11.1 Atmospheric Basics atmosphere
Atmospheric Composition • Air made of a combination of many gases, each with its own unique characteristics.
Atmospheric Composition • When water changes from one state to another, heat is either absorbed or released which greatly affects weather and climate. • The atmosphere also contains solids in the form of tiny particles of dust, salt, and ice.
Atmospheric Composition • Ozone (O3), is a gas formed by the addition of a third oxygen atom to an oxygen molecule (O2). • Evidence indicates that the ozone layer is thinning.
Structure of the Atmosphere • The atmosphere is made up of several different layers differing in composition and temperature.
Troposphere • Layer closest to Earth’s surface, contains most of the mass of the atmosphere, including water vapor. • Most weather takes place in and air pollution. • Decrease in temperature from bottom to top. • The upper limit of the troposphere, called the tropopause, varies in height.
Stratosphere • Made up primarily of concentrated ozone. • O3 absorbs UV radiation, causing it to increase in temperature up to the stratopause.
Mesosphere and Thermosphere • Most meteors burn up in the mesosphere • The thermosphere contains only a small portion of the atmosphere’s mass.
Ionosphere and Exosphere • Made up of electrically charged particles and layers of progressively lighter gases, is part of the thermosphere. • The exosphere, the outermost layer is composed of light gases such as He and H. • There is no clear boundary between the atmosphere and space.
Energy • The Sun provides all energy in the atmosphere. • Energy is transferred to Earth and the atmosphere through radiation, conduction, and convection.
Solar Fundamentals • It’s always daylight somewhere! • While Earth is absorbs radiation, it is also continuously sends energy back into space.
Solar Radiation wavelengths (λ) • Most travels through the atmosphere at short λ, which are not easily absorbed. • Earth’s surface absorbs it and radiates energy with longer λ, warming the atmosphere through conduction and convection.
Conduction • Transfer of energy that occurs when molecules collide. • Energy transfers from particles of air near Earth’s surface to the particles of air in the lowest layer of the atmosphere. • Affects a very thin atmospheric layer near thesurface.
Convection • Transfer of energy by the flow of a heated substance. • Pockets of air near the surface are heated, become and rise. • As warm air rises, it expands and starts cools and sinks. • This is a main mechanism responsible for the vertical motions of air, which in turn cause different types of weather.
11.2 State of the Atmosphere atmosphere
Temperature Versus Heat • Temperature - the measurement of how rapidly or slowly molecules move around. • Heat - the transfer of energy that occurs because of a difference in temperature between substances
Temperature can be measured in degrees Fahrenheit (°F), in degrees Celsius (°C), or kelvins (K).
Dew Point • Temperature to which air must be cooled to reach saturation • Air holds as much water vapor as it possibly can. • Condensation cannot occur until air is saturated.
Critical Temperature Changes • The temperature of the lower atmosphere decreases with increasing distance from Earth’s surface. • If the air is able to continue rising, eventually it will cool to its condensation temperature. • The lifted condensation level, or LCL, is the height at which condensation occurs.
Air Pressure and Density • Gravity causes particles of gas to be pulled toward the center of Earth. • Air pressure increases as you near the bottom of the atmosphere.. Why do you think? • Atmospheric pressure decreases with height because there are fewer and fewer gas particles exerting pressure. • The density of air is proportional to the number of particles of air occupying a particular space.
Pressure-Temperature-Density Relationship • Temperature, pressure, and density are related. • In the atmosphere, temperature is directly proportional to pressure. • The relationship between temperature and density is inversely proportional.
Temperature Inversion • An increase in temperature with height in an atmospheric layer. • Lower layers cooler than layers above • Can act like a lid trapping pollution. • Can have a profound effect on weather conditions.
Wind • Air moves in response to density imbalances created by the unequal heating and cooling of Earth’s surface. • These imbalances create areas of high and low pressure. • Wind = air moving from areas of high to low pressure. • Wind speed increases with height because there is less friction.
Humidity • Amount of water vapor in air. • Relative humidity is the ratio of water vapor in a volume of air compared to how much water vapor that volume of air is able to hold.
Relative Humidity • Varies with temperature • warm air can hold more moisture than cool air. • If the temperature of an air parcel increases and no additional water vapor is added • its relative humidity decreases. • If more water vapor is added to the parcel • its relative humidity increases.
11.3 Moisture in the Atmosphere atmosphere
Cloud Formation • Buoyancy is the tendency for air to rise or sink as a result of differences in density. • Clouds form when warm, moist air rises, expands, and cools in a convection current.
Orographic lifting • Occurs when wind encounters a mountain • The air has no place to go but up. • The air expands and cools resulting in cloud formation.
Cloud Formation • Air masses of different temperatures collide • What happens when warm air collides with cool? • As the warm air cools, the water vapor in it condenses and forms a cloud.
Stability • Resistance of an air mass to rising. • Cooling rate depends somewhat on surface temperature. • Air can become unstable if it is cooler than the surface beneath it. • If temperature conditions are right and the air mass rises rapidly, it can produce the type of clouds associated with thunderstorms.
Energy • As water vapor in the air condenses, heat is released. • Latent heat in water vapor that is not released until condensation occurs. • The amount of water vapor present in the atmosphere is a significant source of energy because of the latent heat it contains.
Lifted Condensation Level • When water vapor condenses in rising air. • If the density of these droplets is great enough, they become visible in the form of a cloud. • This process can take place at many different altitudes and form different cloud shapes.
Types of Clouds • The modern system groups clouds by the altitude at which they form and by their shape. • Low clouds: < 2000 m. • Rising fog, stratus and cumulus • Middle clouds: 2000 m to 6000 m • Layered, mixed ice/liquid, altocumulus and altostratus • High clouds: >6000 m • ice crystals, cirrus and cirrostratus
Clouds of Vertical Development • Under the right conditions, cumulus clouds heated by latent heat, will continue to grow and reach nearly 18,000 m. • Can form cumulonimbus clouds that are capable of producing the torrential rains and strong winds that are characteristic of thunderstorms.
Precipitation • Coalescence- cloud droplets collide and join together to form a larger droplet. • When the droplet becomes too heavy it falls to Earth as precipitation. • Rain, snow, sleet, and hail.
The Water Cycle • Only a small percentage of water is present in the atmosphere at any given time.