Chapter 4: Humidity

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70 Terms

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Hydrologic cycle (water cycle)
continuous movement and exchange of water among the Earth's surface, oceans, and atmosphere including phase changes of water
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Evaporation
process by which a liquid changes into a gas. Occurs when air is warmed. The sun's energy transforms enormous quantities of liquid water into water vapor. Water can evaporate from the oceans, lakes, soil, etc. 85% of water evaporated into the atmosphere
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Condensation
Process by which water vapor becomes a liquid and can form clouds or dew. Occurs when air is cooled. Prescient of cloud condensation nuclei (microscopic bits of dust, smoke, ans sea salt in the air) is important for condensation and cloud formation
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Precipitation
Any form of water particles, either solid or liquid, that falls from the atmosphere and reaches the ground. Under certain conditions, the liquid cloud particles or solid ice crystals collide, coalesce and form, grow in size, and fall to the surface as rain, snow, sleet, or hail. Some falling precipitation evaporates back into the atmosphere
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Transpiration
process by which water is pants is transferred as water vapor to the atmosphere through stomata, or small openings on the underside of leaves
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Groundwater
once precipitation reach the ground,s some water soaks into the ground by percolating downward through small openings in soil and rock
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Runoff
water from rivers, lakes, and the ground returning to the oceans. Occurs when there is excessive precipitation and the ground is saturated (cannot hold anymore water)
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What is the largest source of moisture in the atmosphere?
Oceans
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Humidity
amount of water vapor (doesn't count liquid water) in the air
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Actual humidity
amount of water vapor that is actually in the air
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Saturation humidity
amount of water vapor that could be in the air, depending on air temperature (warmer air can hold more water vapor than colder air)
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Saturation
Atmospheric condition where the level of water vapor is the maximum possible at the existing temperature and pressure
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Air parcel
imaginary volume of air. Large enough to contain a great number of molecules. Small enough that is has relatively uniform properties. Total air pressure inside the parcel is due to the collision of all molecules against the walls of the parcel
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Relative humidity
Ratio of the amount of water vapor in the air compared to the amount required for saturation (maximum the air can hold) at a particular temperature and pressure
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Absolute Humidity
Mass of water vapor in a given volume of air... depends on volume
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Dew Point
Temperature is which air must be cooled, at constant pressure and constant water vapor content, for saturation to occur (units
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Radiational cooling
At night, the ground and overlying air cool by radiating infrared, longwave radiation
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Temperature inversion
increase in temperature with height
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When are temperature inversions common?
clear (little cloud cover and moisture), calm nights, especially with snow on the ground
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Apparent temperature or heat index
what the air temperature feels like to the average person for various combinations of air temperature and relative humidity
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Heat stroke
Physical condition induced by a person's over-exposure to high air temperatures, especially when accompanied by high humidity
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Body temperature during heat stroke
Possible if body temperature greater than 106 F
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Psychrometer
measures relative humidity and dewpoint. Includes 2 liquid in glass thermometers (wet bulb and dry bulb) mounted together on a piece of metal with a handle or chain at the end
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Wet bulb
cloth covering the bulb dipped in water. Lowest temperature achievable by evaporating water in the air
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Dry bulb
kept dry, gives the air temperature
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Wet bulb depression
temperature difference between the dry bulb and wet bulb
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Large depression
low relative humidity
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Small depression
near saturation, high relative humidity
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What happens when the bulbs are equal?
Relative humidity is 100%
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Hygrometer
instrument for measuring relative humidity
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Hair hygrometer
traditional instrument, rarely used today. Inaccurate. Increases relative humidity causes hair/fiber length to increase
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Electrical hygrometer
As water vapor is absorbed, the electrical resistance of the carbon coating changes, and these changes are translated into relative humidity
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Dew point hygrometer
used in automated weather stations
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Dew (condensation)
water that has condensed onto objects near the ground when their temperatures have fallen below dew point of the surface air
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Frost (deposition process)
covering of ice produced by deposition on exposed surfaces when air temperature falls below the frost point
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Deposition
water vapor directly changing into ice without becoming a liquid. When temperature is below 0C
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Frost point
temperature (
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Fog
cloud with its base at the Earth's surface
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Radiation fog
ground fog/valley fog. produced over land due to radiational cooling (light winds)
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Advection fog
warm, moist air moves over a cold surface and is cooled. Wind moves warm air over cool surfaces
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Upslope fog
moist air flows upward over a topographic barrier
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Evaporation fog
water vapor is added to air by evaporation, and the moist air mixes with the relatively drier air can occur during rain
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Clouds
visible aggregate
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High clouds
thin, icy, little moisture, mostly white
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Middle clouds
water droplets and possibly ice crystals, possible precipitation
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Low clouds
largely water droplets
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Cirrostratus
Layered, sheetlike, uniform, mostly ice, can produce halo
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Cirrus
Wispy, fibrous, feathery, white, mostly ice, fair weather
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Cirroculmulus
White cloud patches, ripple pattern, mostly ice
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Altostratus
Grey/bluish sheets, layered, mostly water, often cover whole sky
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Altocumuls
white or gray, layers or patches, wavy rounded masses
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Stratus
gray sheetlike layer near ground, often blocks out sunlight, often drizzle
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Stratocumulus
mostly uniform, lumpy rounded masses with blue sky in between
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Nimbostratus
dark gray, layered, light/moderate precipitation, rarely severe
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Cumulus
flat bases, puffy tops, cottonball, well-defined
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Cumulonimbus
deep dark rain cloud, top anvil, thunderstorms, can be severe
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Geostationary and Polar-orbiting satellites
Weather satellites provide valuable images of clouds over areas without ground-based observations (hurricanes over oceans)
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Geostationary
located above equator; orbit at the same rate as Earth spins; provide continuous monitoring of a specific region
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Polar-orbiting
pass over north and south polar regions, eventually covering the entire planet
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Visible Satellite Imagery
Visible satellite images display the sunlight reflected from the cloud tops
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Cloud condensation nuclei
dust, salt, smoke, etc in air that helps condensation and cloud formation
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Diurnal cycle of relative humidity
peaks at sunrise and lowest in mid-afternoon \= inverse relationship with air temperature
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Desert has \___ relative humidity but \___ water vapor than polar region
lower, greater
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States with abundant fog
Washington, Oregon, Maine, New Hampshire, West Virginia
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Low clouds
stratus, stratocumulus, nimbostratus (nimbo \= raining)
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Mid-level clouds
altostratus, altocumulus
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High clouds
cirrus, cirrostratus, cirrocumulus
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Vertical clouds
Cumulus, cumulonimbus (thunderstorms)
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Types of weather satellites
geostationary (always sitting over equator) and polar-orbiting (orbits around North and South Poles)
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Main controls of regional temperature variations
latitude, land-sea distribution, ocean currents, and elevation