Chapter 8: Circulation of the Atmosphere. Photo from The Cloud Appreciation Society

Transcription

1 Chapter 8: Circulation of the Atmosphere Photo from The Cloud Appreciation Society 1

2 Global Atmospheric Circulation: A Review 2

3 Links to animations and videos shown in class (also posted in lecture slides from Monday): Global Air Circulation (clouds and water vapor = white; precipitation = orange): Hurricane Season: wim_video.htm?wim=2005hurricaneseason Global Atmospheric Circulation animation: ns/noqzs/042_globalwindshc_hs_gg_ins.html Hurricanes 101: Hurricane Wind Patterns: noqzs/044_hurricanes_hs_gg_ins.html 3

4 Atmospheric Heat Transport Water moves heat between latitudes. 4

5 Aquarius Satellite View of Global Salinity, Aug. Sept Atmospheric circulation patterns influence salinity patterns. 5

6 Learning Goals: Circulation of the Atmosphere More solar energy is absorbed near the Equator than near the poles. Atmospheric circulation is driven by this heating difference. The Coriolis effect causes moving objects to move to the right of their initial course, in the northern hemisphere. (to the left in the southern hemisphere) The atmosphere circulates in six large circuits. Hurricane formation is influenced by: Water temperature (needs to be warm!) Coriolis Effect (hurricanes need to spin!) 6

7 Thickness of the Atmosphere Although the density of the atmosphere decreases rapidly with height, the top of the atmosphere is undefined. Overall, the majority of atmospheric mass is contained in a thin layer near the surface. The atmosphere still contains an impressive sum of mass. 7

8 Physical Properties of the Atmosphere Composition Mostly nitrogen (N 2 ) and oxygen (O 2 ) Other gases significant for heattrapping properties 8

9 Permanent Gases 9

10 Variable Gases What is meant by variable?? Variable in space and time. 10

11 Plants and Earth s Environment 11

12 The Hydrologic Cycle What is the main source of water vapor in the atmosphere? 12

13 Composition of the Atmosphere Variable Gases: Water Vapor Water vapor is the most abundant variable gas, as it is added or removed from atmosphere through the hydrologic cycle. 0% (desert, poles why??) to - 4% (tropics) 13

14 Composition of the Atmosphere & Density What are your observations about the composition of air in the atmosphere? (Think about temperature, oxygen, etc ) If oxygen is scarce at high elevations, what does this mean about the density of this air? 14

15 Atmospheric Density and Pressure less overlying weight more overlying weight Due to compressibility, atmospheric mass gradually thins out with height. 15

16 Layers of the Atmosphere Density is so low in the thermosphere that there can be several kilometers in between individual gas molecules! Most humans stay in the lowest layer only. This layer, the troposphere, contains most of the atmosphere s mass. (why?) 16

17 What drives Earth s temperatures? Temperature is lower at higher latitudes: 1) Bigger area 2) More atmosphere 3) Reflection is higher (albedo) 17

18 Although average temperature constant, distribution not equal. Oceans and atmosphere move excess heat from equator to poles. 18

19 If the Earth s latitude causes differences in direct heating of the Earth, what causes seasons? 19

20 Convection, heat transfer by moving fluids. 20

21 Smaller scale examples of convection cells: sea breezes (day) 21

22 Smaller scale examples of convection cells: land breezes (night) 22

23 Movement of the Atmosphere Air always flows from high to low pressure. Wind moving air 23

24 Expect air to rise at Equator, move to poles, and sink. Thickness of atmosphere is not to scale!! 24

25 But that s not what happens Coriolis Effect video 25

26 Coriolis force cause objects to move: right in northern hemisphere left in southern hemisphere 26

27 Global Atmospheric Circulation (again) 27

28 Another What example do you think of isobars this image is showing? 28

29 Hurricanes Hurricanes/Typhoons/Cyclones hurakan: creator god who blew breath across the chaotic water and destroyed people with a great storm and flood (Mayans) hurucan: god of evil (Taino language, Central America) hurican: god of evil (Carib Indians) taifung: big wind (Chinese) kyklon: moving in a circle, like the coil of a snake (Greek) 29

30 Hurricanes around the Globe: The Tropical Setting Typhoons Hurricanes Cyclones The western North Pacific has the highest frequency of tropical cyclones with an average of 16.5 per year.

