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by: Ferne Romaguera


Marketplace > Georgia State University > Geography > GEOG 1112 > INTRO TO WEATHER CLIMATE
Ferne Romaguera
GPA 3.73

Leslie Edwards

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Leslie Edwards
Class Notes
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This 12 page Class Notes was uploaded by Ferne Romaguera on Monday September 21, 2015. The Class Notes belongs to GEOG 1112 at Georgia State University taught by Leslie Edwards in Fall. Since its upload, it has received 50 views. For similar materials see /class/209801/geog-1112-georgia-state-university in Geography at Georgia State University.




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Date Created: 09/21/15
Lecture 12 Chapter 6 Atmospheric and Oceanic Circulations Today we will be discussing wind which involves air pressure A reminder air pressure is pressure produced by the motion size and number of gas molecules in the air and exerted on surfaces in contact with the air It is measured by millibars mb here in the US Air pressure differs over the surface of the earth There are areas of high pressure and areas of low pressure Areas of high pressure usually involve air that is descending Pressure is high as the air becomes increasingly dense and air molecules pile on top of one another creating a ridge of air Areas of low pressure usually involve air that is ascending Pressure is low and the air is less dense because the molecules are spreading out The spreadout air molecules create a trough of air Average sea level pressure is 1013 mb Millibars F Areas of high pressure are dense because air molecules pile on top of one another F Areas of high pressure form ridges T Areas of low pressure are very dense WE Areas of low pressure create troughs Wind What is wind The horizontal movement of air across Earths Surface What produces wind Differences in air pressure density between locations produce wind Winds are named for The direction from which they orginate For example a wind from the west is a westerly wind blows eastward 39 a wind from the south is a southerly wind blows northward Matching l Involve air that is descending C Involve air that is ascending and converging B The horizontal movement of air across Earth s surface A Differences in air pressure density between locations produce this A Originates from the east and moves west E Originates from the west and moves east D 9959 Wind Low Pressure High Pressure Westerly wind Easterly wind mcowgt T Wind moves from low pressure to high pressure Four forces determine the speed and direction of winds 1 Gravitational force 2 Pressure gradient force 3 Coriolis force 4 Friction force 1 Gravitational Force Gravitational force Gravity compresses the atmosphere worldwide with density decreasing as altitude increases Without gravity there would be no atmospheric pressure much less differences in pressure so we could NOT have wind WF Without gravitational force we would have uncontrolled winds 2 The Pressure Gradient Force The pressure gradient force is the force that The force that causes air to move from an area of iHigher to an area of Lower We can plot pressure gradients on weather maps and predict which direction the wind will blow We do so using isobars which are iisolines plotted on a weather map to connect points of equal pressure The spacing between isobars indicates the intensity of the pressure difference Closer isobars denote a iSteep Gradient Isobars spaced wider apart from one another mark a more iGradual gradient A steep pressure gradient causes iFaster air movement from a highpressure area to a low pressure area A gradual gradient creates a iSlower Air ow air ow The pressure gradient force acts at iRight Angles perpendicular to the isobars If the pressure gradient acted alone wind would blow across isobars at right angles Which is not true of Pressure Gradient winds l B They blow from high pressure to low pressure C They are faster where isobars are close together D We can look at isobars on a map and predict where winds will be faster 3 Coriolis Force The Coriolis Force makes wind that travels in a straight path appear to be de ected in relation to Earths rotating surface The Coriolis force de ects wind to the iRight in the Northern Hemisphere and to the le in the Southern Hemisphere Without the Coriolis force winds would move along straight paths between high and low pressure areas The Coriolis force is at work because our planet rotates The pressure gradient force and Coriolis force combine to form geostrophic winds winds that ow parallel to isobars Earth s rotation and centrifugal force add a twist to air movements High pressure and low pressure areas develop a rotary motion So we end up 39 39 39 and 39 39 wise air v t Winds around high pressure areas are moving clockwise in the northern hemisphere counterclockwise in southem hemisphere These high pressure areas are called anticyclones Winds around low pressure areas are moving counterclockwise in the northern hemisphere clockwise in the southem hemisphere These flow pressure areas are called cyclones Lumrln llrsulhng K r m Inne Pm a h M 39 m m1 Three factors affect the Coriolis Force 1 iLatitude The Coriolis effect is izeroiat the equator increases to half at 30 degrees N and S latitude and is maximized at the poles 2 iSpeed The Coriolis effect iincreasesi as the ispeed ofthe moving object increases So the faster the wind speed the greater the de ection 3 iDistance The Coriolis effect does not affect very short distancei and times So water going down the drain isn t