EESA09H3 Lecture Notes - Lecture 3: Hadley Cell, Atmospheric Circulation, Volumetric Heat Capacity
18 May 2018
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EESA09 – Lecture 3: Global Wind Circulation
RECALL – vertical structure of the atmosphere
1. Troposphere
2. Stratosphere
3. Mesosphere
4. Thermosphere
Global Circulation
- Observation – more energy released in Polar Regions than is received from the sun (reverse is
true for equatorial region).
o How to accout for this? Atospheric circulatio - poleward transport by wind
o ALL are interconnected
1. ONE CELL THEORY –one large overturning atmospheric cell (0-90 degrees)
One large Hadley Cell – George Hadley (1685-1768) Brit.lawyer + amateur meteorologist
a. Air rises @ equator, moves poleward & sinks at the pole.
Theory is only reasonable if the earth did NOT rotate. Tilt, land/water contrast also play a
crucial role
b. WHY IT IS NOT ACCURATE ot eough; CANNOT EXPLAIN THE FOLLOWING…
i. Rotation – itroduces the Coriolis Effect
Not explained in the theory: prevailing winds from the E & prevailing winds in
mid-latitudes are from W clearly not observed
ii. Tilt – seasonality
iii. Continentality – causes land/sea variation due to varying thermal inertia (e.g.
Monsoons)
c. Energy transportation:
i. Energy transported as sensible + latent hear
ii. Latent heat transport occurs when moist equatorial air moves poleward, cools,
condenses, and releases l.heat
- Atmospheric Heat Transport → 2 types that are transported in the atmosphere
o Sensible heat – what we ca feel
o Latent heat – heat is stored as water vapours, absorbed when water evaporates,
released when water condenses
1. Rising air cools & sinking air warms
2. Cooling leads to condensation
find more resources at oneclass.com
find more resources at oneclass.com
2. THREE CELL THEORY **better** - N & S: Hadley cell (0-30), Ferrel cell (30-60), Polar cell (60-90)
a. Hadley Cell – near the equator; air rises @ equator, moves poleward & sinks at 30 N&S.
i. Surface flow = equatorward and produces winds from the E (easterly winds)
b. Ferrel Cell – exists roughly b/w 30-60 in each hemisphere (thermally indirect)
i. Surface winds travel N + under influence of Coriolis force veers to the E
(westerlies in midlatitude)
ii. William Ferrel (1817-1891) – American meteorologist & mathematician (1856)
c. Polar Cell – Sinking @ poles, rising @ 60 N&S
i. Polar easterlies produced
- RISING – low pressure belt, cools
- SINKING- high pressure belt, warms
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Rising air cools & sinking air warms, cooling leads to condensation. Recall vertical structure of the atmosphere: troposphere, stratosphere, mesosphere, thermosphere. One large hadley cell george hadley (1685-1768) brit. lawyer + amateur meteorologist: air rises @ equator, moves poleward & sinks at the pole. Theory is only reasonable if the earth did not rotate. Tilt, land/water contrast also play a crucial role: why it is not accurate (cid:858)(cid:374)ot e(cid:374)ough(cid:859); cannot explain the following , rotation i(cid:374)troduces the (cid:858)coriolis effect(cid:859) Atmospheric heat transport 2 types that are transported in the atmosphere: sensible heat what we ca(cid:374) (cid:858)feel(cid:859, latent heat heat is stored as water vapours, absorbed when water evaporates, released when water condenses. Polar cell sinking @ poles, rising @ 60 n&s: polar easterlies produced. Intertropical convergence zone (itcz) area of rising air @ or near equator; heavy precipitation (layered clouds), seasonally it moves either n/s: trade winds winds that blow to the sw, surface component of hadley cell (0-30).
