Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
5/6/2015 1 2 Three Types of Precipitation Relief or Orographic Precipitation • There are three reasons why air is forced upward also forming three types of precipitation. • • Relief Precipitation- caused by winds carrying air up over a mountain barrier. 3 4 Convectional Precipitation • Convectional precipitation results from the heating of the earth's surface. The warm ground heats the air over it. As the air warms, the air molecules begin to move further apart. • With increased distance between molecules, the molecules are less densely packed. Thus, the air becomes “lighter” and rises rapidly into the atmosphere. • As the air rises, it cools. Water vapor in the air condenses into clouds and precipitation. This type of precipitation is common in the Prairies and Ontario 5 6 Frontal Precipitation • When masses of air with different density (moisture and temperature characteristics) meet, warmer air overrides colder air. The warmer air is forced to rise and if conditions are right becomes saturated, causing precipitation. In turn, precipitation can enhance the temperature and moisture contrast along a frontal boundary. 7 • Fronts cause sudden changes in general temperature, and in the humidity and pressure in the air. Warm fronts occur where the warm air scours out a previously lodged cold air mass. The warm air 'overrides' the cooler air and moves upward. Warm fronts are followed by extended periods of light rain and drizzle, because, after the warm air rises above the cooler air (which sinks to the ground), it gradually cools due to the air's expansion while being lifted, which forms clouds and leads to precipitation. 8 9 10 11 12 Hail Hail is formed when updrafts carry raindrops upwards into extremely cold areas of the atmosphere Hail There the raindrops merge and freeze. When the frozen clumps get to heavy they fall to earth Hail Hail can vary in size, from the size of a small stone to that of a baseball! So be careful 13 14 15 • • Symbols on a Weather Map 16 17 18 19 20 21 22 23 1 5/6/2015 16 17 18 19 20 21 22 23 24 25 26 Weather Disturbances Tropical Storms and Hurricanes Introduction Hurricanes are responsible for astonishing amounts of property damage and loss of life in many regions of the world 27 Hurricanes around the globe • Atlantic - hurricanes • Western Pacific – typhoons – highest frequency region • Indian Ocean and Australia – cyclones • South Atlantic - almost none 28 29 The tropical setting where tropical storms usually form • Subsidence (trade wind) inversion on the east side of the subtropical highs traps cooler, moist air (marine layer) at the ocean surface • On the western sides of the ocean basins, the marine layer tends to be warmer and thicker due to higher ocean temperatures -- more hurricanes tend to develop here 30 Hurricane characteristics • Sustained winds greater than 120 km/hr (74 mph) • Average diameter = 600 km (350 mi) • Central pressure = ~ 950 mb to 870 mb 31 32 33 34 35 Hurricane Formation Steps in the formation of hurricanes • Tropical disturbance associated with an easterly wave in the upper air winds • Tropical depression -- at least one closed isobar • Tropical storm -- winds greater than 37 mph • Hurricane (typhoon, cyclone) -- winds greater than 74 mph 36 37 Conditions Necessary for Hurricane Formation • Warm ocean water (> 27oC (81oF)) • Latent heat release • Most frequent in late summer and early autumn • Formation equator ward of 5o • Unstable atmosphere without vertical shear 38 39 2 5/6/2015 • Unstable atmosphere without vertical shear • Once formed – self-propagating system until it runs out of warm water 38 39 Hurricane Destruction and Fatalities are caused by several factors: Wind Heavy rain Tornadoes • Right front quadrant Storm surge • Rise in water level associated with pressure drop 40 41 43 Thunder and Lighting Storms Lighting 44 Tornados 42 3