5 - Atmospheric Circulation Flashcards
Where does a radiation surplus occur?
In the tropics(<30 N/S)
Describe the three cell structure of the atmosphere.
Hadley Cell - warm air rises over the equator and moves poleward, becomes cooled enough to sink at 30 N/S(sub tropical high pressure belt) and then the S.E. trade winds move towards the equator.
Ferrel Cell - determined by Hadley & Polar cell
Polar Cell - warm air rises at 45 N/S, travels poleward sinks as cold air over the poles and then the sub-polar low belt moves back towards the Equator.
What other factors are influences on mean circulation?
Seasons, continents, mountain ridges
Describe the Intertropical Convergence Zone and its influences on the climate.
Rising branch of Hadley cells near the Equator
Belt of low atmospheric pressure and weak winds
Also known as Doldrums where sailing ships get stuck on weak winds
Converging surface flows
Convergence of moist & warm air
Triggers convection
Narrow band of thunderstorms and high precipitation
Moves with seasons
Lags Sun’s position by 1 month behind
Connected to South Asian monsoon
On average, located at 5 N due to large land masses in NH
Describe the Hadley Cell.
Mainly driven by latent heat release in ITCZ, not horizontal temp diff
Air rises moist adiabatically in ITCZ
Moves polewards once in the atmosphere
Westerly winds due to Coriolis
Radiative cooling
Sinks dry adiabatically in subtropics
Belt of high pressure
Desert areas e.g. Sahara
Low surface temperature differences
Return flow form trade winds
Easterly winds due to Coriolis
Walker circulation superimposed
East-West circulation cell due to ocena ocntinent temperature contrast
Connected to El Nino
Small scale cloud systems prevail on daily basis
Name some examples of semi-permanent pressure systems.
Azores(High Atlantic), Pacific High, Icelandic Low, Aleutian Low
These are highs and lows that move only slightly during the course of the year.
Describe the Polar Front Jet Stream
Separates cold polar from warm subtropical air
Large meridional temperature differences
Large pressure differences aloft(10km)
Band of high geostrophic wind
Jet stream from west to east
Weather systems move along jet stream
Defines storm track over North Atlantic
What does monsoon mean?
Arabic for season
Originally referred to seasonal change of wind direction in Arabian Sea
What are the main characteristics of the classic monsoon system?
Wet summers and dry winters
Adjacent oceanic basis
Pronounced, seasonally varying land-sea temperature contrasts
Seasonally reversing surface winds
Large scale regions of low pressure
Similar to land sea breeze but on larger scale and with seasonal variations rather than diurnal
These seasonal changes coincide with north-south movement of ITCZ(and Hadley cell) particularly over land
Affected by Coriolis force because of continental scale of monsoon
On-shore winds can develop even during winter monsoon and bring precipitation to parts of East India
Presence of Himalayas plays big role in precipitation distribution during monsoon season – orographic rainfall due to uplift on mountains triggers precipitation
Where does the majority of ocean circulation occur?
90% of solar radiation absorbed in upper 100m as the water column is inherently stable, therefore minimal vertical mixing
What are the three factors that mainly influence ocean currents?
Wind stress, Coriolis force & thermohaline circulation
How do ocean currents affect the Earth’s climate?
They redistribute about 1/3 to 1/2 of the heat excess from the Equator to the Poles, with temperature and salinity differences typically being small and eddies being important for horizontal mixing.
Describe Ekman Transport
Wind stress drives surface ocean currents:
Coriolis force creates a net transport at right angles to the wind stress – Ekman Transport
Creates upwelling in coastal regions if transport points away from coast
e.g. wind from south to north along coast of Peru creates upwelling that brings up cold and nutrient rich water(Humboldt Current) – this helps with fishing
Upwelling in Equatorial Regions
Due to Coriolis, equatorial currents tend to diverge or move apart causing upwelling in the open ocean
Upwelling correlated with nutrient rich water
Occurs along:
East coasts of SA & Africa
Along Equator
In cold oceans of Northern Hemisphere
How do latitudinal wind belts influence ocean currents?
They produce ocean currents and are generally anticyclonic - clockwise in the NH and vice versa in the SH.
