Meteorology 110 Fall 2015 Weather is always front-page news. Why should you study the weather? Superstorm Sandy flooding Rockaway, Long Island, Oct, 2012 Exceptional drought in Nevada and California. CLIMATE REPORT NATIONAL WEATHER SERVICE NEW YORK NY...THE ISLIP NY CLIMATE SUMMARY FOR AUGUST PRECIPITATION: Yesterday: 13.51 OLD RECORD (YEAR): 0.91 (2013) All the severe thunderstorms in the U.S. in 2014 We had 1057 tornadoes (red), 5537 large hail events (green), and cases of severe straight-line winds (blue). Here are the 1057 tornadoes, every one of them. The U.S. gets more tornadoes than anyplace else on the planet. Still, 2014 was just an average year. On the other hand, 2011 set all kinds of records, including the single-day greatest tornado outbreak, April 27 with 292 tornadoes. But does the weather really affect you? We need to study how the weather works because it affects everybody. We start with the basics. Be patient. We will eventually get to the precision-guided ball lightning (or its real equivalent). See how thin the Atmosphere really is? The density of gases decreases rapidly with height. The atmosphere just peters out as you get higher. Even in outer space, there are a few gas molecules. 95% of the atmosphere is found around 12 miles and below. That is called the troposphere. The Earth is around 8000 miles in diameter (its not a perfect sphere) so how thin is the troposphere where we live? Photographs from spacecraft show the troposphere is a very thin layer. 99% of the air is Nitrogen and Oxygen. All other gases fit into the last 1% and most of that is Argon, an inert gas. You dont need to memorize these numbers but you must know the most abundant gases (N 2 and O 2 ) How did the Atmosphere get to its modern composition? Our original atmosphere was mostly Hydrogen and Helium, the most abundant elements in the universe. Planets with strong gravity (like Jupiter and Saturn) keep their original atmospheres. Earth did not. Replacing the ancient atmosphere with an Oxygen-Nitrogen one Cyanobacteria Stromatolites Cyanobacteria were the first to perform photosynthesis, taking in CO 2 and releasing O 2. They can be found in communities called Stromatolites. Around 2 million years ago, they drove up the Oxygen content of the atmosphere, making it possible for complex plants to develop. Source: High Oxygen levels allow bugs to become much larger than today. Lets talk about the sun The Earth gets almost all its energy from the sun as we go around once per year (here the orbit is viewed almost side-on) This figure and those from the next two slides are from The suns rays spread out in all directions, so the farther away you are, the less energy is actually received. In fact, the sun is so far away (average of 93,000,000 miles), that the rays reach us essentially parallel to each other. It looks like this: Incoming solar radiation is called insolation. When the sun angle changes, so does the insolation. Do you see why? Of course its the Earth that revolves around the sun, not the other way around. In lab this week, well study this. Next: How do we measure the properties of the atmosphere? We measure the weight of the gases with barometers. Torricellis barometer design is still used today. We have one in the Meteorology lab. Once Torricelli began measuring air pressure, he noticed that when it changed, so did the weather. Measuring the properties of atmospheric gases: What changes air pressure? a. Fewer gas molecules (lower density) hitting each other = lower pressure b. More gas molecules (higher density) hitting each other = higher pressure c. More energetic gas molecules (higher temperature) hitting each other = higher pressure This is the gas law: Pressure changes with density and temperature Rather than inches of mercury, meteorologists measure pressure in millibars (mb). In this course, we will also do that. The standard unit is actually hectopascals. 1 hPa = 1 mb. Typically sea-level pressure is around 1000 mb which is rather convenient. While we are familiar with the Fahrenheit scale, the rest of the world uses Celsius (also known as Centigrade). The Kelvin scale is used by scientists. We need to know how to convert from Fahrenheit to Celsius and Kelvin temperatures. Well practice it in lab 3. This is one of Anders Celsius original thermometers. The way temperature changes with height is called a lapse rate. The sign (+/-) of the lapse rate separates the atmosphere into layers to which we give names. We live in the troposphere where the temperature decreases with height. The top of the troposphere is the tropopause, a very important level. Above that is the stratosphere. If air rises, the pressure on it goes down. If it sinks, the pressure goes up. Thats independent of the ambient lapse rate and not caused by heat gain or loss. The word for that is ADIABATIC. Divide the atmospheric into pieces, called air parcels. An air parcel is a small, representative sample of air. They are usually considered to be around 1 square meter or about 3 feet by 3 feet. The molecules are all moving and banging into each other. We feel that as temperature. More collisions = higher temperature. When the air parcels rise or sink, the pressure on them changes. With more molecules near the ground, the pressure is highest there. That forces the molecules in the air parcel into a smaller volume. Smaller volume means more collisions. Result? Higher temperature! The air parcel is cooler when it reaches Oneonta, about 1400 feet above sea level. Lets try another one. Colorado is bisected by the Rocky Mountains What happens to air parcels as they descend the Rockies? Where else in the U.S. could you get a Chinook-like wind? Next: Add water vapor (humidity, clouds, precipitation)