Transcript Weather 2
TOPIC 7 What is wind? Wind is horizontal movement of air parallel to the earth’s surface. Wind requires a magnitude and direction. Wind is named based upon the direction in which it came from or is blowing from. What causes wind? Wind is caused by differences in air pressure. The air will move from areas for higher pressure to areas of lower pressure. The difference in air pressure for a specific distance is called the air pressure gradient. How can air pressure gradient be determined on a map? The closer together the isobars are, the greater the air pressure and the faster the wind speed. How is wind created in locations near water? • Land & Sea breezes – Land breeze • At night, the water cools off slower, resulting in a warmer less dense-low air pressure that rises. Over the land a cooler, denser high air pressure forms. Air moves from high to low pressure. How is wind created in locations near water? continued - Sea Breeze • During the day, land heats up faster creating a low pressure over the land. The water will heat up slower creating a high over the water. The air will move from the high (water) to the low (land). How is wind speed measured? Wind is measured with an instrument called an anemometer. The units for wind speed are miles per hour (mph) or nautical miles per hour (knots) How can wind directions be determined? • Wind direction can be determined by – Air (wind) moves from areas of high pressure to areas of low pressure – Winds are also deflected to the right in the N. hemisphere and to the left in the S. hemisphere (Coriolis Effect) – Wind is named for the direction from which it came. – A wind vane of weather vane shows the wind direction What are jet streams? • Jet streams are parts of convection cells, that are bands of easterly moving air at the top of troposphere – They can blow 200 mph or more – They have an influence over weather pattern movement – You can see the locations on a planetary wind & moisture belts (ESRT pg. 14) What are planetary wind and pressure belts? Planetary wind and pressure belts are general areas or belts in which winds move in a specific direction most of the time – thus they are called prevailing winds. Can the wind and pressure belts shift? Yes, there are seasonal shifts in the wind and pressure belts. The wind belts generally follow the North & South shifts of direct (vertical) rays. What kind of weather changes are associated with seasonal shifts of wind and pressure belts? • Weather changes associated with seasonal shifts are – In the N. hemisphere, during the winter the directs rays shift southward allowing the northerly prevailing winds from Canada to creep down. This gives parts of the U.S colder weather. – In S.E Asia & India, the shifting causes extreme changes called monsoons. • In the summer, winds belts shift northward and cause winds to bring high amounts of rain • In the winter, wind belts shift southward and winds bring dry air from central Asia.