WCC: Water Cycle - Processes Driving Change in the Magnitude of Water Cycle Stores Over Time Flashcards
Why does atmospheric moisture have the lowest residence time?
Evaporation and precipitation is constantly happening
Why do ice caps have the highest residence time?
Once water is stored there, it gets trapped and has nowhere to go, for example it can’t percolate through like it can in the ground
What is melting?
Solid to liquid by heating
What is freezing?
Liquid to solid by heat loss
What is condensation?
Water vapor into liquid water
What is sublimation?
Solid to gas without first becoming a liquid
What is deposition?
Gas to solid without first becoming a liquid
What is latent heat of vaporisation?
The heat energy absorbed when water changes from a liquid to a gas
What is latent heat of fusion?
The heat energy absorbed when water changes from a solid to a liquid
What is latent heat of sublimation?
The heat energy absorbed when a water changes from a solid to a gas
What 6 factors affect the rate of evapotranspiration?
Amount of insolation (solar energy) Availability of water (surface and soil) Humidity of the air Air temperature Amount of wind Amount of vegetation
What is condensation affected by?
Humidity of the air
Temperature
Availability of condensation nuclei / surfaces
What is dew point?
The temperature at which the air becomes saturated causing water to condense
What is precipitation affected by?
Cloud formation affected by: Avaliability of water for evaporation Air temperature - humidity Availability of condensation nuclei Altitude
12 factors affecting runoff generation
rate of infiltration amount of evaporation amount of vegetation amount of precipitation temperature soil type (density) saturation of the land rock type (permeability) wind frozen ground season land use
Residence time of oceans
3,600 years
Residence time of icecaps
15,000 years
Residence time of groundwater
Up to 10,000 years
Residence time of rivers and lakes
2 weeks - 10 years
Residence time of soil moisture
2-50 weeks
Residence time of atmospheric moisture
10 days
Do ocean stores vary in the short term or long term? Give evidence
The long term - during the last Ice Age sea levels were as much as 120m lower
What are the key processes driving change in the magnitude of water stores?
Evapotranspiration Condensation Precipitation Runoff generation Cryospheric processes
What is evaporation?
The transfer of water from liquid state to gaseous state due to energy from solar radiation
Where can evaporation occur from?
Open water or wet surfaces
Where does 90% of evaporated water come from?
Oceans
What is transpiration?
The transportation of water through the roots of a plant and its subsequent release through stomata on the leaves
How does the humidity of the air affect rate of evapotranspiration?
The closer the air is to dew point, the slower the rate of evaporation
Why does the evaporation of water cool its surroundings?
It uses energy in the form of latent heat to evaporate
What is a condensation nucleus?
Tiny particles in the air e.g smoke, salt, dust, that are below the dew point temperature
What happens if a condensation nucleus or surface is below freezing?
Deposition in the form of hoar frost
Why is there more condensation at lower temperatures?
Because as air cools it is able to hold less water vapour
What are the 2 ways condensation occurs?
- When the temperature of air is reduced to dew point but its volume remains constant.
- Adiabatic cooling - when the volume of air increases but there is no addition of heat
How does adiabatic cooling occur in the water cycle?
When air rises and expands in the lower pressure of the upper atmosphere
What is the orographic effect?
When air is forced to rise over hills so cools and condenses
What is the frontal effect?
When masses of air of different temperatures and densities meet. The less dense warm air rises over the denser cold air and condenses.
What is the convectional effect?
When localised warm surfaces heat the air above. This expands, becomes less dense and rises.
What does the global atmospheric circulation model identify?
Latitudinal zones of rising and falling air
What are the 3 interconnected cells present in the global atmospheric circulation model
Hadley
Ferrel
Polar
What does ITCZ stand for?
Inter-Tropical Convergence Zone
What is runoff generation?
The atmospheric moisture that is transferred to oceans as surface runoff or groundwater flow
How do transit times of different types of runoff vary?
Overland flow and river flow is relatively rapid whereas transit times to the ocean for deep groundwater can be thousands of years
When is surface runoff generated?
When rainfall intensity is greater than infiltration capacity or when rain falls on soils that are already saturated
What are the 2 main cryospheric processes?
Accumulation and ablation
What glacial period began 2.58 million years ago and continues today?
the Quaternary glaciation
Describe the glacial periods of the Quaternary glaciation.
Interruptions in the global hydrological cycle. Sea level was approx 120m lower than today due to the large volume of ice on land. Continental glaciers covered large parts of Europe, North America, and Siberia.
Describe the interglacial periods of the Quaternary glaciation.
Global ablation exceeds accumulation.
How many glacial cycles have there been in the past 740,000 years?
8
Why does permafrost rarely occur under ice?
Temperatures aren’t low enough
What cryoshperic processes occur in the long term?
Glacial periods
What cryoshperic processes occur in the short term?
Seasonal accumulation and ablation (melting or ice calving)
What is a glacier’s equilibrium line?
The line marking the altitude where annual accumulation and ablation are equal
In what direction has the equilibrium line been moving in recent decades and why?