31 Hurricane Paths & Basics of Formation Recall video of Hurricane Season 2005, shown in class on 5/23 (link at beginning of these slides) 31

32 Conditions Needed for Hurricane Formation Hurricanes form over oceans with surface temperatures in excess of 27ºC (81ºF), as a result of latent heat release from evaporation. Latent heat release: Remember, water holds a lot of heat. When it transforms into water vapor, it releases some of this heat. Coriolis effect is an important contributor, and as such, hurricanes do not form between 0º and 5º latitude. They form in 5º 20º latitude. 32

33 In the Northern Hemisphere, hurricanes (tropical cyclones) turn counterclockwise, as winds become deflected to the right. In Southern hemisphere, winds spin opposite. 33

34 Anatomy of a hurricane: overview 34

35 Anatomy of a hurricane: in detail 35

36 Saffir-Simpson Scale of Hurricane Intensity 36

37 Historical Storm Tracks 37

38 Hurricane Anatomy and Movement Look! The large-scale wind patterns influence hurricane movement 38

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40 Chapter 9: Circulation of the Ocean Tropical gardens on Britain s Scilly Isles. Only 48 kilometers (30 miles) off the coast of Cornwall at 50 N, these scenic islands lie in the path of the warm waters of the Gulf Stream. 40

41 Learning Goals: Circulation of the Ocean Ocean circulation is driven by winds and by differences in water density. Winds and ocean currents distribute heat worldwide. Surface currents: driven by wind, they move in circular patterns (gyres) around the edges of major ocean basins. Surface = top 100 meters Upwelling supports the most productive fisheries. Thermohaline currents: slow, deep currents that affect the bulk of seawater below the pycnocline. El Niño and La Niña affect ocean and atmosphere. In El Niño years, the normal wind and current flow changes near the coast of Peru (and influences the whole world). 41

42 Thermohaline circulation also known as the global conveyor belt Fundamental process: Gulf Stream & conveyor belt: Conveyor belt animation (takes 1,000 years) 42

43 Deep bottom waters - Arctic caused by cooling waters 43

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45 Thermohaline circulation (temperature and salinity) influence sub-surface circulations. Distributes excess Earth s heat. 45

46 Deep bottom waters Antarctic caused by freezing ice increasing salinity 46

47 Let s take this complicated figure 47

48 and make it simpler: Winds, driven by uneven solar heating and Earth s spin, drive the movement of the ocean s surface currents. Two types of winds are most important to ocean circulation: 1) powerful westerlies and 2) persistent trade winds. 48

49 Northern Hemisphere: Coriolis Effect moves surface waters to right of winds. 49

50 Gyres surface currents circulating around ocean basins Three major causes of gyres: 1.Surface winds 2.Sun s heat 3.Coriolis effect 50

51 For example, the North Atlantic Gyre includes four currents. 51

52 Surface currents can be illustrated by sea surface temperature. Earth has 2 northern gyres, 4 southern. North Pacific Gyre North Atlantic Gyre South Pacific Gyre South Atlantic Gyre Indian Ocean Gyre Circum - Antarctic Gyre Red: Celsius (77 82 F). Yellow: C (68 77 F); Green: C (59 68 F); Blue: 0 15 C (32 59 F). Purple: below the freezing point of fresh water. Note the distortion of the temperature patterns we might expect from the effects of solar heating alone the patterns twist clockwise in the Northern Hemisphere, counterclockwise in the 52 Southern.

53 Surface currents, summarized with names and usual directions. Waters brought from equator warm-water current poles cold-water current 53

54 Ekman spiral two examples of what happens 1. How water is transported in the North Atlantic (as one example of an ocean gyre) 2. Upwelling vs. downwelling 54

55 Ekman spiral and Ekman transport: how the process works Coriolis Effects felt increasingly smaller below sea level. Net Effect 90⁰ motion of winds. 55

56 Center of hill not at basin center as expected. 56

57 If the Coriolis effect didn t exist, ocean gyres would look like this: Because of the Coriolis effect, ocean gyres are curved Key points: The Coriolis effect is strongest near the poles. Red arrows: Water flowing eastward at high latitudes turns sooner to the right (doesn t make a square) Green arrows: water flowing westward near the equator doesn t turn right until it hits a continent 57

58 Western boundary currents are stronger than eastern boundary currents. 58

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63 Upwelling: cold water brings nutrients to the surface. California Current Canary Current Humboldt Current. Benguela Current There are four major upwelling zones, and they are eastern boundary currents: Where are they? 63

64 Normal conditions: not an El Niño year Normally trade winds bring upwelled nutrientrich waters to Peru/Ecuador. 64

65 El Niño - When trade winds slow, upwelling stops. 65

66 A non-el Niño year 66

67 An El Niño year 67

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69 Chapter 10: Waves 69

70 Learning Goals: Waves Waves transmit energy, not water mass. Ocean waves have a disturbing force and a restoring force. Most waves are wind-driven, and most waves are generated by storms. Tsunamis are special, fast long waves generated by seismic events. Also learn at least three other types of waves (these are covered in the slides and in class). 70

