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Questions and Answers
What is the primary factor that determines the dew point temperature?
What is the primary factor that determines the dew point temperature?
What is a characteristic of water vapor?
What is a characteristic of water vapor?
What happens to the amount of water vapor needed for saturation when the temperature increases by 10°C?
What happens to the amount of water vapor needed for saturation when the temperature increases by 10°C?
What is unique about water?
What is unique about water?
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What is the primary mechanism that accounts for the formation of dew and some types of fog?
What is the primary mechanism that accounts for the formation of dew and some types of fog?
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What happens to the bonds between water molecules when ice melts?
What happens to the bonds between water molecules when ice melts?
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What is the purpose of a psychrometer?
What is the purpose of a psychrometer?
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What is the term for the energy involved in changing states of matter?
What is the term for the energy involved in changing states of matter?
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What is indicated by a high dew point temperature?
What is indicated by a high dew point temperature?
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What is required for the formation of dew, fog, or clouds?
What is required for the formation of dew, fog, or clouds?
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What is the approximate amount of energy required to convert 1 gram of water at 100°C into a gas?
What is the approximate amount of energy required to convert 1 gram of water at 100°C into a gas?
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What is the term for the process of converting a gas into a liquid?
What is the term for the process of converting a gas into a liquid?
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What is the primary mechanism that accounts for the formation of clouds?
What is the primary mechanism that accounts for the formation of clouds?
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What is displayed on weather maps?
What is displayed on weather maps?
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What is the term for the amount of water vapor in air?
What is the term for the amount of water vapor in air?
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What happens to the vapor pressure as water continues to evaporate?
What happens to the vapor pressure as water continues to evaporate?
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What is the range of water vapor in the atmosphere?
What is the range of water vapor in the atmosphere?
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What is an example of sublimation?
What is an example of sublimation?
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What is the term used to describe the air when the number of vapor molecules returning to the water equals the number leaving the liquid?
What is the term used to describe the air when the number of vapor molecules returning to the water equals the number leaving the liquid?
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What is the term for the conversion of a gas directly into a solid without passing through the liquid state?
What is the term for the conversion of a gas directly into a solid without passing through the liquid state?
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What happens to the water-vapor capacity when heat is applied to saturated air?
What happens to the water-vapor capacity when heat is applied to saturated air?
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What is the main drawback of using the mixing ratio method to express water vapor content?
What is the main drawback of using the mixing ratio method to express water vapor content?
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What does relative humidity indicate?
What does relative humidity indicate?
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What are the two ways in which relative humidity can change?
What are the two ways in which relative humidity can change?
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What is the main advantage of using relative humidity over mixing ratio?
What is the main advantage of using relative humidity over mixing ratio?
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Why is warm air able to hold more water vapor than cold air?
Why is warm air able to hold more water vapor than cold air?
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What is the primary process responsible for most cloud formation?
What is the primary process responsible for most cloud formation?
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What happens to the atmospheric pressure as altitude increases?
What happens to the atmospheric pressure as altitude increases?
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At what rate does unsaturated air cool for every 1,000 meters it rises?
At what rate does unsaturated air cool for every 1,000 meters it rises?
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What is the term for the rate of cooling of air when it is saturated with water vapor?
What is the term for the rate of cooling of air when it is saturated with water vapor?
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What is the term for the localized pockets of air that rise due to buoyancy?
What is the term for the localized pockets of air that rise due to buoyancy?
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What is the primary reason why air resists vertical movement?
What is the primary reason why air resists vertical movement?
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What is orographic lifting an example of?
What is orographic lifting an example of?
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What determines the stability of air?
What determines the stability of air?
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What happens to the air when it descends down the slope of the mountain after orographic lifting?
What happens to the air when it descends down the slope of the mountain after orographic lifting?
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What happens to air that is cooler than its surrounding air?
What happens to air that is cooler than its surrounding air?
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What is the environmental lapse rate in the given illustration?
What is the environmental lapse rate in the given illustration?
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What is the term for the process where warm, less dense air is forced over cooler, more dense air?
What is the term for the process where warm, less dense air is forced over cooler, more dense air?
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What type of air develops when the environmental lapse rate is less than the wet adiabatic rate?
What type of air develops when the environmental lapse rate is less than the wet adiabatic rate?
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What is the result of convergence of air flow?
What is the result of convergence of air flow?
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What commonly occurs on clear nights when radiation cooling lowers the temperature dramatically near the Earth's surface?
What commonly occurs on clear nights when radiation cooling lowers the temperature dramatically near the Earth's surface?
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What is the term for the rate of cooling of unsaturated air for every 1,000 meters it sinks?
What is the term for the rate of cooling of unsaturated air for every 1,000 meters it sinks?
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What type of air develops when the environmental lapse rate is greater than the dry adiabatic rate?
What type of air develops when the environmental lapse rate is greater than the dry adiabatic rate?
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What happens to the air at the surface if it is unsaturated and rises to 1,000 meters?
What happens to the air at the surface if it is unsaturated and rises to 1,000 meters?
