Weather processes and phenomena

What is gas

water vapour, an invisable gas when tempretures are above 100^oc but can exist below that

what is a liquid

water is stable between 0^oc and 100^oc but can exist as a super heater or super cooled [40^oc <]

what is a solid

water vapor is in a stable phase of mositure below 0^oc

what is the change between gas to solid and solid to gas

• Deposition

• sublimation

what is humidity

how moist the air is due to the water vapour it contains

what is absoloute humidity

the actual ammount if water vapor in a given volume of air g/m³

what is relitive humidity

how close to saturation air is. how much water vapor air is holding compared to the potential it could at that tempreture and pressure.

what is the equation for relitive humidity

actuale water vapour content/ saturation water capacity x100

what is 100% relitive humidity

• Dew point/saturation

what is condensation leval

the specific altitude in the atmosphere at which rising parcel of air cools to its dew point and becomes saturated to form clouds

what is condensaition nucli

• An impurity made up of e.g Dust, polutants, salt, ash

Found in ALL types of precipitation

what is evaporation

the process at which liquid water vapor is transformed into gas [lots of energy needed]

what is sublimation

the process of direct change of state from a solid to a gas without passing through the liquid state

what is condesation

the change of water vapour in gas state into a liquid when air is cooled to dew point

what are the three types of condensation

• Conduction

• Radiation

• Expansion

what is conduction cooling

Contact

• Cooling of air when a direct contact with a cooler surface creates heat transfer from air to that surface

what is radiation cooling

NIGHT

• Cooling caused by loss of heat from earths surface to air via longwave radiation

what is expansion cooling

cooling of air as it rises and expands due to lower pressure

what are the three causes of precipitation

• Frontal

• Convectional

• Orographic uplift

what is albedo

The refelectiveness of a surface

More = reflected

Less = absorbed

what is fog and how is it formed

Tiny water droplets suspended in the air near the ground reduce visability to less than 1km

• moist air is cooled to bellow dew point due to contact with cool air/sea or radiation cooling

what is dew and how is it formed

small droplets of water on leaves, grass, spider webbs ect.

• water vapor condenses onto cold objects. still conditions allow prolonged contact with the object

what are clouds and how are they formed

At low altitudes clouds are suspensions of tiny water droplets with an average diamiter of 0.01mm. These are super cooled where they exist at temps bellow 0^oc but are too light to fall

• Formed where moist air rises, expands and cools aidabetically to bellow dew point and condenses around condensation nucli

what are raindrops and how do they form

Normally 2mm in diamiter

• formed when falling raindrops collide and coalase

what are snowflakes and how is it formed

agrregates of ice crystals arraged in hexigonial patterns

• water vapour in a cloud changes to ice and when crystals fall they collide and change [agrrigation]

what are hailstones and how is it formed

roughly circular, made of alternating layers of opaque rime and clear ice glaze

• formed when ice particles fall and rise in cumulonibous clouds and supper cooled water droplets collide and freeze around them [alcreation]

what is raddiation fog

forms when ground looses heat through long wave raddiation at night

• needs cool/calm/clear skys

what is advection fog

warm moist air moves over a cold surface cooling air to dew point

• happens over sea often

what are the three shapes of cloud

• Stratus

• Cumulos

• Cirrus

what is a stratus coud

• Larger

• Form with strong vertical uplift

• over a wide space

what is a cululous cloud

• More verticle uplift

• in a localised area

• heaped shaped clouds

• flat bases / globular upper surfaces

what are cirrus clouds

• Form where condensation occours

• high hights

• wispy clouds made of ice

what are the sub cattogrys for clouds altitude

• high Cirro

• middle = alto

• low = stratus/cummulous

what are the two types of cloud that produce rain

• Nimbostratus

• Cumulonibus

what are charecteristics of rain clouds

• Large verticle extent

• prevents sunlight = dark/grey

what are nibostratus clouds

thick and dark layer of cloud type

• can be 5000m thick

• steady rain

what are cumulonibus clouds

Thickest cloud type

• dense, black and grey

• large verticle extent [sea leval - tropoporse]

Spreads out at the top making an anvil head

what are the two theories of how precipitation grows

• collision theory

• bergen friendsine theory

what is collision theory

• Diffrent sized water droplets fall at diffrent speed, they collide

what is coalesense

when 2x H₂0 molocules collide

what is aggregation

2x ice crystals collide

what is accreation

when ice molocules collect water to form hail

what is the bergeron-findersen theory

• in mixed clouds (ice crystals + supercooled water droplets),

• ice crystals grow rapidly by vapour deposition as water droplets evaporate.

• Ice crystals grow until heavy enough to fall;

• may melt into raindrops.

• Dominant in mid-latitude clouds.

How is hail formed

• At the top of the cumulonimbus cloud temps = bellow 0^oc

• Freezing occours in upper cloud

• updrafts decreace and ice crystal falls

• it eats liquid water before bieng lifter back into the top of cloud

• this repreats untill it is heavy enough to fall

how is dew formed

On calm cloudless nights radiation cooling occurs

• water vapor condenses on a cloud surface

*If this happens with a slight breeze then it becomes fog

how is fog formed

Close to the earths surface

• cloudless night when ground has become cold

how is advection fog formed

• moisture ladened air moves over the sea and creates fog as it comes into contact with cooling land

what are the steps to convection rainfall

Hot ground heats air above it. Heated air rises as it is less dense

1) Short wave raddiation heats ground

2) ground heats air above it due to convection

3) air expands and cools adiabatically

4) rising air cools the higher it gets

5) at dew point it condenses forming cumbonimbous clouds

common around ITCZ and heavy, intense, short-duration rainfall

what are the steps to frontal uplift

warm air meets cold air and the lighter warm air is forced up on the cold air .

1) Warm air + cold masses meet

2) cold air stays near ground

3) lighter warm air is forced to rise over the denser cold air along a front

4) rising air cools and c nimbostratus louds form

steady prolonged rain

common in low pressure systems and mid lattitudes

what is orographic uplift

1) Moist air approaches high land

2) air forced upwards

3) air cools

4) condensation

5)rainfalls on the windward side

occours at mountins and leaves rain shadow

what is raddiation cooling as precipitation process

1) longwave radiation lets heat release into atmosphere

2) via conduction ground cools

3) cold ground

4) cool air falls to bottom of the valley

5) conduction takes place to form fog/mist