Geography
Global Atmospheric Circulation
Global atmospheric circulation refers to the large-scale movement of air around the Earth, driven by differences in temperature and pressure. This circulation is responsible for the distribution of heat and moisture across the planet, leading to the formation of distinct climate zones. The circulation is influenced by factors such as the rotation of the Earth, the uneven heating of the Earth's surface, and the properties of air and water.
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11 Key excerpts on "Global Atmospheric Circulation"
eBook - PDF- D. R. Bates(Author)
- 2016(Publication Date)
- Pergamon(Publisher)
CHAPTER NINE The General Circulation of the Atmosphere and Oceans E.T.EADY IN THE previous chapter the point was made that in order to make full use of climatic data we have to know how the atmosphere works. We shall now consider what is as yet known about the mechanism, for although the general circulation is only one aspect we find that we cannot understand it without knowing much about other, more detailed, aspects. It will be best to begin with a definition. The general circulation is the global aspect of the motion of the atmo-sphere. We concentrate our attention on broad air-current systems, ignoring for the moment all the complicated and rapidly varying de-tails. Though the emphasis is on wind systems in the first instance, we do not ignore the aspects of weather with which we are usually more directly concerned. It is merely that winds are a convenient basis for discussing associated changes of cloudiness, rain and temperature. We have noted earlier that from the point of view of their dynamics, the oceans and the atmosphere must be considered together as components of a single system. Nevertheless, it will be convenient to begin by concentrating our attention on the atmo-sphere. THE ATMOSPHERE The term 'general circulation' is to some extent misleading, in that it suggests a steady flow of air. Now, when we were attempting to define climate we found that, no matter what period we averaged over in order to eliminate rapid fluctuations, we still found slow temporal variations of the smoothed elements. Similarly, when we average over space in order to smooth out local fluctuations and make clear the broad pattern of the flow, we find that this varies 141 142 THE PLANET EARTH with time, no matter how large the area over which we smooth, and there is still variation if we average over a period as well. At any one instant we may think of the air motion as composed of super-posed flow patterns of different 'scales'.
eBook - PDFAtmospheric Chemistry and Physics
From Air Pollution to Climate Change
- John H. Seinfeld, Spyros N. Pandis(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
P A R T V I The Global Atmosphere, Biogeochemical Cycles, and Climate C H A P T E R 2 1 General Circulation of the Atmosphere The fundamental process driving the global-scale circulation of Earth ’ s atmosphere is the uneven heating of Earth ’ s surface by solar radiation. Although the total energy received by Earth from the sun is balanced by the total energy radiated back to space, this balance does not hold for every location on Earth. The tropics, for example, receive more energy from the sun than is radiated back to space; the polar regions receive less energy than they emit. Figure 21.1 shows the zonally annual averaged absorbed solar and emitted infrared fl uxes, as observed from satellites. We note a net gain of radiative energy between about 40 ° N and 40 ° S, and a net loss of energy in the polar regions. This pattern results largely from the decrease in insolation to the polar regions in winter and from the high surface albedo in the polar regions. The outgoing infrared fl ux displays only a modest latitudinal dependence. As a result of the net gain of radiative energy in the tropics and the net loss in the polar regions, an equator-to-pole temperature gradient is generated. Earth ’ s atmospheric circulation is one mechanism (about 60%) for redistributing energy from areas of the globe with an energy excess to those with an energy de fi cit; Earth ’ s ocean circulation is the other mechanism (about 40%). The circulation of the global atmosphere is one of the most complex, and theoretically deep, areas in fl uid dynamics. It is the subject of several texts [e.g., Holton (1992), Salby (1996)]. To understand atmospheric fl ows at a truly fundamental level requires an advanced fl uid mechanics background. The approach taken here is to describe the general nature of large-scale fl ow in the atmosphere at a level corresponding to a basic course in fl uid mechanics.
eBook - PDF- Alan F. Arbogast(Author)
- 2017(Publication Date)
- Wiley(Publisher)
100 CHAPTER 6 Atmospheric Pressure, Wind, and Global Circulation isobars as geostrophic winds. This process occurs because of the balancing effect that the Coriolis force and pressure gra- dient force have on one another. In other words, the Coriolis force keeps wind from flowing across isobars, whereas the pressure gradient force stops winds from curving up the pressure slope. Finally, when the force of friction is taken into account (Figure 6.14c), the end result is winds that follow an intermediate course relative to the isobars, somewhere bet- ween perpendicular (due to the pressure gradient force) and parallel (due to the Coriolis force) to those lines of equal atmo- spheric pressure. Global Pressure and Atmospheric Circulation In the preceding sections, we looked at the fundamental characteristics of air pressure systems and the variables that influence the process of airflow in the atmosphere. With these concepts in mind, let’s now examine the general circulation of air around the globe. This discussion will refer to the flow of air both in the upper part of the atmosphere and at the surface. The difference between the flow in these different parts of the atmosphere is often noticeable on the ground. If you want to see this difference yourself sometime, look for a partly cloudy day where two distinct layers of clouds occur, one low and another high. When these conditions exist, the clouds in the upper part of the atmosphere are often moving in a slightly different direction or speed from those closer to the surface. As discussed previously, the primary driver of global circulation is the unequal heating of the tropics and the poles. Because of this energy imbalance, the atmosphere works to balance the system through the process of airflow. If the Earth’s surface had a uniform character (i.e., no dis- tinction between continents and oceans), did not rotate, and its axis were not tilted, the circulatory system would be very easy to understand.
