Circulation Flashcards
What is the Boundary Layer?
The layer most influenced by Friction
Atmospheric Ekman pumping, spirals and flow occurs here
What is an Ekman Spiral and what causes it?
Creation of a wind spiral with height.
CAUSE: Friction. Closer to surface = increased frictional drag and obliqueness of wind across isobars
What is the surface degree of obliqueness of an Ekman Spiral over sea? Is this greater than over land?
10-20 degrees - No (land is 25-35 degrees)
What happens with increased height?
Wind gets closer to geostrophic speed
What happens in an anti-cyclone and what sort of pressure system is it?
Air descends and diverges (moves outward) in the boundary layer - high pressure.
What is the process of air movement as a result of high and low pressure systems called?
Ekman Pumping
What is convergence and where does it occur at the surface?
The inward movement of air, occurs in low pressure systems.
What direction do anti-cyclones rotate in the Northern Hemisphere?
Clockwise
How many pressure belts is the Earth’s atmospheric circulation made up of?
4
Which cells are located over the tropics?
Hadley Cells
Which model of atmospheric circulation breaks down as a result of Conservation of Angular Momentum (increase in velocity as radius decreases)?
Hadley’s Uni-Cellular Model of General Circulation
What happens to air at 30 degrees latitude?
It cools and sinks, or gets caught in Jet Streams
What are Trade Winds?
A prevailing pattern of Easterly surface winds found in the tropics. They replace rising air at 30 degrees latitude.
Which circulation cells are directly thermally driven?
Polar Cells
What are horizontal winds travelling East -> West parallel to longitude referred to as?
Zonal Components
Give 3 features of the Topics
1) Weather/climate dominated by Hadley cells and the ITCZ
2) There is zonal pressure distribution and minor Coriolis Effect
3) Inversion Zones exist
What are Inversions?
Areas whereby there is a deviation in normal atmospheric property changes with height.
What causes movement to the Equator in the Subtropics?
Coriolis Effect
Where do you find the Sub-Tropics and what tends to occur at the surface?
30 degrees latitude North and South - divergence (sub-tropical highs)
Where is the influence of the Polar Jet Stream meeting warm Southern Air most significantly felt?
The Mid Latitudes (23-66 degrees latitude)
Give 3 features of the Mid-Latitudes
1) Baroclinic geostrophic current = not just pressure determines air density
2) Pressure changes = Temperature change
3) Strong prevailing winds
What are fast flowing, meandering air currents, caused by temperature differences between Tropical & Polar air masses called?
Jet Streams
2 Types of Jet Stream:
1) Polar (strongest)
2) Subtropical (weaker)
Which type of jet stream is the boundary between Mid-Latitude and Equatorial air?
Sub-Tropical
Give 3 features of the Polar Regions
1) Very strong katabatic winds
2) Responsible for meridional (N->S) flow
3) Arid, thermally driven cells with descending air (divergence)
What is the ITCZ?
A region of strong convective activity at the Equator - where NH and SH trade winds meet.
What has greater seasonal temperature differences than ocean regions?
Continental regions
What land masses have increased pressure in winter and decreased pressure in summer? Give examples.
Large, mid-latitude land masses - eg. North America and Eurasia)
What does low pressure in summers over large, mid-latitude land masses cause?
A cyclonic system: strong inflow of air (convergence) in Summer blowing wind ocean-> land. Thus a warm and moist summer monsoon.
What sort of air flow occurs in winter over large, mid-latitude land masses, and what does it cause?
Outflow - an anti-cyclone develops due to divergence. Wind blows land -> ocean, so winter monsoon is dry & cool
What is Vorticity and what are the 3 elements of this concept?
The rotation/angular velocity of particles in a system.
1) Magnitude
2) Direction
3) Sense of Rotation (positive vorticity = anticlockwise)
What does Vertical Positive Vorticity cause?
Upper level divergence in the Positive Vorticity Advection region - thus rising air (cyclone)
What is the sum of a parcel about its own axis (SHEAR), rotation of a parcel about the axis of a pressure system (CURVATURE) and rotation due to atmospheric motion (CORIOLIS) referred to?
Absolute Vorticity
At what temperature is pure water most dense?
4 degrees Celcius
What is the salinity of standard ocean water?
35ppt - 3.5%
Ocean Circulation is driven by what 2 ‘engines’?
1) Thermohaline Circulation
2) Wind-Driven Surface Circulation
What happens if the wind blows in the same direction for a prolonged duration?
Local surface currents are created.
What is Ekman Transport and what does it cause?
The net transport of water due to coupling between wind and surface waters - causes NET water movement at 90 degrees to wind direction
At what point does influence of wind on ocean circulation cease?
100-150m
As a result of the Coriolis Effect acting to the Right in the NH, at what angle does the surface water current move in relation to wind direction?
45 degrees - this increases with depth as Coriolis effect has longer to act
How is Ekman Spiral different to Ekman Transport?
An Ekman Spiral is the result of the Coriolis effect acting upon the ocean surface in addition to Wind - Ekman Transport is purely the result of Wind Direction.
What do variations in sea surface height (caused by Ekman Transport) cause?
Pressure gradients & Geostrophic Flow at Gyre centres
What is Ekman Pumping?
Downwelling of water due to pressure/density gradients in the vertical water column
What direction does Ekman Transport move water in relation to the coast and what process is associated with this?
Away - Upwelling
Where is upwelling most common?
On the West coasts of continents
Which is worse for biological productivity: Upwelling or Downwelling?
Downwelling
What drives ocean gyres?
1) Balance between pressure gradients caused by elevations
2) depressions of sea surface caused by Ekman Transport and Coriolis Effect
Where do Sub-Tropical gyres sit?
Below areas of high pressure
What controls Thermohaline Circulation, and what drives it?
Temperature and Salinity - driven by high-latitude cooling
What forms at 60 degrees latitude?
Deep Water
What percentage of the Moon’s tide-generating force does the Sun have?
46%
What is longer: Solar or Tidal day? What does this mean?
Tidal Day (24 hours and 50 minutes) - so times of high tide change by 50 mins from one day to the next.
How long does it take for the Moon to orbit Earth?
29.5 days
Where are most intense currents found?
Equatorial Zone, Eastern Japanese Coasts, North America and South Africa.