To higher altitudes as the climate warms
How does water enter long term storage as ice?
Snow falling on glaciers and ice sheets becomes compressed, forming layers of glacial ice
What would the total melting of all the polar ice sheets lead to?
A 60m rise in sea level, adding a large volume of water to the ocean store
What is the direct cause of all forms of precipitation?
Condensation
How can the distribution of precipitation be seen at a global scale?
Through the global atmospheric circulation model
What are the 3 ways adiabatic cooling can form precipitation?
Orographic effect
Frontal effect
Convectional effect
What are clouds?
Areas of the atmosphere where water has condensed into tiny water droplets or small ice crystals
What type of clouds does the convectional effect produce?
Cumulus and cumulonimbus clouds
In the water cycle, what ways can the temperature of air be reduced to dew point while its volume remains constant?
- When warm moist air passes over a cold surface
- On a clear winter’s night when heat is radiated out to space and the ground gets colder, cooling the air directly in contact with it
How many major glacial periods have there been in the Earth’s history?
5
What form does water vapour tend to take when the temperature of air is reduced to dew point while its volume remains constant?
Fog
Name 3 different types of fog
Radiation fog
Advection fog
Steam fog
How does radiation fog form?
Heat is absorbed by the Earth’s surface during the day and radiated out into space during the night. This makes the ground colder, cooling the air directly in contact with it until it reaches dew point.
How does advection fog form?
Warm, moist air moves horizontally over a cold surface such as snow or ice, cooling it until dew point.
[Why is cloud formation an important process driving change in the magnitude of water cycle stores over time and space?]
[Different ways clouds form have different outcomes e.g cloud or fog. Cloud can result in precipitation whereas fog is likely to just evaporate, leading to differences in water stores. The different ways clouds form will vary depending on location - EXAMPLE: california redwoods and advection fog in san fran]
How does steam fog form?
Cool air moves over water that’s still warm form summer. The shallow layer of saturated warm air immediately above the warmer water is cooled beyond the dew point so condensation occurs.
Describe and explain the distribution of steam fog
It is common in the Arctic and Antarctic, however uncommon in temperature climates because it requires very low air temperatures
What is the latitude of the tropic of cancer?
23 degrees N
What is the latitude of the tropic of capricorn?
23 degrees S
Describe the global distribution of cloud formation and its impact on climates.
There is a band of high rainfall at the equator, creating tropical climates, and at 60 degrees north and south, creating temperate climates. There is a lack of cloud formation at 30 degrees north and south as well as at the poles, creating desert climates.
How do the Hadley cells form?
High temperatures at the equator results in high levels of evaporation. The warm, moist air rises, cools and condenses forming towering banks of cloud and heavy rainfall in the ITCZ. Unable to continue rising, the air is forced poleward by the continual rise of air below. At about 30° latitude on either side of the equator, the air travels so much faster than the surface wind speed that it can’t extend further poleward. The now cool, dry, high altitude air begins to sink. As it sinks, it warms adiabatically, decreasing its relative humidity. Near the surface, a frictional return flow completes the loop.
Why is the Ferrel cell considered a secondary circulation feature?
A large part of the energy that drives the Ferrel cell is provided by the polar and Hadley cells circulating on either side and that drag the Ferrel cell with it
How do the Ferrel cells form?
Some of the air sinking from the descending limb of the Hadley cell is forced poleward at it nears the surface. This warm air flows poleward until it meets cold air from the equator at the polar front. The convergence of the warm and cold air results in rising air and cloud formation. Upon reaching the troposphere the air flows back towards the equator.
How do the polar cells form?
Cold air at the poles is forced towards the equator. It meets the warm air of the Ferrel cell flowing polewards from the Tropics at the polar front. The convergence of the warm and cold air results in rising air and cloud formation, and some f the air travels poleward. When the air reaches the pole, it has cooled and is considerably denser than the underlying air. It descends, driving the cold mass of air towards the equator.
At what latitudes do high pressure areas occur?
At the poles and subtropics (30 degrees N and S)
At what latitudes do low pressure areas occur?
At the equator and subpolar areas (60 degrees N and S)
What is the polar front?
The boundary at which cold air from the poles meets warm air from the Tropics between the polar and Ferrel cells
At which pressures to clouds form?
Low pressures
Which winds do the Hadley cells form?
The NE and SE trade winds
Which winds do the Ferrel cells form?
The westerlies
Which direction do winds curve in the northern hemisphere?
To the right of their path
Which direction do winds curve in the southern hemisphere?
To the left of their path
What makes global atmospheric winds curve?
the Coriolis effect
Describe how the ITCZ changes over time.
The latitude of the ITCZ varies with the seasons, as it moves toward the hemisphere with most heat. Therefore in northern summers it is north of the equator, whereas in southern summers it is south of the equator.
How does variation in the ITCZ drive change in the magnitude of water cycle stores over time?
Variation in the ITCZ throughout the year results in the wet and dry seasons of the tropics rather than the cold and warm seasons of higher latitudes. Longer term changes in the ITCZ can result in severe droughts or flooding in nearby areas.
