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  1. Weather

  2. What is weather? • Weather is the day to day conditions of a particular place. • Ex. Sunny, rainy, hot, cold • These conditions are caused by atmospheric pressure, humidity, and temperature.

  3. Atmospheric Pressure • Pressure is the weight of the atmosphere on the Earths surface. • Pressure is lower on the top of mountains and highest at sea level • Drops in air pressure mean unstable conditions (storms) • Atmospheric pressure is measures with barometers

  4. Humidity • Humidity is how much water vapor is in the atmosphere • Air is always collecting evaporated water from rivers, lakes and oceans. • In tropical parts, warm air hold more water vapor and humidity is higher

  5. Relative Humidity • Relative humidity is the measure of how much water vapor is actually in the air compared to how much water vapor the air can hold. • This is measured using a wet and dry hygrometer

  6. Temperature • Temperature is the measure of how cold or hot somewhere is • Temperature is measured using a thermometer, with units in degrees on Fahrenheit (ºF) or Celcius (ºC) scales.  • Temperature is usually higher during the day than at night. Rural areas (the countryside) are often cooler than towns and cities.  • This is because there are more buildings and factories ( known as 'heat islands') which absorb heat during the day, releasing it slowly at night and warming the surrounding air.

  7. Sunshine • The amount of sunshine we have depends on latitude and how much cloud there is in the sky. • In the Eastern Sahara desert, the sun is covered by clouds for less than 100 hours a year. • In Britain we have from 1,850 hours in Southern England to 1,200 hours in North Scotland. • There is usually more sunshine where atmospheric pressure is higher.

  8. Sunshine • Hours of sunshine are usually recorded on a simple machine called a pyrheliometeralso known as a Campbell-Stokes recorder. • It works by using a glass ball to focus the sunlight and rays onto a strip of card. • As the sun moves round during the day, the card is scorched creating a record of how many sunshine hours there were.

  9. Pyrheliometer

  10. Wind • On the surface of the Earth, wind consists of the bulk movement of air. • Wind is caused by differences inatmospheric pressure. • When adifference in atmospheric pressure exists, air moves from the higher to the lower pressure area, resulting in winds of various speeds.   • Extreme wind can cause cyclones and tornadoes

  11. Tornadoes • A tornado is a violently rotating column ofair that is in contact with both the surface of the earth and acloud • Most tornadoes have wind speeds less than 110 miles per hour (177 km/h), are about 250 feet (76 m) across, and travel a few miles (several kilometers) before dissipating. • Themost extreme tornadoes can attain wind speeds of more than 300 miles per hour (483 km/h), stretch more than two miles (3.2 km) across, and stay on the ground for dozens of miles (more than 100 km)

  12. Tornadoes • Tornadoes have been observed on every continent except Antarctica. However, the vast majority of tornadoes occur in theTornado Alley region of the U.S. • They also occasionally occur in south-central and eastern Asia, northern and east-central South America, Southern Africa, northwestern and southeast Europe, western and southeastern Australia, and New Zealand

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