eBook - PDFEssentials of Meteorology
An Invitation to the Atmosphere
- C. Donald Ahrens, Robert Henson(Authors)
- 2017(Publication Date)
- Cengage Learning EMEA(Publisher)
As you may suspect, these winds are part of a much larger circu- lation, the little whirls within larger whirls that we spoke of earlier in this chapter. Indeed, if the rotating high- and low-pressure areas in our atmosphere are like spinning eddies in a huge river, then the flow of air around the globe is like the meandering river itself. When winds through- out the world are averaged over a long period of time, the local wind patterns vanish, and what we see is a picture of the winds on a global scale—what is commonly called the general circulation of the atmosphere. GENERAL CIRCULATION OF THE ATMOSPHERE Before we study the general circulation, we must remember that it only represents the average air flow around the world. Actual winds at any one place and at any given time may vary considerably from this average. Nevertheless, the average can answer why and how the winds blow around the world the way they do—why, for example, prevail- ing surface winds are northeasterly in Honolulu, Hawaii, and westerly in New York City. The average can also give a picture of the mechanism driving these winds, as well as a model of how heat is transported from equatorial regions poleward, keeping the climate in middle latitudes tolerable. The underlying cause of the general circulation is the unequal heating of Earth’s surface. We learned in Chapter 2 that, averaged over the entire earth, incoming solar radiation is roughly equal to outgoing earth radia- tion. However, we also know that this energy balance is not maintained for each latitude, since the tropics experience a net gain in energy, while polar regions suffer a net loss. To balance these inequities, the atmosphere transports warm air poleward and cool air equatorward. Although seemingly simple, the actual flow of air is complex; cer- tainly not everything is known about it.
eBook - PDFIntroduction to Environmental Physics
Planet Earth, Life and Climate
- Peter Hughes, N.J. Mason(Authors)
- 2001(Publication Date)
- CRC Press(Publisher)
Chapter 9 Global weather patterns and climate 9.1 Introduction: atmospheric motion Understanding the prevailing weather conditions in any specific geographical region requires a knowledge of the global climate. To understand the Earth's climate, it is neces- sary to investigate the atmospheric dynamics that lead to the formation of global circula- tion patterns, global wind patterns, and the formation and transport of weather systems around the Earth. This chapter describes the dynamics of air motion in the Earth's atmo- sphere and how it produces characteristic weather patterns and climatic regimes around the world. The atmosphere acts rather like a gigantic heat engine (see Section 2.2.2) in which the temperature difference between the polar and equatorial regions provides the energy supply necessary to drive atmospheric circulation. The conversion of heat energy into kinetic energy leads to motions within the atmosphere which occurs as the winds. Winds are literally millions of tonnes of air in motion - a huge flow of mass that transports warm and cold air, and dry and moist air about the Earth's surface and throughout the depth of the atmosphere. The wind is a basic aspect of life outdoors. In the wintertime it tends to blow more strongly than in the summer, and can be harnessed as a source of power when it blows strongly with a high velocity (see Chapter 5). It provides the motive force for those who sail and, when very strong, can be a major cause of damage in many parts of the world. To appreciate what makes the air move in the first place is, therefore, a crucial ingredient in the understanding of the weather and climate. First, it is useful to discuss the concept of air masses. 9.1. I Air masses and weather fronts An air mass is a large volume of air, extensive enough to cover an area of several million square kilometres across which the temperature and humidity remain reasonably constant.
