Ch. 11 - Atmosphere Atmosphere – 99% Nitrogen and Oxygen Fig. 11-1 (pg. 272) Water vapor and Carbon dioxide make most of the remaining gases Both are critical for regulating the amount of energy the atmosphere absorbs. Water is the only substance in the atmosphere that can be as a solid, liquid, or gas. As water changes from one state to another heat is either absorbed or released. This heat greatly affects the atmospheric motions that create weather and climate. Another component of the atmosphere is the ozone (O3). It absorbs U.V. radiation. If it didn’t absorb U.V. radiation our skin wouldn’t be able to take the intensity very long.

Structure of the Atmosphere Fig. 11-2 (pg. 273) Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere. Troposphere – contains most of the mass of the atmosphere. This is were weather occurs & air pollution. Decrease in temp. with altitude. Stratosphere – Ozone occurs in this layer. Increase in temp. with altitude. Mesosphere – No concentrated ozone. Thermosphere – increase in temp. with altitude. More than 1000° C. Exosphere – He & H are found in this layer. There is not clear boundary between the atmosphere and outer space.

Radiation is the transfer of electromagnetic waves through a vacuum. Shorter waves have more energy. 35% of the solar radiation coming in is reflected back to outer space by the Earth’s surface, atmosphere, or clouds. Another 15% is absorbed into the Earth’s atmosphere. This means 50% of the radiation is directly or indirectly absorbed by the Earth’s surface. Various objects reflect and absorb radiation at different rates. Dark vs. light colors Soil, water, pavement, buildings, etc. --- Lab Probes

Other types of heat transfer… Greenhouse Effect Most of the radiation travels into the atmosphere as shorter waves until it hits the Earth’s surface and if it reflects back it becomes a longer wave, which has less energy and is less likely to escape the Earth’s atmosphere. This trapped energy builds up and helps heat the Earth more evenly. Clouds, carbon dioxide, and other greenhouse gases help to trap this energy. Other types of heat transfer… Conduction – transfer of heat through solids. Convection – transfer of heat through liquids & gases.

State of the Atmosphere Differences in Heat & Temperature Temperature – the average kinetic energy of molecules. How rapidly or slowly molecules move around. Heat – the total kinetic energy of molecules. Occurs because of a difference in temperature between substances. Review the temperature scale… Kelvin, Celsius, Fahrenheit Absolute Zero Freezing Melting

Dew Point – the temperature to which air must be cooled at constant pressure to reach saturation. Condensation can only occur when the air is saturated. The dew point is often called the condensation temperature. An air mass cools off by about 10° C for every 1000 meters increase in altitude. If air continues to rise it will eventually cool to its condensation temperature. The height at which the condensation occurs is called the lifted condensation level.

How is wind created? Due to an imbalance in the density of warm and cold air. Cool air, being more dense, sinks and force warm, less dense air upward. In turn this creates an area of Low and High Pressure. Wind can be thought of as air moving from an area of High Pressure to Low Pressure. Relative Humidity – how much water vapor a volume of air is capable of holding due to temperature. Warmer air is capable of holding more water vapor. Relative humidity is expressed in %.

Moisture in the Atmosphere Weather predictions are determined by cloud type. How does a cloud form? When warm moist air rises, expands, and cools in a convection current. The air condenses around condensation nuclei Condensation nuclei are small particles in the atmosphere --- dust, sea salt, etc. Clouds form several ways. When air rises up a mountain or when air masses of different temperatures causes an up current (orographic lifting). Fig. 11-13 (pg. 286) As the warm air that rises cools, the water vapor in it condenses and forms a cloud Cloud in a bottle Demo

Air masses that resist rising are more stable. The air masses heat flow from the warmer air to the colder surface. The rate at which an air mass cools depends in part on the temp. of the surface beneath the air. If the air is cooler than the surface beneath it then the air can become unstable and produce thunderstorms. Latent heat – stored energy in water vapor. As surface water evaporates energy is transferred into the water vapor and the energy is released as heat only when the water vapor condenses. The amount of latent heat can intensify a weather system.

Types of Clouds As a mass of rising air reaches its lifted condensation level (LCL), water vapor condenses into droplets of water or ice. If the density of the droplets is high enough then a cloud forms. This occurs at various altitudes. Low clouds  Strato – below 2000m Middle clouds  Alto – 2000 to 6000m High clouds  Cirro – above 6000m Table 11-3 (pg. 287)

Cloud Shape Cirrus – wispy, stringy clouds. Cumulus – puffy, lumpy-looking clouds. Stratus – layers or featureless sheets of clouds. Nimbus – low, gray rain clouds. Cumulonimbus clouds – strong rains, winds, and characteristic of thunderstorms. They start as cumulus clouds and if the cloud continues to be warmer than the surrounding air it will grow as the water vapor condenses and the air receives additional warmth from the release of latent heat. An anvil shape is produced as the cloud forms in higher altitudes and ice crystals develop and high wind spread the cloud into this shape. Fig. 11-15.

Precipitation – rain, snow, sleet, and hail. Coalescence – the process in which cloud droplets collide and join together to form larger droplets. The droplets eventually become to heavy and fall as precipitation. Precipitation – rain, snow, sleet, and hail. If a convective current holds the moisture aloft (with up and down movement), then ice pellets and sleet forms. If these convective current are high enough and large enough, then hail forms.