Transcript Air Masses
Air Masses Science 10 Air Mass A large mass of air that has nearly uniform properties such as temperature, humidity and pressure There are five air masses of importance that you should know. Arctic Air Mass Extremely cold temperatures and very little moisture. Originating over the Arctic ocean in winter, when high pressure dominates and differs only slightly from the continental polar (cP) air masses that develop over Siberia and northern Canada. Continental polar (cP) Cold and dry, originating from high latitudes, typically as air flowing out of the polar highs. This air mass often brings the rattling cold, dry and clear weather on a perfect winter day and also dry and warm weather on a pleasant day in summer. Maritime polar (mP): Cool and moist, often originating as continental polar air over the North American and Asian land masses and is modified as it moves out over the Atlantic and Pacific Oceans. Heated by the relatively warm water bodies this air mass becomes rather unstable resulting in blustery showers over the sea and windward coasts. Continental tropical (cT): Hot and very dry, orginating from the arid and desert regions during summer. The least common air mass to affect the British weather. However, approaching from the south and south-east in summer it can bring record heat to southeast Britain, particulary in late-summer. Maritime tropical (mT) Mild and damp in winter, very warm and muggy during summer. Originating from the Azores this air mass approaches the British Isles from the west, leading to overcast skies with prolonged rain for the western half of the country and to many clouds, sometimes broken with drizzle for the eastern half. In summer tropical maritime air often produces warm weather with abundant sunshine in the southeast. High Pressure Systems When an air mass cools over an ocean or a cold region of land, a high pressure system forms. The cooling, descending air exerts more pressure on the region below. This is why it is called a high pressure system. High pressure systems bring clear bright skies. Low Pressure Systems Air masses traveling over warm land or oceans may become low pressure systems. The warming air rises and leaves less dense air below. Water vapour in the air condenses as it reaches the higher altitudes, producing clouds and precipitation. How wind forms: Wind is caused by the movement of air from an area of higher pressure to an area of lower pressure. The rotation of the earth cause wind to move in a clockwise direction around the high pressure centre. The Coriolis Effect The Coriolis effect is the change in the direction of moving air, water or any objects on the Earth’s surface due to the rotation of the Earth. It deflects winds to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. Polar Easterlies also Polar Hadley cells dry, cold prevailing winds that blow from the high-pressure areas of the polar highs at the north and south poles towards lowpressure areas within the Westerlies at high latitudes often weak and irregular Prevailing Westerlies prevailing winds in the middle latitudes between 30 and 60 degrees latitude, blowing from the high pressure area in the horse latitudes towards the poles. blow from the west to the east, and steer extratropical cyclones in this general manner strongest in the winter hemisphere and times when the pressure is lower over the poles Trade Winds the prevailing pattern of easterly surface winds found in the tropics The trade winds blow predominantly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere the trade winds have been used by captains of sailing ships to cross the world's oceans for centuries Horse Latitudes Horse Latitudes or Subtropical High are subtropical latitudes between 30 and 35 degrees both north and south This region, under a ridge of high pressure called the subtropical high, is an area which receives little precipitation and has variable winds mixed with calm. The consistently warm, dry conditions of the horse latitudes also contribute to the existence of temperate deserts Doldrums a low-pressure area around the equator where the prevailing winds are calm The low pressure is caused by the heat at the equator the air rise and travel north and south high in the atmosphere The doldrums are also noted for calm periods when the winds disappear altogether, trapping sail-powered boats for periods of days or weeks