Moisture in the Atmosphere

Question 1

Water Vapour

Answer 1

water as gas. amount of water vapour in atmosphere = humidity. Temp of air affects amount of water vapour

Question 2

Rain

Answer 2

Liquid water found atmosphere when air temperature cool for vapour condense. Water vapour is initially very light and small, and remain suspend in
the air as cloud droplets. They will join together, become heavy and
eventually fall into the ground. Liquid found in atmosphere as clouds or rain

Question 3

Ice

Answer 3

temp of air below 0, water freeze. This how hailstones fall. If water sublimes - becomes snow

Question 4

Coalescence

Answer 4

water droplets bump into each other becoming
bigger as a result of air movement within the cloud.

Question 5

Types of precipitation:

Answer 5

rain snow hail frost sleet

Question 6

What refers to water in the air

Answer 6

Dew point

Condensation level

Humidity

Relative humidity

Question 7

Specific humidity

Answer 7

The mass of the water vapour (in grams) contained in a kilogram of dry air.

Question 8

Absolute humidity

Answer 8

The mass of water vapour (in grams) contained in a cubic metre of dry air.

Question 9

Relative humidity

Answer 9

The proportion of water vapour in an
air parcel compared to the amount of water vapour it
could hold at a given temperature.

Question 10

Saturated air parcel

Answer 10

Relative humidity = 100%. Lots of moisture in air

Question 11

What affects humidity

Answer 11

Temp of air and water present in atmosphere. Warm air holds more moisture

Question 12

Relative Humidity calculations

Answer 12

(Actual amount/Saturation amount) *100 = x%

Question 13

dew point

Answer 13

Temp where air condenses. Higher altitudes = lower dew point temp. Height at which dew pt is reached - condensation level

Question 14

Why does it rain in the Highveld during the
afternoon?

Answer 14

Heating will raise the temperatures and increase evaporation
(also cause convection currents)

Heated air holds more moisture ( expanding air -> more
space to hold moisture) and increases as the day goes on.

By late afternoon the air may be full of moisture and can be
seen as clouds.

Leads to afternoon rainstorms, sometimes have hail too.
(Why? Think convection currents).

When air temperature drop the water condenses and can
cause rain

Question 15

Cumulous cloud shape

Answer 15

Patchy looking

Question 16

Stratus cloud

Answer 16

Layered clouds can form at any height and are the most
common type

Question 17

Nimbus(rain) cloud

Answer 17

Nimbostratus and cumilonimbus

Question 18

Cloud formation

Answer 18

Condensation and water vapor needed.
Rising currents help to suspend water droplets in the sky

Water droplets will fall when they get to heavy.

Solid surfaces in the sky act as condensation nuclei and help
promote the condensation process

Question 19

Coalescence

Answer 19

Air movements in clouds cause tiny droplets to collide

Question 20

Rain formation

Answer 20

Coalescence occurs. More turbulent the air, bigger the drops until become too heavy and fall to earth. Avg rain drop 2mm in diameter.

Question 21

How rainfall show on map

Answer 21

Colour shading and isohyets - lines on map joining places of equal rainfall.

Question 22

trigger action

Answer 22

natural mechanism that causes air to rise

Question 23

Types of rain

Answer 23

Convection(heating), Frontal/cyclonic(Sea) and Relief/orographic(Mountain)

Question 24

Convection rain

Answer 24

Convection rain is a thunderstorm. Surface heating is trigger action.

Question 25

Steps of convection rain

Answer 25

Cumulous stage - hot air rises causing cumulous clouds grow higher. Mature stage - Cumulous clouds reach 7km high. Air gets cold and starts to sink. Both up and down currents are now present. Is now a cumulonimbus cloud. Friction between currents causes electrical imbalance results lightning. Very strong currents result water drops freezing causing hail. Dissipating stage is once everything gets too heavy and falls.

Question 26

Relief rain

Answer 26

Mountains force air to rise causing it to condense and result in rain. The mountain is the trigger action

Question 27

Steps of relief rain

Answer 27

Moist air blows off an ocean and rises up the mountain
range.

The windward side of the mountain is the side the wind
strikes first and the leeward side is the side the wind is
blowing away from

Air rises, cools and condenses on the windward side.

Turbulence causes coalescence and start to fall as rain.

Most moisture is lost on the wind ward side and little is left
on the leeward side.

The drier side of the mountain is called the rain shadow.

Orographic rain is usually gentle rain that lasts as long as the air
coming in from the ocean is being forced up the mountain.

The cloud responsible is normally Nimbostratus but cumulonimbus
can form if the air rises very quickly.

Drakensberg and Cape fold mountains

Question 28

front

Answer 28

boundary between two different kinds of air - usually hot+cold. Fronts develop between warm, moist air masses and dry, cold air masses.

Question 29

frontal rain trigger action

Answer 29

trigger action is the front

Question 30

Frontal rain steps

Answer 30

When the air masses meet the warm air will rise over the cold air as warm air is less dense and lighter.

Warm air will rise, cool and condense.

A warm front has a very gentle slope

With a variety of clouds. The rain falls

from the Nimbostratus.

A cold front has a steeper slope which

makes warm air rise more quickly.

Cumulonimbus clouds

Question 31

Hail formation

Answer 31

Strong convection currents cause up and down currents in the
cumulonimbus clouds.

Water drops carried above freezing level

Begins to fall and collect more water

After each updraft forms a new layer

Continues until hail too heavy and falls. Melts slightly while falling

Question 32

Formation of snow:

Answer 32

Water vapour condensing onto condensation nuclei to form ice
crystals. Turning from water vapour to snow without condensing is
called sublimation

Snow crystals float and freeze onto each other getting bigger

They are six sided and fall from nimbostratus clouds.

Increase in size by further sublimation or by collisions (known as
snow flakes)

Question 33

Dew

Answer 33

Condensed water droplets seen on grass/plants

Question 34

Dew formation

Answer 34

At night land loses heat to terrestrial radiation. The cold land cools the
air above it.

IF the temperature drops below dew point water vapor on the
ground condenses to from dew. Dew most common in spring+autumn in highveld

Question 35

Frost

Answer 35

If temperature drops below freezing, instead of water vapor condensing, it sublimates . Bad for certain plants but good for citrus. Protect plants with fans/artificial heating get frost resistant crops.

Question 36

Frost formation in valleys

Answer 36

Clear calm and windless nights (wind mixes air)

Land on side of the valley cools and begins to sink to valley floor

Warm air at the bottom of valley rises above the cold sinking air to
form the inversion layer.

Cold air on the valley floor cools and pools in the frost pocket. This is
where fog will develop once dew point temperature is reached.

The water droplets will freeze if the temperature hits freezing point.