Chapter 11 – Water in the Atmosphere
- What is humidity?
Humidity is the amount of water vapor present in the air. It plays a key role in cloud formation, precipitation, and human comfort. It varies with temperature and location. - What is absolute humidity?
Absolute humidity is the actual amount of water vapor present in a unit volume of air, expressed in grams per cubic meter (g/m³). It changes with temperature and altitude. - What is specific humidity?
Specific humidity is the weight of water vapor per unit weight of air (including vapor), usually expressed in grams per kilogram (g/kg). It remains constant unless water vapor changes. - What is relative humidity?
Relative humidity is the ratio (in percentage) of the actual water vapor in air to the maximum it can hold at that temperature. It determines dew and precipitation chances. - How does temperature affect relative humidity?
As temperature increases, the air can hold more water vapor, lowering relative humidity if moisture remains constant. Cooler temperatures increase relative humidity. - What is dew point?
The dew point is the temperature at which air becomes saturated with moisture and dew begins to form. It’s a measure of atmospheric moisture. - What is condensation?
Condensation is the process by which water vapor turns into liquid water when air cools to its dew point, forming clouds, fog, dew, or frost. - What are the conditions for condensation?
Air must cool to dew point and have condensation nuclei (like dust or smoke) for water vapor to condense into droplets or ice crystals. - What is sublimation?
Sublimation is the direct change of state from solid (ice) to vapor or vice versa, bypassing the liquid state. Snow and ice can sublimate in dry air. - What are condensation nuclei?
Tiny particles like dust, salt, or smoke that provide a surface for water vapor to condense upon during cloud formation. - What are clouds?
Clouds are visible masses of tiny water droplets or ice crystals suspended in the atmosphere, formed by condensation of water vapor around nuclei. - What are the major cloud types?
Clouds are classified into cirrus, cumulus, stratus, and nimbus based on height and appearance. Each type indicates different weather conditions. - What are cirrus clouds?
High-altitude, wispy clouds composed of ice crystals. They usually indicate fair weather but may signal a change in weather conditions. - What are cumulus clouds?
Fluffy, white clouds with flat bases that form due to convection. They usually bring fair weather but can develop into thunderstorms. - What are stratus clouds?
Layered, gray clouds covering the sky like a blanket. They bring light rain or drizzle and form in stable air conditions. - What are nimbus clouds?
Nimbus refers to rain-bearing clouds. Cumulonimbus and nimbostratus are major types that result in heavy rainfall or storms. - What is fog?
Fog is a cloud at ground level formed when air near the surface cools and reaches saturation. It reduces visibility and can be hazardous. - What is dew?
Dew is moisture condensed from the atmosphere onto cool surfaces like grass or leaves during calm, clear nights when ground temperature drops below dew point. - What is frost?
Frost forms when dew point is below freezing, causing water vapor to change directly into ice crystals on surfaces. - What is precipitation?
Precipitation is any form of water falling from the atmosphere to Earth’s surface, including rain, snow, sleet, and hail, depending on temperature and air conditions. - What is rainfall?
Rainfall is liquid precipitation. It occurs when condensed water droplets grow large enough to overcome updrafts and fall due to gravity. - What is snow?
Snow forms when temperatures are below freezing and water vapor condenses directly into ice crystals, forming snowflakes that fall to the ground. - What is sleet?
Sleet is a form of precipitation where rain passes through a layer of cold air and freezes into small ice pellets before reaching the ground. - What is hail?
Hail forms in strong thunderstorm clouds where raindrops are lifted by updrafts and freeze. They grow larger with repeated freezing cycles before falling. - What is the water cycle?
The continuous movement of water between the atmosphere, land, and oceans through evaporation, condensation, precipitation, and runoff. It maintains Earth’s water balance. - How does wind affect humidity?
Wind can increase evaporation, reducing relative humidity. It also mixes air, distributing moisture and influencing cloud formation and precipitation patterns. - What are the types of rainfall?
There are three types: convectional (from rising warm air), orographic (due to air rising over mountains), and cyclonic (from meeting of air masses). - What is orographic rainfall?
When moist air ascends a mountain, it cools and condenses, causing rainfall on the windward side. The leeward side remains dry (rain shadow). - What is convectional rainfall?
It occurs when surface heating causes air to rise, cool, and condense into cumulonimbus clouds, leading to afternoon showers, common in tropical regions. - What is cyclonic rainfall?
Rainfall associated with cyclones or fronts where warm, moist air rises over cooler air, leading to cloud formation and steady precipitation over large areas.