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61 Cards in this Set

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Define: Air Masses

a body of air that has remained over an area for a period of time and assumed the humidity and temperature of that area

Where do air masses that affect the British Isles originate from?

-from areas of permanent high pressure

-polar or sub-tropical regions

On leaving source - If the air mass follows a maritime (oceanic) track:

humidity increases due to evaporation from ocean

On leaving source - If the air mass follows a continental track:

low humidity

On leaving source - If the air mass heads towards the equator it is...

heated from below

becomes unstable

On leaving source - If the air mass heads towards the poles it is...


becomes stable

Outline unstable air:

-less dense than surrounding air

-more buoyant

-continues to rise

-uncertain weather conditions

-upper layers unstable = thunderstorms

What 5 air masses affect the UK?

1.artic maritime

2.polar continental

3.tropical continental

4.tropical maritime

5.polar maritime

What direction does each individual air mass come from when heading towards the UK?

1.AM - north

2.PC - north east

3.TC - south

4.TM - south west

5.PM - north west

Where and between what two air masses do Depressions form?

between polar maritime (PM) and tropicla maritime (TM)

along polar front

What are the characteristics of the Artic maritime?

-northerly with strong winds

-very cold winters with snow, rain and frost

-rarely occurs in summer

-warms over North Atlantic and becomes unstable

-becomes stable over land

What are the characteristics of the Polar continental?


-unstable over land and sea

-begins stable over continent but unstable as it crosses North sea

-winter; snow to east Britain

-summer; clear skies and high temperatures

What are the characteristics of the Tropical continental?


-only occurs in summer when sub-tropical high pressure moves north

-stable lower layers

-unstable upper layers = thunderstorms



What are the characteristics of the Tropical maritime?

-south west

-occurs in warm section of a depression

-stable then unstable hitting west coast of hills/mountains

-thundery showers

-advection/coastal fog

-warm in summer

What are the characteristics of the Polar maritime?

-north west

-winter;frost/fog inland

-clear during the day

-lowers summer temperatures

-warms over Atlantic = unstable lower layers

-cool conditions yearly

Outline what the weather system a 'Depression' is:

-large travelling low pressure weather system

-meeting of 2 air masses

-number of fronts

-cloudy, rainy, windy weather

-occurs where Pm and Tm meet at polar front

What direction do Depressions spin in the Northern hemisphere?


What is stage 1 of a Depression called?


What happens within stage 1 of a Depression?

1.Pm & Tm meet along polar front on a curve - coriolis effect

2.warmer Tm air is less dense & lighter so rises over Pm air

3.cold air takes space warm air covered before rising

4.the line separating the two masses is a front

5.creates low pressure at ground level and clouds (water vapour has condensed)

What happens within stage 2 of a Depression?

1.increased amplitude of depression due to coriolis effect

2.spinning of depression forms cold and warm fronts

3.pressure falling = increased pressure gradient

4.strong winds

Define: Dew point

the temperature at which the atmosphere is 100% saturated with water vapour and dew forms due to condensation

What weather is associated BEFORE a warm front?

-temperature cools

-pressure falls

-rise in dew point

-prolonged precipitation

What weather is associated BEHIND a warm front?

-temperature increases

-patchy low stratus cloud

-patchy rain

-winds veer and turn clockwise

What weather is associated BEFORE a cold front?

-cold air advances and pushes under warm air

-huge cumulonimbus clouds

-short periods of heavy precipitation

-gusty winds

-mild temperatures

What weather is associated DURING THE PASSING of a cold front?

-sudden temperature drop

-sharp rise in pressure

-heavy rain

-possibly thunder/lightning

What weather is associated when a cold front has COMPLETELY PASSED?

-shower clear

-temperature drops

-pressure continues to rise steadily

-dew point lowering

What is an Occluded front?

-signifies the end of a depression system

-where cold front catches up with warm front

Outline the characteristics of a Anticyclone weather system:

-high pressure

-1 air mass

-can last several days

-brings stable conditions


descending creating an area of high pressure


rising creating an area of low pressure

How are Anticyclones formed?

1.air descends towards earth surface it descends air molecules compressed

3.pressure increases and it warms

4.air warming causes moisture to be evaporated clouds with a clear sky

How large can Anticyclones be and how long can they last for?


-several days

What are the winds like and what direction do they move in within Anticyclones?



What weather is associated with summer Anticyclones?

-clear skies

-high temperatures = thunderstorms

-dry weather

-major anticyclones can deflect low pressure areas to the north = heatwaves

What weather is associated with winter Anticyclones?

-clear skies

-gain of warmth in day

-rapid heatloss at night

-surface cooling = radiation fog and frost

-cold polar continental air can bring snow to east UK

-defection of warmer depressions - freezing conditions

Define: Storm event

an atmospheric disturbance with strong winds, rain, snow or other precipitation often with thunder and lightning

What TWO case studies can be used as an example of a storm event?

-the great storm of 1987

-wet and windy 2012

What are storm hydrographs used for?

-illustrate discharge in relation to climate

-show short term variations

-relationship between rainfall event & discharge

Define: a Flood event

when the capacity of a river to transport water is exceeded and water bursts its banks

Define: Base flow

the normal day to day discharge within the river channel

Define: Storm flow

storm precipitation involving surface runoff and through flow

Define: Peak discharge

point on hydrograph where discharge is the highest

Define: Peak rainfall

point on hydrograph where rainfall is the highest

Define: Lag time

time between peak rainfall & peak discharge

Define: Bankfull discharge

maximum drainage a river channel is capable of carrying without flooding

Define: Falling limb

fall in discharge back to base flow

How does the size of the rivers Drainage basin affect a storm hydrograph?

large = catch more precipitation = higher peak discharge

small = short lag time, precipitation doesnt have far to travel

How does the shape of a rivers Drainage basin affect a storm hydrograph?

circular - short lag time, high peak discharge

long and thin - longer lag time, low peak discharge

How does the gradient of a rivers Drainage basin affect a storm hydrograph?

steep sided basin = shorter lag time

shallow sided basin = longer lag time

If a river has a 'High drainage density' what does this mean?

it may have many streams

can drain quickly

short lag time

If a rivers drainage basin is saturated, what might this mean?

increased surface runoff

reduced infiltration

reduced lag time

How does the rock type in a river basin affect a storm hydrograph?

impermeable - high surface runoff, through flow reduced, reduced lag time, increase in peak discharge

What may intercept precipitation and how?


slows movement of water into channels

increased lag time

evapotranspiration - reduced peak discharge of river

How might man made drainage systems affect storm hydrographs?

shorter lag time

high peak discharge water

cant evaporate/infiltrate

How might an urbanised area affect storm hydrographs?

impermeable surface

infiltration decreases

surface runoff increases

shorter lag time

increased peak discharge

What is a flashy hydrograph?

rapid response to rain fall

short lag time

What is a flat hydrograph?

slower response to rain fall

long lag time

What type of weather system is associated with Gale force winds?

low pressure weather system

high pressure gradient

When do Gale force winds occur?

when air pressure DROPS to a very low level

What are the characteristics of Gale force winds?

very fast winds

cause damage to buildings/roofs

Gale force winds are a common feature of what climate?

Central temperate western maritime (CTWM) climate

worst in autumn when sea temp is warm ot power low pressure cells

magnitude greatest in western UK