Transcript Slide 1
What is meteorology?? (and why should you care?) meteorology—The study of the physics, chemistry, and dynamics of the earth's atmosphere. The American Meteorological Society defines a meteorologist as a person with specialized education "who uses scientific principles to explain, understand, observe, or forecast the earth's atmospheric phenomena and/or how the atmosphere affects the earth and life on the planet." What do we mean by “severe and unusual” weather extremes? Severe weather not only includes things like heavy thunderstorms, lightning, hail, flash floods, and tornadoes. . . . . . but all kinds of hazardous weather In addition to the day to day weather, some meteorologists study longer-term events like El Niño, the ozone hole, acid rain, and global warming Some meteorologists study how dust from Africa can be deposited in Florida, or how changes on the Sun affect our atmosphere. Meteorologists study how destruction of rain forests or eruptions of volcanoes can change the composition of our atmosphere. Europe’s main threats: flooding and heat Extreme weather events are very costly. And have been increasing recently. The first thing we need to know is what the atmosphere is made of Percent composition of dry atmosphere, by volume ppmv: parts per million by volume Gas Volume Nitrogen (N2) 78.084% Oxygen (O2) 20.946% Argon (Ar) 0.9340% Carbon dioxide (CO2) 365 ppmv In other words, more than 98% of the atmosphere is nitrogen and oxygen **Water vapor, not displayed in this dry atmosphere chart, can occupy anywhere from 0 – 4 % volume, making it the most variable atmospheric constituent Amount of carbon dioxide in the atmosphere has changed over time • CO2 acts as a “greenhouse” gas – As heat rises from earth surface, CO2 molecule absorbs it & prevents from escaping to space • Net result: global warming • Impt. caveat: global warming is WAY more complicated than simply looking at chg of CO2 over time – At Mauna Loa, CO2 increased in the last 40 yrs, coincident with avg. sfc. temp of earth increasing ~ 1°C * The relative composition varies from place to place on the surface of the Earth. The reason for this variation is the presence of aerosols and water vapor - both of which vary widely in amount: Aerosols: either tiny liquid droplets, such as fog, or tiny solid particles, such as ice crystals, smoke, sea salt crystals, dust, and volcanic emissions, suspended in the air. Aerosols play very important roles in cloud formation – more on that later! Next we need to know a little about the general structure of the atmosphere. Start with pressure. Consider a column of air 1 inch2 in size extending from sea level to the top of the atmosphere: The weight (=mass X gravity) of the column of air will be about 14.7 lbs Hence, the pressure at sea level is = force/area = 14.7 lbs/inch2 Sea-level pressure is also given in other units: •14.7 lbs/inch2 •1013.25 millibars •1013.25 hPa (hecto Pascals) •29.92 inches of Hg (mercury) Atmospheric pressure decreases exponentially with height. 50% of earth’s air lies in the lowest 6 kilometers (3.7 miles) Atmosphere officially extends up over 100 miles Pressure is basically the “weight” of the air above a location – so if you’re location is sea level, you have the greatest atmospheric pressure. Pressure decreases exponentially with height (more air molecules are found in air at the surface than in the same volume of air aloft) Short clip about meteorologists, weather men, hurricanes, and climate change Atmosphere divided into different levels Meteorologists concern ourselves with the TROPOSPHERE Why?? Definition: TEMPERATURE INVERSION – a layer of the atmosphere where the temperature increases with height Rule of thumb: the word “pause” indicates the top of a layer. Ozone is concentrated in the stratosphere At the top of the troposphere is the tropopause, which marks the beginning of the temp. inversion of the stratosphere Thus the tropopause acts as a good level for the top of buoyant clouds Note that thunderstorm clouds are tallest in the tropics Interesting electromagnetic property of the atmosphere: at night ionosphere has different properties than during the day. Thus, short-wave radio waves (the “AM” frequency) can be reflected and travel long distances – from America to Europe We need to keep in mind a few simple rules: 1.Warm air is less dense (“lighter”) than cold air 2.Humid air is less dense than dry air 3.Less dense air can be forced up over denser air 4.As air is forced upward, it cools and can form clouds and precipitation (if there is enough water vapor) 5.The type of precipitation that falls will depend on the temperature of the air and the ground In addition to forecasting the daily weather, some meteorologists study severe weather, and try to predict where it will occur Some meteorologists also work to be able to better predict what our planet will be like in the future by studying the past OR In short, meteorologists study the Earth system in an effort to help us better understand our planet, for both the short and long time-scales. A few definitions we need to know: Temperature: measure of hotness or coolness of the air. Specifically a measure of the kinetic energy of an air molecule Pressure: the force of air above an area (remember, mass x gravity) Humidity: measure of amount of water vapor in the air