eBook - PDF- Bruce Anderson, Alan H. Strahler(Authors)
- 2012(Publication Date)
- Wiley(Publisher)
This shift would interrupt a major flow pathway for the transfer of heat from equatorial regions to the northern midlat- itudes. This mechanism could result in relatively rapid climatic change and is one explanation for the periodic cycles of warm and cold temperatures experienced in these regions since the melting of continental ice sheets about 12,000 years ago. Heat and Moisture Transport he general circulation of the atmo- sphere and oceans is driven by the un- even heating between high and low latitudes. At the same time, this gen- eral circulation, combined with jet stream distur- bances in the midlatitudes, serves to redistribute excess heat—and moisture—from the Equator to the T Explain how the atmosphere redistributes heat and moisture from low latitudes to high latitudes. Discuss the role the oceans play in redistributing heat to the high latitudes. LEARNING OBJECTIVES CONCEPT CHECK What causes gyre circulations in the ocean to form? What is a western boundary current? Where do they form? How do ocean currents in the northern hemisphere differ from those in the southern hemisphere? How do the currents in the Atlantic differ from those in the Pacific? What is the thermohaline circulation? How does water in the thermohaline circulation traverse the globe? STOP STOP Heat and Moisture Transport 209 poles. Figure 7.21 on page 210, shows the various mechanisms by which this heat and moisture redistri- bution takes place. An important feature of this redistribution is the Hadley cell circulation—a global convection loop in which moist air converges and rises in the intertropical convergence zone (ITCZ) while subsiding and diverg- ing in the subtropical high-pressure belts. The Hadley cell convection loop acts to pump heat from warm equatorial oceans poleward to the subtropi- cal zone. Near the surface, air flowing toward the ITCZ picks up water vapor evaporated by sunlight from warm ocean surfaces, increasing the moisture and latent heat content of the air.
eBook - PDF- Timothy Foresman, Alan H. Strahler(Authors)
- 2012(Publication Date)
- Wiley(Publisher)
In this process, colder water from greater depths rises to the surface. In the tropical regions, ocean currents flow westward, pushed by the northeast and southeast trade winds. In the midlatitudes, currents are pushed in a slow eastward motion by the westerly winds. T he circulation pattern of the atmosphere is closely related to the circulation of the world’s oceans. Together, atmospheric and oceanic circulations transfer energy and moisture around the globe. Cyclical changes in these circulation patterns can affect our weather and climate in dramatic ways. OceanicCirculation151 this slow flow pattern, which links all of the world’s oceans. It is referred to as thermohaline circulation. In this circulation, Atlantic surface water moves north- ward, through the tropics, and becomes saltier, and there- fore denser, by evaporation. The dense, salty water cools as it moves northward, becoming even denser, and eventually it sinks along the northern edge of the Atlantic, creating a slow but steady bottom flow. Eventually the cold water upwells at far distant locations, as described in the figure. Circulation and Energy Transfer Global circulation of the atmosphere and oceans moves energy from low to high latitudes in a flow that is essential to sustaining the global energy balance. Recall from Chap- ter 2 that the Earth has a global energy budget of incom- ing and outgoing radiation. In places where radiant energy flows in faster than it flows out, net radiation is positive, providing an energy surplus. In other places, net radiation can be negative. For the entire Earth and atmosphere, the net radiation is zero over the year. the wind to the water by the friction of the air blowing over the water surface. Because of the Coriolis effect, however, the actual direction of water drift is deflected about 45° from the direction of the driving wind.
eBook - PDFAir Pollution
Concepts, Theory, and Applications
- Christian Seigneur(Author)
- 2019(Publication Date)
- Cambridge University Press(Publisher)
Atmospheric general circulation. This simplified representation depicts schematically the Hadley cells in the subtropical and tropical regions, the Ferrel cells in the temperate regions, the polar cells, the prevailing westerly winds in the mid-latitudes, and the easterly trade winds in the tropical regions. The semi-permanent high-pressure regions (H) are mostly at about 30 ° latitude and at the poles; the semi-permanent low-pressure regions (L) are mostly at 60 ° latitude. 44 Meteorology: General Circulation hemisphere. In the polar regions, the air flows originating from the poles are deviated westward. Figure 3.4 summarizes schematically these main aspects of the atmospheric general circulation. More detailed descriptions are available in the scientific literature (for example, James, 1994). 3.3 Meteorological Regimes 3.3.1 Main Regimes The processes described in Section 3.2 represent a very simple overview of the general atmospheric circulation. As mentioned, the main characteristics of this general circulation occur over the oceans and little over the continents. Indeed, the presence of complex terrain modifies the heat exchanges and atmospheric flows. Furthermore, the chaotic nature of meteorology implies that a small difference in an initial state of the atmosphere can lead to significant differences a few days later. Therefore, within the conceptual representation presented in Section 3.2, several scenarios may develop in relation with permanent structures (e.g., the Hadley cells) and semi-permanent ones (e.g., the Bermuda High and the Icelandic Low in the case of Europe; the Pacific High and the Aleutian Low in the case of North America). These meteorological scenarios are nevertheless limited in terms of their main characteristics, and they can be grouped in several regimes. For example, a representation using four meteorological regimes per season (i.e., 16 weather regimes in total) can be used for Europe.
