Transcript Meteorology
Meteorology Everyday Weather Atmospheric Structure • The atmosphere is made up of four layers: – – – – The Troposphere The Stratosphere The Mesosphere The Thermosphere • As altitude goes up, air pressure goes down The Troposphere • Where most weather occurs (clouds, wind, precipitation, etc.) • Extends to 10 km above the earth’s surface • Temperature decreases as altitude increases The Stratosphere • Contains almost all of the ozone (O3) in the atmosphere • Extends to 50 km above the earth’s surface • Temperature increases as altitude increases The Mesosphere • Pressure varies from .01 mb to 1 mb (very low pressure) • Extends to 80 km above the earth’s surface • Temperature decreases as altitude increases The Thermosphere • Thermosphere is the beginning of the end of the atmosphere, right before you reach the Exosphere, or outer space • Extends to over 300 km above the earth’s surface • Temperature increases as altitude increases, but the molecules are so spread out that it doesn’t “feel” warm Atmospheric Composition • The Atmosphere is composed of two major elements: – Nitrogen (78%) – Oxygen (21%) • And of many other trace elements including Helium, Hydrogen, Carbon Dioxide, and others Air Masses • Four types of air masses: – – – – • • • • • cP Continental Polar cT Continental Tropical mP Maritime Polar mT Maritime Tropical Maritime – over water Continental – over land Polar – colder Tropical – warmer Fronts form when different air masses meet • All individual air masses have constant temperature and moisture levels Fronts • A front is a meeting point of two different air masses • Four types of Fronts – – – – Warm Front Cold Front Stationary Front Occluded Front • Fronts revolve around low pressure systems Warm Fronts • Warm air mass pushes and rises over cold air mass • Move slower than cold fronts • Warm fronts cause light rain that may last for a few days • Clouds form on top of cold air mass • Represented on weather map by red line with semi-circles Cold Fronts • Cold air mass pushes warm air up • Moves faster than a warm front • Cold fronts cause short, intense precipitation • Clouds form on top of cold air mass • Represented on weather map by a blue line with triangles pointing in direction of movement Stationary Fronts • Created when a cold front meets a warm front • Unmoving front (stationary) • Altocumulus clouds form • Shown on a weather map by a warm front on one side and a cold front on the other Occluded Fronts • Cold front and warm front around low pressure system • Cold front (faster) catches up with warm front • Occluded front is warm front merged with cold front • Represented on map by triangles and semicircles pointing in same direction Air Pressure • Air pressure is how much the air above a certain point weighs • Air weighs 14.7 pounds on every square inch of earth at sea level • Measured in inches of mercury and milibars • High and low pressure zones marked on map by H and L • Air flows from high pressure to low pressure Isobars • Isobars show lines of pressure in milibars • Lines drawn in increments of four mb (960,964,968,972,etc) • Sea level air pressure is 1013.25 mb or 29.921 inches of mercury Wind • Wind is caused by differences in pressure • Air flows from high pressure to low pressure • Higher pressure is usually associated with better weather • Lower pressure equals stormier weather Temperature • Measured in degrees Fahrenheit, Celsius, and Kelvin • Water boils at 100° Celsius, 212° Fahrenheit • 0 degrees Kelvin is Absolute Zero, where there is no movement in molecules • C = 5/9*(F-32) • F = (9/5*C)+32 • K = C+273 Isotherms • Isotherms show lines of temperature • Lines drawn in increments of 10° Fahrenheit (20,30,40,50,etc.) Water • Water comes in three states: solid (ice), liquid (water), and gas (water vapor) • The amount of water in a given amount of air is the “moisture content” • Air masses with a higher moisture content are lighter than those with lower moisture contents Clouds Cumulus • Puffy, cotton ball cloud • Associated with fair weather, but can develop into Cumulonimbus, clouds that cause storms Stratus • Low, gray blanket • Cause light to moderate precipitation Stratocumulus • Lumpy, low clouds • Can cause light precipitation Nimbostratus • Dark, low-level clouds • Light to moderate precipitation Cumulonimbus • Dark, tall clouds • Have an “anvil top” from spreading out too much vertically •Cause severe thunderstorms Cirrus • Thin, wispy clouds • Generally come with fair weather Heat Transfer • 3 types of heat transfer: – Conduction – Convection – Radiation Conduction • Conduction is the transfer of heat by direct contact • For example, if you are boiling water with a metal spoon in the pot, the heat from the water will transfer into the spoon Convection • Convection is a type of heat transfer which only occurs in fluids (water, air, etc.) • Hot fluid at the bottom of the “pan” rises (hot air balloon) and cold fluid from the outer top layer rushes to fill its place, warming the cold fluid and cooling the hot fluid Radiation • Radiation is the transfer of heat through the air • For example, roasting marshmallows uses radiation to heat up the marshmallow Insolation • Insolation is incoming solar radiation • Solar rays that come in at an angle are weaker than direct rays • Some of it is reflected off of clouds, particles, water, etc. • This reflected energy is called albedo Albedo • Amount of Insolation which reflects off of a surface • For example, deep snow reflects about 90% of Insolation. • This number expressed as a fraction is the Albedo (9/10) Atmospheric Circulation Intertropical Convergence Zone (ITCZ) • Where tropical easterlies from the Subtropical high zones meet The Jet Stream • The Jet Stream is a large belt of high altitude winds • Airplanes fly along the jet stream to gain a boost in speed and save gasoline • North of the jet stream is a cold air mass and south of the jet stream is a warm air mass Sea Breezes • A sea breeze occurs during the summer, when the land is warmer than the water. This is due to the fact that water heats and cools much more slowly than land Land Breeze • A land breeze occurs in the winter, when the land is cooler than the water. • A way to remember the difference between the breezes is that a land breeze blows out from the land, opposite of a sea breeze The Coriolis Effect • The Coriolis effect is a force which changes direction of winds and objects due to the earth’s rotation •Causes all winds in Northern Hemisphere to turn right, and all winds in Southern Hemisphere to turn left Planetary Wind Belts • The wind belts are a series of high and low pressure zones which result in major wind groups (recall that air flows from high to low pressure) • They include: – Subtropical high at 30° – Subpolar low at 60° – Intertropical convergence zone 3 Cell Model of Circulation 3 Cell Model of Circulation (cont.) • The three cell model of circulation is based on the planetary wind belts and the Coriolis effect. • It is based on three cells: – The Polar Cell – The Ferrel Cell – The Hadley Cell Atmospheric Phenomena Sundogs, Rainbows, Aurora, Virga, etc. Sundogs • Two halos on either side of the sun • Light is reflected from the sun off of ice crystals in cirrus or cirrostratus clouds Rainbows • Bet you’ve seen this before… • Rainbows are caused by light from the sun refracting through water in the air, and splitting the light into all of the different colors in the visible spectrum Aurora • The earth’s magnetic field (right) is pushed by the magnetic field from the sun (solar wind, bottom). This action causes the moving electrons within the earth’s field to collide with gas molecules, which give off light in an aurora (top) Virga • A virga is a form of precipitation that doesn’t reach the ground. The precipitation evaporates somewhere between the clouds and the Earth.