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Earth Science > Moisture in the Atmosphere > Flashcards

Moisture in the Atmosphere Flashcards

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1
Q

Specific humidity

A

The amount of water vapor in the atmosphere (in grams of water per kilogram of air)

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2
Q

Relative humidity

A
  • A comparison of the amount of water vapor in the air (specific humidity) with the maximum amount of water vapor that the air can hold at a given temperature (capacity)
  • A measure of how close the air is to saturation, as a percentage
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3
Q

Capacity

A

The maximum amount of water vapor that the air can hold at a given temperature (in grams of water per kilogram of air)

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4
Q

What happens to capacity as temp goes up?

A
  • When temperature goes up, capacity goes up

- As temp increases, air can hold more water vapor (beaker example)

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5
Q

Relative humidity equation

A

% relative humidity = (specific humidity/capacity) x 100

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6
Q

What does it mean if the relative humidity is 50%?

A

The air is holding half of the amount of water vapor that it can hold

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7
Q

What does it mean if the relative humidity is 25%?

A
  • Air is dry
  • Air can hold much more water vapor than it actually is holding
  • Evaporation is easy (clothes will dry faster)
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8
Q

What does it mean if the relative humidity is 90%?

A
  • Air is very humid
  • Air holding almost as much water vapor as it can hold
  • Evaporation is more difficult
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9
Q

Dew point temperature

A
  • The temperature at which water vapor condenses to liquid water
  • This changes as specific humidity changes
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10
Q

At the dew point temperature…

A

1) the relative humidity is 100%
2) specific humidity = capacity
3) the air is saturated with respect to water vapor (air can hold no more water vapor)

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11
Q

As the temperature falls…

A

1) the capacity falls
2) the specific humidity does not change
3) the relative humidity rises

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12
Q

What happens when the specific humidity is high?

A
  • Temp of air does not have to fall very far before its dew point temperature is reached
  • Air is already close to saturation
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13
Q

What happens when the specific humidity is low? (when air is dry and relative humidity is low)

A
  • Temp will have to decrease substantially before saturation is reached
  • The capacity of the air will have to be substantially lower to be equal to the specific humidity
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14
Q

3 forms of water in the atmosphere

A

1) gas (water vapor)
2) liquid (liquid water)
3) solid (ice, snow, hail)

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15
Q

Condensation

A

Gas to liquid

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16
Q

Evaporation

A

Liquid to gas

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17
Q

Freezing

A

Liquid to solid

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18
Q

Melting

A

Solid to liquid

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19
Q

Sublimation

A

Solid to gas

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20
Q

Crystallization

A

Gas to solid

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21
Q

What happens during evaporation?

A
  • Cooling process
  • Only the most energetic (warmest) water molecules in liquid water will evaporate
  • They leave behind liquid water molecules that are (on average) cooler than the water was before evaporation began
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22
Q

How is relative humidity determined with a psychrometer?

A

Psychrometer: a rod with two thermometers on one end, one that is dry and one with wet gauze on it

1) With it, you swing the thermometers around on the rod, and the wet bulb thermometer temperature will lower to the dew point temperature, because the water on it is evaporating and evaporation is a cooling process
2) Water will evaporate until the bulb reaches the dew point temperature
3) The dry bulb will go to the temperature of the air, and you use the capacity chart to determine what the specific humidity and capacity are
4) Relative humidity would equal specific humidity (capacity at the dew point) over capacity

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23
Q

How do clouds form by the Radiation-Conduction-Convection (RCC) Method?

A

1) During the day, the sun shines on the ground and warms it (radiation)
2) The ground warms the air immediately above it (conduction)
3) Newly warmed air rises due to its relatively low density (convection) to an elevation in the atmosphere where the temp is low enough for condensation to occur (dew point)
3) Clouds form higher up because of colder temps

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24
Q

Condensation nuclei

A
  • Microscopic solid particles onto which water vapor freezes or condenses
    1) Dust (from deserts, agriculture, and space)
    2) Smoke/soot
    3) Sea salt (breaking waves, water droplet evaporates)
    4) Pollen
    5) Pollution
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25
Q

Why are there often more clouds in the afternoon than the morning?

A
  • Air needs time throughout the day to heat up and rise (warm ground warms air)
  • Newly warmed air rises due to its relatively low density (convection) to an elevation in the atmosphere where the temp is low enough for condensation to occur (dew point)
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26
Q

What are many clouds made of so high in the sky any why?

