Weather and climate

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Weather is the condition of the atmosphere today or tomorrow, whilst climate is the average weather over a long period of time. Some climates are the same throughout the year whilst others have seasonal differences. Near the Equator, for example, almost every day is hot and sunny, whith heavy rain in the afternoon. The mediterranean has seasonal differences, with dry summers and wet winters, the opposite to parts of Africa and South-east Asia where summers are wet and winters dry. Differences in pressure also affect climate: Low pressure is rising air which usually brings cloud, rain and wind. Los pressure systems are colled depressions. High pressure is descending air and usually gives fine, dry and settled weather. High pressure systems are called anticyclons. British climate: Temperatures: Latitudes 50ºN between 60ºN. This is far from the Equator, so the sun is only powerful enough to give moderate average temperatures. Winters are much warmer than might be expected for such a high latitude. Rainfall: Relatively wet and receives rainfall throghout the year. The main reason for this is that the prevailing south-westerly winds bring in moist air from the Atlantic Ocean and cause relief rainfall as they cross the mountains of western Britain. Climate variations: In summer the south is warmer than the north, in winter the west is warmer than the east, and the west is wetter than the east. Equatorial climate: Temperatures: High and constant throughout the year an the annual range of temperature is very small (2ºC). Evening temperatures rarely fall below 22ºC while daytime temperatures, due to the afternoon cloud and rain, rarely rise above 32ºC. Places on the Equator receive 12hours of daylight and 12 hours of darkness every day of the year. Rainfall: Annual rainfall totals of places located directly on the Equator exceed 2000mm a year. The rain falls most afternoons in heavy convectional thunderstorms. Tropical continental climate: 1. A very warm, dry season when conditions are similar to those of the hot desert, 2. A hot, wet season when the weather more resembles that of equatorial areas. Temperatures: Are high throughout the year and there is a relatively small annual range. The cooler season occurs when the sun is overhead in the opposite hemisphere. Temperatures rise as the angle of the sun in the sky increases. Rainfall: During the dry season the prevailing trade winds blow from the east. ANy moisture that they carried will have been shed long before they reach the central parts of continents. The dry season is shorter towards the Equator and longer away from the Equator. Mediterranean climate: 1. Hot, dry summers when the weather has similarities with that of the hot deserts, 2. Warm, wet winters when the weather more resembles that of the British Isles. Temperatures: Can be very high in summer. Places on the extreme west coast, are, however, cooler due to the moderting influence of the sea and the presence of a cold ocean current. Rainfall: Summers often experience drought conditions due to the prevailing winds blowing from the dry land. Rain, when it does fall, often comes in short but heavy convectional thunderstorms. Winters can be very wet. Cold climates: Temperatures: Have short and cool summers. THe hours of daylight are long, temperatures remain low owing to the low angle of the sun in the sky and, for inland areas, the distance from the sea. Rainfall: In these areas is very low. There are three main reasons. 1-The air is cold and cant hold much moisture. 2- The distance from the sea further reduces the amount of moisture in the air. 3- AMounts of relief and frontal rain are reduced by the rainshadow effects caused by mountain ranges to the west. Effects of drought: A drought is a long period of weather that is drier than usual. When it lasts for a particularly long time or rainfall amounts are considerably lower than average, it becomes a climatic hazard and can cause severe problems for people. Tropical storms: Are the most destructive storms on Earth. The hurricanes that occur in that region claim an average 20.000 lives each year and cause immense damage to property, vegetation and shipping. A hurricane is a particularly powerful tropical storm. It rotates around an area of intense low pressure and produces veryu high winds and torrential rain. Wind speeds commonly exceed 118m/h and in the most powerful storms hav reached 300km/h in husts. Rainfall is almost continuous. Effects of tropical storms: Are devastating with trees unprooted, buildings destroyed and many people injured or killed.

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