71 Video from 2016 Quiksilver Eddie Aikau Big Wave Invitational Eddie Aikau Big Wave Invitational: Open-ocean swells must reach a minimum height of 20 feet (6.1 m) before the competition can be held. Open-ocean swells of this height generally translate to wave faces in Waimea Bay (Island of O ahu) of 30 feet (9.1 m) to 40 feet (12 m). The tournament has only been held nine times during the history of the event. 71

72 Forces and Features of Types of Ocean Waves All waves have a disturbing and restoring force. 72

73 Question Why would the sight of lowering sea levels and dying fish near shore be a sign of bad things to come? 73

74 First sign of tsunami lowering water levels. Figure 10.36c: An unfortunate effect of the tsunami warning network. Sightseers flocked to O ahu s Makapu u Beach in Hawai i, awaiting a tsunami generated by a 6.5 earthquake centered in the Aleutian Trench on 7 May

75 Figure 10.32: The regional Indonesian capital of Banda Aceh before (a) and after (b) the 26 December 2004 Indian Ocean tsunami. Waves 12 meters (40 feet) high overwashed the peninsula, moved the coastline, and killed 75 thousands of people in moments.

76 Figure 10.32: The regional Indonesian capital of Banda Aceh before (a) and after (b) the 26 December 2004 Indian Ocean tsunami. Waves 12 meters (40 feet) high overwashed the peninsula, moved the coastline, and killed 76 thousands of people in moments.

77 Tsunamis Tsunamis Disturbing force - Geological disturbance Restoring force Gravity. ~450mph, 1m height, 16 mile wavelength. In open ocean, long wavelength not a danger. 77

78 2.5 hours Figure 10.29: A computer simulation of the movement of a 1960 tsunami that originated in western Chile and sent destructive waves to Japan. The images represent the successive positions of the waves (a) 2.5 hours after the earthquake, (b) after 5 hours, (c) after 12.5 hours, (d) after 17.5 hours, and (e) reaching Japan after 22.5 hours of travel. (Source: Research by Philip L. F. Liv, Seung Nam Seo, and Sung Bum Yoon, and Civil Environmental Engineers, Cornell University. Visualization by Catherine Devine, Cornell Theory Center. Used by permission.) 78

79 5 hours 79

80 12.5 hours 80

81 17.5 hours 81

82 22.5 hours 82

83 When tsunamis reach shore, they act like a normal wave. 83

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85 Figure 10.35: The largest wave of the 1 April 1946 tsunami rushes ashore in Hilo. Terrified residents run for their lives; more than 150 died. V-shaped Hilo Bay is an especially dangerous place during a tsunami because its funnel-like outline concentrates the energy of the waves. Fourteen years after the 1946 disaster, a seismic disturbance in the subduction zone off western South America generated a tsunami that drowned 61 people in Hilo. Wave-cut scars on cliffs north of the 85 town suggest that visits by large tsunami are not rare occurrences.

86 Figure 10.36b: Tsunami hazard warning sign in a town in central coastal Oregon. The configuration of the coast and the slope and instability of the bottom in this area make tsunami particularly dangerous. 86

87 The wave goes up, the wave goes down. - Dr. Greg Guannel Although waves move, most of the water does not. Waves transmit energy, not water mass. (learning goal) Figure 10.1: A floating seagull demonstrates that waves travel ahead but that the water itself does not. In this sequence, a wave moves from left to right as the gull (and the water in which it is resting) revolves in an imaginary circle, moving slightly to the left up the front of an approaching wave, then to the crest, and finally sliding to the right down the back of the wave. 87

88 Wind Waves Disturbing Force: Winds Restoring Force: Gravity Ocean waves move more slowly as you go deeper. At a depth that is equal to half of its wavelength, a wave has very little motion. 88

89 Forces and Features of Types of Ocean Waves All waves have a disturbing and restoring force. 89

90 Capillary Waves Disturbing Force: Winds Restoring Force: Cohesion Smallest of ocean waves. 90

91 Wind Waves Disturbing Force: Winds Restoring Force: Gravity Ocean waves move slower as you go deeper. ½ wavelength, very little motion. 91

92 Seiche Waves Seiche standing wave found in basins. Disturbing force: Atmospheric disturbance. Restoring force: Gravity 92

93 Wave heights are dependent on: 1) Wind speed 2) Fetch 3) Wind duration 93

94 Fetch distance over which wind blows 94

95 Eddie Aikau Big Wave Invitational: Open-ocean swells must reach a minimum height of 20 feet (6.1 m) before the competition can be held. Open-ocean swells of this height generally translate to wave faces in Waimea Bay of 30 feet (9.1 m) to 40 feet (12 m). The tournament has only been held nine times during the history of the event. 95

96 Hawaiian waves originated near Aleutian Island storms. Makua Rothman drops down the face of a 4-meter (13-foot) wave at Sunset Beach on the North Shore of the Hawaiian Island of O ahu. 96