A
  • Cold higher up

- Tiny particles of ice

27
Q

Fog

A
  • Clouds forming at surface of Earth
  • Forms on a clear night, the ground’s heat is radiated away to the upper atmosphere and eventually to space
  • The coldness of the ground chills the air above it to its dew point temp, creating condensation in the form of fog
28
Q

Cumulus clouds

A
  • Thick, puffy clouds made from warm air that is rising vertically (=unstable air) because of relatively lower density than surroundings air
  • Flat base (dew point temp)
  • Billowy tops (convection)
  • Often more tall than wide
  • Made form the RCC method and strong vertical motion
  • The RCC method brings warm air to its dew point as it rises in elevation
  • More convection = more clouds
  • Eventually will reach level where it cannot punch through- forms anvil cloud (stratosphere boundary)
29
Q

Stratus clouds

A
  • Grow in layers horizontally to the ground
  • Flat bottoms, flat tops, and thin
  • Cover large portions of the Earth, and produce cloudy days
  • Long precipitation events from this cloud, and they occur at fronts
  • No vertical lift from convection
  • Produces precipitation that reaches the ground
  • Fog- special case
30
Q

Cirrus clouds

A
  • Thin, feathery, wispy clouds made of ice crystals
  • High elevation
  • Sunlight shines through
  • Curly shape- as snow falls out cloud, left behind to form curly shape
  • Can tell what way the wind is blowing at high elevations
  • Snow sublimates miles above surface
  • Tells the moisture content of that atmosphere at a very high elevation
  • Warm air goes up and over cold air wedge, warm air rises, stratus cloud forms, air keeps going, temp decreases
  • Lots of cirrus clouds = storm coming, warm front coming
  • Contrails
31
Q

How does rain form by the collision-coalescence method?

A
  • Water droplets in clouds grow in size by collision with other droplets (similar to the way planets grew in the nebula when the solar system began)
  • When the drop becomes too heavy to remain in the cloud, it falls to Earth as a raindrop
  • Hundreds of thousands of collisions to make one rain drop
  • Big droplets: air movement inside the cloud prevents the drops from falling right away
  • Raindrop made of thousands of microscopic particles + water
32
Q

How does rain form by the Bergeron method?

A
  • More common
  • In a colder cloud with a temperature below freezing
  • Evaporation from supercooled water droplets produces water vapor which crystallizes onto ice/snow
  • Supercooled water droplets get smaller and the snow or ice gets larger
  • Eventually, the snowflakes become too massive to stay in the cloud and fall toward the ground
  • Melt on the way down and hit the surface as rain
  • Air in cloud is saturated, there should be no evaporation but there is because the air is not quite saturated with respect to supercooled water droplets but it is saturated with respect to ice
33
Q

Snow

A
  • This forms when tiny water droplets freeze and continue to grow into a 6-sided crystal by the addition of more frozen water
  • Has a hexagonal core
  • If the snowflake would have stayed in the cloud longer, it would have become a complete filled in hexagon
  • Water molecules form in a flat hexagonal way
  • Shape of snow based on temperature
34
Q

Sleet

A

Snow falls toward the surface but melts on its way down (when. it meets warmer air), but refreezes as it gets closer to the surface (frozen water droplet)

35
Q

Freezing rain

A

-Ground is below freezing
-Melts (when it meets warmer air) , then passes through a layer of air where temp is below freezing but doesn’t melt
instantly freezes on the ground because it needs a solid to freeze on
-Supercooled water droplets
-Black ice

36
Q

Rain

A

Snow melts on its way down and falls as droplets of liquid water

37
Q

During the winter, how do the 4 types of precipitation begin?

A

Begin as snow produced by the Bergeron Process

38
Q

Hail

A

-A frozen precipitation that forms in warmer weather
-They form in tall cumulus or cumulonimbus clouds that have grown to great vertical heights in the atmosphere, driven by powerful currents of rising warm air
The temperature is so cold that water droplets freeze
-They are kept in the cloud by strong updrafts and winds in the cloud
-They only fall when they are too heavy to be kept aloft by winds

39
Q

Why is the sun important?

A

It is the ultimate source of energy that creates change (winds, storms, precipitation) in the atmosphere

40
Q

Virga

A

Precipitation that does not reach the ground, and sublimates on the way down

41
Q

Unstable air

A

Rising air is aid that is rising because of low density, considered to be unstable, and creates clouds

42
Q

Supercooled water

A
  • Liquid water with temp below freezing but has not frozen because it needs something solid to teach it how to freeze, will freeze when it meets ice pellet
  • Absence of condensation nuclei
43
Q

Nimbus cloud

A

Indicates precipitation, a cloud that makes precipitation that reaches the ground

44
Q

Lapse Rate

A
  • The rate at which air temperature falls with increasing altitude
  • 1 degree Celsius per 100 meters
45
Q

Contrail

A
  • A trail of microscopic water droplets that have condensed from the air, that come from engine exhaust from an airplane
  • Special case of cirrus clouds
  • Plane emits water vapor, boots specific humidity, creates saturation
  • No contrail means that the air is really dry or it very rapidly sublimates
  • Lots of contrails = close to saturation
46
Q

Advection fog (and examples)

A
  • Warm, moist air moves horizontally over a cold surface snd is chilled to its dew point
    1) moist air from ocean moves over the colder, snowy land and chills air to dew point temperature
    2) Warm water current (the Gulf Stream), air over current is warm and humid, when a cold current comes in, the warm air over the cold water chills to dew point to create fog
47
Q

If hail is frozen precipitation, why does it usually form in warm weather?

