ATMOSPHERE MOISTURE IN THE ATMOSPHERE MOISTURE IN THE

ATMOSPHERE MOISTURE IN THE ATMOSPHERE

MOISTURE IN THE ATMOSPHERE • Humidity vs. Relative Humidity – Atmosphere contains water vapor – Humidity: amount of water vapor in the air • Humidity is to blame for that muggy, steam-room feeling you experience on certain summer days

MOISTURE IN THE ATMOSPHERE • Humidity vs. Relative Humidity – Relative Humidity: the ratio of water vapor in a volume of air relative to how much water vapor that volume of air is capable of holding. • • • Expressed as a percentage (%) Warm air can hold more moisture than cool air A reading of 100% means that the air is totally saturated with water vapor and cannot hold any more, creating the possibility of rain.

MOISTURE IN THE ATMOSPHERE • Cloud Formation: – Clouds form when warm, moist air rises, expands, and cools in convection current – When millions of droplets of water collect, a cloud forms

MOISTURE IN THE ATMOSPHERE • Cloud formation: – Orographic lifting: • Wind encounters a mountain and has no place to go but up • This rising causes the air to expand cool creating a cloud • Also, if a warm mass of air collides with a cooler mass of air, the warm air is forced above the cool air creating clouds

MOISTURE IN THE ATMOSPHERE • Types of Clouds: • Background: • • • Air rises Water Vapor condenses into droplets of liquid water If density great enough, droplets become visible • Classification: • • • Grouped by altitude of formation and shape Low clouds (STRATO) = below 2000 m Middle clouds (ALTO) = between 2000 m and 6000 m • High clouds (CIRRO) = above 6000 m

MOISTURE IN THE ATMOSPHERE • Types of Clouds: • Low Clouds (STRATO): • Radiation causes surface to become warmer than surrounding air • Temperature rises = air expands • Air rises and begins to cool • Water vapor condenses into water droplets creating a visible cloud

MOISTURE IN THE ATMOSPHERE • Types of Clouds: • Low Clouds (STRATO): • Cumulus cloud: if air does not stay warmer than surrounding air, cumulus cloud forms • • • Flat cloud and spread horizontally Puffy, lumpy looking clouds “Cumulus” = Pile or heap

MOISTURE IN THE ATMOSPHERE • Types of Clouds: • Low Clouds (STRATO): • Nimbus cloud: • Low, gray rain clouds • “Nimbus” = cloud

MOISTURE IN THE ATMOSPHERE • Types of Clouds: • Low Clouds (STRATO): • Stratus: if fog lifts away from Earth’s surface, stratus clouds form • Forms at heights below 2000 m • Layered cloud that covers much or all of sky in given area • Featureless sheets of clouds • “Stratus” = layer

MOISTURE IN THE ATMOSPHERE • Types of Clouds: • Middle Clouds (ALTO): • Either altocumulus or altostratus • Forms between 2000 m and 6000 m • Can be mixture of liquid and ice crystals • Usually layered • Altocumulus resemble white fish scales • Altostratus are dark but thin veils of clouds • Can produce mild precipitation

MOISTURE IN THE ATMOSPHERE • Types of Clouds: • High Clouds (CIRRO): • • Form above heights of 6000 m Made up of ice crystals due to low temperatures • Cirrus clouds: appear wispy and stringy • “Cirrus” = hair • Cirrostratus: forms as a continuous layer that sometimes covers sky • Can vary in thickness from being almost transparent to being able to block out Sun or Moon

MOISTURE IN THE ATMOSPHERE • Types of Clouds: • Vertical Development Clouds: • If air that makes up cumulus cloud is unstable, cloud will be warmer than surface or surrounding air and will grow • As it rises, water vapor condenses • Air receives additional warmth • Cumulonimbus = anvil shaped • Produces torrential rains and strong winds • Associated with thunderstorms

MOISTURE IN THE ATMOSPHERE • Precipitation: • Cloud droplets collide and join together • Coalescence: the process in which a larger droplet forms from collision of cloud droplets • If droplet becomes too heavy to be held in the air, gravity pulls the droplet down as precipitation. • Precipitation: all forms of water both liquid and solid that fall from clouds

MOISTURE IN THE ATMOSPHERE • How do we get snow? • If precipitation forms at cold temperatures, it takes the form of snow • How do we get hailstone or sleet? • Convective currents carry droplets up and down through freezing and nonfreezing air