Transcript Meteorology
Meteorology I. Air Masses Air Mass: a large body of air with uniform temperature and moisture content. A. Types of Air Masses Air masses are classified according to their source regions: 1. 2. 3. 4. Polar = P = cold Tropical = T = warm Maritime (ocean) = m = moist Continental (land) = c = dry B. North American Air Masses 1. Polar cP Canadian: Northern US mP Pacific: cool water off Alaska mP Atlantic: Greenland and Iceland 2. Tropical cT: Mexico, summer only mT: Gulf Coast and Atlantic mT Pacific: heavy rain in the winter Air Mass Characteristics II. Fronts Front: boundary between air masses of different densities. Types of Fronts A. Types of Fronts 1. Cold Front: when a cold air mass overtakes a warm air mass. Cold front storms are fastmoving, short-lived and often violent. What cloud type do you get with a cold front? Squall Line: long line of thunderstorms ahead of a cold front Thunderstorm .... Ocracoke NC – Summer 2013 2. Warm Front: warm air mass overtakes a cold air mass Warm fronts usually produce nimbostratus clouds What will the weather be like? Precipitation over a very large area. 3. Stationary Front: two air masses meet and the front moves parallel Neither air mass is displaced Little movement Precipitation continues for long period of time 4. Occluded Front: fast-moving cold front lifts warm air completely off the ground. Occluded Front: B. Hurricanes severe storms that form over WARM tropical oceans tropical cyclones LOW pressure centers winds spiral rapidly inward counterclockwise rotation winds over 120 km/hr (75 mi/hr) warm, moist air rises rapidly as it condenses it releases latent heat this increases the rate of evaporation and sustains the storm Saffir-Simpson Hurricane Scale used to classify hurricanes divides hurricanes into five categories based on intensities of sustained winds Storm surge is the most dangerous aspect of a hurricane. Typical beach along the coast Sea walls are built to minimize damage Category 1: Minimal storm Winds: 74 to 95 mph Storm surge: Up to 5 feet Category 2: Moderate storm Winds: 96 to 110 mph Storm surge: 6 to 8 feet Category 3: Extensive storm Winds: 111 to 130 mph Storm surge: 9 to 12 feet Category 4: Extreme storm Winds: 131 to 155 mph Storm surge: 13 to 18 feet Category 5: Catastrophic storm Winds: More than 155 mph Storm surge: More than 18 feet 2005 Hurricane Season First year with 28 named storms First year with 15 Hurricanes First year with four category 5 hurricanes First year with four major hurricanes hitting the U.S. C. Tornadoes Smallest most violent shortlived storms Form when thunderstorms meet high altitude winds Tornado Formation Narrow, violent funnel-shaped cyclone; a column of spiral winds that extends downward from a cloud base toward Earth Fujita Scale of Tornado Intensity Before thunderstorms develop, a change in wind direction and an increase in wind speed with increasing height creates an invisible, horizontal spinning effect in the lower atmosphere. Rising air within the thunderstorm updraft tilts the rotating air from horizontal to vertical. An area of rotation, 2-6 miles wide, now extends through much of the storm; Most strong and violent tornadoes form within this area of strong rotation. III. Weather Instruments A. Measuring Air Temperature: thermometer B. Measuring Wind Speed and Direction: anemometer: measures wind speed. wind vane: shows wind direction – The arrow always points into the wind! C. Radar: can detect weather conditions by sending and receiving radio waves. IV. Forecasting the Weather Station Model: cluster of weather symbols plotted around a reporting station showing the current conditions. Wind patterns around areas of HIGH and LOW pressure: