Measuring the Weather
Draw, describe and explain the use and siting of the following instruments at a weather station: rain gauge, maximum-minimum thermometer, wet and dry bulb thermometer (hygrometer), barometer, anemometer and wind vane.
Rain gauges are used to measure rainfall totals over a given time period. They consist of an outer container with a funnel in the top which directs the rain into an inner measuring cylinder. The funnel greatly reduces any water lost to evaporation which would alter the measurement. Rain gauges should be sited in an open location and preferably on a soft surface such as grass to reduce splashes being collected.
Maximum Minimum Thermometer
Used to record the highest and lowest temperatures over a time period (usually 24 hours).
The thermometers have markers which remain at the lowest and highest temperatures.
Thermometers should be placed inside a Stevenson screen so that they are not in direct sunlight or too close to the ground.
Used to measure humidity. Modern hygrometers are usually digital.
Older hygrometers are known as wet & dry bulb thermometers. The difference between the wet bulb & dry bulb readings is known as the depression. A table is used to calculate the % humidity from the temperature and the depression reading.
Used to measure air pressure:
- High pressure indicates stable conditions and clear skies.
- Low pressure indicates windy, cloudy and probably rainy conditions.
Barometers can be sited in most places, often inside a Stevenson screen.
Used to measure wind speed. Mechanical and digital version exist and usually give the reading in miles or km/hour
Anemometers should be sited in a raised location away from obstructions that would interfere with any wind movement (buildings, trees etc).
Used to indicate the direction that the wind is blowing.
Remember that when stating wind direction you refer to the direction it is blowing from. If the wind is blowing to the North its is a Southerly wind.
Make calculations using information from these instruments.
Have an awareness of simple digital instruments which can be used for weather observations.
Climate graphs are the main graphs that you are likely to come across. They are two sets of data displayed on one graph: a red line chart for temperature and a blue bar/column chart for rainfall. The x-axis displays the months. There will be 2 y-axis, usually one on each side. Take care to read the data from the correct y-axis. Make sure you add the correct unit of measurement (mm) in your answer.
Tropicals storms are low-pressure systems that form over oceans. They get their energy from warm sea temperatures and if they become strong enough and the winds start circling they may become categorised as hurricanes or typhoons. Tropical storms bring strong winds, heavy rainfall and sometimes storm surges (large waves pushed by the strong winds).
Tropical storms mostly occur between the equator and the tropics of Capricorn and Cancer, as they travel further north or south the cooler sea temperatures feed them less energy and they weaken. They also weaken quickly when they reach land, the worst affected areas are the coastal regions.