter 13 Weather (Weather instruments) Flashcards
What is a Stevenson screen?
A box with slatted sides that holds thermometers, a hygrometer and a barograph
How is temperature measured?
With a maximum and minimum thermometer
How does a maximum and minimum thermometer work?
As the temperature increases, the Mercury expands and pushes the marker up on the maximum side
As the temperature decreases, the marker rises up the tube on the minimum side
The markers remain at the lowest and highest points
Temperature is shown in degrees Celsius
What are the lines that join places of equal temperature called?
Isotherms
How is average daily temperature calculated?
Adding the highest and lowest temperature of the day and dividing by 2
With what instrument is atmospheric pressure measured?
Barograph/barometer
How does a barograph work?
The corrugated drum is partially emptied of air
When the pressure of the air increases, the drum contracts slightly
When the pressure of the air falls, the drum expands slightly
The movement of the drum is transferred to a pointer by a series of levers
Another drum slowly rotates with graph paper attached
The end of the pointer has an inked in that records the pressure on the graph paper
What is the unit of atmospheric pressure?
Millibars
What are the lines that join places of equal pressure called?
Isobars
What instruments are used to measure wind direction and speed?
Wind vane
Anemometer
How does a wind vane work?
The head of the arrow points towards the direction from which the wind blows
The fin is large and is blown forward by the wind
How does an anemometer work?
Three cups spin in the wind
They rotate faster when wind is stronger
The speed of the wind is read from a dial on a meter
Which direction is wind direction named from?
The direction it comes from
What is the unit of wind speed?
Km/hr
What are the lines that join places of equal wind speed called?
Isotachs
What scale its wind strength measured on?
The Beaufort scale
How is wind strength measured on the Beaufort scale?
By observing the damage it causes to the landscape
There are 12 strengths
What instrument is used to measure precipitation?
Rain gauge
How does a rain gauge work?
Rain gauge is buried in the ground away from buildings not (so water does not fall into it from buildings)
Rain enters cylinder through funnel
Cylinder is marked in millimetres
What are lines that join laces of equal rainfall called?
Isohyets
What instrument is used to measure relative humidity?
Hygrometer
How does a hygrometer work?
The dry bulb temperature is read from the dry bulb thermometer
The wet bulb thermometer gives the temperature of saturated air
A muslin bag dipped in water covers the wet bulb
The difference in temperature between the two thermometers is used to find the relative humidity (greater difference= lower RH)
The measurement is expressed as a percentage
What instrument is used to measure sunshine?
The Campbell stokes sunshine recorder
How does the Campbell stocks sunshine recorder work?
The glass ball or sphere directs the Suns Ray’s onto the strip of paper at the back
The sun burns a mark on the paper which is divided into hourly intervals
