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61 Cards in this Set
- Front
- Back
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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 |
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Where do air masses that affect the British Isles originate from? |
-from areas of permanent high pressure -polar or sub-tropical regions |
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On leaving source - If the air mass follows a maritime (oceanic) track: |
humidity increases due to evaporation from ocean |
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On leaving source - If the air mass follows a continental track: |
low humidity |
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On leaving source - If the air mass heads towards the equator it is... |
heated from below becomes unstable |
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On leaving source - If the air mass heads towards the poles it is... |
cooled becomes stable
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Outline unstable air: |
-less dense than surrounding air -more buoyant -continues to rise -uncertain weather conditions -upper layers unstable = thunderstorms |
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What 5 air masses affect the UK? |
1.artic maritime 2.polar continental 3.tropical continental 4.tropical maritime 5.polar maritime |
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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 |
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Where and between what two air masses do Depressions form? |
between polar maritime (PM) and tropicla maritime (TM)
along polar front |
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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 |
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What are the characteristics of the Polar continental? |
-easterly -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 |
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What are the characteristics of the Tropical continental? |
-south -only occurs in summer when sub-tropical high pressure moves north -stable lower layers -unstable upper layers = thunderstorms -droughts -heatwaves |
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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 |
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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 |
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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
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What direction do Depressions spin in the Northern hemisphere? |
anticlockwise |
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What is stage 1 of a Depression called? |
Embryo |
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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) |
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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 |
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Define: Dew point |
the temperature at which the atmosphere is 100% saturated with water vapour and dew forms due to condensation |
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What weather is associated BEFORE a warm front? |
-temperature cools -pressure falls -rise in dew point -prolonged precipitation |
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What weather is associated BEHIND a warm front? |
-temperature increases -patchy low stratus cloud -patchy rain -winds veer and turn clockwise |
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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 |
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What weather is associated DURING THE PASSING of a cold front? |
-sudden temperature drop -sharp rise in pressure -heavy rain -possibly thunder/lightning |
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What weather is associated when a cold front has COMPLETELY PASSED? |
-shower clear -temperature drops -pressure continues to rise steadily -dew point lowering |
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What is an Occluded front? |
-signifies the end of a depression system -where cold front catches up with warm front
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Outline the characteristics of a Anticyclone weather system: |
-high pressure -1 air mass -can last several days -brings stable conditions |
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Air PRESSURE INCREASES if air is... |
descending creating an area of high pressure |
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Air PRESSURE DECREASES if air is... |
rising creating an area of low pressure |
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How are Anticyclones formed? |
1.air descends towards earth surface 2.as it descends air molecules compressed 3.pressure increases and it warms 4.air warming causes moisture to be evaporated 5.no clouds with a clear sky |
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How large can Anticyclones be and how long can they last for? |
-3000km -several days |
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What are the winds like and what direction do they move in within Anticyclones? |
-calm -clockwise |
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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 |
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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 |
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Define: Storm event |
an atmospheric disturbance with strong winds, rain, snow or other precipitation often with thunder and lightning |
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What TWO case studies can be used as an example of a storm event? |
-the great storm of 1987 -wet and windy 2012 |
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What are storm hydrographs used for? |
-illustrate discharge in relation to climate -show short term variations -relationship between rainfall event & discharge |
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Define: a Flood event |
when the capacity of a river to transport water is exceeded and water bursts its banks |
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Define: Base flow |
the normal day to day discharge within the river channel |
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Define: Storm flow |
storm precipitation involving surface runoff and through flow |
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Define: Peak discharge |
point on hydrograph where discharge is the highest |
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Define: Peak rainfall |
point on hydrograph where rainfall is the highest |
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Define: Lag time |
time between peak rainfall & peak discharge |
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Define: Bankfull discharge |
maximum drainage a river channel is capable of carrying without flooding |
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Define: Falling limb |
fall in discharge back to base flow |
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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 |
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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 |
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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 |
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If a river has a 'High drainage density' what does this mean? |
it may have many streams
can drain quickly
short lag time
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If a rivers drainage basin is saturated, what might this mean? |
increased surface runoff
reduced infiltration
reduced lag time |
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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 |
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What may intercept precipitation and how? |
vegetation
slows movement of water into channels
increased lag time
evapotranspiration - reduced peak discharge of river |
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How might man made drainage systems affect storm hydrographs? |
shorter lag time
high peak discharge water
cant evaporate/infiltrate |
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How might an urbanised area affect storm hydrographs? |
impermeable surface
infiltration decreases
surface runoff increases
shorter lag time
increased peak discharge |
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What is a flashy hydrograph? |
rapid response to rain fall
short lag time
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What is a flat hydrograph? |
slower response to rain fall
long lag time |
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What type of weather system is associated with Gale force winds? |
low pressure weather system
high pressure gradient |
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When do Gale force winds occur? |
when air pressure DROPS to a very low level |
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What are the characteristics of Gale force winds? |
very fast winds
cause damage to buildings/roofs |
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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 |