affected Which is FALSE about the Coriolis Force All True A The Coriolis force de ects wind to the right in the Northern Hemisphere B The Coriolis force de ects wind to the left in the Southern Hemisphere C The pressure gradient force and Coriolis force combine to form geostrophic windsWinds around high pressure areas are moving clockwise in the northern hemisphere counterclockwise in southern hemisphere High pressure areas are called anticyclones Winds around low pressure areas are moving counterclockwise in the northern hemisphere clockwise in the southern hemisphere These low pressure areas are called cyclones Latitude The Coriolis effect is zero at the equator increases to half at 30 degrees N and S latitude and is maximized at the poles Speed The Coriolis effect increases as the speed of the moving object increases So the faster the wind speed the greater the de ection Distance The Coriolis effect does not affect very short distances and times WU Q m P Surface winds but not the geostrophic winds aloft in the atmosphere are affected by one other force friction Friction idrags on the wind as it moves across surfaces It decreases with height above the surface The effect of surface friction extends to a height of around 1600 feet but varies with surface texture wind speed time of day and year and atmospheric conditions In general rougher surfaces produce more friction Near the surface friction disrupts the equilibrium established in geostrophic wind ows between the pressure gradient and Coriolis forces Because surface friction Decrease wind speed it ireduces the effect of the Coriolis force and causes winds to move across isobars at angles This makes the winds De ects back to the left and spiral into cyclones in the northern hemisphere Matching This force moves perpendicular to isobars G This force moves at right angles to isobars G These winds move parallel to isobars A These winds are affected by friction D This force is greater at the poles than the equator C This force is not in effect over very small distances like drains C This force is increases when the speed of a moving object increases C This force involves the spacing between isobars whether gradual or steep G Winds around these move clockwise in the northern hemisphere F Winds around these move counterclockwise in the northern hemisphere E There is a myth that this force affects the direction of water draining C This force produces a drag on wind H This force decreases the Coriolis effect making winds move across isobars at angles H These winds are not affected by friction because they are too far above the surface A ws wwwe D IO39 Jng omwbowgt Geostrophic winds Anticyclones Coriolis force Surface winds Cyclone Anticyclone Pressure gradient force Friction Lecture 13 Outline Notes The Sargasso Sea Under the Bermuda High shelters many animals Including Loggerhead Turtles In the previous class we looked at high pressure and low pressure in the context of in uencing wind and wind direction We will now look at high and low pressure in slightly more detail and see how differences in air pressure across the planet are responsible for globalscale atmospheric circulation Low Pressure Low pressure areas have converging air at the surface that is ascending Air converges at the surface when a particularly warm low pressure spot develops Slight cooler slightly higherpressure air will move towards converge upon the lower pressure area because higl1 pressure moves to low pressure High Pressure The high pressure areas have descending air that converges at the surface as the weight of the air mass forces air to move outward diverge Air can be A J39 from high above or is cold air that doesn t rise There are huge areas on the globe that are characterized by high or low pressure Wind systems have developed around these areas The four main pressure areas transfer energy from the equator towards the poles are 1 Equatorial LowPressure Trough 7 ITCZ 2 Subtropical HighPressure Cells 3 Polar highPressure Cells 4 Subpolar LowPressure Cells Their corresponding winds are Trades 2 Westerlies 3 Polar easterlies 1 Intertropical Convergence Zone ITCZ aka Equatorial LowiPressure Trough Occurs in the tropics between 0 and 20 degrees north and south latitude L39 L this area trough of low quot to L 39 in nlatinn pressure light lessdense ascending air Surface winds the Trades converge along the extent of the trough This converging air is extremely moist and full of latent heat energy Rain and thunderstorms are common as air expands cools and condenses Vertical cloud columns frequently reach the tropopause in thunderous strength and intensity Within the lTCZ the winds are calm or mildly variable because ofthe even pressure gradient and the vertical ascent of air These equatorial calms are called the doldrums because of the dif culty sailing ships experienced in this zone The lTCZ shifts north and south during the year corresponding with the shifting ofthe subsolar point In January the lTCZ is located below the equator quotquot4 quot the sun 39 Tropic of Capricorn In July the lTCZ is located above the eguator The direct rays of the sun are just below the Tropic ofCancer TF The lTCZ is stable staying within 5 degrees ofthe equator throughout the year F TF The lTCZ is a high pressure area F TF Another name for the ITCZ is the Equatorial LowPressure Trough T TF ITCZ stands for intercontinental tropical collision zone F TF The winds that converge in the ITCZ are known as the westerlies F T F The areas of calm that sometimes occur in the ITCZ are known as the Horse Calms F T F The ITCZ shifts in latitude