A Major Component of Earth’s Weather

The Hydrologic Cycle Water can exist as a solid, liquid, or gas on Earth. The movement of water from different reservoirs on Earth (ex. atmosphere, ocean, rivers, and lakes) is known as the Water Cycle.

Movement of Energy Gases are warmer than solids Gas molecules have more energy than solid molecules. Evaporating water absorbs energy from the environment. (making it cooler) Condensing water releases heat to the environment. (Latent Heat)

The Atmosphere as a Solvent Once water evaporates, it dissolves in the atmosphere the same way sugar dissolves in coffee. If the atmosphere has too much water, it will condense and precipitate out. Sugar in coffee will precipitate out if the coffee cools down.

Humidity Humidity measures the amount of water vapor in the air. Relative Humidity - percentage of water in the air to how much it can hold (based on temperature). Absolute Humidity – mass of water vapor `per kg dry air

Saturated and Unsaturated Air The atmosphere is said to be saturated when it holds all the water vapor it can hold. Warm air can hold more water vapor than cold air. Within clouds, fog, and areas of precipitation, the atmosphere is saturated.

Dew Point Dew Point - temperature air must be lowered for saturation to occur. Air is saturated if dew point = temperature.

Calculating Relative Humidity

Measuring Relative Humidity Wet-Bulb temperature – temperature evaporation cools a thermometer. Dry air evaporates more water, lower web-bulb temperature. Wet Bulb Depression – Difference between Air temperature and wet bulb temperature, used to measure dew point.

What are Clouds? Clouds are droplets of water/ice crystals suspended in the atmosphere. Fog – Cloud at the Earth’s surface

How Clouds Form Need to lift evaporated water up into the atmosphere Heating of Earth’s surface, lowers density of air. Fronts Prevailing Winds off an ocean blowing into mountains.

How Clouds Form Condensation Nuclei – A microscopic particle suspended in the atmosphere that water can condense upon. Examples: - Sand grains - Salt from ocean spray - Dust/Pollen - Pollution Clouds form when water vapor condenses upon condensation nuclei.

Lapse Rates Air cools as it rises into the troposphere because pressure decreases. Dry air cools faster than moist air because latent heat released from condensation. The rate air cools when raised into the atmosphere is called a lapse rate.

Adiabatic Lapse Rates Adiabatic – heating or cooling of a gas due to pressure changes DALR - Dry adiabatic lapse rate = 5.5 о F / 1000 feet WALR – Wet adiabatic lapse rate = 3.3 о F / 1000 feet Dew Point Lapse Rate = 1 о F / 1000 feet

Atmospheric Stability Warm air rises because it is less dense than cold air. If the dew point is less than the air temperature, air rises at the DALR. When the dew point = air temperature, air rises at the SALR. The height where saturation occurs is called the Lifted Condensation Level (LCL)

Atmospheric Stability (cont’d) If a lifted parcel adiabatically cools and is warmer than the ELR, than air is said to be unstable. Unstable air is warmer than the environment, so it will continue to rise. If a lifted parcel adiabatically cools and is colder than the environment, then it is stable. Stable air is colder than the environment and sinks back to lower levels because its more dense.

Stability Which atmosphere is stable, warm air above cold air or cold air above warm air?

Temperature Inversion When warm air sits on top of cold air. When this happens, any air that rises will immediately sink because it will be colder than its environment. Traps air pollution and cause serious air quality issues. The stratosphere is a temperature inversion.

Orographic Lifting Prevailing Winds off oceans run into mountains and is force upwards. The side facing the ocean (called windward) has lots of precipitation. The leeward side (facing away from ocean) is dry and usually a desert.