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

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 These imbalances create areas of high and low pressure. 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

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.