A

-Warm air creates very strong convection currents which shoot wind upward, and continuously push the ice crystals up and floating in the cloud until they become too heavy to be held up by the convection currents.

48
Q

Evaporation fog (steam fog)

A
  • When cool air moves over a warm body of water, and causes warm water to evaporate
  • As the water vapor rises it cools down to its dew point
  • Air temperature colder than the water, warmer air over lake surrounded by cold air, warm air rises and chilled to its dew point, in early morning or night
49
Q

Radiation fog

A
  • After cold, clear night, temperature inversion, ground gets cold because it radiates all the heat
  • The cold ground touches the warmer air above it, cooling the air to its dew point
  • Most common type
50
Q

How do clouds form by Orographic Lifting?

A

1) Air gets pushed up the slope of a mountain by wind, cools to its dew point temperature as it rises, relative humidity increases
2) This is because as the air rises, it spreads out and thins and as it does this it cools
3) Air warms up as it goes back down, capacity goes up
4) One side wet and one side dry (rain shadow on side opposite mountain)
5) On the other side of the mountain, it is very dry because as the cloud passes over the mountain it starts to sink, and sinking air inhibits the formation of clouds
6) Most common in the Cascades, moist air from Pacific, very dry air on other side of mountains

51
Q

How do clouds form by fronts?

A

Front: boundary between to different high pressure systems
1) Cold front meets warm front, two air masses have different densities
2) Advancing warm air goes over the cool air, causing it to reach its dew point temperature, causing the formation of clouds
Warm front: wedge of cold air, warm air rises over
Stratus clouds
(Similar to orographic lifting)

52
Q

Estimate the elevation of the base of a cumulus cloud

A

[(Air Temperature - Dew Point Temperature) / 0.8] x 100

53
Q

How do dew and frost form?

A
  • Clear night with little wind

- When radiation from the ground causes heat to escape, cooling the ground and air touching it to the dew point.

54
Q

What does not change with temp?

A

Dew point and specific humidity

55
Q

When is the relative humidity the highest?

A

Just after dawn (capacity lowest, relative humidity highest)

56
Q

What happens when the relative humidity is 100%?

A

Specific humidity = capacity

57
Q

Alfred Wegener

A

Said continents moving around Earth
Came up with Bergeron Process
Bergeron stole his idea

58
Q

Composition of clouds:

A
  • Microscopic particles of water ice and/or microscopic droplets of liquid water
  • Lower part of cloud greater than 0: microscopic droplets of water
  • Higher part of cloud less than -40: microscopic particles of ice
  • Temp between 0 and -40 (middle part of cloud) made of ice particles + supercooled water droplets
  • Ice and water denser than air, but they are so small and light that the motion of air in the atmosphere keeps them moving
59
Q

Height of base of cumulus cloud formula

A

[(air temp – dew point temp) at surface / (adiabatic lapse rate – dew point lapse rate)] x 100

((air temp - dew point temp) at surface / 0.8) x 100

60
Q

What is the adiabatic lapse rate and the dew point lapse rate:

A

Adiabatic: Air cools 1 C per 100 meters

Dew point: 0.2 C / 100 meters

61
Q

Using a psychrometer, how is the difference between the wet and dry bulb thermometers can be a measure of the moisture content of the atmosphere?

A
  • As the liquid around the gauze evaporates, the temperature of the wet bulb thermometer will fall below the air temperature because evaporation is a cooling process
  • The lower the relative humidity is, the lower the wet bulb will read because evaporation is taking place with ease
  • The higher the relative humidity, the closer the air is to saturation and the less the wet bulb thermometer will fall
  • If relative humidity was 100%, dry bulb and wet bulb would be the air temp
62
Q

What ways can the moisture content of the atmosphere be determined?

A

1)

2) A psychrometer

63
Q

What do you need for clouds to form?

A

1) You need low temp, moist air, condensation nuclei
2) Temp of moist air goes down until it reaches its dew point, condensation begins, tiny droplets of condensed water form around condensation nuclei

64
Q

Acid rain

A

-Co2 +H20&raquo_space; H2CO3
-5.6, slight acidic
-In a cloud, air pollution mixes with cloud droplets, to form acidic cloud droplets
Examples
1) H2S or SO2 produced by burning coal, mixes with water droplets to form a weak sulfuric acid
2) Nitrous oxides from automobile exhaust mix with water to form nitric acid
-Affects limestone, fish, crops

Earth Science (16 decks)

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