during the year from roughly 40 degrees north to 40 degrees south F T F Huge thunderstorms that can reach as high as the tropopause occur in the ITCZ T T F The air rises in the ITCZ because continual insolation warms the area T 2 Subtropical High Pressure Cells Poleward of both sides of the ITCZ air is descending creating the subtropical highpressure cells These cells occur between 20 and 35 degrees latitude in both hemispheres northern and southern The air is d in part because moisture has been squeezed out of it by the rains of the ITCZ The air also warms as it descends because it becomes denser and the air molecules are closer together The subtropical high cells move north and south along with the ITCZ They expand in summer and shrink in the winter There are actually several subtropical high pressure areas Notable ones include The Bermuda high in the western Atlantic The Azores high in the eastern Atlantic The Paci c high which dominates the northern Paci c in July T F Subtropical High Pressure cells occur poleward of both sides of the ITCZ between between 20 and 35 degrees latitude in both hemispheres T T F In subtropical high pressure cells the air is dry in part because moisture has been squeezed out of it by the rains of the ITCZ T T F The air also cools as it descends because it becomes denser and the air molecules are closer together F T F The subtropical high pressure cells shrink in summer and expand in the winter F T F The Bermuda high is a subtropical high pressure cell in the Paci c Ocean F T F The Azores high is a subtropical high pressure cell in the eastern Atlantic T The dry windless descending air of these subtropical highs give them the names the calms of Capricorn and the calms of Cancer They are also called the horse latitudes perhaps because in past centuries en 39 uiu u t have to share water with the livestock The eastem quot 39 39 39 quot ocean currents than do the western sides This contributes to the occurrence ofmany ofthe world39s major deserts which are on the western sides of continents esmfmah t tt it the chz generate Eartth principle surface winds the Trade Winds andthe Westerlies r A The 39 the subtropical highs nan 39 L lTr inthetropics ih L side ofthe subtropical highs The Westerlies and the Trades create ahuge circulation pattern and rise along the ch2 some converge back south and west to fonn the Trade Winds This cycle of n u Winds As they descen nn in ri I pattern Hadley Cell CrossSection I IIE I is o 39 s5 iEQ ZD39S saw u Holsv Lamudas mi Dolnmnis 39 Force All west forming the Westerlies TF The dry windless ue Lcuuiu air 39 39 39 quot A L A 39L F TF The eastern 394 L 39 currents than do the western sides T TF Many ofthe world39s major deserts are on the eastern side ofthe subtropical high western sides of continents T TF Air converges towards the subtropical high pressure cells F TFThe u u n 39 hemi nhem quot 39 39 hemi nhem F T F The Northerlies are the dominant surface winds in the midlatitudes They are on the poleward side of the subtropical sides F T F The trade winds are westerlies that converge into the ITCZ They are on the equator side of the subtropical highs F T F The cycle of ITCZ winds converging rising descending and converging again forms the Bradley Cell F 3 Polar High Pressure Cells The polar atmosphere receives little energy from the sun to put it into motion Cold and dry winds move away from the polar region in an anticyclonic direction This forms weak variable winds named the polar easterlies In the northern hemisphere polar high pressure tends to locate over Canada and Siberia The Canadian and Siberian Highs rather than over the relatively warmer Arctic Ocean A high called the Antarctic Higl1 forms over Antarctica 4 Subpolar Low Pressure Cells At around degrees north and south latitude the cold of the polar highs meets the warm of the subtropical highs The area of contrast between cold and warm air forms the polar front where these very different masses of air do battle When the warm air of the subtropical high meets the cold air of the polar high it is forced upward over the cold air Cooling and condensation occurs Low pressure cyclonic storms form These storms cells move over northwest North America and Europe Similar storms form beyond Antarctica The polar front moves in a great range latitudinally because of Rossby Waves to be covered next time Froplcal trnpapause snmsphere lmrnplr al l2 lream 39 m quot 39 mas wlnns Fq fw an E gt F 2 w a 0 t l Aim 39 y circulation cilculallan Copyllgth zoos Fearsnn Prenllce Hall mc 1 WhatispressureregionA called E 2 WhatispressuteregionB called D 3 WhatispressureregionCcalled A 4 WhatispressureregionD called B andc 5 WhatisVlflndl called G 7 Whatisznd3 called F s 39IheSibed 39 39 9 The Canadian High isan example of E 10 The Bermuda Azores and Paci c are examples ofwhich A A Subtropical High B Equatorial Low Pressure trough c 1T D SubPolar Low Pressure Cells E Polar 39gh F Westerlies G Polar easterlies Winds 1 Vllhere are the doldrums D 2 Where are the horse latitudes C 1409MB u ooo 9 wow Where do towering thunderstorms occur D Where is the Polar Front B Which expand and move poleward in summer C Which shrink and move equatorward in winter C 3Wlhereisthel elar liirent Z The eastern side of this forms deserts on the western sides of continents C Which forms from air that is descending and warming C Which forms from cold air such as over snowy sites A Which is warm ascending air D Polar high pressure Subpolar low pressure Subtropical High pressure ITCZ Equatorial low pressure


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