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What prevents vertical mixing of the atmosphere and can trap pollutants near the Earth's surface?
What prevents vertical mixing of the atmosphere and can trap pollutants near the Earth's surface?
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What type of clouds can form when the air is considerably warmer than air aloft?
What type of clouds can form when the air is considerably warmer than air aloft?
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What is the primary reason why an average cloud droplet cannot reach the Earth's surface?
What is the primary reason why an average cloud droplet cannot reach the Earth's surface?
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What is the minimum diameter of a droplet for it to be considered rain?
What is the minimum diameter of a droplet for it to be considered rain?
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In which region do clouds contain droplets that form through the Bergeron process?
In which region do clouds contain droplets that form through the Bergeron process?
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What is the term for the fall of small particles of ice that are clear to translucent?
What is the term for the fall of small particles of ice that are clear to translucent?
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What is the definition of clouds?
What is the definition of clouds?
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What is the purpose of a rain gauge?
What is the purpose of a rain gauge?
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What is the ratio of snow to water equivalent?
What is the ratio of snow to water equivalent?
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What are the three basic forms of clouds?
What are the three basic forms of clouds?
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What is the characteristic of high clouds?
What is the characteristic of high clouds?
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What is the term for the process of ice crystals growing through the consumption of excess water vapor?
What is the term for the process of ice crystals growing through the consumption of excess water vapor?
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What is the main difference between fog and clouds?
What is the main difference between fog and clouds?
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What is the primary difference between rain and drizzle?
What is the primary difference between rain and drizzle?
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In which process do hygroscopic particles remove water vapor from the air?
In which process do hygroscopic particles remove water vapor from the air?
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What is the term for clouds that have bases in the low range and extend into the middle and high ranges?
What is the term for clouds that have bases in the low range and extend into the middle and high ranges?
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What is the term for fog that occurs when warm, moist air moves over a cool surface?
What is the term for fog that occurs when warm, moist air moves over a cool surface?
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What is the term for the deposit of ice crystals formed by the freezing of supercooled fog or cloud droplets on objects?
What is the term for the deposit of ice crystals formed by the freezing of supercooled fog or cloud droplets on objects?
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Why do some clouds produce precipitation, while others do not?
Why do some clouds produce precipitation, while others do not?
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What is the term for clouds that are associated with stable conditions, but can grow dramatically in height under the correct conditions?
What is the term for clouds that are associated with stable conditions, but can grow dramatically in height under the correct conditions?
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What is the term for fog that occurs when cool air moves over warm water?
What is the term for fog that occurs when cool air moves over warm water?
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Why do cloud droplets fall very slowly?
Why do cloud droplets fall very slowly?
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What is conditional instability in the atmosphere?
What is conditional instability in the atmosphere?
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What happens when stable air is forced aloft?
What happens when stable air is forced aloft?
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What is necessary for condensation to occur in the atmosphere?
What is necessary for condensation to occur in the atmosphere?
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What is unique about hygroscopic nuclei?
What is unique about hygroscopic nuclei?
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What type of clouds are associated with lifting unstable air?
What type of clouds are associated with lifting unstable air?
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What happens when air is cooled to its dew point?
What happens when air is cooled to its dew point?
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What is the role of condensation nuclei in the atmosphere?
What is the role of condensation nuclei in the atmosphere?
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What is characteristic of clouds formed from unstable air?
What is characteristic of clouds formed from unstable air?
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Study Notes
Water Vapor and Atmospheric Processes
- Water vapor is an odorless, colorless gas that can change states of matter at Earth's temperatures and pressures.
- It is the only substance that exists as a solid, liquid, and gas in the atmosphere.
- Composed of 2 hydrogen atoms bonded to an oxygen atom.
States of Matter of Water
- Solid (ice):
- Water molecules are held together by molecular attractions, forming a tight, orderly arrangement.
- Molecules vibrate about fixed sites and are not free to move about.
- Melting occurs when molecular movements increase, breaking bonds between water molecules.
- Liquid (water):
- Water molecules are tightly packed but move fast enough to slide past one another.
- As molecular movement increases, remaining molecular attractions are broken, allowing molecules to escape and become water vapor.
- Gas (water vapor):
- Water molecules are widely spaced and exhibit energetic, random motion.
- Water vapor is compressible and distinguished from liquid water in this way.
Energy and State Changes
- Changing states of matter requires heat (energy) to be absorbed or released.
- Measured in calories.
- Latent heat:
- Latent heat of melting: 80 calories to change 1 gram of ice at 0°C to liquid.
- Latent heat of fusion (freezing): 80 calories to change 1 gram of liquid water at 0°C to solid.
- Latent heat of vaporization: approximately 600 calories to change 1 gram of water at 100°C to gas.
- Latent heat of condensation: approximately 600 calories to change 1 gram of water vapor at 100°C to liquid.
Additional State Changes
- Sublimation: conversion of a solid directly into a gas without passing through the liquid state.
- Deposition: conversion of a gas directly into a solid without passing through the liquid state.
