Weather instruments

• Weather is the state of the atmosphere at any given time
• There are 7 weather elements: humidity,rainfall,cloud cover,wind direction and speed, air pressure, temperature and sunlight
• 7 Weather elements: humidty
• Weather station is were the elements of weather are studied carefully and measured.
• Maximum thermometer measure max temp in 24 hrs
• In the maximum thermometer mercury expands and pushes the index Elon with the tube when temperature rises
• When temp falls in the maximum thermometer the mercury contracts and live the index behind
• The maximum thermometer is read but the scale of the index with was in contact with the mercury
• when temp falls in minimum thermometer the alcohol contracts and meniscus plus the index along the tube
• when temp rises in the minimum thermometer alcohol expands leaving the meniscus where the index was
• m temp is read by the sale at the end of the index closest to the meniscus
• In a sixes thermometer when temp rises the alcohol expands in the left limb pulls the mercury down the left hand limb and up the right hand limb. Alcohol is vapourised and occupies spaces in the bulb
• In the sixes thermometer when temp falls, alcohol contracts in the left limb and alcohol vapour in the bulb liquifies. Causing mercury to flow in reverse direction, metal index marks the temp reached
• Humidity is the amount of water in air
• Hygrometer is two thermometers dry and wet bulb thermometer
• Hygrometer is kept in a Stevenson screen
• in a hygrometer one thermometer is dipped in a water bath wrapped around muslin (wet bulb thermometer)
• The other thermometer has no water bath and has no muslin (dry bulb thermometer )
• If air is not saturated the water evaporates from muslin cooling the dry bulb thermometer causing mercury to contract
• Dry bulb thermometer offers higher reading
• The temp of humidity is calculated by the differences of the two thermometers
• small difference = hight humidity, Large difference= low humidity, no difference= saturated air
• Air pressure is the forces exerted by the air of the earth surface
• Pressure is varied with 2 elements altitude and temperature
• In a mercury barometre, mercury sits in shallow dish surrounding tube. the mercury above the dish will adjust to match atmospheric pressure above the dish.
• The tube in the mercury barometer is marked with number of atmospheres or bars
• In an aneroid barometer there are chambers with contract and expand depending on atmospheric pressure around it. Mechanical tools measure how much chambers contract and expand
• Raingauges are a glass jar and funnel that fits to container top. The gauge is sunk 30cm all to prevent water splash. The gauge is put into an open space so that there will be no run-off. Gauge is emptied after every 24hrs
• wind vane as a metal shaft, pivoted shaft and horizontal shifting alarm. When wind blows the alarm swings until the pointer faces the direction of wind. the direction is mark by compass points on arms fixed on the metal shaft
• Cup anemometre inicates wind speed. there are 3-4 metal cups fixed to rotate on the shaft. when there is wind these cups rotate and the stronger the wind is the faster the cups blow. the number of rotations is recorded to give speed of wind in km/hr
• Beaufort scale shows to estimate wind speed by observing the way objects are blown by wind
• Sushine recover measures sunlight. it is a glass sphere with a metal frame containing sensitised card. It is marked with hourly intervals.It is positioned to the sun's rays. when the sunshines in burns the sensitised card and the length of the mask is converted to hrs/mins
• Clouds are classified in shape, movement and height
• Clouds are made up of water vapour and ice particles
• Mist and fog are made of water droplets so they form a cloud type
• Clouds show the type of weather usually about to occur
• high clouds= 6000-12000m, middle clouds 2100-6000m, low clouds below 2000m, clouds of great vertical extent 1500-9000m