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Introduction to Meteorology & Climate
Climate & Earth System Science
Peter LynchMeteorology & Climate Centre
School of Mathematical SciencesUniversity College Dublin
Introduction to Meteorology & Climate
Introduction toMeteorology & Climate
MAPH 10050
Peter Lynch
Meteorology & Climate CentreSchool of Mathematical SciencesUniversity College Dublin
Introduction to Meteorology & Climate
Chapter 07Chapter 07
Global Scale Winds
Introduction to Meteorology & Climate
Lecture 14
Introduction to Meteorology & Climate
Simple Introductory Examples:Transport of heat to equalize temperature
Explain on blackboard
• Bar of steel: one end in the fridge, one in the oven.
• Tank of water: heated at one end, cooled at the other.
Introduction to Meteorology & Climate
Voyage of ChristopherColumbus
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Introduction to Meteorology & Climate
Fitzroy &
Darwin
BeagleVoyage
Introduction to Meteorology & Climate
Fig. 7.10
Composite image (clouds & surface temperature). Note the line of clouds along the ITCZ
Introduction to Meteorology & Climate Introduction to Meteorology & Climate
Introduction to Meteorology & Climate
Mean Monthly Cloud Cover (%) in JanuaryMean Monthly Cloud Cover (%) in January
Introduction to Meteorology & Climate
Mean Monthly Cloud Cover (%) in JulyMean Monthly Cloud Cover (%) in July
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Introduction to Meteorology & Climate
GLOBAL CIRCULATIONGeorge Hadley first suggested in 1735 the general concept of atmospheric circulation – a single cell, to explain the existence of the easterly winds at the surfaceCold air at pole - high pressure at surface. Warm air at equator - low pressure at surface. Pressure gradient force at surface will move air from pole to equator at surface. Return path at high altitudes. Coriolis force produces easterlies
Introduction to Meteorology & Climate
Hadley Hadley CellCell
Introduction to Meteorology & Climate
GLOBAL CIRCULATIONIn reality, we have three cells, with boundaries at about 30º and 60º latitude.
This results in sinking air at 30ºN and 30ºS. But sinking suppresses cloud development and precipitation. Hence most of the worlds deserts occur along these latitudes.
These are the horse latitudes.
Circulation at the surface moves from 30ºto the equator – easterly winds.
Introduction to Meteorology & Climate
Three cell
model
Introduction to Meteorology & Climate
Lecture 15
Introduction to Meteorology & Climate
GLOBAL CIRCULATIONGLOBAL CIRCULATIONBetween 30º and 60º the circulation at the surface is from 30º to 60º, giving rise to westerly winds.Between 60º and the Poles, the flow is from the Pole to 60º, leading to easterly winds at the surface.Upwelling at the equator and at 60º –precipitation.The Doldrums.
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Introduction to Meteorology & Climate
Conservation of Angular Momentum
Demonstration:Nut-on-a-string
Introduction to Meteorology & Climate
Conservation of Angular Momentum:
As the parcel of air moves from the equator towards the poles, its velocity increases to conserve angular momentum.
At the same time the Coriolis force acts to produce a strong westerly wind – the sub-tropical jet stream.
Introduction to Meteorology & Climate Introduction to Meteorology & Climate
Introduction to Meteorology & Climate
JET STREAMSJET STREAMS
As the air moves from the equator to 30º at high altitudes, its velocity increases to conserve angular momentum.
At the same time the Coriolis force acts to produce a strong westerly wind – the sub-tropical jet stream
A similar jet forms at 60º – the polar jet, or polar front jet.
Introduction to Meteorology & Climate
SUBTROPICAL AND POLAR JET STREAMS IN RELATION TO THE THREE CELLS
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Introduction to Meteorology & Climate
Cloud band from Pacific to Florida follows Sub-tropical jet
Introduction to Meteorology & Climate
Average Global Sea-level Pressure
Extra-tropical WesterliesIcelandic Low; Bermuda HighTrade winds; ITCZDoldrums; Horse latitudes
Introduction to Meteorology & Climate Introduction to Meteorology & Climate
Introduction to Meteorology & Climate
Average Global Winds
Extra-tropical WesterliesIcelandic Low; Bermuda HighTrade winds; ITCZDoldrums; Horse latitudes
Introduction to Meteorology & Climate
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Introduction to Meteorology & Climate Introduction to Meteorology & Climate
Lecture 16
Introduction to Meteorology & Climate
WESTERLIES
In the upper troposphere:
High pressure over equator, low pressure over poles.Net flow from the equator to the poles.This flow plus Coriolis effect produces westerlies.Winds are (nearly) geostrophicPressure gradient increases with altitude. So does the wind speedJet streams are part of the westerlies
Introduction to Meteorology & Climate
Introduction to Meteorology & Climate
WAVES IN THE WESTERLIES
Dish pan experiment.C. G. Rossby.Waves along the jet streams are known as Rossby waves.Three to six of them around the globe. The air flow along the edge of the waves can be rapid, however the waves move slowly – about 15º per day. Higher jet stream speeds in the winter. Jets shifts south in the winter, north in the summer.
Introduction to Meteorology & Climate
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Introduction to Meteorology & Climate Introduction to Meteorology & Climate
(A) Zonal flow pattern – air flows parallel to latitudes.
(B) Meridional flow pattern.
(C) Combination of the two flows.
Index Cycle
Introduction to Meteorology & Climate Introduction to Meteorology & Climate
Introduction to Meteorology & Climate
Long Waves & Short Waves
Introduction to Meteorology & Climate
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Introduction to Meteorology & Climate Introduction to Meteorology & Climate
Rossby waves in a dish-pan
Introduction to Meteorology & Climate
WESTERLIES AND THE HEAT BUDGET
Major function of atmospheric dynamics is to move heat from the equator to the poles.
But how can winds move heat when the predominate wind direction is zonal (E to W, or W to E)?
The meanderings of the jet streams continually mix cold and warm air, thus transporting heat.
Introduction to Meteorology & Climate
POLEWARD TRANSPORT OF HEAT BY THE OCEANS AND ATMOSPHERE
Introduction to Meteorology & Climate
Mean position of the ITCZ
in January and July
Introduction to Meteorology & Climate
THE SW MONSOON