eBook - PDF- Tom Garrison, Robert Ellis(Authors)
- 2017(Publication Date)
- Cengage Learning EMEA(Publisher)
Air warms, expands, becomes less dense, and rises over the radiator. Air cools, contracts, becomes more dense, and falls near the cold glass window. The circular current of air in the room, a convection current , is caused by the difference in temperature between the ends of the room. A similar process occurs over the surface of the Earth. As discussed earlier, surface temperatures are higher at the equator than at the poles, and air can gain heat from warm surroundings. Since air is free to move over Earth’s surface, it would be reasonable to assume that an air circulation pattern like the one shown in Figure 5.8 would develop over Earth. In this ideal model, air heated in the tropics would expand and become less dense, rise to high altitude, turn poleward, and “pile up” as it converged near the poles. The air would then cool and contract by radiating heat into space, sink to the surface, turn equatorward, and then flow along the surface back to the tropics to complete the circuit. But this is not what happens. Global circulation of air is governed by two factors: uneven solar heating and the rotation of Earth. The eastward rotation of Earth on its axis deflects the moving air or water (or any moving object having mass) away from its initial course. This deflection is called the Coriolis effect in honor of Gaspard Gustave de Coriolis, the French scientist who worked out its mathematics in 1835. An under-standing of the Coriolis effect is important to an understand-ing of atmospheric and oceanic circulation. Figure 5.6 The seasons (shown for the Northern Hemisphere) are caused by variations in the amount of incoming solar energy as Earth makes its annual rotation around the sun on an axis tilted by 23 1 ⁄ 2 °. During the Northern Hemisphere winter, the Southern Hemisphere is tilted toward the sun and the Northern Hemisphere receives less light and heat. During the Northern Hemisphere summer, the situa-tion is reversed.
eBook - PDF- Zeeya Merali, Brian J. Skinner(Authors)
- 2012(Publication Date)
- Wiley(Publisher)
That is why weather systems in the continental United States (and southern Canada) travel from west to east. If you take some time to study Figure 15.12, these circulation patterns will become clearer. trade winds Sur- face winds that blow from about 30° north and south latitude to- ward the intertropical convergence zone. Winds Aloft e’ve looked at air flows at or near Earth’s surface, including both local and global wind patterns. But how does air move at the higher levels of the troposphere? As with air near the surface, winds at upper levels of the atmosphere move in response to pressure gradients and are influenced by the Coriolis effect. A simple physical principle states that pressure de- creases less rapidly with height in warmer air than in colder air. Also recall that the solar energy reaching Earth is greatest near the Equator and least near the poles, re- sulting in a temperature gradient from the Equator to the poles. This gives rise to a pressure gradient; because the atmosphere is warmer near the Equator than the poles, a pressure-gradient force pushes air toward the poles. Explain how pressure gradients develop at upper atmospheric levels. Discuss the geostrophic wind. Show how Rossby waves develop and grow. Define jet streams. LEARNING OBJECTIVES W 468 CHAPTER 15 Global Circulation and Weather Systems THE GEOSTROPHIC WIND How does a pressure-gradient force pushing toward the poles produce wind, and what will the wind’s direction be? Any wind motion is subject to the Coriolis force, which turns it to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. So pole- ward air motion is toward the east, creating westerly winds in both hemispheres. Unlike air moving close to the surface, an upper air parcel moves without encountering friction because it is so far from the source of friction—the surface. So there are only two forces operating on the air parcel: the pressure-gradient force and the Coriolis force.
eBook - PDFOceanography
An Invitation to Marine Science
- Tom Garrison(Author)
- 2015(Publication Date)
- Cengage Learning EMEA(Publisher)
Now locate these features: the doldrums (or ITCZ), the horse latitudes, the prevailing westerlies, and the trade winds. Why is atmospheric circulation between the two hemispheres centered about the meteorological equator, not the geographical equator? Why is there a difference? (Hint: Think of the heat capacity of water and which hemisphere contains more surface water.) What’s a monsoon? Do we experience monsoons in the continental United States? How do sea breezes and land breezes form? Northeast monsoon Northwest monsoon I T C Z Geographical equator I T C Z Southwest monsoon African southwest monsoon Southeast monsoon Geographical equator a January b July a During the monsoon circulations of January a and July b , surface winds are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. c The summer monsoon in Kol-kata (Calcutta), India, one of the world’s wettest places. Rainfall in the region can exceed 10 meters (425 inches) per year! Figure 8.19 Monsoon patterns. THINKING BEYOND THE FIGURE Do monsoons form outside Asia? STEVE RAYMER/National Geographic © Cengage Learning. Data from Alan D. Iselino. © Cengage Learning. Data from Alan D. Iselino. Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. CIRCULATION OF THE ATMOSPHERE 233 8.5 Storms Are Variations in Large-Scale Atmospheric Circulation Storms are regional atmospheric disturbances characterized by strong winds, often accompanied by precipitation. Few natu-ral events underscore human insignificance like a great storm.
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