Water Vapor in the Atmosphere
- Water vapor comprises a small amount of gases within the atmosphere (1/10 of 1% to 4%).
- Most important gas in understanding atmospheric processes.
- Humidity is the general term for the amount of water vapor in air.
Measures of Water Vapor Content
- Mixing ratio: mass of water vapor in a unit of air compared to the remaining mass of dry air.
- Relative humidity: ratio of air's actual water vapor content compared with the amount required for saturation at that temperature.
- Dew-point temperature: temperature to which a parcel of air would need to be cooled to reach saturation.
Condensation and Cloud Formation
- Condensation occurs when air is cooled to its dew point temperature.
- Requires a surface on which water vapor can condense (e.g., particulate matter, condensation nuclei).
- Clouds can consist of water droplets, ice crystals, or both.
Cloud Formation Mechanisms
- Adiabatic temperature change: change in temperature that occurs without heat being added or removed.
- Orographic lifting: air is forced to rise over a mountainous region, causing adiabatic cooling and cloud formation.
- Frontal wedging: warmer, less dense air is forced over cooler, denser air, causing it to rise and cool.
- Convergence: pileup of horizontal airflow results in upward movement.
- Localized convective lifting: unequal surface heating causes localized pockets of air to rise due to buoyancy.
Air Stability
- Stable air: when a parcel of air is cooler than the surrounding air, it will sink.
- Unstable air: when a parcel of air is warmer than the surrounding air, it will rise.
- Environmental lapse rate: rate of temperature change with altitude.
- Adiabatic temperature change: changes in temperature caused by expansion or compression.
Types of Air Stability
- Absolute stability: develops when the environmental lapse rate is less than the wet adiabatic rate.
- Absolute instability: develops when the environmental lapse rate is greater than the dry adiabatic rate.
- Conditional instability: develops when moist air has an environmental lapse rate between the dry and wet adiabatic rates.### Clouds
- Clouds are visible aggregates of minute droplets of water or tiny ice crystals
- Classified by form and height:
- Cirrus: high, white, and thin; can occur as patches, veil-like sheets, or wispy fibers
- Cumulus: globular individual cloud masses; normally have a flat base and the appearance of rising domes or towers
- Stratus: sheets or layers that cover much or all of the sky; typically have no distinct individual cloud units
- Three levels of cloud height:
- High clouds: have bases above 20,000 feet
- Middle clouds: occupy heights from 6,500 to 20,000 feet
- Low clouds: form below 6,500 feet
Cloud Classification
- High clouds:
- Cirrus
- Cirrostratus
- Cirrocumulus
- Middle clouds:
- Altocumulus
- Altostratus
- Low clouds:
- Stratus
- Stratocumulus
- Nimbostratus
- Clouds of vertical development:
- Cumulus clouds can grow dramatically in height under correct conditions, forming cumulonimbus
Fog
- Fog is a cloud with its base at or very near the ground
- Typically reduces visibility
- Officially reported when visibility is reduced to 1 km (0.6 miles) or less
- Types of fog:
- Fogs Caused by Cooling:
- Advection fog: occurs when warm, moist air moves over a cool surface
- Radiation fog: forms on cool, clear nights when the Earth's surface cools rapidly by radiation
- Upslope fog: occurs when relatively humid air moves up a sloping terrain
- Evaporation Fogs:
- Steam fog: occurs when cool air moves over warm water, producing saturation
- Frontal (or precipitation) fog: occurs when frontal wedging occurs, producing precipitation that evaporates to produce fog
- Fogs Caused by Cooling:
Precipitation
- Cloud droplets are very small (20 micrometers), requiring a large size to reach the Earth's surface
- Two processes result in large volume droplets:
- Bergeron process:
- Relies on supercooling and supersaturation
- Dominant in mid-latitudes where cold clouds exist
- Collision-coalescence process:
- Occurs in warm clouds where large droplets form
- Requires giant condensation nuclei or hygroscopic particles
- Bergeron process:
- Types of precipitation:
- Rain: drops of water with a diameter of at least 0.5 millimeters
- Drizzle: fine uniform drops of water with a diameter of less than 0.5 millimeters
- Snow: precipitation in the form of ice crystals or aggregates of crystals
- Sleet: small particles of ice that are clear to translucent
- Glaze: raindrops that fall and freeze, resulting in a thick coating of ice
- Hail: hard, rounded, pellets or irregular lumps of ice
- Rime: deposit of ice crystals formed by the freezing of supercooled fog or cloud droplets on objects
Measuring Precipitation
- Rain is measured using a rain gauge, which collects and conducts rain into a cylindrical measuring tube
- Snow has two measurements: depth and water equivalent
- General ratio: 10 parts snow equals 1 part water
- Ratio varies based on physical properties of snow
- Weather radar is used to estimate rainfall and rate of rainfall
- Radio waves are transmitted and reflected by larger raindrops, ice crystals, or hailstones
- Reflected signal (echo) is displayed
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Description
Learn about the physical properties of water vapor, its states of matter, and how temperature affects molecular motion. Understand the importance of water vapor in atmospheric processes.
