5 - Atmospheric Circulation Flashcards
(18 cards)
Where does a radiation surplus occur?
In the tropics(<30 N/S)
(Ahrens, 2019)
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 60 N/S, travels poleward sinks as cold air over the poles and then the sub-polar low belt moves back towards the Equator.
(Ahrens, 2019)
What other factors are influences on mean atmospheric circulation?
Seasons, continents, mountain ridges
Describe the Intertropical Convergence Zone and how it varies throughout the year.
Rising branch of Hadley cells near the Equator, characterised by a belt of low atmospheric pressure, weak winds and converging surface flows
(Also known as Doldrums where sailing ships get stuck on weak winds)
Convergence of moist & warm air, which triggers convection
It also moves with seasons, as it lags behind Sun’s position by 1 month
On average, located at 5 N due to large land masses in NH
(Ahrens, 2019)
What are the ITCZ’s influences on the climate?
A narrow band of thunderstorms and high precipitation
It is also connected to South Asian monsoon
(Ahrens, 2019)
Describe the Hadley Cell.
Strongest of the 3 cells
Moist air rises adiabatically in ITCZ, then moves polewards in the tropopause as westerly winds due to the Coriolis
Sinks as dry air adiabatically in subtropics - this creates subtropical high pressure belt and therefore, desert areas such as Sahara exists
Return forms trade winds - easterly winds due to Coriolis
Walker circulation superimposed - East-West circulation cell due to ocean continent temperature contrast - connected to El Nino
Small scale cloud systems prevail on daily to seasonal scales
(Ahrens, 2019)
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, with large pressure differences aloft(10km), a band of high geostrophic wind and a jet stream from west to east
Weather systems move along jet stream - this defines storm track over North Atlantic
(Ahrens, 2019)
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(e.g. differential heating between Asian landmass and North Indian and Northwest Pacific Oceans leads to seasonal wind reversal)
Large-scale regions of low pressure
Similar to land-sea breeze but on a larger scale and with seasonal variations rather than diurnal
These seasonal changes coincide with the north-south movement of the ITCZ(and Hadley cell), particularly over land
On-shore winds can develop even during the winter monsoon and bring precipitation to parts of East India
(Ahrens, 2019)
What are some factors that affect the South-East Asian Monsoon?
Coriolis force: affects monsoon winds because of the continental scale of the monsoon
Presence of the Himalayas: plays a big role in precipitation distribution during the monsoon season, orographic rainfall due to uplift on the mountains triggers precipitation
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
(Biggs, 2003)
Describe Ekman Transport
Wind stress drives surface ocean currents:
Coriolis force creates a net transport at right angles to the wind stress – Ekman Transport
(Ekman, 1902)
How do Ekman Transport create upwelling?
Upwelling in coastal regions:
If transport points away from the coast
e.g., wind from south to north along the 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
(Bigg, 2003)
Where does Ekman Transport occur globally?
East coasts of SA & Africa, along the Equator, and the cold oceans of the Northern Hemisphere
How does wind driven ocean circulation occur?
Due to friction, wind drags the ocean surface
Coriolis force modifies water movement
Wind driven surface water movement confined to upper ~100m
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.
